Materials

16 pages, 4195 KiB

Open AccessEditor’s ChoiceArticle

Notch Effects on the Stress Intensity Factor and on the Fatigue Crack Path for Eccentric Circular Internal Cracks in Elliptically Notched Round Bars under Tensile Loading

by Jesús Toribio, Beatriz González, Juan-Carlos Matos and Iván González

Materials 2022, 15(24), 9091; https://doi.org/10.3390/ma15249091 - 19 Dec 2022

Cited by 2 | Viewed by 2389

Abstract

In this paper, stress intensity factor (SIF) solutions are numerically obtained for notched bars subjected to tensile loading containing an eccentric circular inner crack located in the cross-section corresponding to the notch root. The finite element method and the J-integral have been [...] Read more.

In this paper, stress intensity factor (SIF) solutions are numerically obtained for notched bars subjected to tensile loading containing an eccentric circular inner crack located in the cross-section corresponding to the notch root. The finite element method and the J-integral have been used to obtain the SIF and to analyze the effect on it of three elliptical notch geometries (of equal radial depth). The results show how the SIF is greater in the notched bars than in the smooth bar and within the former when the axial semi-axis of the notch rises, its effect being greater as the diameter and eccentricity of the inner crack increase. In addition, the fatigue growth of an eccentric crack induces an increase in such eccentricity, greater as the notch axial semi-axis increases. The cause of these phenomena can be attributed to the constraint loss caused by the notch, which also facilitates bending of the specimen due to the asymmetry generated by the crack eccentricity. Full article

(This article belongs to the Special Issue Research and Modeling of Materials Fatigue and Fracture)

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17 pages, 10100 KiB

Open AccessEditor’s ChoiceArticle

Processing and Properties of Tungsten-Steel Composites and FGMs Prepared by Spark Plasma Sintering

by Jiří Matějíček, Radek Mušálek, Zdeněk Dlabáček, Veronika Klevarová and Lenka Kocmanová

Materials 2022, 15(24), 9037; https://doi.org/10.3390/ma15249037 - 17 Dec 2022

Cited by 2 | Viewed by 2147

Abstract

Tungsten is the prime candidate material for the plasma-facing components of fusion reactors. For the joining of tungsten armor to the cooling system or support structure, composites or graded interlayers can be used to reduce the stress concentration at the interface. These interlayers [...] Read more.

Tungsten is the prime candidate material for the plasma-facing components of fusion reactors. For the joining of tungsten armor to the cooling system or support structure, composites or graded interlayers can be used to reduce the stress concentration at the interface. These interlayers can be produced by several technologies. Among these, spark plasma sintering appears advantageous because of its ability to fabricate fully dense parts at lower temperatures and in a shorter time than traditional powder metallurgy techniques, thanks to the concurrent application of temperature, pressure, and electrical current. In this work, spark plasma sintering of tungsten-steel composites and functionally graded layers (FGMs) was investigated. As a first step, pure tungsten and steel powders of different sizes were sintered at a range of temperatures to find a suitable temperature window for fully dense compacts. Characterization of the sintered compacts included structure (by SEM); porosity (by the Archimedean method and image analysis); thermal diffusivity (by the flash method) and mechanical properties (microhardness and flexural strength). Compacts with practically full density and fine grains were obtained; while the temperature needed to achieve full sintering decreased with decreasing powder size (down to about 1500 °C for the 0.4 μm powder). For fully sintered compacts, the hardness and thermal diffusivity increased with decreasing powder size. Composites with selected tungsten/steel ratios were produced at several conditions and characterized. At temperatures of 1100 °C or above, intermetallic formation was observed in the composites; nevertheless, without a detrimental effect on the mechanical strength. Finally, the formation of graded layers and tungsten-steel joints in various configurations was demonstrated. Full article

(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing - Series II)

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19 pages, 9321 KiB

Open AccessEditor’s ChoiceArticle

Effective Attenuation of Electromagnetic Waves by Synergetic Effect of α-Fe₂O₃ and MWCNT/Graphene in LDPE-Based Composites for EMI Applications

by Praveen Manjappa, Hari Krishna Rajan, Mamatha Gowdaru Mahesh, Karthikeya Gulur Sadananda, Manjunatha Channegowda, Girish Kumar Shivashankar and Nagabhushana Bhangi Mutt

Materials 2022, 15(24), 9006; https://doi.org/10.3390/ma15249006 - 16 Dec 2022

Cited by 18 | Viewed by 2762

Abstract

In this study, a polymer nanocomposite is synthesized using magnetic and conducting fillers for enhanced electromagnetic interference (EMI) shielding. Alfa-ferrite (α-Fe₂O₃) nanoparticles with minimal multiwalled carbon nanotube (MWCNT) as low as 5 weight % in combination with variable concentrations [...] Read more.

In this study, a polymer nanocomposite is synthesized using magnetic and conducting fillers for enhanced electromagnetic interference (EMI) shielding. Alfa-ferrite (α-Fe₂O₃) nanoparticles with minimal multiwalled carbon nanotube (MWCNT) as low as 5 weight % in combination with variable concentrations of graphene nanoplatelets (GNP) are used as fillers in low-density polyethylene (LDPE) polymer matrix. Nanofillers and the polymer matrix are characterized by various techniques such as XRD, SEM, color mapping, EDAX, TGA, etc. The EMI shielding efficiency of the LDPE-based nanocomposites is tested using Vector Network Analyzer (VNA). The results showed that composite with LDPE:MWCNT:GNP:α-FO-50:5:40:5 displayed enhanced EMI shielding (in X-band (8.2–12.4 GHz) compared to other concentrations studied. This is due to the superior ohmic, dielectric, and magnetic losses at this particular composition and to the synergism amongst the filler. An attenuation of 99.99% was achieved for 5% α-Fe₂O₃. The mechanistic aspects of the shielding are discussed using permittivity, conductivity, and attenuation. Full article

(This article belongs to the Special Issue Facile Synthesis and Applications of Doped Metal Oxide Nanomaterials)

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12 pages, 1427 KiB

Open AccessEditor’s ChoiceArticle

Critical Current Density in d-Wave Hubbard Superconductors

by José Samuel Millán, Jorge Millán, Luis A. Pérez and Harold S. Ruiz

Materials 2022, 15(24), 8969; https://doi.org/10.3390/ma15248969 - 15 Dec 2022

Viewed by 2654

Abstract

In this work, the Generalized Hubbard Model on a square lattice is applied to evaluate the electrical current density of high critical temperature d-wave superconductors with a set of Hamiltonian parameters allowing them to reach critical temperatures close to 100 K. The [...] Read more.

In this work, the Generalized Hubbard Model on a square lattice is applied to evaluate the electrical current density of high critical temperature d-wave superconductors with a set of Hamiltonian parameters allowing them to reach critical temperatures close to 100 K. The appropriate set of Hamiltonian parameters permits us to apply our model to real materials, finding a good quantitative fit with important macroscopic superconducting properties such as the critical superconducting temperature (

T_{c}

) and the critical current density

(J_{c})

. We propose that much as in a dispersive medium, in which the velocity of electrons can be estimated by the gradient of the dispersion relation

\nabla ε (k)

, the electron velocity is proportional to

\nabla E (k)

in the superconducting state (where

E (k) = \sqrt{{(ε (k) - μ)}^{2} + Δ^{2} (k)}

is the dispersion relation of the quasiparticles, and k is the electron wave vector). This considers the change of

ε (k)

with respect to the chemical potential (

μ

) and the formation of pairs that gives rise to an excitation energy gap

Δ (k)

in the electron density of states across the Fermi level. When

ε (k) = μ

at the Fermi surface (FS), only the term for the energy gap remains, whose magnitude reflects the strength of the pairing interaction. Under these conditions, we have found that the d-wave symmetry of the pairing interaction leads to a maximum critical current density in the vicinity of the antinodal k-space direction

(π, 0)

of approximately

1.407236 \times 10^{8}

A/cm², with a much greater current density along the nodal direction

(\frac{π}{2}, \frac{π}{2})

of

2.214702 \times 10^{9}

A/cm². These results allow for the establishment of a maximum limit for the critical current density that could be attained by a d-wave superconductor. Full article

(This article belongs to the Special Issue Advances in Superconducting Materials: Characterization, Properties and Applications)

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17 pages, 3390 KiB

Open AccessEditor’s ChoiceArticle

A Doubly Fmoc-Protected Aspartic Acid Self-Assembles into Hydrogels Suitable for Bone Tissue Engineering

by Katerina Petropoulou, Varvara Platania, Maria Chatzinikolaidou and Anna Mitraki

Materials 2022, 15(24), 8928; https://doi.org/10.3390/ma15248928 - 14 Dec 2022

Cited by 4 | Viewed by 2590

Abstract

Hydrogels have been used as scaffolds for biomineralization in tissue engineering and regenerative medicine for the repair and treatment of many tissue types. In the present work, we studied an amino acid-based material that is attached to protecting groups and self-assembles into biocompatible [...] Read more.

Hydrogels have been used as scaffolds for biomineralization in tissue engineering and regenerative medicine for the repair and treatment of many tissue types. In the present work, we studied an amino acid-based material that is attached to protecting groups and self-assembles into biocompatible and stable nanostructures that are suitable for tissue engineering applications. Specifically, the doubly protected aspartic residue (Asp) with fluorenyl methoxycarbonyl (Fmoc) protecting groups have been shown to lead to the formation of well-ordered fibrous structures. Many amino acids and small peptides which are modified with protecting groups display relatively fast self-assembly and exhibit remarkable physicochemical properties leading to three-dimensional (3D) networks, the trapping of solvent molecules, and forming hydrogels. In this study, the self-assembling fibrous structures are targeted toward calcium binding and act as nucleation points for the binding of the available phosphate groups. The cell viability, proliferation, and osteogenic differentiation of pre-osteoblastic cells cultured on the formed hydrogel under various conditions demonstrate that hydrogel formation in CaCl₂ and CaCl₂-Na₂HPO₄ solutions lead to calcium ion binding onto the hydrogels and enrichment with phosphate groups, respectively, rendering these mechanically stable hydrogels osteoinductive scaffolds for bone tissue engineering. Full article

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14 pages, 6868 KiB

Open AccessEditor’s ChoiceArticle

Efficient Activation of Peroxymonosulfate by V-Doped Graphitic Carbon Nitride for Organic Contamination Remediation

by Zhi Deng, Zhenhua Huang, Jun Liu, Yongkui Huang and Peili Lu

Materials 2022, 15(24), 8936; https://doi.org/10.3390/ma15248936 - 14 Dec 2022

Cited by 5 | Viewed by 1765

Abstract

Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS) activation have been developed as an ideal pathway for completely eradication of recalcitrant organic pollutants from water environment. Herein, the V-doped graphitic carbon nitride (g-C₃N₄) is rationally fabricated by one-step thermal [...] Read more.

Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS) activation have been developed as an ideal pathway for completely eradication of recalcitrant organic pollutants from water environment. Herein, the V-doped graphitic carbon nitride (g-C₃N₄) is rationally fabricated by one-step thermal polymerization method to activate PMS for contamination decontamination. The results demonstrate the V atoms are successfully integrated into the framework of g-C₃N₄, which can effectively improve light absorption intensity and enhance charge separation. The V-doped g-C₃N₄ displays superior catalytic performance for PMS activation. Moreover, the doping content has a great influence on the activation performances. The radical quenching experiments confirm •O₂⁻, SO₄^•−, and h⁺ are the significant species in the catalytic reaction. This work would provide a feasible strategy to exploit efficient g-C₃N₄-based material for PMS activation. Full article

(This article belongs to the Section Catalytic Materials)

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11 pages, 3082 KiB

Open AccessEditor’s ChoiceArticle

Effect of Poly(vinyl alcohol) Concentration on the Micro/Mesopore Structure of SBA15 Silica

by Seongmin Kim, Minuk Jung, Seongsoo Han, Ho-Seok Jeon and Yosep Han

Materials 2022, 15(24), 8900; https://doi.org/10.3390/ma15248900 - 13 Dec 2022

Viewed by 1716

Abstract

In this work, a series of micro/mesoporous SBA15 silica materials were synthesized using P123 and poly(vinyl alcohol) (PVA) as co-templates. The pore structure of the prepared SBA15 was observed to be a function of the PVA concentration. When the amount of PVA was [...] Read more.

In this work, a series of micro/mesoporous SBA15 silica materials were synthesized using P123 and poly(vinyl alcohol) (PVA) as co-templates. The pore structure of the prepared SBA15 was observed to be a function of the PVA concentration. When the amount of PVA was relatively small, the specific surface area, micropore volume, and pore wall thickness of the synthesized SBA15 were considerably large. By contrast, when a large amount of PVA was added, the pore wall thickness was greatly reduced, but the mesopore volume and size increased. This is because the added PVA interacted with the polyethylene oxide (PEO) in the shells of the P123 micelles. Furthermore, when the amount of PVA was increased, the core polypropylene oxide (PPO) block also increased, owing to the enhanced aggregation of the P123/PVA mixed micelles. This research contributes to a basic comprehension of the cooperative interactions and formation process underlying porous silica materials, assisting in the rational design and synthesis of micro/mesoporous materials. Full article

(This article belongs to the Special Issue Recent Development of Surface Chemistry of Nanomaterials)

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13 pages, 2229 KiB

Open AccessEditor’s ChoiceArticle

Shelf Life Prediction of Picric Acid via Model-Based Kinetic Analysis of Its Thermal Decomposition

by Roberto Sanchirico, Marco Luca Santonocito, Valeria Di Sarli and Luciana Lisi

Materials 2022, 15(24), 8899; https://doi.org/10.3390/ma15248899 - 13 Dec 2022

Cited by 9 | Viewed by 2194

Abstract

A priori knowledge of the shelf life of energetic materials (EMs) is relevant due to its direct association with safety and functionality. This paper proposes a quick and reliable approach to predicting the shelf life of EMs whose thermal decomposition is an autocatalytic [...] Read more.

A priori knowledge of the shelf life of energetic materials (EMs) is relevant due to its direct association with safety and functionality. This paper proposes a quick and reliable approach to predicting the shelf life of EMs whose thermal decomposition is an autocatalytic process once their failure threshold has been defined as a function of the limiting extent of conversion. This approach is based on the assumption of a kinetic law consistent with the autocatalytic behavior and on the subsequent extraction, via a suitable procedure of parameter identification, of the kinetics of thermal decomposition from differential scanning calorimetry (DSC) data gathered under dynamic conditions at three different heating rates. Its reliability is proven for picric acid (PA) through the comparison of kinetic predictions with evaluations of conversion obtained by using high performance liquid chromatography (HPLC) analysis for samples subjected to isothermal and non-isothermal accelerated aging tests, as well as for a sample of naturally aged material, i.e., PA, stored at room temperature for more than 10 years. Full article

(This article belongs to the Section Advanced Materials Characterization)

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21 pages, 4659 KiB

Open AccessEditor’s ChoiceArticle

Lignocellulosic-Based Activated Carbon-Loaded Silver Nanoparticles and Chitosan for Efficient Removal of Cadmium and Optimization Using Response Surface Methodology

by Sujata Mandal, Sreekar B. Marpu, Mohammad A. Omary, Catalin C. Dinulescu, Victor Prybutok and Sheldon Q. Shi

Materials 2022, 15(24), 8901; https://doi.org/10.3390/ma15248901 - 13 Dec 2022

Cited by 5 | Viewed by 2618

Abstract

The cadmium-contaminated water body is a worldwide concern for the environment and toxic to human beings and the removal of cadmium ions from drinking and groundwater sustainably and cost-effectively is important. A novel nano-biocomposite was obtained by impregnating silver nanoparticles (AgNPs) within kenaf-based [...] Read more.

The cadmium-contaminated water body is a worldwide concern for the environment and toxic to human beings and the removal of cadmium ions from drinking and groundwater sustainably and cost-effectively is important. A novel nano-biocomposite was obtained by impregnating silver nanoparticles (AgNPs) within kenaf-based activated carbon (KAC) in the presence of chitosan matrix (CS) by a simple, facile photoirradiation method. The nano-biocomposite (CS-KAC-Ag) was characterized by an environmental scanning electron microscope equipped with energy dispersive X-ray spectroscopy (ESEM-EDX), Fourier-transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) method. A Box–Behnken design of response surface methodology (RSM) was used to optimize the adsorption of Cd²⁺. It was found that 95.1% of Cd²⁺ (10 mg L⁻¹) was eliminated at pH 9, contact time of 120 min, and adsorbent dosage of 20 mg, respectively. The adsorption of Cd²⁺ by CS-KAC-Ag is also in agreement with the pseudo-second-order kinetic model with an R² (coefficient of determination) factor greater than 99%. The lab data were also corroborated by tests conducted using water samples collected from mining sites in Mexico. Along with Cd²⁺, the CS-KAC-Ag exhibited superior removal efficiency towards Cr⁶⁺ (91.7%) > Ni²⁺ (84.4%) > Co²⁺ (80.5%) at pH 6.5 and 0.2 g L⁻¹ dose of the nano-adsorbent. Moreover, the adsorbent was regenerated, and the adsorption capacity remained unaltered after five successive cycles. The results showed that synthesized CS-KAC-Ag was a biocompatible and versatile porous filtering material for the decontamination of different toxic metal ions. Full article

(This article belongs to the Special Issue Materials for Heavy Metals Removal from Waters)

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25 pages, 6085 KiB

Open AccessEditor’s ChoiceArticle

Assessment of Mineralogical Characteristics of Clays and the Effect of Waste Materials on Their Index Properties for the Production of Bricks

by Aamar Danish, Ermedin Totiç, Muhammed Bayram, Mücahit Sütçü, Osman Gencel, Ertuğrul Erdoğmuş and Togay Ozbakkaloglu

Materials 2022, 15(24), 8908; https://doi.org/10.3390/ma15248908 - 13 Dec 2022

Cited by 18 | Viewed by 4136

Abstract

Significant research investigations on the characteristics of unexplored clay deposits are being conducted in light of the growing need for clay in the ceramic industry and the variable chemistry of clays. Parallel to this, the generation of waste materials like fly ash, ferrochrome [...] Read more.

Significant research investigations on the characteristics of unexplored clay deposits are being conducted in light of the growing need for clay in the ceramic industry and the variable chemistry of clays. Parallel to this, the generation of waste materials like fly ash, ferrochrome slag, and silica fume is also increasing, responsible for environmental degradation. This paper aims to study the mineralogical properties of pure clays (one specimen from Siberia and five specimens from different locations in Turkey), and the effect of mentioned waste materials on the index properties of clays obtained. This study is divided into two phases, wherein in the first phase, the pure clay specimens are analyzed against mineralogical properties (i.e., chemical composition, thermal analysis, and particle size distribution). While in the second phase, index properties of pure clay specimens and clay specimens modified with 0–50% fly ash, ferrochrome slag, and silica fume are analyzed. The results reveal that the clay specimens from Turkey (USCS classification: CL) are fit for the ceramic industry and bricks production, and incorporation of waste materials can further improve their index properties. It is also observed that incorporation of 10–30% fly ash and ferrochrome slag have higher efficiency in reducing the plasticity index of clays studied as compared to the addition of silica fume. Full article

(This article belongs to the Special Issue Environmental Impact on Mechanical Properties of Construction Materials)

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12 pages, 2315 KiB

Open AccessEditor’s ChoiceArticle

Forming-Free Tunable Analog Switching in WO_x/TaO_x Heterojunction for Emulating Electronic Synapses

by Chandreswar Mahata, Juyeong Pyo, Beomki Jeon, Muhammad Ismail, Myounggon Kang and Sungjun Kim

Materials 2022, 15(24), 8858; https://doi.org/10.3390/ma15248858 - 12 Dec 2022

Cited by 7 | Viewed by 2166

Abstract

In this work, the sputtered deposited WO_x/TaO_x switching layer has been studied for resistive random-access memory (RRAM) devices. Gradual SET and RESET behaviors with reliable device-to-device variability were obtained with DC voltage sweep cycling without an electroforming process. The memristor [...] Read more.

In this work, the sputtered deposited WO_x/TaO_x switching layer has been studied for resistive random-access memory (RRAM) devices. Gradual SET and RESET behaviors with reliable device-to-device variability were obtained with DC voltage sweep cycling without an electroforming process. The memristor shows uniform switching characteristics, low switching voltages, and a high R_ON/R_OFF ratio (~10²). The transition from short-term plasticity (STP) to long-term potentiation (LTP) can be observed by increasing the pulse amplitude and number. Spike-rate-dependent plasticity (SRDP) and paired-pulse facilitation (PPF) learning processes were successfully emulated by sequential pulse trains. By reducing the pulse interval, the synaptic weight change increases due to the residual oxygen vacancy near the conductive filaments (CFs). This work explores mimicking the biological synaptic behavior and further development for next-generation neuromorphic applications. Full article

(This article belongs to the Section Electronic Materials)

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26 pages, 8095 KiB

Open AccessEditor’s ChoiceArticle

Deposition of Sol–Gel ZnO:Mg Films and Investigation of Their Structural and Optical Properties

by Tatyana Ivanova, Antoaneta Harizanova, Tatyana Koutzarova, Benedicte Vertruyen and Raphael Closset

Materials 2022, 15(24), 8883; https://doi.org/10.3390/ma15248883 - 12 Dec 2022

Cited by 18 | Viewed by 2760

Abstract

This work presents a facile sol–gel method for the deposition of ZnO and ZnO:Mg films. The films are spin coated on silicon and quartz substrates. The impact of magnesium concentrations (0, 0.5, 1, 2 and 3 wt%) and post-annealing treatments (300–600 °C) on [...] Read more.

This work presents a facile sol–gel method for the deposition of ZnO and ZnO:Mg films. The films are spin coated on silicon and quartz substrates. The impact of magnesium concentrations (0, 0.5, 1, 2 and 3 wt%) and post-annealing treatments (300–600 °C) on the film’s structural, vibrational and optical properties is investigated. Undoped ZnO films crystallize in the wurtzite phase, with crystallite sizes ranging from 9.1 nm (300 °C) to 29.7 nm (600 °C). Mg doping deteriorates the film crystallization and shifting of 002 peak towards higher diffraction angles is observed, indicating the successful incorporation of Mg into the ZnO matrix. ZnO:Mg films (2 wt%) possess the smallest crystallite size, ranging from 6.2 nm (300 °C) to 25.2 nm (600 °C). The highest Mg concentration (3 wt%) results into a segregation of the MgO phase. Lattice constants, texture coefficients and Zn–O bond lengths are discussed. The diminution of the c lattice parameter is related to the replacement of Zn²⁺ by Mg²⁺ in the ZnO host lattice. The vibrational properties are studied by Fourier transform infrared (FTIR) spectroscopy. IR lines related to Mg–O bonds are found for ZnO:Mg films with dopant concentrations of 2 and 3 wt%. The optical characterization showed that the transmittance of ZnO:Mg thin films increased from 74.5% (undoped ZnO) to about 89.1% and the optical band gap energy from 3.24 to 3.56 eV. Mg doping leads to a higher refractive index compared to undoped ZnO films. The FESEM (field emission scanning electron microscopy) technique is used for observation of the surface morphology modification of ZnO:Mg films. The doped ZnO films possess a smoother grained surface structure, opposite to the wrinkle-type morphology of undoped sol–gel ZnO films. The smoother surface leads to improved transparency of ZnO:Mg films. Full article

(This article belongs to the Special Issue Structural, Morphological, and Optical Properties of Functional Thin Films)

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15 pages, 5449 KiB

Open AccessEditor’s ChoiceArticle

Deterioration of Mechanical Properties and the Damage Constitutive Model of Corroded Steel in an Industrial Environment

by Zongxing Zhang, Yuxuan Xu, Guangchong Qin, Shanhua Xu and Rou Li

Materials 2022, 15(24), 8841; https://doi.org/10.3390/ma15248841 - 11 Dec 2022

Cited by 6 | Viewed by 1766

Abstract

To investigate the degradation law of the mechanical properties of corroded steel, the standard specimens from machining steel members in service for 9 years in an industrial environment were subjected to tensile tests. The influences of different degrees and types of corrosion on [...] Read more.

To investigate the degradation law of the mechanical properties of corroded steel, the standard specimens from machining steel members in service for 9 years in an industrial environment were subjected to tensile tests. The influences of different degrees and types of corrosion on the fracture path, stress-strain curve, and mechanical properties of specimens were discussed. Finally, the damage constitutive model of corroded steel was established based on the damage mechanics theory. The results showed that the failure modes of corroded specimens were related to the degrees and types of corrosion. The fracture morphology of specimens with general corrosion were step-like and the fractures of steel were uneven. However, those with local corrosion were mainly flat-like, and the fracture path was along the cross section where the larger corrosion pits were located. The fracture path of the specimen was related to the interaction of the corroded surface and internal material defects (holes). Meanwhile, with the increase of corrosion degree, the yield platform of stress-strain curve gradually became shorter, or even disappeared, and the ultimate strain and elongation at break decreased, implying that the ductility of steel became worse. Ultimately, the good agreement between the curves of the model and test indicated that the damage model could reflect the damage development process of corroded steel in the tensile process better. Corrosion damage resulted in the decrease in the damage threshold, and the damage variable D decreased by the time fracture occurred and the maximum reduction rate was up to 62.5%. Full article

(This article belongs to the Section Corrosion)

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11 pages, 3918 KiB

Open AccessEditor’s ChoiceArticle

Acousto–Optic Modulation and Deflection of Terahertz Radiation

by Pavel Alekseevich Nikitin, Vasily Valerievich Gerasimov and Ildus Shevketovich Khasanov

Materials 2022, 15(24), 8836; https://doi.org/10.3390/ma15248836 - 10 Dec 2022

Cited by 4 | Viewed by 2048

Abstract

It is known that one of the ways to increase the energy efficiency of acousto–optic devices is to use ultrasound beams with a higher power density. It has been established experimentally that the use of a partially electroded ultrasonic transducer significantlyincreases the energy [...] Read more.

It is known that one of the ways to increase the energy efficiency of acousto–optic devices is to use ultrasound beams with a higher power density. It has been established experimentally that the use of a partially electroded ultrasonic transducer significantlyincreases the energy efficiency of the acousto–optic modulator of terahertz radiation. In addition, the operation of an acousto–optic deflector of terahertz radiation with the use of a sectioned ultrasound transducer was theoretically investigated. It showed that a deflector of this kind enables one to achieve higher angular resolution. Full article

(This article belongs to the Special Issue Acousto-Optical Spectral Technologies)

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20 pages, 36857 KiB

Open AccessEditor’s ChoiceArticle

Use of Magnesium Silicate Contaminated with Organic Compounds in Ceramic Materials as a Pore Modifier

by Jolanta Pranckevičienė and Ina Pundienė

Materials 2022, 15(24), 8833; https://doi.org/10.3390/ma15248833 - 10 Dec 2022

Cited by 2 | Viewed by 1393

Abstract

This study investigated the use of organic compound waste (OCW) contaminated magnesium silicate/diatomite in ceramics. Substituting part of the clay (between 5 and 20 wt.%) with OCW modifies a pore structure and enhances the ceramic product’s thermal conductivity, density, and frost resistance. Prepared [...] Read more.

This study investigated the use of organic compound waste (OCW) contaminated magnesium silicate/diatomite in ceramics. Substituting part of the clay (between 5 and 20 wt.%) with OCW modifies a pore structure and enhances the ceramic product’s thermal conductivity, density, and frost resistance. Prepared samples were tested at 1000–1060 °C temperatures and their structural parameters and Maage factor, useful for frost resistance prediction, were evaluated. Results show that OCW modifies the porous structure and improves the insulating properties of the ceramic body. Increasing OCW content up to 15% in the ceramic body decreases density by up to 15.0%, and thermal conductivity by up to 42.5%, because of the modified pore structure. According to structural parameters calculation, the higher frost resistance can be predicted for ceramic bodies containing 5–10% of OCW, according to Maage factor calculation ceramic bodies containing 5–20% of OCW are frost resistant. Designed ceramic products can be attractive for use in construction due to improved energy efficiency and reduced energy consumption in buildings due to their low thermal conductivity, satisfactory mechanical strength, and sustainability based on predicted frost resistance. Full article

(This article belongs to the Section Construction and Building Materials)

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9 pages, 1920 KiB

Open AccessEditor’s ChoiceArticle

Crystallographically Textured and Magnetic LaCu-Substituted Ba-Hexaferrite with Excellent Gyromagnetic Properties

by Zan Jiao, Yuantao Wang, Meng Wei, Qifan Li, Ziyu Li, Alexander S. Sokolov, Chengju Yu, Xiaona Jiang, Chuanjian Wu, Zhongwen Lan, Ke Sun, Zhong Yu and Vincent G. Harris

Materials 2022, 15(24), 8792; https://doi.org/10.3390/ma15248792 - 9 Dec 2022

Cited by 3 | Viewed by 1917

Abstract

Excellent gyromagnetic properties of textured, bulk Ba-hexaferrite samples are required for low-loss, self-biased applications for microwave and millimeter-wave (MMW) devices. However, conventionally processed bulk Ba-hexaferrite ceramics typically demonstrate low remanent magnetization values, 4πM_r, of 2.0~3.0 kG, and relatively large ferromagnetic [...] Read more.

Excellent gyromagnetic properties of textured, bulk Ba-hexaferrite samples are required for low-loss, self-biased applications for microwave and millimeter-wave (MMW) devices. However, conventionally processed bulk Ba-hexaferrite ceramics typically demonstrate low remanent magnetization values, 4πM_r, of 2.0~3.0 kG, and relatively large ferromagnetic resonance (FMR) linewidths, ΔH_FMR, of 0.8~2 kOe. These properties lead to the development of high-performance, practical devices. Herein, crystallographically textured Ba-hexaferrite samples, of the composition Ba_0.8La_0.2Fe_11.8Cu_0.2O₁₉, having excellent functional properties, are proposed. These materials exhibit strong anisotropy fields, H_a, of ~14.6 kOe, high remanent magnetization, 4πM_r, of 3.96 kGs, and a low ΔH_FMR of 401 Oe at zero-bias field at the Q-band. Concomitantly, the broadband millimeter-wave transmittance was utilized to determine the complex permeability, μ*, and permittivity, ε*, of textured hexaferrites. Based on Schlöemann’s theory of complex permeability, μ*, the remanent magnetization, 4πM_r, anisotropy field, H_a, and effective linewidth, ΔH_eff, were estimated; these values agree well with measured values. Full article

(This article belongs to the Special Issue Ferrites：Preparation, Micro-Structures and Properties)

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13 pages, 2232 KiB

Open AccessEditor’s ChoiceArticle

High Seebeck Coefficient from Screen-Printed Colloidal PbSe Nanocrystals Thin Film

by Viviana Sousa, Guillaume Savelli, Oleg I. Lebedev, Kirill Kovnir, José H. Correia, Eliana M. F. Vieira, Pedro Alpuim and Yury V. Kolen’ko

Materials 2022, 15(24), 8805; https://doi.org/10.3390/ma15248805 - 9 Dec 2022

Cited by 6 | Viewed by 2404

Abstract

Thin-film thermoelectrics (TEs) with a thickness of a few microns present an attractive opportunity to power the internet of things (IoT). Here, we propose screen printing as an industry-relevant technology to fabricate TE thin films from colloidal PbSe quantum dots (QDs). Monodisperse 13 [...] Read more.

Thin-film thermoelectrics (TEs) with a thickness of a few microns present an attractive opportunity to power the internet of things (IoT). Here, we propose screen printing as an industry-relevant technology to fabricate TE thin films from colloidal PbSe quantum dots (QDs). Monodisperse 13 nm-sized PbSe QDs with spherical morphology were synthesized through a straightforward heating-up method. The cubic-phase PbSe QDs with homogeneous chemical composition allowed the formulation of a novel ink to fabricate 2 μm-thick thin films through robust screen printing followed by rapid annealing. A maximum Seebeck coefficient of 561 μV K⁻¹ was obtained at 143 °C and the highest electrical conductivity of 123 S m⁻¹ was reached at 197 °C. Power factor calculations resulted in a maximum value of 2.47 × 10⁻⁵ W m⁻¹ K⁻² at 143 °C. To the best of our knowledge, the observed Seebeck coefficient value is the highest reported for TE thin films fabricated by screen printing. Thus, this study highlights that increased Seebeck coefficients can be obtained by using QD building blocks owing to quantum confinement. Full article

(This article belongs to the Special Issue Nanostructural Thin Films: Microstructure and Optical Properties)

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10 pages, 3489 KiB

Open AccessEditor’s ChoiceArticle

Effects of UV Absorber on Zirconia Fabricated with Digital Light Processing Additive Manufacturing

by Jin-Ho Kang, Kumaresan Sakthiabirami, Hyun-Ah Kim, Seyed Aliakbar Hosseini Toopghara, Mee-Jin Jun, Hyun-Pil Lim, Chan Park, Kwi-Dug Yun and Sang-Won Park

Materials 2022, 15(24), 8726; https://doi.org/10.3390/ma15248726 - 7 Dec 2022

Cited by 7 | Viewed by 2365

Abstract

This study evaluated the effect of UV absorbers on the dimensional accuracy of zirconia specimens fabricated by additive manufacturing using a digital light process. Zirconia suspension for additive manufacturing was prepared by setting the volume fractions (0, 0.005, 0.05, and 0.1%) of various [...] Read more.

This study evaluated the effect of UV absorbers on the dimensional accuracy of zirconia specimens fabricated by additive manufacturing using a digital light process. Zirconia suspension for additive manufacturing was prepared by setting the volume fractions (0, 0.005, 0.05, and 0.1%) of various UV absorbers. The effect of UV absorber content was evaluated through curing thickness, geometric overgrowth model design, linear deviation, and microstructure evaluation before and after sintering. Statistical analysis was performed by Kruskal–Wallis H and post-tested by the Bonferroni correction method. There was no significant difference in the cure depth according to the presence or absence of the UV absorber, the difference in geometric overgrowth was from 2.1 to 12.5%, and the overgrowth significantly decreased as the amount of added UV absorber increased. This result may contribute to improved precision of 3D multilayer ceramic products. Full article

(This article belongs to the Special Issue Zirconia and Innovative Biomaterials for Dental and Biomedical Applications)

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25 pages, 5700 KiB

Open AccessEditor’s ChoiceArticle

Nonlinear Analytical Procedure for Predicting Debonding of Laminate from Substrate Subjected to Monotonic or Cyclic Load

by Marco Lamberti, Francesco Ascione, Annalisa Napoli, Ghani Razaqpur and Roberto Realfonzo

Materials 2022, 15(23), 8690; https://doi.org/10.3390/ma15238690 - 6 Dec 2022

Cited by 6 | Viewed by 2019

Abstract

The bonding of steel/fiber-reinforced polymer (SRP/FRP) laminate strips to concrete/masonry elements has been found to be an effective and efficient technology for improving the elements’ strength and stiffness. However, premature laminate–substrate debonding is commonly observed in laboratory tests, which prevents the laminate from [...] Read more.

The bonding of steel/fiber-reinforced polymer (SRP/FRP) laminate strips to concrete/masonry elements has been found to be an effective and efficient technology for improving the elements’ strength and stiffness. However, premature laminate–substrate debonding is commonly observed in laboratory tests, which prevents the laminate from reaching its ultimate strength, and this creates uncertainty with respect to the level of strengthening that can be achieved. Therefore, for the safe and effective application of this technology, a close estimate of the debonding load is necessary. Towards this end, in this paper, a new, relatively simple, semi-analytic model is presented to determine the debonding load and the laminate stress and deformation, as well as the interfacial slip, for concrete substrates bonded to SRP/FRP and subjected to monotonic or cyclic loading. In the model, a bond-slip law with a linearly softening branch is combined with an elasto-plastic stress-strain relationship for SRP. The model results are compared with available experimental data from single-lap shear tests, with good agreement between them. Full article

(This article belongs to the Special Issue Mechanical Properties and Application of Adhesive Materials)

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20 pages, 10130 KiB

Open AccessEditor’s ChoiceArticle

Open Hole Tension of 3D Printed Aligned Discontinuous Composites

by Narongkorn Krajangsawasdi, Ian Hamerton, Benjamin K. S. Woods, Dmitry S. Ivanov and Marco L. Longana

Materials 2022, 15(23), 8698; https://doi.org/10.3390/ma15238698 - 6 Dec 2022

Cited by 6 | Viewed by 2739

Abstract

This paper explores the use of Discontinuous Aligned Fibre Filament (DcAFF), a novel discontinuous fibre reinforced thermoplastic filament for 3D printing, to produce structural complex parts. Compared to conventional composite manufacturing, 3D printing has great potential in steering fibres around small structural features. [...] Read more.

This paper explores the use of Discontinuous Aligned Fibre Filament (DcAFF), a novel discontinuous fibre reinforced thermoplastic filament for 3D printing, to produce structural complex parts. Compared to conventional composite manufacturing, 3D printing has great potential in steering fibres around small structural features. In this current study, the initial thin carbon fibre (CF)-poly(L-lactic acid) (PLA) tape, produced with the High Performance Discontinuous Fibre (HiPerDiF) technology, is now reshaped into a circular cross-section filament, the DcAFF, using a bespoke machine designed to be scalable to high production rates rather than using a labour-intensive manual moulding method as in previous work. The filaments are then fed to a general-purpose 3D printer. Tensile and open-hole tensile tests were considered in this paper for mechanical and processability of DcAFF. The 3D printed specimens fabricated with the DcAFF show superior tensile properties compared to other PLA-based 3D printed composites, even those containing continuous fibres. Curvilinear open-hole tensile test samples were fabricated to explore the processability and performances of such material in complex shapes. The mechanical performance of the produced specimens was benchmarked against conventionally laid-up specimens with a cut hole. Although the steered specimens produced have lower strength than the fully consolidated samples, the raster generated by the printing path has turned the failure mechanism of the composite from brittle to ductile. Full article

(This article belongs to the Special Issue 3D Printing and Additive Manufacturing of Polymer and Composites)

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9 pages, 1620 KiB

Open AccessEditor’s ChoiceArticle

On the Quantum Confinement Effects in Ultrathin PdO Films by Experiment and Theory

by Alexandros Barnasas, Christos S. Garoufalis, Dimitrios I. Anyfantis, Panagiotis Poulopoulos and Sotirios Baskoutas

Materials 2022, 15(23), 8700; https://doi.org/10.3390/ma15238700 - 6 Dec 2022

Cited by 2 | Viewed by 2253

Abstract

Radio frequency magnetron sputtering conducted in a high vacuum with a base pressure of

1 \times 10^{- 6}

mbar was used to deposit ultrathin palladium films on Corning glass. The thickness of these films ranged from 0.4 to 13 nanometers. PdO films [...] Read more.

Radio frequency magnetron sputtering conducted in a high vacuum with a base pressure of

1 \times 10^{- 6}

mbar was used to deposit ultrathin palladium films on Corning glass. The thickness of these films ranged from 0.4 to 13 nanometers. PdO films were produced after being post-annealed in a furnace at temperatures of 530 degrees Celsius in the presence of air. The results of an atomic force microscopy study showed that the material possessed a high crystalline quality with a low roughness. When looking at Tauc plots to determine the position of the direct optical band gap, the thicker films show a value that is relatively close to 2.2 eV. When the film thickness was reduced all the way down to 0.7 nm, a significant “blue shift” of more than 0.5 eV was observed. In order to provide a more in-depth understanding of the experiment, theoretical calculations based on the Hartree–Fock approximation as applied to an electron-hole system were performed in the framework of the effective mass approximation. The findings are regarded as empirical proof of the existence of quantum confinement effects. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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12 pages, 2681 KiB

Open AccessEditor’s ChoiceArticle

Effective BMP-2 Release and Mineralization on a Graphene Oxide/Polyvinylpyrrolidone Hydrogel Forming Poly (ε-Caprolactone) Nanofibrous Scaffolds

by Jin-Oh Jeong, Sung-In Jeong, Youn-Mook Lim and Jong-Seok Park

Materials 2022, 15(23), 8642; https://doi.org/10.3390/ma15238642 - 4 Dec 2022

Cited by 7 | Viewed by 2425

Abstract

PCL nanofibrous scaffolds are widely used as bone scaffolds, and they can increase the efficiency of bone regeneration by loading drugs and/or growth factors onto them. However, to obtain a more effective bone regeneration effect, it is necessary to increase drug loading and [...] Read more.

PCL nanofibrous scaffolds are widely used as bone scaffolds, and they can increase the efficiency of bone regeneration by loading drugs and/or growth factors onto them. However, to obtain a more effective bone regeneration effect, it is necessary to increase drug loading and release efficiency. In this study, conductive hydrogel forming nanofibrous scaffolds were prepared to increase drug efficiency. GO has an excellent conductivity and biocompatibility, making it an efficient conductive polymer for bone differentiation. Electrospun PCL was immersed in a mixed solution of GO and PVP and then crosslinked using gamma-ray irradiation. It was confirmed that GO/PVP-PCL was successfully prepared through its characterization (morphology, thermal, chemical, electrical, and biological properties). In addition, drug-release efficiency was confirmed by electrical stimulation after loading the sample with BMP-2, a bone-regeneration growth factor. Compared to PCL, it was confirmed that GO/PVP-PCL has an approximately 20% improved drug-release efficiency and an excellent mineralization of the scaffolds using SBF. After culturing MG63 cells on GO/PVP-PCL, a high effect on osteodifferentiation was confirmed by ALP activity. Therefore, GO/PVP-PCL prepared by a gamma-ray-induced crosslinking reaction is expected to be used as biomaterial for bone-tissue engineering. Full article

(This article belongs to the Special Issue Advances in Functional Hydrogel Biomaterials)

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12 pages, 8249 KiB

Open AccessEditor’s ChoiceArticle

Bidirectional Terahertz Vortex Beam Regulator

by Jiusheng Li, Fenglei Guo, Shuping Zhang and Chao Liu

Materials 2022, 15(23), 8639; https://doi.org/10.3390/ma15238639 - 3 Dec 2022

Cited by 2 | Viewed by 2455

Abstract

Most of the reported vortex beam generators with orbital angular momentum (OAM) in the terahertz region only operate in either the reflection mode or the transmission mode, which greatly limits the integration and application in terahertz technology systems. Herein, we propose a full-space [...] Read more.

Most of the reported vortex beam generators with orbital angular momentum (OAM) in the terahertz region only operate in either the reflection mode or the transmission mode, which greatly limits the integration and application in terahertz technology systems. Herein, we propose a full-space vortex beam regulator at two different frequencies. By changing the VO₂ phase transition state, the transmission and reflection mode OAM beams can be flexibly controlled by a single metasurface. For the transmission mode, the proposed structure realizes an OAM beam at the topological charges of l = 1 and 2 at 0.6 THz and 1.4 THz. For the reflection mode, our structure generates an OAM beam at the topological charges of l = 1 and 2 at 0.9 THz and 1.5 THz. Based on the superposition theorem and convolution operation principle, the regulation of an OAM vortex beam with a specific deflection angle and a symmetrical deflection OAM vortex beam are realized. The designed metasurface integrates multiple transmitted and reflected vortex beam functions in full space and has potential application in different terahertz systems. Full article

(This article belongs to the Special Issue Design and Applications of Terahertz Metamaterials)

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20 pages, 796 KiB

Open AccessEditor’s ChoiceReview

Regeneration of the Pulp Tissue: Cell Homing versus Cell Transplantation Approach: A Systematic Review

by Elisabeth Tirez and Mariano S. Pedano

Materials 2022, 15(23), 8603; https://doi.org/10.3390/ma15238603 - 2 Dec 2022

Cited by 4 | Viewed by 2387

Abstract

Background: The main objective of this systematic review was to compare the apical healing, root maturation and histological characteristics of teeth treated with cell-based versus cell-free techniques. Methods: The methodology of this review was based on the PRISMA (Preferred Reporting Items for Systematic [...] Read more.

Background: The main objective of this systematic review was to compare the apical healing, root maturation and histological characteristics of teeth treated with cell-based versus cell-free techniques. Methods: The methodology of this review was based on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. A literature search strategy was carried out on PubMed, EMBASE and the Web of Science databases. The last search was done on 1 August 2021. Articles written in languages other than English were excluded. Two researchers independently selected the studies and extracted the data. As no randomized clinical trials were available, animal studies were included. Results: In total, 26 studies were included in the systematic review: 22 articles only researched the cell-free technique, 3 articles compared the cell-based to the cell-free technique, and 1 article compared the cell-based technique to apexification. In terms of apical healing, qualitative analysis of the data suggested that there seems to be no significant difference between cell-free and cell-based techniques. The results regarding tooth maturation are contradictory. The main difference between the cell-free and the cell-based techniques seems to be the histology of the treated tooth. The cell-free technique seems to result in cementum-like, bone-like or periodontal ligament-like tissue. One study, on the other hand, found that the cell-based technique resulted in regeneration of the whole pulp with an odontoblast layer, connective tissue, blood vessels and neuronal tissue. Conclusions: Currently, the number of randomized clinical trials on this topic are very scarce. This is probably due to the limited infrastructure and lack of resources to apply the cell-based technique. Even though both techniques seem to be promising for clinical application, long-term data need to be provided regarding the healing and reparative patterns. Full article

(This article belongs to the Special Issue Advanced Dental Materials and Methods for Tooth Bioengineering and Regenerative Dentistry)

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11 pages, 3188 KiB

Open AccessEditor’s ChoiceArticle

N⁺-Implantation on Nb Coating as Protective Layer for Metal Bipolar Plate in PEMFCs and Their Electrochemical Characteristics

by Yu-Sung Kim, Jin-Young Choi, Cheong-Ha Kim, In-Sik Lee, Shinhee Jun, Daeil Kim, Byung-Chul Cha and Dae-Wook Kim

Materials 2022, 15(23), 8612; https://doi.org/10.3390/ma15238612 - 2 Dec 2022

Cited by 3 | Viewed by 1676

Abstract

Nitrogen ions were implanted into the coated Nb layer by plasma immersion ion implantation to improve resistance to corrosion of a metal bipolar plate. Due to nitrogen implantation, the corrosion behavior of the Nb layer was enhanced. The electron microscope observation reveals that [...] Read more.

Nitrogen ions were implanted into the coated Nb layer by plasma immersion ion implantation to improve resistance to corrosion of a metal bipolar plate. Due to nitrogen implantation, the corrosion behavior of the Nb layer was enhanced. The electron microscope observation reveals that the microstructure of the Nb layer became denser and had fewer defects with increasing implantation energy. As a result, the densified structure effectively prevented direct contact with the corrosive electrolyte. In addition, at a higher implantation rate (6.40 × 10¹⁷ N₂/cm²), a thin amorphous layer was formed on the surface, and the implanted nitrogen ions reacted at neighboring Nb sites, resulting in the localized formation of nitrides. Such phase and structural changes contributed to further improve corrosion resistance. In particular, the implanted Nb layer at bias voltage of 10 kV exhibited a current density more than one order of magnitude smaller with a two times faster stabilization than the as-deposited Nb layer under the PEMFC operating conditions. Full article

(This article belongs to the Special Issue Surface Engineering & Coating Technologies for Corrosion and Tribocorrosion Resistance)

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12 pages, 2092 KiB

Open AccessEditor’s ChoiceArticle

Hybrid Dispersion Model Characterization of PAZO Azopolymer Thin Films over the Entire Transmittance Spectrum Measured in the UV/VIS/NIR Spectral Region

by Dorian Minkov, Lian Nedelchev, George Angelov, Emilio Marquez, Blaga Blagoeva, Georgi Mateev and Dimana Nazarova

Materials 2022, 15(23), 8617; https://doi.org/10.3390/ma15238617 - 2 Dec 2022

Cited by 3 | Viewed by 1780

Abstract

Notwithstanding the significant optical applicability of PAZO polymer films, there are no accurate data about their optical characteristics. To remedy this shortcoming, in this study three PAZO polymer thin films are characterized, with dissimilar thicknesses, on glass substrates using only one UV/VIS/NIR transmittance [...] Read more.

Notwithstanding the significant optical applicability of PAZO polymer films, there are no accurate data about their optical characteristics. To remedy this shortcoming, in this study three PAZO polymer thin films are characterized, with dissimilar thicknesses, on glass substrates using only one UV/VIS/NIR transmittance spectrum T(λ) per sample and an original hybrid dispersion model (HDM). HDM is based on the Tauc–Lorentz model, the new amorphous dispersion formula, the Tauc–Lorentz–Urbach model of Foldyna and the Tauc–Lorentz–Urbach model of Rodriguez. HDM with two oscillators is employed in characterizations of the PAZO polymer films in the range [300, 2500] nm, whereby the root-mean-square deviation (RMSD) of the fitted transmittance spectrum with respect to T(λ) does not exceed 1.6 × 10⁻³. Decreasing RMSD by 2.3% to 94.4% is demonstrated by employing HDM compared with the above mentioned four popular dispersion models, for each one of the studied films. HDM is applicable to amorphous films independent of their thickness as well as to cases of non-transparent substrate. Full article

(This article belongs to the Special Issue Structural, Morphological, and Optical Properties of Functional Thin Films)

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12 pages, 2174 KiB

Open AccessEditor’s ChoiceArticle

Deep Tissue Characterization with Optical Coherence Elastography: A Comparison of Different Methods

by Asha Parmar, Gargi Sharma, Andreas Ramming and Kanwarpal Singh

Materials 2022, 15(23), 8558; https://doi.org/10.3390/ma15238558 - 1 Dec 2022

Cited by 3 | Viewed by 2044

Abstract

The measurement of the biomechanical properties of the skin is of great interest since these properties play an important role in the development of several diseases such as skin cancer and systemic sclerosis. In this direction, several diagnostic tools have been developed to [...] Read more.

The measurement of the biomechanical properties of the skin is of great interest since these properties play an important role in the development of several diseases such as skin cancer and systemic sclerosis. In this direction, several diagnostic tools have been developed to analyze the mechanical properties of the skin. Optical coherence elastography (OCE) is one of the emerging imaging techniques used for the characterization of the mechanical properties of the tissue quantitatively. In systemic sclerosis patients, the measurement of the mechanical properties of the deeper skin layers is desirable compared to the superficial layers. There are several variants of OCE that exist, but it is still not clear which method is more suitable for the measurement of the mechanical properties of the deeper tissue. In this work, we tested three common methods, the pulsed excitation method, the continuous wave excitation method, and the resonant frequency method, for the measurement of the mechanical properties of the deeper layers in the tissue. We found out that the pulsed wave excitation method provides the most reliable measurements in the shortest possible time compared to the other two methods. Full article

(This article belongs to the Special Issue Optical Methods for Characterization of Biological Materials)

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16 pages, 1156 KiB

Open AccessEditor’s ChoiceArticle

Effects of Functionalized Materials and Bacterial Metabolites on Quality Indicators in Composts

by Krzysztof Gondek, Piotr Micek, Monika Mierzwa-Hersztek, Jerzy Kowal, Krzysztof Andres, Katarzyna Szczurowska, Marcin Lis and Krzysztof Smoroń

Materials 2022, 15(23), 8564; https://doi.org/10.3390/ma15238564 - 1 Dec 2022

Cited by 6 | Viewed by 1969

Abstract

The addition of functionalized materials (biochar, zeolite, and diatomite) and lyophilized metabolic products of Pseudomonas sp. and Bacillus subtilis to composted biomass may bring many technological and environmental benefits. In this study, we verify the effects of biochar, zeolite Na-P1 (Na₆Si [...] Read more.

The addition of functionalized materials (biochar, zeolite, and diatomite) and lyophilized metabolic products of Pseudomonas sp. and Bacillus subtilis to composted biomass may bring many technological and environmental benefits. In this study, we verify the effects of biochar, zeolite Na-P1 (Na₆Si₁₀Al₆O₃₂·12 H₂O), diatomite (SiO_{2_}nH₂O), and bacterial metabolites on the composting of biomass prepared from poultry litter, corn straw, grass, leonardite, and brown coal. The experimental design included the following treatments: C—biomass without the addition of functionalized materials and bacterial metabolites, CB—biomass with the addition of biochar, CBM—biomass with the addition of biochar and bacterial metabolites, CZ—biomass with the addition of zeolite, CZM—biomass with the addition of zeolite and bacterial metabolites, CD—biomass with the addition of diatomite, and CDM—biomass with the addition of diatomite and bacterial metabolites. Composts were analyzed for enzymatic and respiratory activities, mobility of heavy metals, and the presence of parasites. The results of this study revealed that, among the analyzed functionalized materials, the addition of diatomite to the composted biomass (CD and CDM) resulted in the most effective immobilization of Cd, Zn, Pb, and Cu. Zinc immobilization factors (IFHM) for diatomite-amended composts averaged 30%. For copper, each functionalized material was found to enhance mobilization of the element in bioavailable forms; similar observations were made for lead, except for the compost to which biochar and bacterial metabolites were added (CBM). The determined values of biochemical indicators proved the different effects of the applied functionalized materials and bacterial metabolites on the microbial communities colonizing individual composts. The dehydrogenase activity (DhA) was lower in all combinations as compared with the control, indicating an intensification of the rate of processes in the studied composts. The highest basal respiration (BR) and substrate-induced respiration (SIR) activities were determined in composts with the addition of bacterial metabolites (CBM, CZM, and CDM). The addition of functionalized materials completely inactivated Eimeria sp. in all combinations. In the case of Capillaria sp., complete inactivation was recorded for the combination with zeolite as well as biochar and diatomite without bacterial metabolites (CB, CZ, and CD). Full article

(This article belongs to the Special Issue Nanomaterials for the Environmental Remediation of Water and Soil)

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17 pages, 8633 KiB

Open AccessEditor’s ChoiceArticle

Effect of an Anaerobic Fermentation Process on 3D-Printed PLA Materials of a Biogas-Generating Reactor

by Adrian Cioabla, Virgil-Florin Duma, Corina Mnerie, Ralph-Alexandru Erdelyi, George Mihai Dobre, Adrian Bradu and Adrian Podoleanu

Materials 2022, 15(23), 8571; https://doi.org/10.3390/ma15238571 - 1 Dec 2022

Cited by 8 | Viewed by 2249

Abstract

3D-printed materials are present in numerous applications, from medicine to engineering. The aim of this study is to assess their suitability for an application of interest today, that of testing of 3D-printed polylactic acid (PLA)-based reactors for biogas production using anaerobic digestion. The [...] Read more.

3D-printed materials are present in numerous applications, from medicine to engineering. The aim of this study is to assess their suitability for an application of interest today, that of testing of 3D-printed polylactic acid (PLA)-based reactors for biogas production using anaerobic digestion. The impact of temperature, pH, and aqueous phase on the tested bioreactor is investigated, together with the effect of the gaseous phase (i.e., produced biogas). Two batches of materials used separately, one after another inside the bioreactor were considered, in a realistic situation. Two essential parameters inside the reactor (i.e., pH and temperature) were continuously monitored during a time interval of 25 to 30 days for each of the two biogas-generating processes. To understand the impact of these processes on the walls of the bioreactor, samples of 3D-printed material were placed at three levels: at the top (i.e., outside the substrate), in the middle, and at the bottom of the bioreactor. The samples were analyzed using a non-destructive imaging method, Optical Coherence Tomography (OCT). An in-house developed swept-source (SS) OCT system, master–slave (MS) enhanced, operating at a central wavelength of 1310 nm was utilized. The 3D OCT images related to the degradation level of the material of the PLA samples were validated using Scanning Electron Microscopy (SEM). The differences between the impact of the substrate on samples situated at the three considered levels inside the reactor were determined and analyzed using their OCT B-scans (optical cross-section images). Thus, the impact of the biogas-generating process on the interior of the bioreactor was demonstrated and quantified, as well as the capability of OCT to perform such assessments. Therefore, future work may target OCT for in situ investigations of such bioreactors. Full article

(This article belongs to the Special Issue Advanced Optical Methods for Materials Sciences)

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9 pages, 9526 KiB

Open AccessEditor’s ChoiceArticle

Interface Characterization of Bimetallic Ti-6Al-4V/Ti2AlNb Structures Prepared by Selective Laser Melting

by Igor Polozov, Anna Gracheva and Anatoly Popovich

Materials 2022, 15(23), 8528; https://doi.org/10.3390/ma15238528 - 30 Nov 2022

Cited by 9 | Viewed by 2218

Abstract

Additive Manufacturing (AM) of multimaterial components is a promising way of fabricating parts with improved functional properties. It allows for the combination of materials with different properties into a single component. The Ti₂AlNb-based intermetallic alloy provides high temperature strength, while the [...] Read more.

Additive Manufacturing (AM) of multimaterial components is a promising way of fabricating parts with improved functional properties. It allows for the combination of materials with different properties into a single component. The Ti₂AlNb-based intermetallic alloy provides high temperature strength, while the Ti-6Al-4V (Ti64) alloy has good fracture toughness, ductility, and a relatively low cost. A combination of these alloys into a single component can be used to produce advanced multimaterial parts. In this work, Ti₂AlNb/Ti-6Al-4V bimetallic structures were fabricated from pre-alloyed powders using the Selective Laser Melting (SLM) process. The effects of high-temperature substrate preheating, post-processing by annealing, and hot isostatic pressing on defect formation, the microstructural evolution of the interface area, and the mechanical properties of the bimetallic samples were investigated. High-temperature substrate preheating during the SLM process was necessary to prevent reheat cracking of the Ti₂AlNb part, while annealing and hot isostatic pressing post-processing improved the chemical and microstructural homogeneity of the transition zone and enhanced the tensile properties of the bimetallic structure. Full article

(This article belongs to the Special Issue Advances in Materials, Design and Modeling of Additive Manufacturing)

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14 pages, 5110 KiB

Open AccessEditor’s ChoiceArticle

Deep Eutectic Solvent for Facile Synthesis of Mn₃O₄@N-Doped Carbon for Aqueous Multivalent-Based Supercapacitors: New Concept for Increasing Capacitance and Operating Voltage

by Nikola Zdolšek, Ivana Perović, Snežana Brković, Gvozden Tasić, Miloš Milović and Milica Vujković

Materials 2022, 15(23), 8540; https://doi.org/10.3390/ma15238540 - 30 Nov 2022

Cited by 8 | Viewed by 2707

Abstract

The capacitance and operating voltage of supercapacitors as well as their energy density have been increased by development of different materials and electrolytes. In this paper, two strategies, for the first time, were used to improve energy density: Mn₃O₄- [...] Read more.

The capacitance and operating voltage of supercapacitors as well as their energy density have been increased by development of different materials and electrolytes. In this paper, two strategies, for the first time, were used to improve energy density: Mn₃O₄- and N-dual doped carbon electrode and aqueous mixture of multivalent ions as electrolyte. Mn₃O₄- and N-dual doped carbon was prepared by a novel and cost-effective procedure using deep eutectic solvent. XRD, XPS, and FTIR confirmed presence of Mn₃O₄ and nitrogen, while SEM and EDS elemental mapping showed micrometer-sized nanosheets with uniform distribution of C, O, N, and Mn atoms. Charge storage behavior of carbon was tested in aqueous multivalent-based electrolytes and their mixture (Ca²⁺-Al³⁺). Regarding both specific capacitance and workable voltage, the Ca²⁺-Al³⁺ mixed electrolyte was found as the best optimal solution. The calcium addition to the Al-electrolyte allows the higher operating voltage than in the case of individual Al(NO₃)₃ electrolyte while the addition of Al³⁺ ion in the Ca(NO₃)₂ electrolyte improves the multivalent-ion charge storage ability of carbon. As a result, the specific energy density of two-electrode Mn₃O₄@N-doped carbon//Al(NO₃)₂+Ca(NO₃)₂//Mn₃O₄@N-doped carbon supercapacitor (34 Wh kg⁻¹ at 0.1 A g⁻¹) overpasses the reported values obtained for Mn-based carbon supercapacitors using conventional aqueous electrolytes. Full article

(This article belongs to the Special Issue Advanced Materials for Electrochemical Energy Conversion and Storage - Volume II)

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17 pages, 6004 KiB

Open AccessEditor’s ChoiceArticle

Experimental and Numerical Study of Thermal Residual Stresses on Multimaterial Adherends in Single-Lap Joints

by Beatriz D. Simões, Paulo D. P. Nunes, Farin Ramezani, Ricardo J. C. Carbas, Eduardo A. S. Marques and Lucas F. M. da Silva

Materials 2022, 15(23), 8541; https://doi.org/10.3390/ma15238541 - 30 Nov 2022

Cited by 14 | Viewed by 3135

Abstract

The presence of residual stresses in composite materials can significantly affect material performance, especially when integrated in bonded joints. These stresses, often generated during the cure process, can cause cracking and distortion of the material, and are caused by differences in the coefficients [...] Read more.

The presence of residual stresses in composite materials can significantly affect material performance, especially when integrated in bonded joints. These stresses, often generated during the cure process, can cause cracking and distortion of the material, and are caused by differences in the coefficients of thermal expansion or cure shrinkage. In the current research, multimaterial adherends combining carbon-fibre-reinforced polymer (CFRP) and aluminium in a single-lap joint (SLJ) configuration are analysed, allowing us to understand the effect of the thermal residual stresses, developed during the curing process, in the overall performance of the joints. A numerical model resorting to a finite element analysis (FEA) is developed to assess and predict the behaviour of the joints. The use of FML (fibre metal laminates) was found to significantly improve the strength of the joints, as well as the failure mode. The proposed geometry performed similarly to the comparable FML geometry, in addition to a decrease in the joint weight. Full article

(This article belongs to the Special Issue Sandwich Composites: Design, Simulation and Applications)

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30 pages, 1927 KiB

Open AccessEditor’s ChoiceReview

Frontiers of Hydroxyapatite Composites in Bionic Bone Tissue Engineering

by Jingcun Shi, Wufei Dai, Anand Gupta, Bingqing Zhang, Ziqian Wu, Yuhan Zhang, Lisha Pan and Lei Wang

Materials 2022, 15(23), 8475; https://doi.org/10.3390/ma15238475 - 28 Nov 2022

Cited by 27 | Viewed by 3918

Abstract

Bone defects caused by various factors may cause morphological and functional disorders that can seriously affect patient’s quality of life. Autologous bone grafting is morbid, involves numerous complications, and provides limited volume at donor site. Hence, tissue-engineered bone is a better alternative for [...] Read more.

Bone defects caused by various factors may cause morphological and functional disorders that can seriously affect patient’s quality of life. Autologous bone grafting is morbid, involves numerous complications, and provides limited volume at donor site. Hence, tissue-engineered bone is a better alternative for repair of bone defects and for promoting a patient’s functional recovery. Besides good biocompatibility, scaffolding materials represented by hydroxyapatite (HA) composites in tissue-engineered bone also have strong ability to guide bone regeneration. The development of manufacturing technology and advances in material science have made HA composite scaffolding more closely related to the composition and mechanical properties of natural bone. The surface morphology and pore diameter of the scaffold material are more important for cell proliferation, differentiation, and nutrient exchange. The degradation rate of the composite scaffold should match the rate of osteogenesis, and the loading of cells/cytokine is beneficial to promote the formation of new bone. In conclusion, there is no doubt that a breakthrough has been made in composition, mechanical properties, and degradation of HA composites. Biomimetic tissue-engineered bone based on vascularization and innervation show a promising future. Full article

(This article belongs to the Special Issue Feature Papers in the Section Advanced and Functional Ceramics and Glasses)

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42 pages, 10728 KiB

Open AccessEditor’s ChoiceArticle

On the Stability of Complex Concentrated (CC)/High Entropy (HE) Solid Solutions and the Contamination with Oxygen of Solid Solutions in Refractory Metal Intermetallic Composites (RM(Nb)ICs) and Refractory Complex Concentrated Alloys (RCCAs)

by Panos Tsakiropoulos

Materials 2022, 15(23), 8479; https://doi.org/10.3390/ma15238479 - 28 Nov 2022

Cited by 8 | Viewed by 2083

Abstract

In as-cast (AC) or heat-treated (HT) metallic ultra-high temperature materials often “conventional” and complex-concentrated (CC) or high-entropy (HE) solid solutions (sss) are observed. Refractory metal containing bcc sss also are contaminated with oxygen. This paper studied the stability of CC/HE Nb_ss and [...] Read more.

In as-cast (AC) or heat-treated (HT) metallic ultra-high temperature materials often “conventional” and complex-concentrated (CC) or high-entropy (HE) solid solutions (sss) are observed. Refractory metal containing bcc sss also are contaminated with oxygen. This paper studied the stability of CC/HE Nb_ss and the contamination with oxygen of Nb_ss in RM(INb)ICs, RM(Nb)ICs/RCCAs and RM(Nb)ICs/RHEAs. “Conventional” and CC/HE Nb_ss were compared. “Conventional” Nb_ss can be Ti-rich only in AC alloys. Ti-rich Nb_ss is not observed in HT alloys. In B containing alloys the Ti-rich Nb_ss is usually CC/HE. The CC/HE Nb_ss is stable in HT alloys with simultaneous addition of Mo, W with Hf, Ge+Sn. The implications for alloy design of correlations between the parameter δ of “conventional” and CC/HE Nb_ss with the B or the Ge+Sn concentration in the Nb_ss and of relationships of other solutes with the B or Ge+Sn content are discussed. The CC/HE Nb_ss has low Δχ, VEC and Ω and high ΔS_mix, |ΔH_mix| and δ parameters, and is formed in alloys that have high entropy of mixing. These parameters are compared with those of single-phase bcc ss HEAs and differences in ΔH_mix, δ, Δχ and Ω, and similarities in ΔS_mix and VEC are discussed. Relationships between the parameters of alloy and “conventional” Nb_ss also apply for CC/HE Nb_ss. The parameters δ_ss and Ω_ss, and VEC_ss and VEC_alloy can differentiate between types of alloying additions and their concentrations and are key regarding the formation or not of CC/HE Nb_ss. After isothermal oxidation at a pest temperature (800 ^oC/100 h) the contaminated with oxygen Nb_ss in the diffusion zone is CC/HE Nb_ss, whereas the Nb_ss in the bulk can be “conventional” Nb_ss or CC/HE Nb_ss. The parameters of “uncontaminated” and contaminated with oxygen sss are linked with linear relationships. There are correlations between the oxygen concentration in contaminated sss in the diffusion zone and the bulk of alloys with the parameters Δχ_Nbss, δ_Nbss and VEC_Nbss, the values of which increase with increasing oxygen concentration in the ss. The effects of contamination with oxygen of the near surface areas of a HT RM(Nb)IC with Al, Cr, Hf, Si, Sn, Ti and V additions and a high vol.% Nb_ss on the hardness and Young’s modulus of the Nb_ss, and contributions to the hardness of the Nb_ss in B free or B containing alloys are discussed. The hardness and Young’s modulus of the bcc ss increased linearly with its oxygen concentration and the change in hardness and Young’s modulus due to contamination increased linearly with [O]^2/3. Full article

(This article belongs to the Special Issue Mechanics and Analysis of Advanced Materials and Structures)

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13 pages, 2289 KiB

Open AccessEditor’s ChoiceArticle

Dissolution Assay of Bupropion/Naltrexone Hydrochloride Salts of Bilayer Composition Tablets Following the Development and Validation of a Novel HPLC Method

by Anna Apostolidi, Chrystalla Protopapa, Angeliki Siamidi, Marilena Vlachou and Yannis Dotsikas

Materials 2022, 15(23), 8451; https://doi.org/10.3390/ma15238451 - 27 Nov 2022

Cited by 4 | Viewed by 2511

Abstract

Compounded medicinal products containing bupropion hydrochloride (BUP·HCl) and naltrexone hydrochloride (NTX·HCl) are available as adjunct therapy for the management of weight in obese/overweight adults. The present work describes the development and validation of a novel RP-HPLC method for a simultaneous quantitation during the [...] Read more.

Compounded medicinal products containing bupropion hydrochloride (BUP·HCl) and naltrexone hydrochloride (NTX·HCl) are available as adjunct therapy for the management of weight in obese/overweight adults. The present work describes the development and validation of a novel RP-HPLC method for a simultaneous quantitation during the dissolution of both drugs from compounded bilayer composition tablets. The method involves a Nucleosil 100-3 C-18 column (4.6 × 150 mm) and a mobile phase of a 70%/30% v/v ACN/KH₂PO₄·H₂O aqueous solution of a 5 mM concentration. The flow rate was set at 1.35 mL/min and the detection was conducted using UV spectrophotometry (λ_max 214 nm). The method was validated according to the ICH guidelines and fulfilled the specifications for the specificity, linearity, accuracy, precision and stability for both the sample and standard solutions. Furthermore, the robustness of the method was evaluated by applying a fractional factorial experimental design and by utilizing both graphical and statistical approaches to identify the HPLC factors that should be strictly controlled during the analysis. The method proved to be suitable for the analysis of the dissolution samples and, consequently, the release of BUP·HCl and NTX·HCl from the formulations. Full article

(This article belongs to the Special Issue Drug Delivery: Recent Developments and Future Prospects)

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16 pages, 2455 KiB

Open AccessEditor’s ChoiceReview

Current Status of the Open-Circuit Voltage of Kesterite CZTS Absorber Layers for Photovoltaic Applications—Part I, a Review

by Iulian Boerasu and Bogdan Stefan Vasile

Materials 2022, 15(23), 8427; https://doi.org/10.3390/ma15238427 - 26 Nov 2022

Cited by 17 | Viewed by 2201

Abstract

Herein, based on the reviewed literature, the current marketability challenges faced by kesterite CZTS based-solar cells is addressed. A knowledge update about the attempts to reduce the open circuit voltage deficit of kesterite CZTS solar cells will be addressed, with a focus on [...] Read more.

Herein, based on the reviewed literature, the current marketability challenges faced by kesterite CZTS based-solar cells is addressed. A knowledge update about the attempts to reduce the open circuit voltage deficit of kesterite CZTS solar cells will be addressed, with a focus on the impact of Cu/Zn order/disorder and of Se doping. This review also presents the strengths and weaknesses of the most commercially attractive synthesis methods for synthesizing thin kesterite CZTS films for photovoltaic applications. Full article

(This article belongs to the Special Issue Synthesis, Characterization and Multipurpose Applications of Advanced Micro and Nanomaterials Used in Life and Materials Science)

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12 pages, 3293 KiB

Open AccessEditor’s ChoiceArticle

Polycrystalline PbTe:In Films on Amorphous Substrate: Structure and Physical Properties

by Vadim Kovalyuk, Evgeniia Sheveleva, Mark Auslender, Gregory Goltsman, Roni Shneck and Zinovi Dashevsky

Materials 2022, 15(23), 8383; https://doi.org/10.3390/ma15238383 - 25 Nov 2022

Cited by 7 | Viewed by 1826

Abstract

Polycrystalline PbTe:In films on a polyimide substrate were obtained and investigated. Their structural and transport properties in a wide range of temperatures (10–300 K) were studied. The unique feature of In impurity in PbTe is the stabilization of the Fermi level (pinning effect) [...] Read more.

Polycrystalline PbTe:In films on a polyimide substrate were obtained and investigated. Their structural and transport properties in a wide range of temperatures (10–300 K) were studied. The unique feature of In impurity in PbTe is the stabilization of the Fermi level (pinning effect) that allowed for the preparation polycrystalline films with the same carrier concentration. We found that heat treatment in an argon atmosphere does not change the average grain size and carrier concentration for as-grown films but greatly increases the Hall mobility and the electron mean free path. By comparing the mobility in the bulk and in the film after heat treatment, we extracted the value of the mobility that arises due to scattering at the grain boundary barriers. The ultimate goal of the present study is the development of these films in designing portable uncooled photodetectors for the mid-IR range. Full article

(This article belongs to the Section Thin Films and Interfaces)

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22 pages, 6172 KiB

Open AccessEditor’s ChoiceArticle

Thermodynamic Modeling and Experimental Validation of Acetic Acid Attack on Hardened Cement Paste: Effect of Silica Fume

by Felix Berger, Andreas Bogner, Astrid Hirsch, Neven Ukrainczyk, Frank Dehn and Eduardus Koenders

Materials 2022, 15(23), 8355; https://doi.org/10.3390/ma15238355 - 24 Nov 2022

Cited by 8 | Viewed by 1905

Abstract

Concrete structures are increasingly becoming exposed to organic acid attack conditions, such as those found in agriculture and food-related industries. This paper aims to experimentally verify the thermodynamic modeling of cement pastes under acetic acid attack. For this, a modeling approach implemented in [...] Read more.

Concrete structures are increasingly becoming exposed to organic acid attack conditions, such as those found in agriculture and food-related industries. This paper aims to experimentally verify the thermodynamic modeling of cement pastes under acetic acid attack. For this, a modeling approach implemented in IPHREEQC via Matlab is described, and results are compared with measured pH and compositions of equilibrated solutions (MP-AES) as well as unreacted/precipitated solids (XRF, XRD and STA) for a wide range of acid concentrations. The 11% replacement of cement by silica fume (SF) led to a 60 or 70% reduction (measured or modeled, respectively) of Portlandite content in the hardened cement paste due to the pozzolanic reaction resulting in higher content of CSH phases, which has effects on the progression of dissolution processes and a resulting pH with increased acid concentrations. Considering that no fitting parameter was used, the model predictions showed good agreement with measured values of pH, dissolved ion concentrations and composition of the remaining (degraded) solids overall. The discrepancies here were more pronounced at very high acid concentrations (equilibrium pH < ~4), i.e., after the full dissolution of hydrate phases due to limitations in the model used to describe Al-, Si- and Fe-gel phases and/or identified experimental challenges in precipitation of calcium and aluminum acetate hydrates. Full article

(This article belongs to the Special Issue Mathematical Modeling of Building Materials)

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23 pages, 8891 KiB

Open AccessEditor’s ChoiceArticle

Effects of Na₂CO₃/Na₂SiO₃ Ratio and Curing Temperature on the Structure Formation of Alkali-Activated High-Carbon Biomass Fly Ash Pastes

by Chengjie Zhu, Ina Pundienė, Jolanta Pranckevičienė and Modestas Kligys

Materials 2022, 15(23), 8354; https://doi.org/10.3390/ma15238354 - 24 Nov 2022

Cited by 11 | Viewed by 2652

Abstract

This study explored unprocessed high-carbon biomass fly ash (BFA) in alkali-activated materials (AAM) with less alkaline Na₂CO₃ as the activator. In this paper, the effects of the Na₂CO₃/Na₂SiO₃ (C/S) ratio and curing temperature [...] Read more.

This study explored unprocessed high-carbon biomass fly ash (BFA) in alkali-activated materials (AAM) with less alkaline Na₂CO₃ as the activator. In this paper, the effects of the Na₂CO₃/Na₂SiO₃ (C/S) ratio and curing temperature (40 °C and 20 °C) on the setting time, structure formation, product synthesis, and physical-mechanical properties of alkali-activated BFA pastes were systematically investigated. Regardless of curing temperature, increasing the C/S ratio increased the density and compressive strength of the sample while a decrease in water absorption. The higher the curing temperature, the faster the structure evolution during the BFA-based alkaline activation synthesis process and the higher the sample’s compressive strength. According to XRD and TG/DTA analyses, the synthesis of gaylussite and C-S-H were observed in the sample with an increasing C/S ratio. The formation of the mentioned minerals contributes to the compressive strength growth of alkali-activated BFA pastes with higher C/S ratios. The findings of this study contribute to the applicability of difficult-to-recycle waste materials such as BFA and the development of sustainable BFA-based AAM. Full article

(This article belongs to the Special Issue Recent Developments in Geopolymers and Alkali-Activated Materials)

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8 pages, 2270 KiB

Open AccessEditor’s ChoiceArticle

The Effect of a Nucleation Layer on Morphology and Grain Size in MOCVD-Grown β-Ga₂O₃ Thin Films on C-Plane Sapphire

by Lauris Dimitrocenko, Gundars Strikis, Boris Polyakov, Liga Bikse, Sven Oras and Edgars Butanovs

Materials 2022, 15(23), 8362; https://doi.org/10.3390/ma15238362 - 24 Nov 2022

Cited by 9 | Viewed by 2432

Abstract

β-Ga₂O₃ thin films grown on widely available c-plane sapphire substrates typically exhibit structural defects due to significant lattice and thermal expansion mismatch, which hinder the use of such films in electronic devices. In this work, we studied the impact of [...] Read more.

β-Ga₂O₃ thin films grown on widely available c-plane sapphire substrates typically exhibit structural defects due to significant lattice and thermal expansion mismatch, which hinder the use of such films in electronic devices. In this work, we studied the impact of a nucleation layer on MOCVD-grown β-Ga₂O₃ thin film structure and morphology on a c-plane sapphire substrate. The structure and morphology of the films were investigated by X-ray diffraction, atomic force microscopy, transmission and scanning electron microscopy, while the composition was confirmed by X-ray photoelectron spectroscopy and micro-Raman spectroscopy. It was observed that the use of a nucleation layer significantly increases the grain size in the films in comparison to the films without, particularly in the samples in which H₂O was used alongside O₂ as the oxygen source for the nucleation layer growth. Our study demonstrates that a nucleation layer can play a critical role in obtaining high quality β-Ga₂O₃ thin films on c-plane sapphire. Full article

(This article belongs to the Special Issue Wide and Ultra-Wide Bandgap Semiconductor Materials for Power Devices)

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9 pages, 3088 KiB

Open AccessEditor’s ChoiceArticle

Smart Humidly Adaptive Yarns and Textiles from Twisted and Coiled Viscose Fiber Artificial Muscles

by Mingrui Guo, Yangyang Peng, Zihan Chen, Nan Sheng and Fengxin Sun

Materials 2022, 15(23), 8312; https://doi.org/10.3390/ma15238312 - 23 Nov 2022

Cited by 3 | Viewed by 2228

Abstract

The self-adaptive nature of smart textiles to the ambient environment has made them an indispensable part of emerging wearable technologies. However, current advances generally suffer from complex material preparation, uncomfortable fitting feeling, possible toxicity, and high cost in fabrication, which hinder the real-world [...] Read more.

The self-adaptive nature of smart textiles to the ambient environment has made them an indispensable part of emerging wearable technologies. However, current advances generally suffer from complex material preparation, uncomfortable fitting feeling, possible toxicity, and high cost in fabrication, which hinder the real-world application of smart materials in textiles. Herein, humidity-response torsional and tensile yarn actuators from twisted and coiled structures are developed using commercially available, cost-effective, and biodegradable viscose fibers based on yarn-spinning and weaving technologies. The twisted yarn shows a reversible torsional stroke of 1400° cm⁻¹ in 5 s when stimulated by water fog with a spraying speed of 0.05 g s⁻¹; the coiled yarn exhibits a peak tensile stroke of 900% upon enhancing the relative humidity. Further, textile manufacturing allows for the scalable fabrication to create fabric artificial muscles with high-dimensional actuation deformations and human-touch comfort, which can boost the potential applications of the humidly adaptive yarns in smart textile and advanced textile materials. Full article

(This article belongs to the Special Issue Advanced Textile Materials: Design, Properties and Applications)

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13 pages, 2859 KiB

Open AccessEditor’s ChoiceArticle

Polarization of Acoustic Waves in Two-Dimensional Phononic Crystals Based on Fused Silica

by Mikhail V. Marunin and Nataliya V. Polikarpova

Materials 2022, 15(23), 8315; https://doi.org/10.3390/ma15238315 - 23 Nov 2022

Cited by 4 | Viewed by 2553

Abstract

The two-dimensional square-lattice phononic crystal is one of the recently proposed acoustic metamaterials. Strong anisotropic propagation of elastic waves makes the material promising for various potential applications in acoustics and acousto-optics. This paper presents a study of the propagation of elastic waves in [...] Read more.

The two-dimensional square-lattice phononic crystal is one of the recently proposed acoustic metamaterials. Strong anisotropic propagation of elastic waves makes the material promising for various potential applications in acoustics and acousto-optics. This paper presents a study of the propagation of elastic waves in two-dimensional phononic crystals based on fused silica. The band structures of a phononic crystal are obtained by solving the wave equation in its variational form by the finite element method. The main phononic crystal acoustic characteristics that are of practical interest in acousto-optics are calculated based on the analysis of the dispersion relations. It is shown that the choice of the phononic crystal geometry makes it possible to control the distributions of both the inverse phase velocities and the energy walk-off angles of acoustic modes. The calculations of the acoustic modes’ polarization are in a particular focus. It is demonstrated that under certain conditions, there are exactly three acoustic modes propagating in a phononic crystal, the averaged polarization vectors of which are mutually orthogonal for any directions of the acoustic wave’s propagation. It is argued that the acoustic properties of phononic crystals meet the requirements of acousto-optics. Full article

(This article belongs to the Special Issue Acousto-Optical Spectral Technologies)

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19 pages, 3905 KiB

Open AccessEditor’s ChoiceArticle

Surface Modification of 3D-Printed PCL/BG Composite Scaffolds via Mussel-Inspired Polydopamine and Effective Antibacterial Coatings for Biomedical Applications

by Kanwal Ilyas, Muhammad Asim Akhtar, Ezzeddine Ben Ammar and Aldo R. Boccaccini

Materials 2022, 15(23), 8289; https://doi.org/10.3390/ma15238289 - 22 Nov 2022

Cited by 8 | Viewed by 3398

Abstract

A wide variety of composite scaffolds with unique geometry, porosity and pore size can be fabricated with versatile 3D printing techniques. In this work, we fabricated 3D-printed composite scaffolds of polycaprolactone (PCL) incorporating bioactive glass (BG) particles (13-93 and 13-93B3 compositions) by using [...] Read more.

A wide variety of composite scaffolds with unique geometry, porosity and pore size can be fabricated with versatile 3D printing techniques. In this work, we fabricated 3D-printed composite scaffolds of polycaprolactone (PCL) incorporating bioactive glass (BG) particles (13-93 and 13-93B3 compositions) by using fused deposition modeling (FDM). The scaffolds were modified with a “mussel-inspired surface coating” to regulate biological properties. The chemical and surface properties of scaffolds were analyzed by Fourier transform infrared spectroscopy (FTIR), contact angle and scanning electron microscopy (SEM). Polydopamine (PDA) surface-modified composite scaffolds exhibited attractive properties. Firstly, after the surface modification, the adhesion of a composite coating based on gelatin incorporated with strontium-doped mesoporous bioactive glass (Sr-MBGNs/gelatin) was significantly improved. In addition, cell attachment and differentiation were promoted, and the antibacterial properties of the scaffolds were increased. Moreover, the bioactivity of these scaffolds was also significantly influenced: a hydroxyapatite layer formed on the scaffold surface after 3 days of immersion in SBF. Our results suggest that the promoting effect of PDA coating on PCL-BG scaffolds leads to improved scaffolds for bone tissue engineering. Full article

(This article belongs to the Special Issue Porous Ceramics, Glasses and Composites)

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16 pages, 4871 KiB

Open AccessEditor’s ChoiceArticle

Near-Infrared Artificial Optical Synapse Based on the P(VDF-TrFE)-Coated InAs Nanowire Field-Effect Transistor

by Rui Shen, Yifan Jiang, Zhiwei Li, Jiamin Tian, Shuo Li, Tong Li and Qing Chen

Materials 2022, 15(22), 8247; https://doi.org/10.3390/ma15228247 - 21 Nov 2022

Cited by 6 | Viewed by 2897

Abstract

Optical synapse is the basic component for optical neuromorphic computing and is attracting great attention, mainly due to its great potential in many fields, such as image recognition, artificial intelligence and artificial visual perception systems. However, optical synapse with infrared (IR) response has [...] Read more.

Optical synapse is the basic component for optical neuromorphic computing and is attracting great attention, mainly due to its great potential in many fields, such as image recognition, artificial intelligence and artificial visual perception systems. However, optical synapse with infrared (IR) response has rarely been reported. InAs nanowires (NWs) have a direct narrow bandgap and a large surface to volume ratio, making them a promising material for IR detection. Here, we demonstrate a near-infrared (NIR) (750 to 1550 nm) optical synapse for the first time based on a poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE))-coated InAs NW field-effect transistor (FET). The responsivity of the P(VDF-TrFE)-coated InAs NW FET reaches 839.3 A/W under 750 nm laser illumination, demonstrating the advantage of P(VDF-TrFE) coverage. The P(VDF-TrFE)-coated InAs NW device exhibits optical synaptic behaviors in response to NIR light pulses, including excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF) and a transformation from short-term plasticity (STP) to long-term plasticity (LTP). The working mechanism is attributed to the polarization effect in the ferroelectric P(VDF-TrFE) layer, which dominates the trapping and de-trapping characteristics of photogenerated holes. These findings have significant implications for the development of artificial neural networks. Full article

(This article belongs to the Special Issue III-V Nanostructures and Their Devices)

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13 pages, 8194 KiB

Open AccessEditor’s ChoiceArticle

Effect of TiO₂ Additives on the Stabilization of h-YbFeO₃ and Promotion of Photo-Fenton Activity of o-YbFeO₃/h-YbFeO₃/r-TiO₂ Nanocomposites

by Sofia Tikhanova, Anna Seroglazova, Maria Chebanenko, Vladimir Nevedomskiy and Vadim Popkov

Materials 2022, 15(22), 8273; https://doi.org/10.3390/ma15228273 - 21 Nov 2022

Cited by 11 | Viewed by 2061

Abstract

Nanostructured hexagonal rare-earth orthoferrites (h-RfeO₃, R = Sc, Y, Tb-Lu) are well known as a highly effective base for visible-light-driven heterojunction photocatalysts. However, their application is limited by metastability, leading to difficulties in synthesis due to the irreversible transformation [...] Read more.

Nanostructured hexagonal rare-earth orthoferrites (h-RfeO₃, R = Sc, Y, Tb-Lu) are well known as a highly effective base for visible-light-driven heterojunction photocatalysts. However, their application is limited by metastability, leading to difficulties in synthesis due to the irreversible transformation to a stable orthorhombic structure. In this work, we report on a simple route to the stabilization of h-YbFeO₃ nanocrystals by the synthesis of multiphase nanocomposites with titania additives. The new I-type heterojunction nanocomposites of o-YbFeO₃/h-YbFeO₃/r-TiO₂ were obtained by the glycine–nitrate solution combustion method with subsequent heat treatment of the products. An increase in the mole fraction of the h-YbFeO₃ phase in nanocomposites was found with the titanium addition, indicating its stabilizing effect via limiting mass transfer over heat treatment. The complex physicochemical analysis shows multiple contacts of individual nanocrystals of o-YbFeO₃ (44.4–50.6 nm), h-YbFeO₃ (7.5–17.6 nm), and rutile r-TiO₂ (~5 nm), confirming the presence of the heterojunction structure in the obtained nanocomposite. The photocatalytic activity of h-YbFeO₃/o-YbFeO₃/r-TiO₂ nanocomposites was evaluated by the photo-Fenton degradation of the methyl violet under visible light (λ ≥ 400 nm). It was demonstrated that the addition of 5 mol.% of TiO₂ stabilizes h-YbFeO₃, which allowed us to achieve a 41.5 mol% fraction, followed by a three-time increase in the photodecomposition rate constant up to 0.0160 min⁻¹. Full article

(This article belongs to the Special Issue New Advances in Nanomaterials)

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12 pages, 3059 KiB

Open AccessEditor’s ChoiceArticle

Development of Root Caries Prevention by Nano-Hydroxyapatite Coating and Improvement of Dentin Acid Resistance

by Miyu Iwasaki, Ryouichi Satou and Naoki Sugihara

Materials 2022, 15(22), 8263; https://doi.org/10.3390/ma15228263 - 21 Nov 2022

Cited by 1 | Viewed by 2295

Abstract

There is no established method for optimizing the use of dentin to prevent root caries, which are increasing in the elderly population. This study aimed to develop a new approach for root caries prevention by focusing on bioapatite (BioHap), a new biomaterial, combined [...] Read more.

There is no established method for optimizing the use of dentin to prevent root caries, which are increasing in the elderly population. This study aimed to develop a new approach for root caries prevention by focusing on bioapatite (BioHap), a new biomaterial, combined with fluoride. Bovine dentin was used as a sample, and an acid challenge was performed in three groups: no fluoride (control group), acidulated phosphate fluoride treatment (APF group), and BioHap + APF treatment (BioHap group). After applying the new compound, the acid resistance of dentin was compared with that of APF alone. The BioHap group had fewer defects and an increased surface hardness than the APF group. The BioHap group had the smallest lesion depth and least mineral loss among all groups. Using a scanning electron microscope in the BioHap group showed the closure of dentinal tubules and a coating on the surface. The BioHap group maintained a coating and had higher acid resistance than the APF group. The coating prevents acid penetration, and the small particle size of BioHap and its excellent reactivity with fluoride are thought to have contributed to the improvement of acid resistance in dentin. Topical fluoride application using BioHap protects against root caries. Full article

(This article belongs to the Special Issue Materials for Hard Tissue Repair and Regeneration (Second Volume))

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14 pages, 2144 KiB

Open AccessEditor’s ChoiceArticle

Hydroxyapatite Affects the Physicochemical Properties of Contemporary One-Step Self-Etch Adhesives

by Yutaro Motoyama, Monica Yamauti, Masatoshi Nakajima, Masaomi Ikeda, Junji Tagami, Yasushi Shimada and Keiichi Hosaka

Materials 2022, 15(22), 8255; https://doi.org/10.3390/ma15228255 - 21 Nov 2022

Cited by 3 | Viewed by 2692

Abstract

The study aimed to evaluate the influence of the manipulation surfaces on the physical properties of one-step self-etch adhesives (1-SEAs). Scotchbond Universal (SBU), Clearfil Universal Bond Quick ER (UBQ), and an experimental adhesive (UBQ_exp) were manipulated on different surfaces: manufacturer’s Teflon-based [...] Read more.

The study aimed to evaluate the influence of the manipulation surfaces on the physical properties of one-step self-etch adhesives (1-SEAs). Scotchbond Universal (SBU), Clearfil Universal Bond Quick ER (UBQ), and an experimental adhesive (UBQ_exp) were manipulated on different surfaces: manufacturer’s Teflon-based dispensing dish (TD) or hydroxyapatite plate (HA). After manipulation of the adhesives, the pH of each 1-SEA was measured. Samples of each adhesive/manipulation surface were prepared and subjected to water sorption (WS)/solubility (SL) and flexural strength tests. The modulus of elasticity (E) was measured in dry and wet conditions before and after 24 h water storage, and the percentage of variation of E (ΔE) was calculated. Results were analyzed using the t-test with Bonferroni corrections (α = 0.05). When adhesives were manipulated on the HA plate, there was a significant increase in the adhesives’ pH. WS and SL of all 1-SEAs decreased when the HA was used. Only SBU showed higher flexural strength when manipulated on the HA compared to the manipulation on TD under dry and wet conditions. For each 1-SEA, the use of HA resulted in significantly higher E in dry and wet conditions. ΔE of all adhesives was smaller with the manipulation on HA than on TD. It was concluded that the manipulation of 1-SEA on a hydroxyapatite plate considerably affected the adhesives’ properties. Full article

(This article belongs to the Special Issue Unraveling the Properties of Tooth Adhesive Interfaces for the Benefit of the Longevity of Restorations)

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19 pages, 5130 KiB

Open AccessEditor’s ChoiceArticle

Tailoring the Stability of Ti-Doped Sr₂Fe_1.4Ti_xMo_0.6−xO_6−δ Electrode Materials for Solid Oxide Fuel Cells

by Kun Zheng, Maciej Albrycht, Min Chen, Kezhen Qi and Paweł Czaja

Materials 2022, 15(22), 8268; https://doi.org/10.3390/ma15228268 - 21 Nov 2022

Cited by 5 | Viewed by 1969

Abstract

In this work, the stability of Sr₂(FeMo)O_6−δ-type perovskites was tailored by the substitution of Mo with Ti. Redox stable Sr₂Fe_1.4Ti_xMo_0.6−xO_6−δ (x = 0.1, 0.2 and 0.3) perovskites were successfully obtained [...] Read more.

In this work, the stability of Sr₂(FeMo)O_6−δ-type perovskites was tailored by the substitution of Mo with Ti. Redox stable Sr₂Fe_1.4Ti_xMo_0.6−xO_6−δ (x = 0.1, 0.2 and 0.3) perovskites were successfully obtained and evaluated as potential electrode materials for SOFCs. The crystal structure as a function of temperature, microstructure, redox stability, and thermal expansion properties in reducing and oxidizing atmospheres, oxygen content change, and transport properties in air and reducing conditions, as well as chemical stability and compatibility towards typical electrolytes have been systematically studied. All Sr₂Fe_1.4Ti_xMo_0.6−xO_6−δ compounds exhibit a regular crystal structure with Pm-3m space group, showing excellent stability in oxidizing and reducing conditions. The increase of Ti-doping content in materials increases the thermal expansion coefficient (TEC), oxygen content change, and electrical conductivity in air, while it decreases the conductivity in reducing condition. All three materials are stable and compatible with studied electrolytes. Interestingly, redox stable Sr₂Fe_1.4Ti_0.1Mo_0.5O_6−δ, possessing 1 μm grain size, low TEC (15.3 × 10⁻⁶ K⁻¹), large oxygen content change of 0.72 mol·mol⁻¹ between 30 and 900 °C, satisfactory conductivity of 4.1–7.3 S·cm⁻¹ in 5% H₂ at 600–800 °C, and good transport coefficients D and k, could be considered as a potential anode material for SOFCs, and are thus of great interest for further studies. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications)

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18 pages, 4137 KiB

Open AccessEditor’s ChoiceArticle

Characterization of a Magnesium Fluoride Conversion Coating on Mg-2Y-1Mn-1Zn Screws for Biomedical Applications

by Sofia Gambaro, M. Lucia Nascimento, Masoud Shekargoftar, Samira Ravanbakhsh, Vinicius Sales, Carlo Paternoster, Marco Bartosch, Frank Witte and Diego Mantovani

Materials 2022, 15(22), 8245; https://doi.org/10.3390/ma15228245 - 20 Nov 2022

Cited by 10 | Viewed by 3061

Abstract

MgF₂-coated screws made of a Mg-2Y-1Mn-1Zn alloy, called NOVAMag^® fixation screws (biotrics bioimplants AG), were tested in vitro for potential applications as biodegradable implants, and showed a controlled corrosion rate compared to non-coated screws. While previous studies regarding [...] Read more.

MgF₂-coated screws made of a Mg-2Y-1Mn-1Zn alloy, called NOVAMag^® fixation screws (biotrics bioimplants AG), were tested in vitro for potential applications as biodegradable implants, and showed a controlled corrosion rate compared to non-coated screws. While previous studies regarding coated Mg-alloys have been carried out on flat sample surfaces, the present work focused on functional materials and final biomedical products. The substrates under study had a complex 3D geometry and a nearly cylindrical-shaped shaft. The corrosion rate of the samples was investigated using an electrochemical setup, especially adjusted to evaluate these types of samples, and thus, helped to improve an already patented coating process. A MgF₂/MgO coating in the µm-range was characterized for the first time using complementary techniques. The coated screws revealed a smoother surface than the non-coated ones. Although the cross-section analysis revealed some fissures in the coating structure, the electrochemical studies using Hanks’ salt solution demonstrated the effective role of MgF₂ in retarding the alloy degradation during the initial stages of corrosion up to 24 h. The values of polarization resistance (Rp) of the coated samples extrapolated from the Nyquist plots were significantly higher than those of the non-coated samples, and impedance increased significantly over time. After 1200 s exposure, the Rp values were 1323 ± 144 Ω.cm² for the coated samples and 1036 ± 198 Ω.cm² for the non-coated samples, thus confirming a significant decrease in the degradation rate due to the MgF₂ layer. The corrosion rates varied from 0.49 mm/y, at the beginning of the experiment, to 0.26 mm/y after 1200 s, and decreased further to 0.01 mm/y after 24 h. These results demonstrated the effectiveness of the applied MgF₂ film in slowing down the corrosion of the bulk material, allowing the magnesium-alloy screws to be competitive as dental and orthopedic solutions for the biodegradable implants market. Full article

(This article belongs to the Special Issue Research and Development of New Metal-Based Biomaterials)

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10 pages, 2578 KiB

Open AccessEditor’s ChoiceArticle

Charge Trap States of SiC Power TrenchMOS Transistor under Repetitive Unclamped Inductive Switching Stress

by Juraj Marek, Jozef Kozarik, Michal Minarik, Aleš Chvála, Matej Matus, Martin Donoval, Lubica Stuchlikova and Martin Weis

Materials 2022, 15(22), 8230; https://doi.org/10.3390/ma15228230 - 19 Nov 2022

Cited by 2 | Viewed by 2120

Abstract

Silicon carbide (SiC) has been envisioned as an almost ideal material for power electronic devices; however, device reliability is still a great challenge. Here we investigate the reliability of commercial 1.2-kV 4H-SiC MOSFETs under repetitive unclamped inductive switching (UIS). The stress invoked degradation [...] Read more.

Silicon carbide (SiC) has been envisioned as an almost ideal material for power electronic devices; however, device reliability is still a great challenge. Here we investigate the reliability of commercial 1.2-kV 4H-SiC MOSFETs under repetitive unclamped inductive switching (UIS). The stress invoked degradation of the device characteristics, including the output and transfer characteristics, drain leakage current, and capacitance characteristics. Besides the shift of steady-state electrical characteristics, a significant change in switching times points out the charge trapping phenomenon. Transient capacitance spectroscopy was applied to investigate charge traps in the virgin device as well as after UIS stress. The intrinsic traps due to metal impurities or

Z_{1, 2}

transitions were recognized in the virgin device. The UIS stress caused suppression of the second stage of the

Z_{1, 2}

transition, and only the first stage,

Z_{1}^{0}

, was observed. Hence, the UIS stress is causing the reduction of multiple charging of carbon vacancies in SiC-based devices. Full article

(This article belongs to the Special Issue Feature Papers in Electronic Materials Section (Volume 2)—15th Anniversary of Materials)

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