Materials

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 1960

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 4 | Viewed by 2065

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 1514

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 5 | Viewed by 2282

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 9 | Viewed by 3667

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 2903

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 12 | Viewed by 3042

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 2603

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 2612

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 6 | Viewed by 2775

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 2669

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 2048

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 10 | Viewed by 3368

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 1895

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 2845

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 8 | Viewed by 3041

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 1878

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 2283

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 1965

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 2 | Viewed by 2252

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 1632

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 8 | Viewed by 3277

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 2165

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 2558

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 2056

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 2159

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 7 | Viewed by 2198

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 18 | Viewed by 4655

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 1572

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 1666

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 9 | Viewed by 3592

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 2489

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 13 | Viewed by 4670

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 103 | Viewed by 5211

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 6 | Viewed by 2855

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 1679

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 35 | Viewed by 4851

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 24 | Viewed by 3262

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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11 pages, 1889 KiB

Open AccessEditor’s ChoiceArticle

Wall Shear Stress Analysis and Optimization in Tissue Engineering TPMS Scaffolds

by Tiago H. V. Pires, John W. C. Dunlop, André P. G. Castro and Paulo R. Fernandes

Materials 2022, 15(20), 7375; https://doi.org/10.3390/ma15207375 - 21 Oct 2022

Cited by 12 | Viewed by 2390

Abstract

When designing scaffolds for bone tissue engineering (BTE), the wall shear stress (WSS), due to the fluid flow inside the scaffold, is an important factor to consider as it influences the cellular process involved in new tissue formation. The present work analyzed the [...] Read more.

When designing scaffolds for bone tissue engineering (BTE), the wall shear stress (WSS), due to the fluid flow inside the scaffold, is an important factor to consider as it influences the cellular process involved in new tissue formation. The present work analyzed the average WSS in Schwartz diamond (SD) and gyroid (SG) scaffolds with different surface topologies and mesh elements using computational fluid dynamics (CFD) analysis. It was found that scaffold meshes with a smooth surface topology with tetrahedral elements had WSS levels 35% higher than the equivalent scaffold with a non-smooth surface topology with hexahedral elements. The present work also investigated the possibility of implementing the optimization algorithm simulated annealing to aid in the design of BTE scaffolds with a specific average WSS, with the outputs showing that the algorithm was able to reach WSS levels in the vicinity of 5 mPa (physiological range) within the established limit of 100 iterations. This proved the efficacy of combining CFD and optimization methods in the design of BTE scaffolds. Full article

(This article belongs to the Special Issue Design and Micromechanical Behavior of Orthopaedic Devices for Bone Repair and Regeneration)

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14 pages, 3715 KiB

Open AccessEditor’s ChoiceArticle

Corrosion Crack Morphology and Creep Analysis of Members Based on Meso-Scale Corrosion Penetration

by Bin Zeng, Yiping Yang, Fuyuan Gong and Koichi Maekawa

Materials 2022, 15(20), 7338; https://doi.org/10.3390/ma15207338 - 20 Oct 2022

Cited by 4 | Viewed by 1941

Abstract

In this paper, to study the development of load-carrying capacity and long-term creep performance of reinforced concrete beams under different corrosion patterns, the rate-dependent model of concrete is used as the basis to consider the creep development process from the meso-scale level. The [...] Read more.

In this paper, to study the development of load-carrying capacity and long-term creep performance of reinforced concrete beams under different corrosion patterns, the rate-dependent model of concrete is used as the basis to consider the creep development process from the meso-scale level. The porosity mechanics method is used to simulate the generation and penetration process of corrosion products. Three corrosion conditions are set: bottom longitudinal reinforcement corrosion, top longitudinal reinforcement corrosion and all reinforcement corrosion. The corrosion rate is used as the variable in each corrosion condition. The results show that: (1) the greater the corrosion rate in all conditions, the lower the bearing capacity. In addition, the corrosion of top longitudinal reinforcement causes the damage form of the beam to change to brittle damage; (2) the creep coefficient decreases with the increase in corrosion rate in all working conditions, but the main factor for this phenomenon is the obvious increase in initial deformation. Consequently, it is not suitable to follow the conventional creep concept (deformation development/initial deformation) for the development of plastic deformation of damaged members. It is more reasonable to use the global deflection to describe the long-term deformation of corrosion-damaged members. Full article

(This article belongs to the Special Issue Multi-Scale Structural Characterization of Cement-Based Composites)

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36 pages, 8306 KiB

Open AccessEditor’s ChoiceReview

Gallium Oxide for Gas Sensor Applications: A Comprehensive Review

by Jun Zhu, Zhihao Xu, Sihua Ha, Dongke Li, Kexiong Zhang, Hai Zhang and Jijun Feng

Materials 2022, 15(20), 7339; https://doi.org/10.3390/ma15207339 - 20 Oct 2022

Cited by 44 | Viewed by 7393

Abstract

Ga₂O₃ has emerged as a promising ultrawide bandgap semiconductor for numerous device applications owing to its excellent material properties. In this paper, we present a comprehensive review on major advances achieved over the past thirty years in the field of [...] Read more.

Ga₂O₃ has emerged as a promising ultrawide bandgap semiconductor for numerous device applications owing to its excellent material properties. In this paper, we present a comprehensive review on major advances achieved over the past thirty years in the field of Ga₂O₃-based gas sensors. We begin with a brief introduction of the polymorphs and basic electric properties of Ga₂O₃. Next, we provide an overview of the typical preparation methods for the fabrication of Ga₂O₃-sensing material developed so far. Then, we will concentrate our discussion on the state-of-the-art Ga₂O₃-based gas sensor devices and put an emphasis on seven sophisticated strategies to improve their gas-sensing performance in terms of material engineering and device optimization. Finally, we give some concluding remarks and put forward some suggestions, including (i) construction of hybrid structures with two-dimensional materials and organic polymers, (ii) combination with density functional theoretical calculations and machine learning, and (iii) development of optical sensors using the characteristic optical spectra for the future development of novel Ga₂O₃-based gas sensors. Full article

(This article belongs to the Special Issue Development of Novel Functional Materials for the Manufacture of Electronic and Optoelectronic Devices)

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22 pages, 6169 KiB

Open AccessEditor’s ChoiceReview

A Review of Magnetic Flux Leakage Nondestructive Testing

by Bo Feng, Jianbo Wu, Hongming Tu, Jian Tang and Yihua Kang

Materials 2022, 15(20), 7362; https://doi.org/10.3390/ma15207362 - 20 Oct 2022

Cited by 60 | Viewed by 8539

Abstract

Magnetic flux leakage (MFL) testing is a widely used nondestructive testing (NDT) method for the inspection of ferromagnetic materials. This review paper presents the basic principles of MFL testing and summarizes the recent advances in MFL. An analytical expression for the leakage magnetic [...] Read more.

Magnetic flux leakage (MFL) testing is a widely used nondestructive testing (NDT) method for the inspection of ferromagnetic materials. This review paper presents the basic principles of MFL testing and summarizes the recent advances in MFL. An analytical expression for the leakage magnetic field based on the 3D magnetic dipole model is provided. Based on the model, the effects of defect size, defect orientation, and liftoff distance have been analyzed. Other influencing factors, such as magnetization strength, testing speed, surface roughness, and stress, have also been introduced. As the most important steps of MFL, the excitation method (a permanent magnet, DC, AC, pulsed) and sensing methods (Hall element, GMR, TMR, etc.), have been introduced in detail. Finally, the algorithms for the quantification of defects and the applications of MFL have been introduced. Full article

(This article belongs to the Special Issue Electromagnetic Nondestructive Testing)

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19 pages, 2664 KiB

Open AccessEditor’s ChoiceArticle

Performance of Capsules in Self-Healing Cementitious Material

by Mouna A. Reda and Samir E. Chidiac

Materials 2022, 15(20), 7302; https://doi.org/10.3390/ma15207302 - 19 Oct 2022

Cited by 11 | Viewed by 2857

Abstract

Encapsulation is a very promising technique that is being explored to enhance the autonomous self-healing of cementitious materials. However, its success requires the survival of self-healing capsules during mixing and placing conditions, while still trigger the release of a healing agent upon concrete [...] Read more.

Encapsulation is a very promising technique that is being explored to enhance the autonomous self-healing of cementitious materials. However, its success requires the survival of self-healing capsules during mixing and placing conditions, while still trigger the release of a healing agent upon concrete cracking. A review of the literature revealed discontinuities and inconsistencies in the design and performance evaluation of self-healing cementitious material. A finite element model was developed to study the compatibility requirements for the capsule and the cementing material properties while the cement undergoes volume change due to hydration and/or drying. The FE results have provided insights into the observed inconsistencies and the importance of having capsules’ mechanical and geometrical properties compatible with the cementitious matrix. Full article

(This article belongs to the Special Issue Self-Healing Cementitious Material System)

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10 pages, 4878 KiB

Open AccessEditor’s ChoiceArticle

Versatile Medium Entropy Ti-Based Bulk Metallic Glass Composites

by Tianzeng Liu, Yanchun Zhao, Li Feng and Pan Gong

Materials 2022, 15(20), 7304; https://doi.org/10.3390/ma15207304 - 19 Oct 2022

Cited by 1 | Viewed by 1550

Abstract

An ultra-strong Ti-based bulk metallic glass composite was developed via the transformation-induced plasticity (TRIP) effect to enhance both the ductility and work-hardening capability of the amorphous matrix. The functionally graded composites with a continuous gradient microstructure were obtained. It was found that the [...] Read more.

An ultra-strong Ti-based bulk metallic glass composite was developed via the transformation-induced plasticity (TRIP) effect to enhance both the ductility and work-hardening capability of the amorphous matrix. The functionally graded composites with a continuous gradient microstructure were obtained. It was found that the austenitic center possesses good plasticity and toughness. Furthermore, the amorphous surface exhibited high strength and hardness, as well as excellent wear corrosion resistance. Compared with the Ti-6Al-4V alloy, bulk metallic glass composites (BMGCs) exhibit better spontaneous passivation behavior during the potential dynamic polarization. No crystallization was observed on the friction surface, indicating their good friction-reduction and anti-wear properties. Full article

(This article belongs to the Special Issue Physical Metallurgy of Metals and Alloys)

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20 pages, 4900 KiB

Open AccessEditor’s ChoiceArticle

Bio-Activation of HA/β-TCP Porous Scaffolds by High-Pressure CO₂ Surface Remodeling: A Novel “Coating-from” Approach

by Clémentine Aubry, Christophe Drouet, Thierry Azaïs, Hyoung-Jun Kim, Jae-Min Oh, Ipek Karacan, Joshua Chou, Besim Ben-Nissan, Séverine Camy and Sophie Cazalbou

Materials 2022, 15(20), 7306; https://doi.org/10.3390/ma15207306 - 19 Oct 2022

Cited by 1 | Viewed by 2557

Abstract

Biphasic macroporous Hydroxyapatite/β-Tricalcium Phosphate (HA/β-TCP) scaffolds (BCPs) are widely used for bone repair. However, the high-temperature HA and β-TCP phases exhibit limited bioactivity (low solubility of HA, restricted surface area, low ion release). Strategies were developed to coat such BCPs with biomimetic apatite [...] Read more.

Biphasic macroporous Hydroxyapatite/β-Tricalcium Phosphate (HA/β-TCP) scaffolds (BCPs) are widely used for bone repair. However, the high-temperature HA and β-TCP phases exhibit limited bioactivity (low solubility of HA, restricted surface area, low ion release). Strategies were developed to coat such BCPs with biomimetic apatite to enhance bioactivity. However, this can be associated with poor adhesion, and metastable solutions may prove difficult to handle at the industrial scale. Alternative strategies are thus desirable to generate a highly bioactive surface on commercial BCPs. In this work, we developed an innovative “coating from” approach for BCP surface remodeling via hydrothermal treatment under supercritical CO₂, used as a reversible pH modifier and with industrial scalability. Based on a set of complementary tools including FEG-SEM, solid state NMR and ion exchange tests, we demonstrate the remodeling of macroporous BCP surface with the occurrence of dissolution–reprecipitation phenomena involving biomimetic CaP phases. The newly precipitated compounds are identified as bone-like nanocrystalline apatite and octacalcium phosphate (OCP), both known for their high bioactivity character, favoring bone healing. We also explored the effects of key process parameters, and showed the possibility to dope the remodeled BCPs with antibacterial Cu²⁺ ions to convey additional functionality to the scaffolds, which was confirmed by in vitro tests. This new process could enhance the bioactivity of commercial BCP scaffolds via a simple and biocompatible approach. Full article

(This article belongs to the Special Issue Bio-Inspired and Biomimetic Materials for Healthcare: From Nature to Clinics)

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10 pages, 2602 KiB

Open AccessEditor’s ChoiceArticle

Characterization of Porous CuO Films for H₂S Gas Sensors

by Dawoon Jung, Sehoon Hwang, Hyun-Jong Kim, Jae-Hee Han and Ho-Nyun Lee

Materials 2022, 15(20), 7270; https://doi.org/10.3390/ma15207270 - 18 Oct 2022

Cited by 10 | Viewed by 2287

Abstract

Using a thermal evaporator, various porous Cu films were deposited according to the deposition pressure. CuO films were formed by post heat treatment in the air. Changes in morphological and structural characteristics of films were analyzed using field-emission scanning electron microscopy (FE-SEM) and [...] Read more.

Using a thermal evaporator, various porous Cu films were deposited according to the deposition pressure. CuO films were formed by post heat treatment in the air. Changes in morphological and structural characteristics of films were analyzed using field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). Relative density and porosity were quantitatively calculated. CuO films with various pores ranging from 39.4 to 95.2% were successfully manufactured and were applied as gas sensors for H₂S detection on interdigitated electrode (IDE) substrate. Resistance change was monitored at 325 °C and an increase in porosity of the film improved the sensor performance. The CuO-10 gas sensor with a high porosity of 95.2% showed a relatively high response (2.7) and a fast recovery time (514 s) for H₂S 1.5 ppm. It is confirmed that the porosity of the CuO detection layer had a significant effect on response and recovery time. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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25 pages, 3871 KiB

Open AccessEditor’s ChoiceReview

Structural Changes in Metallic Glass-Forming Liquids on Cooling and Subsequent Vitrification in Relationship with Their Properties

by D. V. Louzguine-Luzgin

Materials 2022, 15(20), 7285; https://doi.org/10.3390/ma15207285 - 18 Oct 2022

Cited by 27 | Viewed by 3863

Abstract

The present review is related to the studies of structural changes observed in metallic glass-forming liquids on cooling and subsequent vitrification in terms of radial distribution function and its analogues. These structural changes are discussed in relationship with liquid’s properties, especially the relaxation [...] Read more.

The present review is related to the studies of structural changes observed in metallic glass-forming liquids on cooling and subsequent vitrification in terms of radial distribution function and its analogues. These structural changes are discussed in relationship with liquid’s properties, especially the relaxation time and viscosity. These changes are found to be directly responsible for liquid fragility: deviation of the temperature dependence of viscosity of a supercooled liquid from the Arrhenius equation through modification of the activation energy for viscous flow. Further studies of this phenomenon are necessary to provide direct mathematical correlation between the atomic structure and properties. Full article

(This article belongs to the Special Issue Glass Science and First-Order Transitions at a Turning Point)

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14 pages, 2095 KiB

Open AccessEditor’s ChoiceArticle

Multifunctional Microspheres Based on D-Mannose and Resveratrol for Ciprofloxacin Release

by Roberta Cassano, Federica Curcio, Debora Procopio, Marco Fiorillo and Sonia Trombino

Materials 2022, 15(20), 7293; https://doi.org/10.3390/ma15207293 - 18 Oct 2022

Cited by 5 | Viewed by 2418

Abstract

This article describes the preparation, characterization, and performance evaluation of functional microspheres useful for the release of ciprofloxacin. The particles were obtained using D-mannose, a natural aldohexose sugar, and resveratrol, a powerful antioxidant. In particular, the above compounds were initially converted into D-mannose [...] Read more.

This article describes the preparation, characterization, and performance evaluation of functional microspheres useful for the release of ciprofloxacin. The particles were obtained using D-mannose, a natural aldohexose sugar, and resveratrol, a powerful antioxidant. In particular, the above compounds were initially converted into D-mannose carboxylate and resveratrol methacrylate and, therefore, subjected to an esterification reaction. The resulting product was used for the preparation of the microspheres which were characterized by light scattering, FT-IR spectrophotometry and scanning electron microscopy (SEM). Subsequently, their degree of bloating was evaluated at pH 1.2 to simulate the pH of the stomach, at pH 6.8 and pH 7.4 to mimic the intestinal environment. The antibiotic ciprofloxacin was then loaded into the microspheres, with an encapsulation efficiency of 100%. The cumulative amount of drug released was 55% at pH 6.8 and 99% at pH 7.4. The tests conducted to evaluate the antibacterial activity demonstrated the ability of the microspheres obtained to inhibit the growth of Escherichia coli. The antioxidant efficacy, due to the presence of resveratrol in their structure, was confirmed using rat liver microsomal membranes. The results obtained have highlighted how the microspheres based on D-mannose and resveratrol can be considered promising multifunctional vectors useful in the treatment of intestinal and urinary infections. Full article

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

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10 pages, 1990 KiB

Open AccessEditor’s ChoiceCommunication

The Research on Anti-Nickel Contamination Mechanism and Performance for Boron-Modified FCC Catalyst

by Chengyuan Yuan, Lei Zhou, Qiang Chen, Chengzhuang Su, Zhongfu Li and Guannan Ju

Materials 2022, 15(20), 7220; https://doi.org/10.3390/ma15207220 - 17 Oct 2022

Cited by 4 | Viewed by 1623

Abstract

Fluid catalytic cracking (FCC) is still a key process in the modern refining area, in which nickel-contamination for an FCC catalyst could obviously increase the dry gas and coke yields and thus seriously affect the stability of the FCC unit. From the points [...] Read more.

Fluid catalytic cracking (FCC) is still a key process in the modern refining area, in which nickel-contamination for an FCC catalyst could obviously increase the dry gas and coke yields and thus seriously affect the stability of the FCC unit. From the points of surface acidity modification and Ni-passivation, in this paper, a boron-modified FCC catalyst (BM-Cat) was prepared using the in situ addition method with B₂O₃ as a boron source and emphatically investigated its mechanism and performance of anti-nickel contamination. The mechanism research results suggested that, in calcination, boron could destroy the structure of the Y zeolite and thus decrease the total acid sites and strong acid sites of the Y zeolite from 291.5 and 44.6 μmol·g⁻¹ to 244.2 and 32.1 μmol·g⁻¹, respectively, which could obviously improve the dry gas and coke selectivity of the catalyst and thus enhance the nickel capacity for BM-Cat; on the other hand, under hydrothermal conditions, boron could react with NiO and form into NiB₂O₄, which could obviously raise the range of the reduction temperature for NiO from 350–600 °C to 650–800 °C and thus promote the nickel-passivation ability for BM-Cat. Therefore, evaluation results of heavy oil catalytic cracking indicated that, under the same nickel-contamination condition, in contrast to the compared catalyst (C-Cat), the dry gas yield, coke yield, and H₂/CH₄ of BM-Cat obviously decreased by 0.77 percentage points, 2.09 percentage points, and 13.53%, respectively, with light yield and total liquid yield increasing by 3.25 and 2.08 percentage points, respectively, which fully demonstrates the excellent anti-nickel contamination performance of BM-Cat. Full article

(This article belongs to the Section Catalytic Materials)

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21 pages, 7475 KiB

Open AccessEditor’s ChoiceArticle

Entalpy of Mixing, Microstructure, Structural, Thermomagnetic and Mechanical Properties of Binary Gd-Pb Alloys

by Piotr Gębara, Mariusz Hasiak, Jozef Kovac and Michal Rajnak

Materials 2022, 15(20), 7213; https://doi.org/10.3390/ma15207213 - 16 Oct 2022

Viewed by 1567

Abstract

The aim of the present work is to study the phase composition, microstructure and magnetocaloric effect of binary Gd_100−xPb_x (where x = 5, 10, 15 and 20) alloys. The XRD and SEM/EDX analysis confirmed a biphasic structure built by Gd(Pb) [...] Read more.

The aim of the present work is to study the phase composition, microstructure and magnetocaloric effect of binary Gd_100−xPb_x (where x = 5, 10, 15 and 20) alloys. The XRD and SEM/EDX analysis confirmed a biphasic structure built by Gd(Pb) and Gd₅Pb₃ phases. The analysis of M vs. T curves showed the evolution of the Curie point of recognized phases. The temperature dependences of magnetic entropy change revealed two maxima corresponding to the recognized phases. The analysis of the exponent n (ΔS_M_max = C(B_max)ⁿ) confirmed the multiphase composition of the produced alloys. The same behavior was also observed in investigations of mechanical properties. Full article

(This article belongs to the Special Issue Structure, Magnetocaloric Properties, and Thermodynamic Modeling of Alloys)

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