Materials

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 2117

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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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 3198

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 2209

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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13 pages, 5396 KiB

Open AccessEditor’s ChoiceArticle

Cu Nanowires and Nanoporous Ag Matrix Fabricated through Directional Solidification and Selective Dissolution of Ag–Cu Eutectic Alloys

by Jiaxing Xu, Jianjun Gao, Hongling Qin, Zhiyang Liu, Linpeng Zhu, Haibin Geng, Ligang Yao and Zhilong Zhao

Materials 2022, 15(22), 8189; https://doi.org/10.3390/ma15228189 - 18 Nov 2022

Cited by 3 | Viewed by 1846

Abstract

Cu nanowires and a nanoporous Ag matrix were fabricated through directional solidification and selective dissolution of Ag–Cu eutectic alloys. Ag-39.9at.%Cu eutectic alloys were directionally solidified at growth rates of 14, 25, and 34 μm/s at a temperature gradient of 10 K/cm. The Cu [...] Read more.

Cu nanowires and a nanoporous Ag matrix were fabricated through directional solidification and selective dissolution of Ag–Cu eutectic alloys. Ag-39.9at.%Cu eutectic alloys were directionally solidified at growth rates of 14, 25, and 34 μm/s at a temperature gradient of 10 K/cm. The Cu phase in the Ag matrix gradually changed from lamellar to fibrous with an increase in the growth rate. The Ag matrix phase was selectively dissolved, and Cu nanowires of 300–600 nm in diameter and tens of microns in length were prepared in 0.1 M borate buffer with a pH of 9.18 at a constant potential of 0.7 V (vs. SCE). The nanoporous Ag matrix was fabricated through selective dissolution of Cu fiber phase in 0.1 M acetate buffer with a pH of 6.0 at a constant potential of 0.5 V (vs. SCE). The diameter of Ag pores decreased with increasing growth rate. The diameter and depth of Ag pores increased when corrosion time was extended. The depth of the pores was 30 μm after 12 h. Full article

(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)

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12 pages, 5900 KiB

Open AccessEditor’s ChoiceArticle

Susceptibility of High-Manganese Steel to High-Temperature Cracking

by Gabriela Fojt-Dymara, Marek Opiela and Wojciech Borek

Materials 2022, 15(22), 8198; https://doi.org/10.3390/ma15228198 - 18 Nov 2022

Cited by 10 | Viewed by 2210

Abstract

Tests were carried out on two high-Mn steels: 27Mn-4Si-2Al-Nb with Nb microaddition and 24Mn-3Si-1.5Al-Nb-Ti with Nb and Ti microadditions. High-manganese austenitic steels, due to their good strength and plastic properties belong to the AHSS (Advanced High-Strength Steel) group and are used in the [...] Read more.

Tests were carried out on two high-Mn steels: 27Mn-4Si-2Al-Nb with Nb microaddition and 24Mn-3Si-1.5Al-Nb-Ti with Nb and Ti microadditions. High-manganese austenitic steels, due to their good strength and plastic properties belong to the AHSS (Advanced High-Strength Steel) group and are used in the automotive industry. The main difficulties faced during the casting of the steel and hot working are hot cracks, which can appear in the surface of the ingot. Cracks on the edges of the sheet after hot rolling are the reason for cutting the edges of the sheet and increasing production costs and material losses. The main reason for the formation of hot cracks is the decrease in metal ductility in the high-temperature brittleness range (HTBR). The width of the HTBR depends on mechanical properties and microstructural factors, i.e., non-metallic inclusions or intermetallic phases at austenite grain boundaries. In this paper, a hot tensile test was performed. The research was performed on the GLEEBLE 3800 thermomechanical simulator. This test allows us to determine the width of the high-temperature brittleness range (HTBR), the Nil Strength Temperature (NST), the Nil Ductility Temperature (NDT), and the Ductility Recovery Temperature (DRT). Hot ductility was determined from the value of the reduction in area R(A). The obtained results make it possible to determine the temperature of the beginning of hot working from the tested high-Mn steels. Fractographic research enabled us to define mechanisms of hot cracking. It was found that hot cracks form as a result of disruptions in the liquid film on crystals’ boundaries. Full article

(This article belongs to the Special Issue Recent Industry and Engineering Achievements and Their Impact on Material and Manufacturing Processes)

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15 pages, 4913 KiB

Open AccessEditor’s ChoiceArticle

Effect of Poling on Multicatalytic Performance of 0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Sr_0.3)TiO₃ Ferroelectric Ceramic for Dye Degradation

by Akshay Gaur, Shivam Dubey, Zainab Mufarreh Elqahtani, Samia ben Ahmed, Mohammed Sultan Abdulghaffar Al-Buriahi, Rahul Vaish and Vishal Singh Chauhan

Materials 2022, 15(22), 8217; https://doi.org/10.3390/ma15228217 - 18 Nov 2022

Cited by 27 | Viewed by 2726

Abstract

Ferroelectric materials with a spontaneous polarization are proven to be potential multicatalysts in water remediation applications. The composition of 0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Sr_0.3)TiO₃ (BST-BZT) was examined for photocatalysis, piezocatalysis, and piezo-photocatalysis processes by degrading an [...] Read more.

Ferroelectric materials with a spontaneous polarization are proven to be potential multicatalysts in water remediation applications. The composition of 0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Sr_0.3)TiO₃ (BST-BZT) was examined for photocatalysis, piezocatalysis, and piezo-photocatalysis processes by degrading an azo dye named methylene blue (MB). Generally, dis-aligned dipoles restrict the catalytic activities due to which the BST-BZT powder sample was poled by the corona poling technique. Coupled piezocatalysis and photocatalysis process, i.e., the piezo-photocatalysis process has shown maximum dye degradation. There was a significant improvement in degradation efficiency by using a poled BST-BZT sample compared to the unpoled sample in all processes, thus the results suggest an extensive scope of poled ferroelectric ceramic powder in the catalysis field. Full article

(This article belongs to the Special Issue Ferromagnetic and Ferroelectric Materials: Synthesis, Applications, and Techniques)

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20 pages, 6065 KiB

Open AccessEditor’s ChoiceArticle

Structural Phase Transitions and Thermal Degradation Process of MAPbCl₃ Single Crystals Studied by Raman and Brillouin Scattering

by Furqanul Hassan Naqvi and Jae-Hyeon Ko

Materials 2022, 15(22), 8151; https://doi.org/10.3390/ma15228151 - 17 Nov 2022

Cited by 15 | Viewed by 3347

Abstract

Raman spectroscopy was applied to MAPbCl₃ single crystals in a wide frequency range from 10 to 3500 cm⁻¹ over a broad temperature range from −196 °C to 200 °C including both two structural phase transitions and a thermal degradation range. Low-frequency [...] Read more.

Raman spectroscopy was applied to MAPbCl₃ single crystals in a wide frequency range from 10 to 3500 cm⁻¹ over a broad temperature range from −196 °C to 200 °C including both two structural phase transitions and a thermal degradation range. Low-frequency lattice modes of MAPbCl₃ were revealed for the first time, which showed discontinuous anomalies along with the change in the number of Raman modes at the transition points of −114 °C and −110 °C. Several Raman modes related to the C–N stretching and MA rocking modes in addition to the lattice modes displayed temperature dependences similar to those of MAPbBr₃ in both Raman shifts and half widths, indicating that the MA cation arrangement and H–halide bond interactions behave similarly in both systems during the phase transition. The substantial increase in the half widths of nearly all Raman modes especially suggests that the dynamic disorder caused by the free rotational motions of MA cations induces significant anharmonicity in the lattice and thus, reduces the phonon lifetimes. High-temperature Raman and Brillouin scattering measurements showed that the spectral features changed drastically at ~200 °C where the thermal decomposition of MAPbCl₃ into PbCl₂ began. This result exhibits that combined Raman and Brillouin spectroscopic techniques can be a useful tool in monitoring temperature-induced or temporal changes in lead-based halide perovskite materials. Full article

(This article belongs to the Special Issue Emerging Dielectric, Piezoelectric and Ferroelectric Ceramic and Crystalline Materials and Their Applications)

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12 pages, 3522 KiB

Open AccessEditor’s ChoiceArticle

Analysis of Acousto-Optic Figure of Merit in KGW and KYW Crystals

by Konstantin B. Yushkov, Natalya F. Naumenko and Vladimir Ya. Molchanov

Materials 2022, 15(22), 8183; https://doi.org/10.3390/ma15228183 - 17 Nov 2022

Cited by 3 | Viewed by 2148

Abstract

Monoclinic potassium rare-earth crystals are known as efficient materials for solid-state lasers and acousto-optic modulators. A number of specific configurations for acousto-optic devices based on those crystals have recently been proposed, but the acousto-optic effect of those crystals has only been analyzed fragmentarily [...] Read more.

Monoclinic potassium rare-earth crystals are known as efficient materials for solid-state lasers and acousto-optic modulators. A number of specific configurations for acousto-optic devices based on those crystals have recently been proposed, but the acousto-optic effect of those crystals has only been analyzed fragmentarily for some interaction directions. In this work, we numerically searched for the global maxima of an acousto-optic figure of merit for isotropic diffraction in KGd(WO₄)₂ and KY(WO₄)₂ crystals. It was demonstrated that the global maxima of the acousto-optic figure of merit in those crystals occur in the slow optical mode propagating along the crystal’s twofold symmetry axis and in the acoustic wave propagating orthogonally, both for quasi-longitudinal and quasi-shear acoustic modes. The proposed calculation method can be readily used for the optimization of the acousto-optic interaction geometry in crystals with arbitrary symmetry. Full article

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

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15 pages, 5642 KiB

Open AccessEditor’s ChoiceArticle

Nitrogen-Doped Porous Carbon from Biomass with Efficient Toluene Adsorption and Superior Catalytic Performance

by Jing Zhang, Jianwu Zou, Xiang Xu, Zhuang Li, Zheng Zeng and Liqing Li

Materials 2022, 15(22), 8115; https://doi.org/10.3390/ma15228115 - 16 Nov 2022

Cited by 4 | Viewed by 2151

Abstract

The chemical composition and surface groups of the carbon support affect the adsorption capacity of toluene. To investigate the effect of catalyst substrate on the catalytic performance, two different plant biomasses, banana peel and sugarcane peel, were used as carbon precursors to prepare [...] Read more.

The chemical composition and surface groups of the carbon support affect the adsorption capacity of toluene. To investigate the effect of catalyst substrate on the catalytic performance, two different plant biomasses, banana peel and sugarcane peel, were used as carbon precursors to prepare porous carbon catalyst supports (Cba, Csu, respectively) by a chemical activation method. After decorating PtCo₃ nanoparticles onto both carbon supports (Cba, Csu), the PtCo₃-su catalyst demonstrated better catalytic performance for toluene oxidation (T₁₀₀ = 237 °C) at a high space velocity of 12,000 h⁻¹. The Csu support possessed a stronger adsorption capacity of toluene (542 mg g⁻¹), resulting from the synergistic effect of micropore volume and nitrogen-containing functional groups, which led to the PtCo₃-su catalyst exhibiting a better catalytic performance. Moreover, the PtCo₃-su catalyst also showed excellent stability, good water resistance properties, and high recyclability, which can be used as a promising candidate for practical toluene catalytic combustion. Full article

(This article belongs to the Section Catalytic Materials)

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17 pages, 3659 KiB

Open AccessEditor’s ChoiceReview

Aerospace Environmental Challenges for Electrical Insulation and Recent Developments for Electrified Aircraft

by Maricela Lizcano, Tiffany S. Williams, Euy-Sik E. Shin, Diana Santiago and Baochau Nguyen

Materials 2022, 15(22), 8121; https://doi.org/10.3390/ma15228121 - 16 Nov 2022

Cited by 23 | Viewed by 4484

Abstract

The growing trend towards high voltage electrical assets and propulsion in the aeronautics and space industry pose new challenges in electrical insulation materials that cannot be overlooked. Transition to new high voltage electrified systems with unprecedented high levels of voltage, power, and efficiency [...] Read more.

The growing trend towards high voltage electrical assets and propulsion in the aeronautics and space industry pose new challenges in electrical insulation materials that cannot be overlooked. Transition to new high voltage electrified systems with unprecedented high levels of voltage, power, and efficiency must be safe and reliable. Improvements in both performance and safety of megawatt power systems is complicated because of the need for additional power transmission wiring and cabling and new safety requirements that have the potential of making the resulting systems heavier. To mitigate this issue, novel lightweight materials and system solutions are required that would result in lower specific weights in the insulator and conductor. Although reduced size and weight of system components can be achieved with new concepts, designs, and technologies, the high voltage (≥300 V) operation presents a significant challenge. This challenge is further complicated when considering the extreme operating environment that is experienced in aircraft, spacecraft, and targeted human exploration destinations. This paper reviews the extreme environmental challenges for aerospace electrical insulation and the needs associated with operating under high voltage and extreme environments. It also examines several recently developed robust lightweight electrical insulation materials that could enhance insulation performance and life. In aerospace, research must consider mass when developing new technologies. The impact of these recent developments provides a pathway which could enable next generation high altitude all electric aircraft, lightweight power transmission cables for a future sustained presence on the Moon and missions to Mars using HV propulsion, such as spacecraft with Nuclear Electric Propulsion systems. Full article

(This article belongs to the Special Issue Advances in Electric Insulating Materials and Applications)

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18 pages, 3689 KiB

Open AccessEditor’s ChoiceArticle

Mouldability of Additively Manufactured Attachments on Multipoint Tools

by Thomas Herzog, Carsten Tille and Hermann Seitz

Materials 2022, 15(22), 8137; https://doi.org/10.3390/ma15228137 - 16 Nov 2022

Cited by 1 | Viewed by 1952

Abstract

Enhanced multipoint moulding with additive attachments (EMMA) is a process combining vacuum-assisted multipoint moulding (VAMM) and additively manufactured moulding attachments for carbon fibre reinforced plastics (CFRP) component production. The aim of this initial study is to investigate the mouldability of the additively manufactured [...] Read more.

Enhanced multipoint moulding with additive attachments (EMMA) is a process combining vacuum-assisted multipoint moulding (VAMM) and additively manufactured moulding attachments for carbon fibre reinforced plastics (CFRP) component production. The aim of this initial study is to investigate the mouldability of the additively manufactured attachments on the multipoint tool. For this purpose, two different test specimens were defined, the VAMM machine was adjusted, the attachments were additively built with the robot on the curved silicone interpolation layer and lastly, the CFRP specimens were moulded. The fabrication results were analysed with surface comparisons to check that there was no displacement of the attachments during moulding. A visual evaluation of the manufactured components was carried out, and the overall dimensional accuracy was assessed by comparing the surface with the target geometry. The results showed a very good agreement between the shapes before and after the moulding and thus prove that the attachments were not postponed in the moulding process. The optical evaluation confirms good moulding results for the parts manufactured with the enhanced multipoint moulding with additive attachments. Moreover, the evaluation shows that the major parts of the specimens comply with the permissible tolerance of t = 6 mm defined in ISO 20457. To the authors’ best knowledge, this is the first study that has investigated the entire EMMA process and systematically proved the mouldability of the additively manufactured attachments on multipoint tools. Full article

(This article belongs to the Special Issue Advanced Manufacturing Technologies)

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19 pages, 9414 KiB

Open AccessEditor’s ChoiceArticle

Electrical Resistivity and Joule Heating Characteristics of Cementitious Composites Incorporating Multi-Walled Carbon Nanotubes and Carbon Fibers

by Muhammad Usama Salim, Farzana Mustari Nishat, Taekgeun Oh, Doo-Yeol Yoo, Yooseob Song, Togay Ozbakkaloglu and Jung Heum Yeon

Materials 2022, 15(22), 8055; https://doi.org/10.3390/ma15228055 - 15 Nov 2022

Cited by 16 | Viewed by 3535

Abstract

This study investigates the electrical heating (also known as Joule heating) characteristics of cementitious composites containing multi-walled carbon nanotubes (CNT) and carbon fibers (CF) as electrically conductive media in an attempt to develop an eco-friendly and sustainable solution to snow and ice removal [...] Read more.

This study investigates the electrical heating (also known as Joule heating) characteristics of cementitious composites containing multi-walled carbon nanotubes (CNT) and carbon fibers (CF) as electrically conductive media in an attempt to develop an eco-friendly and sustainable solution to snow and ice removal on roadway pavements during the winter season. Various dosages of CNT and CF between 0 and 1.0% (by weight of cement) were tested to find the optimum mixture proportions that yield high-energy and efficient electrical-heating performance with superior mechanical properties. The electrical properties were characterized by measuring the electrical resistivity and temperature rise when attached to a power source. Furthermore, this study examined how the crack width affects the electrical resistivity of cementitious composites containing CNT and/or CF. Compressive and flexural strengths were also measured at different ages of 1, 3, 7, and 28 days to identify how the additions of CNT and CF affect the mechanical properties. Results have shown that adding CF in combination with CNT substantially reduces the electrical resistivity and, in turn, improves the heating performance, as CFs further densify the electrically conductive network in the hydrated matrix; adding either CNT or CF alone was not an effective option to enhance the electrical characteristics. The findings of this study are expected to provide essential information for the design and construction of an electrically heated concrete pavement system with promoted energy efficiency, which will offer a promising solution to enhance winter road maintenance, improve public safety, and provide substantial social cost savings. Full article

(This article belongs to the Special Issue Advanced Concrete Technology – Smart and Multifunctional Cementitious Composites)

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14 pages, 1355 KiB

Open AccessEditor’s ChoiceArticle

Exploiting Partial Solubility in Partially Fluorinated Thermoplastic Blends to Improve Adhesion during Fused Deposition Modeling

by Pau Saldaña-Baqué, Jared W. Strutton, Rahul Shankar, Sarah E. Morgan and Jena M. McCollum

Materials 2022, 15(22), 8062; https://doi.org/10.3390/ma15228062 - 15 Nov 2022

Cited by 1 | Viewed by 2026

Abstract

This work studies the effect of interlayer adhesion on mechanical performance of fluorinated thermoplastics produced by fused deposition modeling (FDM). Here, we study the anisotropic mechanical response of 3D-printed binary blends of poly (vinylidene fluoride) (PVDF) and poly (methyl methacrylate) (PMMA) with the [...] Read more.

This work studies the effect of interlayer adhesion on mechanical performance of fluorinated thermoplastics produced by fused deposition modeling (FDM). Here, we study the anisotropic mechanical response of 3D-printed binary blends of poly (vinylidene fluoride) (PVDF) and poly (methyl methacrylate) (PMMA) with the isotropic mechanical response of these blends fabricated via injection molding. Various PVDF/PMMA filament compositions were produced by twin-screw extrusion and, subsequently, injection-molded or 3D printed into dog-bone shapes. Specimen mechanical and thermal properties were evaluated by mode I tensile testing and differential scanning calorimetry, respectively. Results show that higher PMMA concentration not only improved the tensile strength and decreased ductility but reduced PVDF crystallization. As expected, injection-molded samples revealed better mechanical properties compared to 3D printed specimens. Interestingly, 3D printed blends with lower PMMA content demonstrated better diffusion (adhesion) across interfaces than those with a higher amount of PMMA. The present study provides new findings that may be used to tune mechanical response in 3D printed fluorinated thermoplastics, particularly for energy applications. Full article

(This article belongs to the Special Issue Advanced Manufacturing Technologies)

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13 pages, 1954 KiB

Open AccessEditor’s ChoiceArticle

Adhesive Bioinspired Coating for Enhancing Glass-Ceramics Scaffolds Bioactivity

by Devis Bellucci, Annachiara Scalzone, Ana Marina Ferreira, Valeria Cannillo and Piergiorgio Gentile

Materials 2022, 15(22), 8080; https://doi.org/10.3390/ma15228080 - 15 Nov 2022

Cited by 5 | Viewed by 2125

Abstract

Bioceramic scaffolds, composed of a biphasic composite containing bioactive glass and hydroxyapatite, were prepared in this work to overcome the intrinsic limits of the two components taken separately (in particular, their specific reactivities and dissolution rates, which should be tunable as a function [...] Read more.

Bioceramic scaffolds, composed of a biphasic composite containing bioactive glass and hydroxyapatite, were prepared in this work to overcome the intrinsic limits of the two components taken separately (in particular, their specific reactivities and dissolution rates, which should be tunable as a function of the given clinical requirements). To mimic the biological environment and tune the different stages of cellular response, a coating with gelatin and chondroitin sulphate via Layer-by-Layer (LbL) assembly was presented and discussed. The resulting functionalized scaffolds were affected by the coating in terms of microstructure and porosity. In addition, the LbL coating significantly enhanced the seeded cell behaviour, with high adhesion, proliferation and osteogenic activity, as revealed by the alkaline phosphatase activity and overexpression of osteopontin and osteocalcin. Full article

(This article belongs to the Special Issue Spotlight on Bioactive Glasses)

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10 pages, 3001 KiB

Open AccessEditor’s ChoiceArticle

Effect of Samples Size on the Water Removal and Shrinkage of Eucalyptus urophylla × E. grandis Wood during Supercritical CO₂ Dewatering

by Honghai Liu, Zhilan Li, Xiaokai Zhang and Simin Zhou

Materials 2022, 15(22), 8073; https://doi.org/10.3390/ma15228073 - 15 Nov 2022

Cited by 1 | Viewed by 1587

Abstract

Eucalyptus urophydis E. grandis green wood with different lengths were dewatered using CO₂ that was cyclically alternated between the supercritical fluid and gas phases. The results indicate that shorter specimens can be dewatered to below the fiber saturation point (FSP). There was no [...] Read more.

Eucalyptus urophydis E. grandis green wood with different lengths were dewatered using CO₂ that was cyclically alternated between the supercritical fluid and gas phases. The results indicate that shorter specimens can be dewatered to below the fiber saturation point (FSP). There was no significant difference in the dewatering rate between the specimens of 20 and 50 mm in length. The dewatering was faster when the moisture content (MC) was over the FSP, leading to a greater gradient and a non-uniform distribution of moisture. The MC distributions in all specimens had no clear differences between in tangential and radial directions. Supercritical CO₂ dewatering generated a different moisture gradient than conventional kiln drying. Most water was dewatered from the end-grain section of the wood along the fiber direction, but a small amount of water was also removed in the transverse directions. There was no deformation in the specimens when the MC was above the FSP. Full article

(This article belongs to the Section Biomaterials)

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14 pages, 3173 KiB

Open AccessEditor’s ChoiceArticle

Tb³⁺ Ion Optical and Magneto-Optical Properties in the Cubic Crystals KTb₃F₁₀

by Uygun V. Valiev, Denis N. Karimov, Chong-Geng Ma, Odiljon Z. Sultonov and Vasiliy O. Pelenovich

Materials 2022, 15(22), 7999; https://doi.org/10.3390/ma15227999 - 12 Nov 2022

Cited by 6 | Viewed by 2389

Abstract

The optical and magneto-optical characteristics of KTb₃F₁₀ crystals in the transition region of ⁵D₄ → ⁷F₆ 4f⁸ configurations of the Tb³⁺ ion at temperatures of 90 and 300 K were studied. The schemes [...] Read more.

The optical and magneto-optical characteristics of KTb₃F₁₀ crystals in the transition region of ⁵D₄ → ⁷F₆ 4f⁸ configurations of the Tb³⁺ ion at temperatures of 90 and 300 K were studied. The schemes of the optical transitions in the KTb₃F₁₀ crystals were constructed, and the energies of most of the Stark sublevels of the ground ⁷F₆ and excited ⁵D₄ multiplets of the Tb³⁺ ion split by the C_4v symmetry crystal environment were determined. The presence of three- and two-doublet states in the energy spectra of the Tb³⁺ion multiplets ⁷F₆ and ⁵D₄, respectively, was established, which is in good agreement with theoretical predictions. The use of the wavefunctions of the Stark sublevels of multiplets split by a tetragonal crystal field and combining in the studied optical transition made it possible to explain some of the magnetic and magneto-optical features observed in the KTb₃F₁₀ single crystals. Full article

(This article belongs to the Section Optical and Photonic Materials)

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17 pages, 7884 KiB

Open AccessEditor’s ChoiceReview

Biofunctional Layered Double Hydroxide Nanohybrids for Cancer Therapy

by Joonghak Lee, Hee Seung Seo, Wooram Park, Chun Gwon Park, Yukwon Jeon and Dae-Hwan Park

Materials 2022, 15(22), 7977; https://doi.org/10.3390/ma15227977 - 11 Nov 2022

Cited by 10 | Viewed by 3792

Abstract

Layered double hydroxides (LDHs) with two-dimensional nanostructure are inorganic materials that have attractive advantages such as biocompatibility, facile preparation, and high drug loading capacity for therapeutic bioapplications. Since the intercalation chemistry of DNA molecules into the LDH materials were reported, various LDH nanohybrids [...] Read more.

Layered double hydroxides (LDHs) with two-dimensional nanostructure are inorganic materials that have attractive advantages such as biocompatibility, facile preparation, and high drug loading capacity for therapeutic bioapplications. Since the intercalation chemistry of DNA molecules into the LDH materials were reported, various LDH nanohybrids have been developed for biomedical drug delivery system. For these reasons, LDHs hybridized with numerous therapeutic agents have a significant role in cancer imaging and therapy with targeting functions. In this review, we summarized the recent advances in the preparation of LDH nanohybrids for cancer therapeutic strategies including gene therapy, chemotherapy, immunotherapy, and combination therapy. Full article

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

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14 pages, 2787 KiB

Open AccessEditor’s ChoiceArticle

High Piezoelectric Output Voltage from Blue Fluorescent N,N-Dimethyl-4-nitroaniline Nano Crystals in Poly-L-Lactic Acid Electrospun Fibers

by Rosa M. F. Baptista, Bruna Silva, João Oliveira, Vahideh B. Isfahani, Bernardo Almeida, Mário R. Pereira, Nuno Cerca, Cidália Castro, Pedro V. Rodrigues, Ana Machado, Michael Belsley and Etelvina de Matos Gomes

Materials 2022, 15(22), 7958; https://doi.org/10.3390/ma15227958 - 10 Nov 2022

Cited by 4 | Viewed by 2982

Abstract

N,N-dimethyl-4-nitroaniline is a piezoelectric organic superplastic and superelastic charge transfer molecular crystal that crystallizes in an acentric structure. Organic mechanical flexible crystals are of great importance as they stand between soft matter and inorganic crystals. Highly aligned poly-l-lactic acid polymer [...] Read more.

N,N-dimethyl-4-nitroaniline is a piezoelectric organic superplastic and superelastic charge transfer molecular crystal that crystallizes in an acentric structure. Organic mechanical flexible crystals are of great importance as they stand between soft matter and inorganic crystals. Highly aligned poly-l-lactic acid polymer microfibers with embedded N,N-dimethyl-4-nitroaniline nanocrystals are fabricated using the electrospinning technique, and their piezoelectric and optical properties are explored as hybrid systems. The composite fibers display an extraordinarily high piezoelectric output response, where for a small stress of 5.0 × 10³ Nm⁻², an effective piezoelectric voltage coefficient of g_eff = 4.1 VmN⁻¹ is obtained, which is one of the highest among piezoelectric polymers and organic lead perovskites. Mechanically, they exhibit an average increase of 67% in the Young modulus compared to polymer microfibers alone, reaching 55 MPa, while the tensile strength reaches 2.8 MPa. Furthermore, the fibers show solid-state blue fluorescence, important for emission applications, with a long lifetime decay (147 ns) lifetime decay. The present results show that nanocrystals from small organic molecules with luminescent, elastic and piezoelectric properties form a mechanically strong hybrid functional 2-dimensional array, promising for applications in energy harvesting through the piezoelectric effect and as solid-state blue emitters. Full article

(This article belongs to the Special Issue Low Dimensional Functionalized Electrospun Nanostructured Materials: Synthesis, Applications and Technology)

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23 pages, 3683 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in Selenophene-Based Materials for Organic Solar Cells

by Xuan Liu, Xin Jiang, Kaifeng Wang, Chunyang Miao and Shiming Zhang

Materials 2022, 15(22), 7883; https://doi.org/10.3390/ma15227883 - 8 Nov 2022

Cited by 14 | Viewed by 3227

Abstract

Due to the low cost, light weight, semitransparency, good flexibility, and large manufacturing area of organic solar cells (OSCs), OSCs have the opportunity to become the next generation of solar cells in some specific applications. So far, the efficiency of the OSC device [...] Read more.

Due to the low cost, light weight, semitransparency, good flexibility, and large manufacturing area of organic solar cells (OSCs), OSCs have the opportunity to become the next generation of solar cells in some specific applications. So far, the efficiency of the OSC device has been improved by more than 20%. The optical band gap between the lowest unoccupied molecular orbital (LUMO) level and the highest occupied molecular orbital (HOMO) level is an important factor affecting the performance of the device. Selenophene, a derivative of aromatic pentacyclic thiophene, is easy to polarize, its LUMO energy level is very low, and hence the optical band gap can be reduced. In addition, the selenium atoms in selenophene and other oxygen atoms or sulfur atoms can form an intermolecular interaction, so as to improve the stacking order of the active layer blend film and improve the carrier transport efficiency. This paper introduces the organic solar active layer materials containing selenium benzene in recent years, which can be simply divided into donor materials and acceptor materials. Replacing sulfur atoms with selenium atoms in these materials can effectively reduce the corresponding optical band gap of materials, improve the mutual solubility of donor recipient materials, and ultimately improve the device efficiency. Therefore, the sulfur in thiophene can be completely replaced by selenium or oxygen of the same family, which can be used in the active layer materials of organic solar cells. This article mainly describes the application of selenium instead of sulfur in OSCs. Full article

(This article belongs to the Special Issue Advances of Photoelectric Functional Materials and Devices)

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14 pages, 3480 KiB

Open AccessEditor’s ChoiceArticle

Aerogel Composites Produced from Silica and Recycled Rubber Sols for Thermal Insulation

by Alyne Lamy-Mendes, Ana Dora Rodrigues Pontinha, Paulo Santos and Luísa Durães

Materials 2022, 15(22), 7897; https://doi.org/10.3390/ma15227897 - 8 Nov 2022

Cited by 14 | Viewed by 2710

Abstract

Hydrophobic rubber-silica aerogel panels (21.5 × 21.5 × 1.6 cm³) were fabricated from silica and rubber sols and reinforced with several fiber types (recycled tire textile fibers, polyester blanket, silica felt, glass wool). A recycled rubber sol was prepared using peracetic [...] Read more.

Hydrophobic rubber-silica aerogel panels (21.5 × 21.5 × 1.6 cm³) were fabricated from silica and rubber sols and reinforced with several fiber types (recycled tire textile fibers, polyester blanket, silica felt, glass wool). A recycled rubber sol was prepared using peracetic acid and incorporated for the first time in TEOS-based sol-gel chemistry. The composites exhibited good thermal stability up to 400 °C and very low thermal conductivity, in the superinsulation range when using polyester fibers (16.4 ± 1.0 mW·m⁻¹·K⁻¹), and of 20–30 mW·m⁻¹·K⁻¹ for the remaining fibers. They could also endure cyclic compression loads with near full recovery, thus showing very promising properties for insulation of buildings. Full article

(This article belongs to the Special Issue Advance in Environmentally Friendly Materials)

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14 pages, 3565 KiB

Open AccessEditor’s ChoiceArticle

Effect of Two-Step Sintering on Properties of Alumina Ceramics Containing Waste Alumina Powder

by Milan Vukšić, Irena Žmak, Lidija Ćurković and Andraž Kocjan

Materials 2022, 15(21), 7840; https://doi.org/10.3390/ma15217840 - 7 Nov 2022

Cited by 2 | Viewed by 2762

Abstract

This study aims to evaluate the recycling potential of solid waste alumina powder (WAP) by utilization of the two-step sintering (TSS) process. For the study, WAP was collected as an industrial scrap after the machining process for the formation of green alumina compacts. [...] Read more.

This study aims to evaluate the recycling potential of solid waste alumina powder (WAP) by utilization of the two-step sintering (TSS) process. For the study, WAP was collected as an industrial scrap after the machining process for the formation of green alumina compacts. The alumina samples were prepared according to the slip casting method by preparing suspensions containing commercial alumina with 0.8 μm average particle size and by adding up to 20 dwb. % (i.e., expressed on a dry weight basis) of WAP with 3.4 μm average particle size. The samples were sintered at optimized TSS conditions and compared with conventional one-step sintering (OSS) by conducting morphological analyses. The average grain size (AGS) was determined from the obtained field emission scanning electron microscopy (FESEM) images, while the sample porosity was calculated based on apparent densities. The obtained micrographs after TSS implementation revealed a partially textured microstructure. Furthermore, a comparison of the mechanical properties of alumina samples lacking or containing 20 dwb. % of WAP obtained after sintering is presented. The indentation fracture toughness (~3.2 MPa m^1/2) and Vickers hardness data (~14.5 GPa) showed a positive effect of adding WAP to alumina samples. The slightly improved mechanical properties of ceramic samples containing waste alumina are a consequence of lower porosity, which is due to the remaining sintering additives in WAP. The collected results demonstrate the possibility of using TSS for sintering ceramic materials that contain WAP. Full article

(This article belongs to the Special Issue Advances in Ceramics and Glass: Processing, Sintering, Properties and Applications)

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19 pages, 6527 KiB

Open AccessEditor’s ChoiceArticle

Effect of Substrate Temperature on the Structural, Optical and Electrical Properties of DC Magnetron Sputtered VO₂ Thin Films

by Chunzi Zhang, Ozan Gunes, Shi-Jie Wen, Qiaoqin Yang and Safa Kasap

Materials 2022, 15(21), 7849; https://doi.org/10.3390/ma15217849 - 7 Nov 2022

Cited by 10 | Viewed by 2908

Abstract

This study focuses on the effect of the substrate temperature (T_S) on the quality of VO₂ thin films prepared by DC magnetron sputtering. T_S was varied from 350 to 600 °C and the effects on the surface morphology, [...] Read more.

This study focuses on the effect of the substrate temperature (T_S) on the quality of VO₂ thin films prepared by DC magnetron sputtering. T_S was varied from 350 to 600 °C and the effects on the surface morphology, microstructure, optical and electrical properties of the films were investigated. The results show that T_S below 500 °C favors the growth of V₂O₅ phase, whereas higher T_S (≥500 °C) facilitates the formation of the VO₂ phase. Optical characterization of the as-prepared VO₂ films displayed a reduced optical transmittance (

\tilde{T}

) across the near-infrared region (NIR), reduced phase transition temperature (T_t), and broadened hysteresis width (ΔH) through the phase transition region. In addition, a decline of the luminous modulation

(Δ {\tilde{T}}_{lum})

and solar modulation (

Δ {\tilde{T}}_{sol}

) efficiencies of the as-prepared films have been determined. Furthermore, compared with the high-quality films reported previously, the electrical conductivity (σ) as a function of temperature (T) reveals reduced conductivity contrast (Δσ) between the insulating and metallic phases of the VO₂ films, which was of the order of 2. These outcomes indicated the presence of defects and unrelaxed lattice strain in the films. Further, the comparison of present results with those in the literature from similar works show that the preparation of high-quality films at T_S lower than 650 °C presents significant challenges. Full article

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

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12 pages, 4228 KiB

Open AccessEditor’s ChoiceArticle

Basic Characteristics of Dose Distributions of Photons Beam for Radiotherapeutic Applications Using YAG:Ce Crystal Detectors

by Janusz Winiecki, Sandra Witkiewicz-Lukaszek, Paulina Michalska, Seweryn Jakubowski, Sergiy Nizhankovskiy and Yuriy Zorenko

Materials 2022, 15(21), 7861; https://doi.org/10.3390/ma15217861 - 7 Nov 2022

Cited by 4 | Viewed by 2811

Abstract

Thermostimulated luminescence (TSL) dosimetry is a versatile tool for the assessment of dose from ionizing radiation. In this work, the Ce³⁺ doped Y₃Al₅O₁₂ garnet (YAG:Ce) with a density ρ = 4.56 g/cm³ and effective atomic number [...] Read more.

Thermostimulated luminescence (TSL) dosimetry is a versatile tool for the assessment of dose from ionizing radiation. In this work, the Ce³⁺ doped Y₃Al₅O₁₂ garnet (YAG:Ce) with a density ρ = 4.56 g/cm³ and effective atomic number Z_eff = 35 emerged as a prospective TSL material in radiotherapy applications due to its excellent radiation stability, uniformity of structural and optical properties, high yield of TSL, and good position of main glow peak around 290–300 °C. Namely, the set of TSL detectors produced from the YAG:Ce single crystal is used for identification of the uniformity of dose and energy spectra of X-ray radiation generated by the clinical accelerator with 6 MV and 15 MV beams located in Radiotherapy Department at the Oncology Center in Bydgoszcz, Poland. We have found that the YAG:Ce crystal detects shows very promising results for registration of X-ray radiation generated by the accelerator with 6 MV beam. The next step in the research is connected with application of TSL detectors based on the crystals of much heavier garnets than YAG. It is estimated that the LuAG:Ce garnet crystals with high density ρ = 6.0 g/cm³ and Z_eff = 62 can be used to evaluate the X-rays produced by the accelerator with the 15 MV beam. Full article

(This article belongs to the Special Issue Materials for Luminescent Detectors and Transformers of Ionizing Radiation)

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14 pages, 1934 KiB

Open AccessEditor’s ChoiceArticle

Kinetics of Catalyst-Free and Position-Controlled Low-Pressure Chemical Vapor Deposition Growth of VO₂ Nanowire Arrays on Nanoimprinted Si Substrates

by Sergey V. Mutilin, Lyubov V. Yakovkina, Vladimir A. Seleznev and Victor Ya. Prinz

Materials 2022, 15(21), 7863; https://doi.org/10.3390/ma15217863 - 7 Nov 2022

Cited by 4 | Viewed by 2103

Abstract

In the present article, the position-controlled and catalytic-free synthesis of vanadium dioxide (VO₂) nanowires (NWs) grown by the chemical vapor deposition (CVD) on nanoimprinted silicon substrates in the form of nanopillar arrays was analyzed. The NW growth on silicon nanopillars with [...] Read more.

In the present article, the position-controlled and catalytic-free synthesis of vanadium dioxide (VO₂) nanowires (NWs) grown by the chemical vapor deposition (CVD) on nanoimprinted silicon substrates in the form of nanopillar arrays was analyzed. The NW growth on silicon nanopillars with different cross-sectional areas was studied, and it has been shown that the NWs’ height decreases with an increase in their cross-sectional area. The X-ray diffraction technique, scanning electron microscopy, and X-ray photoelectron spectroscopy showed the high quality of the grown VO₂ NWs. A qualitative description of the growth rate of vertical NWs based on the material balance equation is given. The dependence of the growth rate of vertical and horizontal NWs on the precursor concentration in the gas phase and on the growth time was investigated. It was found that the height of vertical VO₂ NWs along the [100] direction exhibited a linear dependence on time and increased with an increase in the precursor concentration. For horizontal VO₂ NWs, the height along the direction [011] varied little with the growth time and precursor concentration. These results suggest that the high-aspect ratio vertical VO₂ NWs formed due to different growth modes of their crystal faces forming the top of the growing VO₂ crystals and their lateral crystal faces related to the difference between the free energies of these crystal faces and implemented experimental conditions. The results obtained permit a better insight into the growth of high-aspect ratio VO₂ NWs and into the formation of large VO₂ NW arrays with a controlled composition and properties. Full article

(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)

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13 pages, 4146 KiB

Open AccessEditor’s ChoiceArticle

Double-Layered Polymer Microcapsule Containing Non-Flammable Agent for Initial Fire Suppression

by Dong Hun Lee, Soonhyun Kwon, Young Eun Kim, Na Yeon Kim and Ji Bong Joo

Materials 2022, 15(21), 7831; https://doi.org/10.3390/ma15217831 - 6 Nov 2022

Cited by 12 | Viewed by 3560

Abstract

Fire in energy storage systems, such as lithium-ion batteries, has been raised as a serious concern due to the difficulty of suppressing it. Fluorine-based non-flammable agents used as internal substances leaked through the fine pores of the polymer outer shell, leading to a [...] Read more.

Fire in energy storage systems, such as lithium-ion batteries, has been raised as a serious concern due to the difficulty of suppressing it. Fluorine-based non-flammable agents used as internal substances leaked through the fine pores of the polymer outer shell, leading to a degradation of fire extinguishing performance. To improve the durability of the fire suppression microcapsules and the stability of the ouster shell, a complex coacervation was used, which could be microencapsulated at a lower temperature, and the polymer shell was coated with urea-formaldehyde (UF) resin. The outermost UF resin formed elaborate bonds with the gelatin-based shell, and thus, the structure of the outer shell became denser, thereby improving the loss resistance of the inner substance and thermal stability. The double-layered microcapsules had an average particle diameter of about 309 μm, and a stable outer shell formed with a mass loss of 0.005% during long-term storage for 100 days. This study confirmed that the double-layered microcapsules significantly improved thermal stability, resistance to core material loss, core material content and fire suppression performance compared to single wall microcapsules. These results indicated that the double-layered structure was suitable for the production of microcapsules for initial fire suppression, including highly volatile non-flammable agents with a low boiling point. Full article

(This article belongs to the Special Issue Materials Design for Energy Conversion and Storage II)

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11 pages, 8272 KiB

Open AccessEditor’s ChoiceArticle

Time-Resolved Four-Channel Jones Matrix Measurement of Birefringent Materials Using an Ultrafast Laser

by Zhenjia Cheng, Yuqin Zhang, Xuan Liu, Chengshan Guo, Changwei He, Guiyuan Liu and Hongsheng Song

Materials 2022, 15(21), 7813; https://doi.org/10.3390/ma15217813 - 5 Nov 2022

Cited by 1 | Viewed by 1978

Abstract

A method for ultrafast time-resolved four-channel Jones matrix measurement of birefringent materials using an ultrafast laser is investigated. This facilitated the acquisition of a four-channel angular multiplexing hologram in a single shot. The Jones matrix information of a birefringent sample was retrieved from [...] Read more.

A method for ultrafast time-resolved four-channel Jones matrix measurement of birefringent materials using an ultrafast laser is investigated. This facilitated the acquisition of a four-channel angular multiplexing hologram in a single shot. The Jones matrix information of a birefringent sample was retrieved from the spatial spectrum of a hologram. The feasibility of this approach was established by measuring the Jones matrix of starch granules in microfluidic chips and the complex amplitude distribution and phase delay distribution of liquid crystal cell at different voltages. Moreover, when the picosecond laser was switched to a femtosecond laser, ultrafast measurements were possible provided that the time interval between two detection pulses was larger than the pulse width. Full article

(This article belongs to the Special Issue Optical Imaging and Detection Applied in Characterizing Material Properties)

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15 pages, 2998 KiB

Open AccessEditor’s ChoiceArticle

Functional Evaluation of 3D Liver Models Labeled with Polysaccharide Functionalized Magnetic Nanoparticles

by Yoshitaka Miyamoto, Yumie Koshidaka, Katsutoshi Murase, Shoichiro Kanno, Hirofumi Noguchi, Kenji Miyado, Takeshi Ikeya, Satoshi Suzuki, Tohru Yagi, Naozumi Teramoto and Shuji Hayashi

Materials 2022, 15(21), 7823; https://doi.org/10.3390/ma15217823 - 5 Nov 2022

Cited by 2 | Viewed by 2905

Abstract

Establishing a rapid in vitro evaluation system for drug screening is essential for the development of new drugs. To reproduce tissues/organs with functions closer to living organisms, in vitro three-dimensional (3D) culture evaluation using microfabrication technology has been reported in recent years. Culture [...] Read more.

Establishing a rapid in vitro evaluation system for drug screening is essential for the development of new drugs. To reproduce tissues/organs with functions closer to living organisms, in vitro three-dimensional (3D) culture evaluation using microfabrication technology has been reported in recent years. Culture on patterned substrates with controlled hydrophilic and hydrophobic regions (Cell-able^TM) can create 3D liver models (miniature livers) with liver-specific Disse luminal structures and functions. MRI contrast agents are widely used as safe and minimally invasive diagnostic methods. We focused on anionic polysaccharide magnetic iron oxide nanoparticles (Resovist^®) and synthesized the four types of nanoparticle derivatives with different properties. Cationic nanoparticles (TMADM) can be used to label target cells in a short time and have been successfully visualized in vivo. In this study, we examined the morphology of various nanoparticles. The morphology of various nanoparticles showed relatively smooth-edged spherical shapes. As 3D liver models, we prepared primary hepatocyte–endothelial cell heterospheroids. The toxicity, CYP3A, and albumin secretory capacity were evaluated in the heterospheroids labeled with various nanoparticles. As the culture period progressed, the heterospheroids labeled with anionic and cationic nanoparticles showed lower liver function than non-labeled heterospheroids. In the future, there is a need to improve the method of creation of artificial 3D liver or to design a low-invasive MRI contrast agent to label the artificial 3D liver. Full article

(This article belongs to the Special Issue Synthesis and Applications of Nanoparticles)

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13 pages, 2883 KiB

Open AccessEditor’s ChoiceArticle

A Low Temperature Growth of Cu₂O Thin Films as Hole Transporting Material for Perovskite Solar Cells

by Anna L. Pellegrino, Francesca Lo Presti, Emanuele Smecca, Salvatore Valastro, Giuseppe Greco, Salvatore Di Franco, Fabrizio Roccaforte, Alessandra Alberti and Graziella Malandrino

Materials 2022, 15(21), 7790; https://doi.org/10.3390/ma15217790 - 4 Nov 2022

Cited by 10 | Viewed by 3211

Abstract

Copper oxide thin films have been successfully synthesized through a metal–organic chemical vapor deposition (MOCVD) approach starting from the copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate), Cu(tmhd)₂, complex. Operative conditions of fabrication strongly affect both the composition and morphologies of the copper oxide thin films. The [...] Read more.

Copper oxide thin films have been successfully synthesized through a metal–organic chemical vapor deposition (MOCVD) approach starting from the copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate), Cu(tmhd)₂, complex. Operative conditions of fabrication strongly affect both the composition and morphologies of the copper oxide thin films. The deposition temperature has been accurately monitored in order to stabilize and to produce, selectively and reproducibly, the two phases of cuprite Cu₂O and/or tenorite CuO. The present approach has the advantages of being industrially appealing, reliable, and fast for the production of thin films over large areas with fine control of both composition and surface uniformity. Moreover, the methylammonium lead iodide (MAPI) active layer has been successfully deposited on the ITO/Cu₂O substrate by the Low Vacuum Proximity Space Effusion (LV-PSE) technique. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM) analyses have been used to characterize the deposited films. The optical band gap (E_g), ranging from 1.99 to 2.41 eV, has been determined through UV-vis analysis, while the electrical measurements allowed to establish the p-type conductivity behavior of the deposited Cu₂O thin films with resistivities from 31 to 83 Ω cm and carrier concentration in the order of 1.5–2.8 × 10¹⁶ cm⁻³. These results pave the way for potential applications of the present system as a hole transporting layer combined with a perovskite active layer in emergent solar cell technologies. 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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17 pages, 3174 KiB

Open AccessEditor’s ChoiceArticle

Bond-Orbital-Resolved Piezoelectricity in Sp²-Hybridized Monolayer Semiconductors

by Zongtan Wang, Yulan Liu and Biao Wang

Materials 2022, 15(21), 7788; https://doi.org/10.3390/ma15217788 - 4 Nov 2022

Viewed by 1937

Abstract

Sp²-hybridized monolayer semiconductors (e.g., planar group III-V and IV-IV binary compounds) with inversion symmetry breaking (ISB) display piezoelectricity governed by their σ- and π-bond electrons. Here, we studied their bond-orbital-resolved electronic piezoelectricity (i.e., the σ- and π-piezoelectricity). We formulated a tight-binding [...] Read more.

Sp²-hybridized monolayer semiconductors (e.g., planar group III-V and IV-IV binary compounds) with inversion symmetry breaking (ISB) display piezoelectricity governed by their σ- and π-bond electrons. Here, we studied their bond-orbital-resolved electronic piezoelectricity (i.e., the σ- and π-piezoelectricity). We formulated a tight-binding piezoelectric model to reveal the different variations of σ- and π-piezoelectricity with the ISB strength (

Δ

). As

Δ

varied from positive to negative, the former decreased continuously, but the latter increased piecewise and jumped at

Δ = 0

due to the criticality of the π-electrons’ ground-state geometry near this quantum phase-transition point. This led to a piezoelectricity predominated by the π-electrons for a small

| Δ |

. By constructing an analytical model, we clarified the microscopic mechanisms underlying the anomalous π-piezoelectricity and its subtle relations with the valley Hall effect. The validation of our models was justified by applying them to the typical sp² monolayers including hexagonal silicon carbide, Boron-X (X = N, P, As, Ab), and a BN-doped graphene superlattice. Full article

(This article belongs to the Special Issue Metasurfaces Meet Two-Dimensional Materials)

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12 pages, 4518 KiB

Open AccessEditor’s ChoiceArticle

A Gaussian to Vector Vortex Beam Generator with a Programmable State of Polarization

by Jacek Piłka, Michał Kwaśny, Adam Filipkowski, Ryszard Buczyński, Mirosław A. Karpierz and Urszula A. Laudyn

Materials 2022, 15(21), 7794; https://doi.org/10.3390/ma15217794 - 4 Nov 2022

Cited by 4 | Viewed by 2379

Abstract

We study an optical device designed for converting the polarized Gaussian beam into an optical vortex of tunable polarization. The proposed device comprised a set of three specially prepared nematic liquid crystal cells and a nano-spherical phase plate fabricated from two types of [...] Read more.

We study an optical device designed for converting the polarized Gaussian beam into an optical vortex of tunable polarization. The proposed device comprised a set of three specially prepared nematic liquid crystal cells and a nano-spherical phase plate fabricated from two types of glass nanotubes. This device generates a high-quality optical vortex possessing one of the multiple polarization states from the uniformly polarized input Gaussian beam. Its small size, simplicity of operation, and electrical steering can be easily integrated into the laboratory and industrial systems, making it a promising alternative to passive vortex retarders and spatial light modulators. Full article

(This article belongs to the Special Issue Photonic Sensor Materials: Properties and Applications)

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19 pages, 2955 KiB

Open AccessEditor’s ChoiceArticle

Carbon and Graphene Coatings for the Thermal Management of Sustainable LMP Batteries for Automotive Applications

by Luigi Sequino, Gaetano Sebastianelli and Bianca Maria Vaglieco

Materials 2022, 15(21), 7744; https://doi.org/10.3390/ma15217744 - 3 Nov 2022

Cited by 5 | Viewed by 2052

Abstract

The increment of battery temperature during the operation caused by internal heat generation is one of the main issues to face in the management of storage systems for automotive and power generation applications. The temperature strongly affects the battery efficiency, granting the best [...] Read more.

The increment of battery temperature during the operation caused by internal heat generation is one of the main issues to face in the management of storage systems for automotive and power generation applications. The temperature strongly affects the battery efficiency, granting the best performance in a limited range. The investigation and testing of materials for the improvement of heat dissipation are crucial for modern battery systems that must provide high power and energy density. This study presents an analysis of the thermal behavior of a lithium-polymer cell, which can be stacked in a battery pack for electric vehicles. The cell is sheltered with layers of two different materials: carbon and graphene, used in turn, to dissipate the heat generated during the operation in natural convection. Optical diagnostics in the infrared band is used to evaluate the battery surface temperature and the effect of the coatings. Experiments are performed in two operating conditions varying the current demand. Moreover, two theoretical correlations are used to estimate the thermal parameters of the battery with a reverse-logic approach. The convective heat transfer coefficient h and the specific heat capacity c_p of the battery are evaluated and provided for the Li-ion battery under investigation for different coatings’ conductivity. The results highlight the advantage of using a coating and the effect of the coating properties to reduce the battery temperature under operation. In particular, graphene is preferable because it provides the lowest battery temperature in the most intense operating condition. Full article

(This article belongs to the Special Issue Advanced Materials, Sensors and Smart Components for Modern, Intelligent, and Sustainable Vehicles)

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20 pages, 5210 KiB

Open AccessEditor’s ChoiceArticle

Damping Behaviour and Mechanical Properties of Restorative Materials for Primary Teeth

by Thomas Niem, Roland Frankenberger, Stefanie Amend, Bernd Wöstmann and Norbert Krämer

Materials 2022, 15(21), 7698; https://doi.org/10.3390/ma15217698 - 2 Nov 2022

Cited by 3 | Viewed by 2344

Abstract

The energy dissipation capacity and damping ability of restorative materials used to restore deciduous teeth were assessed compared to common mechanical properties. Mechanical properties (flexural strength, modulus of elasticity, modulus of toughness) for Compoglass F, Dyract eXtra, SDR flow, Tetric Evo Ceram, Tetric [...] Read more.

The energy dissipation capacity and damping ability of restorative materials used to restore deciduous teeth were assessed compared to common mechanical properties. Mechanical properties (flexural strength, modulus of elasticity, modulus of toughness) for Compoglass F, Dyract eXtra, SDR flow, Tetric Evo Ceram, Tetric Evo Ceram Bulk Fill, and Venus Diamond were determined using a 4-point bending test. Vickers hardness and Martens hardness, together with its plastic index (η_ITdis), were recorded using instrumented indentation testing. Leeb hardness (HLD) and its deduced energy dissipation data (HLD_dis) were likewise determined. The reliability of materials was assessed using Weibull analysis. For common mechanical properties, Venus Diamond always exhibited the significantly highest results and SDR flow the lowest, except for flexural strength. Independently determined damping parameters (modulus of toughness, HLD_dis, η_ITdis) invariably disclosed the highest values for SDR flow. Composite materials, including SDR flow, showed markedly higher reliabilities (Weibull modulus) than Compoglass F and Dyract eXtra. SDR flow showed pronounced energy dissipation and damping characteristics, making it the most promising material for a biomimetic restoration of viscoelastic dentin structures in deciduous teeth. Future developments in composite technology should implement improved resin structures that facilitate damping effects in artificial restorative materials. Full article

(This article belongs to the Special Issue Experimental Characterization and Numerical Modelling of Damping Capacity for Classical and Innovative Materials)

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13 pages, 5524 KiB

Open AccessEditor’s ChoiceArticle

Experimental Test of Reinforced Timber of FRCM-PBO with Pull-Off Adhesion Method

by Piotr Sokołowski, Paulina Bąk-Patyna, Dominika Bysiec and Tomasz Maleska

Materials 2022, 15(21), 7702; https://doi.org/10.3390/ma15217702 - 2 Nov 2022

Cited by 2 | Viewed by 1708

Abstract

The article describes the results of pull-off adhesion strength of the FRCM-PBO (Fiber Reinforced Cementitious Matrix-p-Phenylene benzobis oxazole) composite adhered to the epoxy resin layer which is the connector with the timber beam. In addition, this paper shows the results of the tests [...] Read more.

The article describes the results of pull-off adhesion strength of the FRCM-PBO (Fiber Reinforced Cementitious Matrix-p-Phenylene benzobis oxazole) composite adhered to the epoxy resin layer which is the connector with the timber beam. In addition, this paper shows the results of the tests of resistance to pull-off the epoxy resin layer from the pine beam. The tests were carried out based on the Polish Standard PN-EN 1542. The Pearson linear correlation analysis was also carried out in order to determine the correlation between the obtained results and the destructive forces. The factors that occurred during the test that may affect its results, such as the method of applying the bursting force, surface preparation of the tested elements and the types of substrate destruction, were also characterized. The experimental data show that in all the tested samples, non-initial adhesive destruction between the adhesive layer and the disc was observed. Full article

(This article belongs to the Special Issue Rheology and Mechanical Properties of Wood and Wood-Based Materials)

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31 pages, 1972 KiB

Open AccessEditor’s ChoiceReview

A Critical Review on Modification Methods of Cement Composites with Nanocellulose and Reaction Conditions during Nanocellulose Production

by Małgorzata Szafraniec, Ewelina Grabias-Blicharz, Danuta Barnat-Hunek and Eric N. Landis

Materials 2022, 15(21), 7706; https://doi.org/10.3390/ma15217706 - 2 Nov 2022

Cited by 10 | Viewed by 3433

Abstract

Nanocellulose (NC) is a natural polymer that has driven significant progress in recent years in the study of the mechanical properties of composites, including cement composites. Impressive mechanical properties, ability to compact the cement matrix, low density, biodegradability, and hydrophilicity of the surface [...] Read more.

Nanocellulose (NC) is a natural polymer that has driven significant progress in recent years in the study of the mechanical properties of composites, including cement composites. Impressive mechanical properties, ability to compact the cement matrix, low density, biodegradability, and hydrophilicity of the surface of nanocellulose particles (which improves cement hydration) are some of the many benefits of using NCs in composite materials. The authors briefly presented a description of the types of NCs (including the latest, little-known shapes), showing the latest developments in their manufacture and modification. Moreover, NC challenges and opportunities are discussed to reveal its hidden potential, as well as the use of spherical and square/rectangular nanocellulose to modify cement composites. Intending to emphasize the beneficial use of NC in cementitious composites, this article discusses NC as an eco-friendly, low-cost, and efficient material, particularly for recycling readily available cellulosic waste. In view of the constantly growing interest in using renewable and waste materials in a wide range of applications, the authors hope to provide progress in using nanocellulose (NC) as a modifier for cement composites. Furthermore, this review highlights a gap in research regarding the preparation of new types of NCs, their application, and their impact on the properties of cementitious composites. Finally, the authors summarize and critically evaluate the type, dosage, and application method of NC, as well as the effects of these variables on the final properties of NC-derived cement composites. Nevertheless, this review article stresses up-to-date challenges for NC-based materials as well as future remarks in light of dwindling natural resources (including building materials), and the principles of a circular economy. Full article

(This article belongs to the Special Issue Science and Technology for Silicate-Based Construction and Building Materials)

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13 pages, 3507 KiB

Open AccessEditor’s ChoiceArticle

Thermochemical Study of CH₃NH₃Pb(Cl₁_−xBr_x)₃ Solid Solutions

by Maxim Mazurin, Angelika Shelestova, Dmitry Tsvetkov, Vladimir Sereda, Ivan Ivanov, Dmitry Malyshkin and Andrey Zuev

Materials 2022, 15(21), 7675; https://doi.org/10.3390/ma15217675 - 1 Nov 2022

Cited by 1 | Viewed by 2277

Abstract

Hybrid organic–inorganic perovskite halides, and, in particular, their mixed halide solid solutions, belong to a broad class of materials which appear promising for a wide range of potential applications in various optoelectronic devices. However, these materials are notorious for their stability issues, including [...] Read more.

Hybrid organic–inorganic perovskite halides, and, in particular, their mixed halide solid solutions, belong to a broad class of materials which appear promising for a wide range of potential applications in various optoelectronic devices. However, these materials are notorious for their stability issues, including their sensitivity to atmospheric oxygen and moisture as well as phase separation under illumination. The thermodynamic properties, such as enthalpy, entropy, and Gibbs free energy of mixing, of perovskite halide solid solutions are strongly required to shed some light on their stability. Herein, we report the results of an experimental thermochemical study of the CH₃NH₃Pb(Cl_1−xBr_x)₃ mixed halides by solution calorimetry. Combining these results with molecular dynamics simulation revealed the complex and irregular shape of the compositional dependence of the mixing enthalpy to be the result of a complex interplay between the local lattice strain, hydrogen bonds, and energetics of these solid solutions. Full article

(This article belongs to the Special Issue New Energy Storage Materials for Rechargeable Batteries)

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31 pages, 14539 KiB

Open AccessEditor’s ChoiceArticle

Sol-Gel Derived Silica-Titania Waveguide Films for Applications in Evanescent Wave Sensors—Comprehensive Study

by Paweł Karasiński, Magdalena Zięba, Ewa Gondek, Jacek Nizioł, Sandeep Gorantla, Krzysztof Rola, Alicja Bachmatiuk and Cuma Tyszkiewicz

Materials 2022, 15(21), 7641; https://doi.org/10.3390/ma15217641 - 31 Oct 2022

Cited by 11 | Viewed by 2649

Abstract

Composite silica-titania waveguide films of refractive index ca. 1.8 are fabricated on glass substrates using a sol-gel method and dip-coating technique. Tetraethyl orthosilicate and tetraethyl orthotitanate with molar ratio 1:1 are precursors. Fabricated waveguides are annealed at 500 °C for 60 min. Their [...] Read more.

Composite silica-titania waveguide films of refractive index ca. 1.8 are fabricated on glass substrates using a sol-gel method and dip-coating technique. Tetraethyl orthosilicate and tetraethyl orthotitanate with molar ratio 1:1 are precursors. Fabricated waveguides are annealed at 500 °C for 60 min. Their optical properties are studied using ellipsometry and UV-Vis spectrophotometry. Optical losses are determined using the streak method. The material structure and chemical composition, of the silica-titania films are analyzed using transmission electron microscopy (TEM) and electron dispersive spectroscopy (EDS), respectively. The surface morphology was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM) methods. The results presented in this work show that the waveguide films are amorphous, and their parameters are stable for over a 13 years. The optical losses depend on their thickness and light polarization. Their lowest values are less than 0.06 dB cm⁻¹. The paper presents the results of theoretical analysis of scattering losses on nanocrystals and pores in the bulk and interfaces of the waveguide film. These results combined with experimental data clearly indicate that light scattering at the interface to a glass substrate is the main source of optical losses. Presented waveguide films are suitable for application in evanescent wave sensors. Full article

(This article belongs to the Section Optical and Photonic Materials)

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7 pages, 1236 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of Effective Mass in InGaAsN/GaAs Quantum Wells Using Transient Spectroscopy

by Lubica Stuchlikova, Beata Sciana, Arpad Kosa, Matej Matus, Peter Benko, Juraj Marek, Martin Donoval, Wojciech Dawidowski, Damian Radziewicz and Martin Weis

Materials 2022, 15(21), 7621; https://doi.org/10.3390/ma15217621 - 30 Oct 2022

Cited by 1 | Viewed by 2124

Abstract

Transient spectroscopies are sensitive to charge carriers released from trapping centres in semiconducting devices. Even though these spectroscopies are mostly applied to reveal defects causing states that are localised in the energy gap, these methods also sense-charge from quantum wells in heterostructures. However, [...] Read more.

Transient spectroscopies are sensitive to charge carriers released from trapping centres in semiconducting devices. Even though these spectroscopies are mostly applied to reveal defects causing states that are localised in the energy gap, these methods also sense-charge from quantum wells in heterostructures. However, proper evaluation of material response to external stimuli requires knowledge of material properties such as electron effective mass in complex structures. Here we propose a method for precise evaluation of effective mass in quantum well heterostructures. The infinite well model is successfully applied to the InGaAsN/GaAs quantum well structure and used to evaluate electron effective mass in the conduction and valence bands. The effective mass m/m₀ of charges from the conduction band was 0.093 ± 0.006, while the charges from the valence band exhibited an effective mass of 0.122 ± 0.018. 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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12 pages, 1144 KiB

Open AccessEditor’s ChoiceArticle

Octahedral Tilting in Homologous Perovskite Series CaMoO3-SrMoO3-BaMoO3 Probed by Temperature-Dependent EXAFS Spectroscopy

by Georgijs Bakradze and Alexei Kuzmin

Materials 2022, 15(21), 7619; https://doi.org/10.3390/ma15217619 - 30 Oct 2022

Cited by 3 | Viewed by 2278

Abstract

Local distortions in perovskites can be induced by cation displacements and/or by the tilting and rotating of cation–anion octahedra. Both phenomena have been subject to intense investigations over many years. However, there are still controversies in the results obtained from experimental techniques that [...] Read more.

Local distortions in perovskites can be induced by cation displacements and/or by the tilting and rotating of cation–anion octahedra. Both phenomena have been subject to intense investigations over many years. However, there are still controversies in the results obtained from experimental techniques that are sensitive to long-range order (X-ray, neutron, or electron diffraction) and those sensitive to short-range order (X-ray absorption spectroscopy). In this study, we probed the details of the local environment in AMoO₃ perovskites (A = Ca, Sr, Ba) using extended X-ray absorption fine structure (EXAFS) in a wide temperature range (10–300 K). An advanced analysis of the EXAFS spectra within the multiple-scattering formalism using the reverse Monte Carlo method enhanced by an evolutionary algorithm allowed us (i) to extract detailed information on metal–oxygen and metal–metal radial distribution functions, and metal–oxygen–metal and oxygen–metal–oxygen bond angle distribution functions, and (ii) to perform polyhedral analysis. The obtained results demonstrate the strong sensitivity of the EXAFS spectra to the tilting of [MoO₆] octahedra induced by the differences in the sizes of alkaline earth metal cations (Ca²⁺, Sr²⁺, and Ba²⁺). Full article

(This article belongs to the Special Issue Perovskite Nanomaterials for Functional Devices and Sensors)

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12 pages, 1973 KiB

Open AccessEditor’s ChoiceArticle

Robust Porous TiN Layer for Improved Oxygen Evolution Reaction Performance

by Gaoyang Liu, Faguo Hou, Xindong Wang and Baizeng Fang

Materials 2022, 15(21), 7602; https://doi.org/10.3390/ma15217602 - 29 Oct 2022

Cited by 8 | Viewed by 2273

Abstract

The poor reversibility and slow reaction kinetics of catalytic materials seriously hinder the industrialization process of proton exchange membrane (PEM) water electrolysis. It is necessary to develop high-performance and low-cost electrocatalysts to reduce the loss of reaction kinetics. In this study, a novel [...] Read more.

The poor reversibility and slow reaction kinetics of catalytic materials seriously hinder the industrialization process of proton exchange membrane (PEM) water electrolysis. It is necessary to develop high-performance and low-cost electrocatalysts to reduce the loss of reaction kinetics. In this study, a novel catalyst support featured with porous surface structure and good electronic conductivity was successfully prepared by surface modification via a thermal nitriding method under ammonia atmosphere. The morphology and composition characterization-confirmed that a TiN layer with granular porous structure and internal pore-like defects was established on the Ti sheet. Meanwhile, the conductivity measurements showed that the in-plane electronic conductivity of the as-developed material increased significantly to 120.8 S cm⁻¹. After IrO_x was loaded on the prepared TiN-Ti support, better dispersion of the active phase IrO_x, lower ohmic resistance, and faster charge transfer resistance were verified, and accordingly, more accessible catalytic active sites on the catalytic interface were developed as revealed by the electrochemical characterizations. Compared with the IrO_x/Ti, the as-obtained IrO_x/TiN-Ti catalyst demonstrated remarkable electrocatalytic activity (

η_{{10 mA cm}^{- 2}}

= 302 mV) and superior stability (overpotential degradation rate: 0.067 mV h⁻¹) probably due to the enhanced mass adsorption and transport, good dispersion of the supported active phase IrO_x, increased electronic conductivity and improved corrosion resistance provided by the TiN-Ti support. Full article

(This article belongs to the Special Issue Advanced Materials in Catalysis and Adsorption)

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19 pages, 4770 KiB

Open AccessEditor’s ChoiceArticle

Electrical Conductivity of Additively Manufactured Copper and Silver for Electrical Winding Applications

by John Robinson, Sai Priya Munagala, Arun Arjunan, Nick Simpson, Ryan Jones, Ahmad Baroutaji, Loganathan T. Govindaraman and Iain Lyall

Materials 2022, 15(21), 7563; https://doi.org/10.3390/ma15217563 - 28 Oct 2022

Cited by 19 | Viewed by 4914

Abstract

Efficient and power-dense electrical machines are critical in driving the next generation of green energy technologies for many industries including automotive, aerospace and energy. However, one of the primary requirements to enable this is the fabrication of compact custom windings with optimised materials [...] Read more.

Efficient and power-dense electrical machines are critical in driving the next generation of green energy technologies for many industries including automotive, aerospace and energy. However, one of the primary requirements to enable this is the fabrication of compact custom windings with optimised materials and geometries. Electrical machine windings rely on highly electrically conductive materials, and therefore, the Additive Manufacturing (AM) of custom copper (Cu) and silver (Ag) windings offers opportunities to simultaneously improve efficiency through optimised materials, custom geometries and topology and thermal management through integrated cooling strategies. Laser Powder Bed Fusion (L-PBF) is the most mature AM technology for metals, however, laser processing highly reflective and conductive metals such as Cu and Ag is highly challenging due to insufficient energy absorption. In this regard, this study details the 400 W L-PBF processing of high-purity Cu, Ag and Cu–Ag alloys and the resultant electrical conductivity performance. Six Cu and Ag material variants are investigated in four comparative studies characterising the influence of material composition, powder recoating, laser exposure and electropolishing. The highest density and electrical conductivity achieved was 88% and 73% IACS, respectively. To aid in the application of electrical insulation coatings, electropolishing parameters are established to improve surface roughness. Finally, proof-of-concept electrical machine coils are fabricated, highlighting the potential for 400 W L-PBF processing of Cu and Ag, extending the current state of the art. Full article

(This article belongs to the Special Issue 3D & 4D Printing in Engineering Applications)

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19 pages, 46216 KiB

Open AccessEditor’s ChoiceArticle

Dynamic Characterization of Hexagonal Microstructured Materials with Voids from Discrete and Continuum Models

by Marco Colatosti, Farui Shi, Nicholas Fantuzzi and Patrizia Trovalusci

Materials 2022, 15(21), 7524; https://doi.org/10.3390/ma15217524 - 27 Oct 2022

Cited by 3 | Viewed by 1630

Abstract

The mechanical response of materials such as fiber and particle composites, rocks, concrete, and granular materials, can be profoundly influenced by the existence of voids. The aim of the present work is to study the dynamic behavior of hexagonal microstructured composites with voids [...] Read more.

The mechanical response of materials such as fiber and particle composites, rocks, concrete, and granular materials, can be profoundly influenced by the existence of voids. The aim of the present work is to study the dynamic behavior of hexagonal microstructured composites with voids by using a discrete model and homogenizing materials, such as micropolar and classical Cauchy continua. Three kinds of hexagonal microstructures, named regular, hourglass, and skew, are considered with different length scales. The analysis of free vibration of a panel described as a discrete system, as a classical and as a micropolar continuum, and the comparison of results in terms of natural frequencies and modes show the advantage of the micropolar continuum in describing dynamic characteristics of orthotropic composites (i.e., regular and hourglass microstructures) with respect to the Cauchy continuum, which gives a higher error in frequency evaluations for all three hexagonal microstructured materials. Moreover, the micropolar model also satisfactorily predicts the behavior of skewed microstructured composites. Another advantage shown here by the micropolar continuum is that, like the discrete model, this continuum is able to present the scale effect of microstructures, while maintaining all the advantages of the field description. The effect of void size is also investigated and the results show that the first six frequencies of the current problem decrease by increasing in void size. Full article

(This article belongs to the Special Issue Modeling of Constitutive Laws for Traditional and Innovative Building Materials)

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10 pages, 3742 KiB

Open AccessEditor’s ChoiceArticle

Ultra-Short Polarization Rotator Based on Flat-Shaped Photonic Crystal Fiber Filled with Liquid Crystal

by Rui Liu, Tiesheng Wu, Yiping Wang, Zhihui Liu, Weiping Cao, Dan Yang, Zuning Yang, Yan Liu and Xu Zhong

Materials 2022, 15(21), 7526; https://doi.org/10.3390/ma15217526 - 27 Oct 2022

Cited by 2 | Viewed by 1731

Abstract

In this study we demonstrate a high-performance polarization rotator (PR) based on flat-shaped photonic crystal fiber. The flat surfaces of the fiber are plated on gold films as electrodes, and the core of the structure is filled with liquid crystal. The polarization rotation [...] Read more.

In this study we demonstrate a high-performance polarization rotator (PR) based on flat-shaped photonic crystal fiber. The flat surfaces of the fiber are plated on gold films as electrodes, and the core of the structure is filled with liquid crystal. The polarization rotation characteristics of the flat-shaped fiber can be effectively adjusted by applying external voltage. The optical properties are analyzed using the finite element method (FEM). The results show that the magnitude of the modulation voltage is closely related to the thickness of the flat fiber. When the fiber thickness is 20 μm, only 100 V is required to achieve the highest PR performance. In the wavelength of the 1.55 μm band (~200 nm bandwidth), the conversion length of the PR is only 3.99 μm, the conversion efficiency is close to 100%, and the minimum crosstalk value is −26.2 dB. The presented PR, with its excellent performance, might enable promising applications in the communication system and the photonic integrated circuits. Full article

(This article belongs to the Special Issue Advances in Crystal Material: Design, Characterization, and Applications)

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18 pages, 2991 KiB

Open AccessEditor’s ChoiceReview

Minimization of Adverse Effects Associated with Dental Alloys

by Marianna Arakelyan, Gianrico Spagnuolo, Flavia Iaculli, Natalya Dikopova, Artem Antoshin, Peter Timashev and Anna Turkina

Materials 2022, 15(21), 7476; https://doi.org/10.3390/ma15217476 - 25 Oct 2022

Cited by 11 | Viewed by 3733

Abstract

Metal alloys are one of the most popular materials used in current dental practice. In the oral cavity, metal structures are exposed to various mechanical and chemical factors. Consequently, metal ions are released into the oral fluid, which may negatively affect the surrounding [...] Read more.

Metal alloys are one of the most popular materials used in current dental practice. In the oral cavity, metal structures are exposed to various mechanical and chemical factors. Consequently, metal ions are released into the oral fluid, which may negatively affect the surrounding tissues and even internal organs. Adverse effects associated with metallic oral appliances may have various local and systemic manifestations, such as mouth burning, potentially malignant oral lesions, and local or systemic hypersensitivity. However, clear diagnostic criteria and treatment guidelines for adverse effects associated with dental alloys have not been developed yet. The present comprehensive literature review aims (1) to summarize the current information related to possible side effects of metallic oral appliances; (2) to analyze the risk factors aggravating the negative effects of dental alloys; and (3) to develop recommendations for diagnosis, management, and prevention of pathological conditions associated with metallic oral appliances. Full article

(This article belongs to the Special Issue Current and Future Trends in Dental Materials, Volume II)

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14 pages, 3857 KiB

Open AccessEditor’s ChoiceArticle

Fatigue Evaluation for Innovative Excavator Arms Made of Composite Material

by Luigi Solazzi, Andrea Buffoli and Federico Ceresoli

Materials 2022, 15(21), 7480; https://doi.org/10.3390/ma15217480 - 25 Oct 2022

Cited by 2 | Viewed by 2639

Abstract

This research reports the results related to the evaluation of the fatigue phenomenon of the arms of a medium–large excavator made of composite material (carbon fiber) instead of the classic constructional steel S355 (UNI EN 10025-3). In the numerical sizing phase, it was [...] Read more.

This research reports the results related to the evaluation of the fatigue phenomenon of the arms of a medium–large excavator made of composite material (carbon fiber) instead of the classic constructional steel S355 (UNI EN 10025-3). In the numerical sizing phase, it was obtained that the overall weight of the excavator’s arms made of composite material is about 35% of the same components made of steel, obviously with equal performance in terms of the safety static coefficient, rigidity, and critical buckling load. The evaluation of the fatigue behaviour (assuming 5.25 × 10⁶ load cycles) applied for each load condition analyzed (levelling from the maximum distance to the minimum, lifting at the maximum distance, lifting at the minimum distance and rotation) shows the magnitude of the safety coefficients both related to the allowable stress and relative to the number of cycles acceptable. The assumption instead of combined cycles (involving one or more load conditions) leads to a significant reduction in the magnitude of the safety coefficients. The implementation of a loading cycle plan resulting from the different load conditions must be reliably assessed to evaluate as accurately as possible the fatigue behavior of the excavator arms made of composite material. Full article

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

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34 pages, 5241 KiB

Open AccessEditor’s ChoiceReview

Radiopaque Crystalline, Non-Crystalline and Nanostructured Bioceramics

by Maziar Montazerian, Geovanna V. S. Gonçalves, Maria E. V. Barreto, Eunice P. N. Lima, Glauber R. C. Cerqueira, Julyana A. Sousa, Adrine Malek Khachatourian, Mairly K. S. Souza, Suédina M. L. Silva, Marcus V. L. Fook and Francesco Baino

Materials 2022, 15(21), 7477; https://doi.org/10.3390/ma15217477 - 25 Oct 2022

Cited by 14 | Viewed by 4872

Abstract

Radiopacity is sometimes an essential characteristic of biomaterials that can help clinicians perform follow-ups during pre- and post-interventional radiological imaging. Due to their chemical composition and structure, most bioceramics are inherently radiopaque but can still be doped/mixed with radiopacifiers to increase their visualization [...] Read more.

Radiopacity is sometimes an essential characteristic of biomaterials that can help clinicians perform follow-ups during pre- and post-interventional radiological imaging. Due to their chemical composition and structure, most bioceramics are inherently radiopaque but can still be doped/mixed with radiopacifiers to increase their visualization during or after medical procedures. The radiopacifiers are frequently heavy elements of the periodic table, such as Bi, Zr, Sr, Ba, Ta, Zn, Y, etc., or their relevant compounds that can confer enhanced radiopacity. Radiopaque bioceramics are also intriguing additives for biopolymers and hybrids, which are extensively researched and developed nowadays for various biomedical setups. The present work aims to provide an overview of radiopaque bioceramics, specifically crystalline, non-crystalline (glassy), and nanostructured bioceramics designed for applications in orthopedics, dentistry, and cancer therapy. Furthermore, the modification of the chemical, physical, and biological properties of parent ceramics/biopolymers due to the addition of radiopacifiers is critically discussed. We also point out future research lacunas in this exciting field that bioceramists can explore further. Full article

(This article belongs to the Special Issue Advances in Functional Ceramic Materials: Fabrication, Properties, and High-Temperature Applications)

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20 pages, 3621 KiB

Open AccessEditor’s ChoiceArticle

Prediction of Ecofriendly Concrete Compressive Strength Using Gradient Boosting Regression Tree Combined with GridSearchCV Hyperparameter-Optimization Techniques

by Zaineb M. Alhakeem, Yasir Mohammed Jebur, Sadiq N. Henedy, Hamza Imran, Luís F. A. Bernardo and Hussein M. Hussein

Materials 2022, 15(21), 7432; https://doi.org/10.3390/ma15217432 - 23 Oct 2022

Cited by 117 | Viewed by 5456

Abstract

A crucial factor in the efficient design of concrete sustainable buildings is the compressive strength (Cs) of eco-friendly concrete. In this work, a hybrid model of Gradient Boosting Regression Tree (GBRT) with grid search cross-validation (GridSearchCV) optimization technique was used to predict the [...] Read more.

A crucial factor in the efficient design of concrete sustainable buildings is the compressive strength (Cs) of eco-friendly concrete. In this work, a hybrid model of Gradient Boosting Regression Tree (GBRT) with grid search cross-validation (GridSearchCV) optimization technique was used to predict the compressive strength, which allowed us to increase the precision of the prediction models. In addition, to build the proposed models, 164 experiments on eco-friendly concrete compressive strength were gathered for previous researches. The dataset included the water/binder ratio (W/B), curing time (age), the recycled aggregate percentage from the total aggregate in the mixture (RA%), ground granulated blast-furnace slag (GGBFS) material percentage from the total binder used in the mixture (GGBFS%), and superplasticizer (kg). The root mean square error (RMSE) and coefficient of determination (R²) between the observed and forecast strengths were used to evaluate the accuracy of the predictive models. The obtained results indicated that—when compared to the default GBRT model—the GridSearchCV approach can capture more hyperparameters for the GBRT prediction model. Furthermore, the robustness and generalization of the GSC-GBRT model produced notable results, with RMSE and R² values (for the testing phase) of 2.3214 and 0.9612, respectively. The outcomes proved that the suggested GSC-GBRT model is advantageous. Additionally, the significance and contribution of the input factors that affect the compressive strength were explained using the Shapley additive explanation (SHAP) approach. Full article

(This article belongs to the Special Issue Mechanical Behavior of Concrete Materials and Structures: Experimental Evidence and Analytical Models (Volume II))

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19 pages, 4011 KiB

Open AccessEditor’s ChoiceArticle

The Influence of Air Nanobubbles on Controlling the Synthesis of Calcium Carbonate Crystals

by Yongxiang Wu, Minyi Huang, Chunlin He, Kaituo Wang, Nguyen Thi Hong Nhung, Siming Lu, Gjergj Dodbiba, Akira Otsuki and Toyohisa Fujita

Materials 2022, 15(21), 7437; https://doi.org/10.3390/ma15217437 - 23 Oct 2022

Cited by 7 | Viewed by 2990

Abstract

Numerous approaches have been developed to control the crystalline and morphology of calcium carbonate. In this paper, nanobubbles were studied as a novel aid for the structure transition from vaterite to calcite. The vaterite particles turned into calcite (100%) in deionized water containing [...] Read more.

Numerous approaches have been developed to control the crystalline and morphology of calcium carbonate. In this paper, nanobubbles were studied as a novel aid for the structure transition from vaterite to calcite. The vaterite particles turned into calcite (100%) in deionized water containing nanobubbles generated by high-speed shearing after 4 h, in comparison to a mixture of vaterite (33.6%) and calcite (66.3%) by the reaction in the deionized water in the absence of nanobubbles. The nanobubbles can coagulate with calcite based on the potential energy calculated and confirmed by the extended DLVO (Derjaguin–Landau–Verwey–Overbeek) theory. According to the nanobubble bridging capillary force, nanobubbles were identified as the binder in strengthening the coagulation between calcite and vaterite and accelerated the transformation from vaterite to calcite. Full article

(This article belongs to the Special Issue Characterization and Processing of Complex Materials)

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12 pages, 2210 KiB

Open AccessEditor’s ChoiceArticle

Antiferromagnet–Ferromagnet Transition in Fe_1−xCu_xNbO₄

by Diego S. Evaristo, Raí F. Jucá, João M. Soares, Rodolfo B. Silva, Gilberto D. Saraiva, Robert S. Matos, Nilson S. Ferreira, Marco Salerno and Marcelo A. Macêdo

Materials 2022, 15(21), 7424; https://doi.org/10.3390/ma15217424 - 22 Oct 2022

Cited by 2 | Viewed by 1750

Abstract

Iron niobates, pure and substituted with copper (Fe_1−xCu_xNbO₄ with x = 0–0.15), were prepared by the solid-state method and characterized by X-ray diffraction, Raman spectroscopy, and magnetic measurements. The results of the structural characterizations revealed the high solubility [...] Read more.

Iron niobates, pure and substituted with copper (Fe_1−xCu_xNbO₄ with x = 0–0.15), were prepared by the solid-state method and characterized by X-ray diffraction, Raman spectroscopy, and magnetic measurements. The results of the structural characterizations revealed the high solubility of Cu ions in the structure and better structural stability compared to the pure sample. The analysis of the magnetic properties showed that the antiferromagnetic–ferromagnetic transition was caused by the insertion of Cu²⁺ ions into the FeNbO₄ structure. The pure FeNbO₄ structure presented an antiferromagnetic ordering state, with a Néel temperature of approximately 36.81K. The increase in substitution promoted a change in the magnetic ordering, with the state passing to a weak ferromagnetic order with a transition temperature (T_c) higher than the ambient temperature. The origin of the ferromagnetic ordering could be attributed to the increase in super-exchange interactions between Fe/Cu ions in the Cu²⁺-O-Fe³⁺ chains and the formation of bound magnetic polarons in the oxygen vacancies. Full article

(This article belongs to the Special Issue Ferromagnetic and Ferroelectric Materials: Synthesis, Applications, and Techniques)

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11 pages, 1712 KiB

Open AccessEditor’s ChoiceArticle

Destabilization of the Charge Density Wave and the Absence of Superconductivity in ScV₆Sn₆ under High Pressures up to 11 GPa

by Xiaoxiao Zhang, Jun Hou, Wei Xia, Zhian Xu, Pengtao Yang, Anqi Wang, Ziyi Liu, Jie Shen, Hua Zhang, Xiaoli Dong, Yoshiya Uwatoko, Jianping Sun, Bosen Wang, Yanfeng Guo and Jinguang Cheng

Materials 2022, 15(20), 7372; https://doi.org/10.3390/ma15207372 - 21 Oct 2022

Cited by 37 | Viewed by 5012

Abstract

RV₆Sn₆ (R = Sc, Y, or rare earth) is a new family of kagome metals that have a similar vanadium structural motif as AV₃Sb₅ (A = K, Rb, Cs) compounds. Unlike AV [...] Read more.

RV₆Sn₆ (R = Sc, Y, or rare earth) is a new family of kagome metals that have a similar vanadium structural motif as AV₃Sb₅ (A = K, Rb, Cs) compounds. Unlike AV₃Sb₅, ScV₆Sn₆ is the only compound among the series of RV₆Sn₆ that displays a charge density wave (CDW) order at ambient pressure, yet it shows no superconductivity (SC) at low temperatures. Here, we perform a high-pressure transport study on the ScV₆Sn₆ single crystal to track the evolutions of the CDW transition and to explore possible SC. In contrast to AV₃Sb₅ compounds, the CDW order of ScV₆Sn₆ can be suppressed completely by a pressure of about 2.4 GPa, but no SC is detected down to 40 mK at 2.35 GPa and 1.5 K up to 11 GPa. Moreover, we observed that the resistivity anomaly around the CDW transition undergoes an obvious change at ~2.04 GPa before it vanishes completely. The present work highlights a distinct relationship between CDW and SC in ScV₆Sn₆ in comparison with the well-studied AV₃Sb₅. Full article

(This article belongs to the Special Issue Quantum Materials and Emergent Phenomena under Extreme Conditions)

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21 pages, 4470 KiB

Open AccessEditor’s ChoiceArticle

Hydroxyapatite Coating on Ti-6Al-7Nb Alloy by Plasma Electrolytic Oxidation in Salt-Based Electrolyte

by Avital Schwartz, Alexey Kossenko, Michael Zinigrad, Yosef Gofer, Konstantin Borodianskiy and Alexander Sobolev

Materials 2022, 15(20), 7374; https://doi.org/10.3390/ma15207374 - 21 Oct 2022

Cited by 25 | Viewed by 3370

Abstract

Titanium alloys have good biocompatibility and good mechanical properties, making them particularly suitable for dental and orthopedic implants. Improving their osseointegration with human bones is one of the most essential tasks. This can be achieved by developing hydroxyapatite (HA) on the treating surface [...] Read more.

Titanium alloys have good biocompatibility and good mechanical properties, making them particularly suitable for dental and orthopedic implants. Improving their osseointegration with human bones is one of the most essential tasks. This can be achieved by developing hydroxyapatite (HA) on the treating surface using the plasma electrolytic oxidation (PEO) method in molten salt. In this study, a coating of titanium oxide-containing HA nanoparticles was formed on Ti-6Al-7Nb alloy by PEO in molten salt. Then, samples were subjected to hydrothermal treatment (HTT) to form HA crystals sized 0.5 to 1 μm. The effect of the current and voltage frequency for the creation of the coating on the morphology, chemical, and phase composition was studied. The anti-corrosion properties of the samples were studied using the potentiodynamic polarization test (PPT) and electrochemical impedance spectroscopy (EIS). An assessment of the morphology of the sample formed at a frequency of 100 Hz shows that the structure of this coating has a uniform submicron porosity, and its surface shows high hydrophilicity and anti-corrosion properties (4.90 × 10⁶ Ohm·cm²). In this work, for the first time, the process of formation of a bioactive coating consisting of titanium oxides and HA was studied by the PEO method in molten salts. Full article

(This article belongs to the Special Issue Multiple Applications of Hydroxyapatite-Based Materials)

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