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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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31 pages, 1474 KiB  
Review
A Comprehensive Analysis of the UVC LEDs’ Applications and Decontamination Capability
by Talita Nicolau, Núbio Gomes Filho, Jorge Padrão and Andrea Zille
Materials 2022, 15(8), 2854; https://doi.org/10.3390/ma15082854 - 13 Apr 2022
Cited by 26 | Viewed by 4721
Abstract
The application of light-emitting diodes (LEDs) has been gaining popularity over the last decades. LEDs have advantages compared to traditional light sources in terms of lifecycle, robustness, compactness, flexibility, and the absence of non-hazardous material. Combining these advantages with the possibility of emitting [...] Read more.
The application of light-emitting diodes (LEDs) has been gaining popularity over the last decades. LEDs have advantages compared to traditional light sources in terms of lifecycle, robustness, compactness, flexibility, and the absence of non-hazardous material. Combining these advantages with the possibility of emitting Ultraviolet C (UVC) makes LEDs serious candidates for light sources in decontamination systems. Nevertheless, it is unclear if they present better decontamination effectiveness than traditional mercury vapor lamps. Hence, this research uses a systematic literature review (SLR) to enlighten three aspects: (1) UVC LEDs’ application according to the field, (2) UVC LEDs’ application in terms of different biological indicators, and (3) the decontamination effectiveness of UVC LEDs in comparison to conventional lamps. UVC LEDs have spread across multiple areas, ranging from health applications to wastewater or food decontamination. The UVC LEDs’ decontamination effectiveness is as good as mercury vapor lamps. In some cases, LEDs even provide better results than conventional mercury vapor lamps. However, the increase in the targets’ complexity (e.g., multilayers or thicker individual layers) may reduce the UVC decontamination efficacy. Therefore, UVC LEDs still require considerable optimization. These findings are stimulating for developing industrial or final users’ applications. Full article
(This article belongs to the Special Issue Advanced Materials for Biophotonics Applications)
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12 pages, 2860 KiB  
Article
Tuning of Magnetic Damping in Y3Fe5O12/Metal Bilayers for Spin-Wave Conduit Termination
by Adam Krysztofik, Nikolai Kuznetsov, Huajun Qin, Lukáš Flajšman, Emerson Coy and Sebastiaan van Dijken
Materials 2022, 15(8), 2814; https://doi.org/10.3390/ma15082814 - 12 Apr 2022
Cited by 9 | Viewed by 3149
Abstract
In this work, we investigate the structural and dynamic magnetic properties of yttrium iron garnet (YIG) films grown onto gadolinium gallium garnet (GGG) substrates with thin platinum, iridium, and gold spacer layers. Separation of the YIG film from the GGG substrate by a [...] Read more.
In this work, we investigate the structural and dynamic magnetic properties of yttrium iron garnet (YIG) films grown onto gadolinium gallium garnet (GGG) substrates with thin platinum, iridium, and gold spacer layers. Separation of the YIG film from the GGG substrate by a metal film strongly affects the crystalline structure of YIG and its magnetic damping. Despite the presence of structural defects, however, the YIG films exhibit a clear ferromagnetic resonance response. The ability to tune the magnetic damping without substantial changes to magnetization offers attractive prospects for the design of complex spin-wave conduits. We show that the insertion of a 1-nm-thick metal layer between YIG and GGG already increases the effective damping parameter enough to efficiently absorb spin waves. This bilayer structure can therefore be utilized for magnonic waveguide termination. Investigating the dispersionless propagation of spin-wave packets, we demonstrate that a damping unit consisting of the YIG/metal bilayers can dissipate incident spin-wave signals with reflection coefficient R < 0.1 at a distance comparable to the spatial width of the wave packet. Full article
(This article belongs to the Special Issue Magnetic and Structural Properties of Ferromagnetic Thin Films)
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18 pages, 5077 KiB  
Article
Synthesis and Characterization of a Crystalline Imine-Based Covalent Organic Framework with Triazine Node and Biphenyl Linker and Its Fluorinated Derivate for CO2/CH4 Separation
by Stefanie Bügel, Malte Hähnel, Tom Kunde, Nader de Sousa Amadeu, Yangyang Sun, Alex Spieß, Thi Hai Yen Beglau, Bernd M. Schmidt and Christoph Janiak
Materials 2022, 15(8), 2807; https://doi.org/10.3390/ma15082807 - 11 Apr 2022
Cited by 19 | Viewed by 4803
Abstract
A catalyst-free Schiff base reaction was applied to synthesize two imine-linked covalent organic frameworks (COFs). The condensation reaction of 1,3,5-tris-(4-aminophenyl)triazine (TAPT) with 4,4′-biphenyldicarboxaldehyde led to the structure of HHU-COF-1 (HHU = Heinrich-Heine University). The fluorinated analog HHU-COF-2 was obtained with 2,2′,3,3′,5,5′,6,6′-octafluoro-4,4′-biphenyldicarboxaldehyde. Solid-state NMR, [...] Read more.
A catalyst-free Schiff base reaction was applied to synthesize two imine-linked covalent organic frameworks (COFs). The condensation reaction of 1,3,5-tris-(4-aminophenyl)triazine (TAPT) with 4,4′-biphenyldicarboxaldehyde led to the structure of HHU-COF-1 (HHU = Heinrich-Heine University). The fluorinated analog HHU-COF-2 was obtained with 2,2′,3,3′,5,5′,6,6′-octafluoro-4,4′-biphenyldicarboxaldehyde. Solid-state NMR, infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis confirmed the successful formation of the two network structures. The crystalline materials are characterized by high Brunauer–Emmett–Teller surface areas of 2352 m2/g for HHU-COF-1 and 1356 m2/g for HHU-COF-2. The products of a larger-scale synthesis were applied to prepare mixed-matrix membranes (MMMs) with the polymer Matrimid. CO2/CH4 permeation tests revealed a moderate increase in CO2 permeability at constant selectivity for HHU-COF-1 as a dispersed phase, whereas application of the fluorinated COF led to a CO2/CH4 selectivity increase from 42 for the pure Matrimid membrane to 51 for 8 wt% of HHU-COF-2 and a permeability increase from 6.8 to 13.0 Barrer for the 24 wt% MMM. Full article
(This article belongs to the Special Issue Synthesis, Porous Structure Analysis, and Application of Sorbents in CO2 Capture)
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14 pages, 9547 KiB  
Article
Development and Analysis of Coding and Tailored Metamaterial for Terahertz Frequency Applications
by Tayaallen Ramachandran, Mohammad Rashed Iqbal Faruque, Mohammad Tariqul Islam, Mayeen Uddin Khandaker, Amal Alqahtani and D. A. Bradley
Materials 2022, 15(8), 2777; https://doi.org/10.3390/ma15082777 - 10 Apr 2022
Cited by 8 | Viewed by 2495
Abstract
This study represents the development and analysis of the types of metamaterial structures for terahertz frequency. Recently, investigations about unique coding metamaterial have become well-known among the scientific community since it can manipulate electromagnetic (EM) waves by utilizing various coding sequences. Therefore, several [...] Read more.
This study represents the development and analysis of the types of metamaterial structures for terahertz frequency. Recently, investigations about unique coding metamaterial have become well-known among the scientific community since it can manipulate electromagnetic (EM) waves by utilizing various coding sequences. Therefore, several coding and tailored metamaterial designs were compared and numerically analyzed the performances in this research work. The 1-bit coding metamaterial made up of only “0” and “1” elements by adopting two types of unit cells with 0 and π phase responses were analyzed for the coding metamaterial. Moreover, for the numerical simulation analyses, the well-known Computer Simulation Technology (CST) Microwave Studio software was adopted. This investigation focused on the frequency ranges from 0 to 5 THz. On the other hand, the proposed designs were simulated to find their scattering parameter behavior. The comparison of coding and tailored metamaterial revealed slight differences in the RCS values. The coding metamaterial designs manifested RCS values less than −50 dBm2, while tailored metamaterial designs exhibited less than −60 dBm2. Furthermore, the proposed designs displayed various transmission coefficient result curves for both types of metamaterial. Moreover, the bistatic far-field scattering patterns of both metamaterial designs were presented in this work. In a nutshell, the 1-bit coding metamaterial with a unique sequence can influence the EM waves and realize different functionalities. Full article
(This article belongs to the Special Issue Design and Applications of Terahertz Metamaterials)
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18 pages, 2088 KiB  
Article
Probabilistic Assessment of the Dynamic Viscosity of Self-Compacting Steel-Fiber Reinforced Concrete through a Micromechanical Model
by Ángel De La Rosa, Gonzalo Ruiz, Enrique Castillo and Rodrigo Moreno
Materials 2022, 15(8), 2763; https://doi.org/10.3390/ma15082763 - 9 Apr 2022
Cited by 3 | Viewed by 1749
Abstract
This article develops a probabilistic approach to a micromechanical model to calculate the dynamic viscosity in self-compacting steel-fiber reinforced concrete (SCSFRC), which implies a paradigm shift in the approach of the deterministic models used. It builds on a previous work by the authors [...] Read more.
This article develops a probabilistic approach to a micromechanical model to calculate the dynamic viscosity in self-compacting steel-fiber reinforced concrete (SCSFRC), which implies a paradigm shift in the approach of the deterministic models used. It builds on a previous work by the authors in which Bayesian analysis is applied to rheological micromechanical models in cement paste, self-compacting mortar, and self-compacting concrete. As a consequence of the varied characteristics of the particles in these suspensions (in terms of materials, shapes, size distributions, etc.), as well as their random nature, it seems appropriate to study these systems with probabilistic models. The Bayesian analysis, thorough Markov Chain Monte Carlo and Gibbs Sampling methods, allows the conversion of parametric-deterministic models into parametric-probabilistic models, which results in enrichment in engineering and science. The incorporation of steel fibers requires a new term in the model to account for their effect on the dynamic viscosity of SCSFRC, and this new term is also treated here with the Bayesian approach. The paper uses an extensive collection of experimental data to obtain the probability density functions of the parameters for assessing the dynamic viscosity in SCSFRC. The results obtained with these parameters’ distributions are much better than those calculated with the theoretical values of the parameters, which indicates that Bayesian methods are appropriated to respond to questions in complex systems with complex models. Full article
(This article belongs to the Special Issue Cement-Based Materials Applied in Sustainable Construction)
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19 pages, 9038 KiB  
Article
Enhanced Mechanical and Durability Properties of Cement Mortar by Using Alumina Nanocoating on Carbon Nanofibers
by Huda Al Qader, Ahmed M. Jasim, Hani Salim, Yangchuan Xing and David Stalla
Materials 2022, 15(8), 2768; https://doi.org/10.3390/ma15082768 - 9 Apr 2022
Cited by 8 | Viewed by 3945
Abstract
This study evaluated the effect of carbon nanofibers (CNFs) coated by aluminum oxide Al2O3 as a reinforcement on compressive strength, frost resistance, and drying shrinkage of cement mortars. Three weight ratios of 0.125%, 0.25%, and 0.5% of Al2O [...] Read more.
This study evaluated the effect of carbon nanofibers (CNFs) coated by aluminum oxide Al2O3 as a reinforcement on compressive strength, frost resistance, and drying shrinkage of cement mortars. Three weight ratios of 0.125%, 0.25%, and 0.5% of Al2O3/CNFs and bare CNF cement mortars were compared with reference cement mortar samples. The reactive porous and high surface area layer of alumina induced the hydration reaction and promoted the production of well-distributed hydration gel. Derivative thermal analysis–differential thermogravimetric (TGA-DTG) and X-ray powder diffraction (XRD) characterization showed that Al2O3/CNFs reinforcement led to greater hydration gel production than bare CNFs. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were performed to study the coating and microstructure of the cement mortars evaluated in this paper. The results show that the optimum enhancement of the cement mortar properties was obtained at ratios of 0.125% for Al2O3/CNFs and 0.25% for CNFs. This enhancement was greater with Al2O3/CNFs-reinforced specimens in terms of high compressive strength, less compressive strength degradation after 150 cycles, and less drying shrinkage. The low use of the CNFs in Al2O3/CNFs samples indicates the coating is an economical and promising approach for improving the performance of cement mortars. Full article
(This article belongs to the Special Issue Modeling and Testing of Reinforced Concrete or Composite Structures Using Advanced New Materials)
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10 pages, 766 KiB  
Article
Pressure Tuning of Superconductivity of LaPt4Ge12 and PrPt4Ge12 Single Crystals
by Gustavo A. Lombardi, Kamal Mydeen, Roman Gumeniuk, Andreas Leithe-Jasper, Walter Schnelle, Ricardo D. dos Reis and Michael Nicklas
Materials 2022, 15(8), 2743; https://doi.org/10.3390/ma15082743 - 8 Apr 2022
Cited by 1 | Viewed by 2215
Abstract
We carried out electrical resistivity and X-ray diffraction (XRD) studies on the filled skutterudite superconductors LaPt4Ge12 and PrPt4Ge12 under hydrostatic pressure. The superconducting transition temperature Tc is linearly suppressed upon increasing pressure, though the effect of [...] Read more.
We carried out electrical resistivity and X-ray diffraction (XRD) studies on the filled skutterudite superconductors LaPt4Ge12 and PrPt4Ge12 under hydrostatic pressure. The superconducting transition temperature Tc is linearly suppressed upon increasing pressure, though the effect of pressure on Tc is rather weak. From the analysis of the XRD data, we obtain bulk moduli of B=106 GPa and B=83 GPa for LaPt4Ge12 and PrPt4Ge12, respectively. The knowledge of the bulk modulus allows us to compare the dependence of Tc on the unit-cell volume from our pressure study directly with that found in the substitution series La1−xPrxPt4Ge12. We find that application of hydrostatic pressure can be characterized mainly as a volume effect in LaPt4Ge12 and PrPt4Ge12, while substitution of Pr for La in La1−xPrxPt4Ge12 yields features going beyond a simple picture. Full article
(This article belongs to the Special Issue Advances in Superconducting Materials: Characterization, Properties and Applications)
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16 pages, 4224 KiB  
Article
The Role of the Built-In Electric Field in Recombination Processes of GaN/AlGaN Quantum Wells: Temperature- and Pressure-Dependent Study of Polar and Non-Polar Structures
by Kamil Koronski, Krzysztof P. Korona, Serhii Kryvyi, Aleksandra Wierzbicka, Kamil Sobczak, Stanislaw Krukowski, Pawel Strak, Eva Monroy and Agata Kaminska
Materials 2022, 15(8), 2756; https://doi.org/10.3390/ma15082756 - 8 Apr 2022
Cited by 3 | Viewed by 4010
Abstract
In this paper, we present a comparative analysis of the optical properties of non-polar and polar GaN/AlGaN multi-quantum well (MQW) structures by time-resolved photoluminescence (TRPL) and pressure-dependent studies. The lack of internal electric fields across the non-polar structures results in an improved electron [...] Read more.
In this paper, we present a comparative analysis of the optical properties of non-polar and polar GaN/AlGaN multi-quantum well (MQW) structures by time-resolved photoluminescence (TRPL) and pressure-dependent studies. The lack of internal electric fields across the non-polar structures results in an improved electron and hole wavefunction overlap with respect to the polar structures. Therefore, the radiative recombination presents shorter decay times, independent of the well width. On the contrary, the presence of electric fields in the polar structures reduces the emission energy and the wavefunction overlap, which leads to a strong decrease in the recombination rate when increasing the well width. Taking into account the different energy dependences of radiative recombination in non-polar and polar structures of the same geometry, and assuming that non-radiative processes are energy independent, we attempted to explain the ‘S-shape’ behavior of the PL energy observed in polar GaN/AlGaN QWs, and its absence in non-polar structures. This approach has been applied previously to InGaN/GaN structures, showing that the interplay of radiative and non-radiative recombination processes can justify the ‘S-shape’ in polar InGaN/GaN MQWs. Our results show that the differences in the energy dependences of radiative and non-radiative recombination processes cannot explain the ‘S-shape’ behavior by itself, and localization effects due to the QW width fluctuation are also important. Additionally, the influence of the electric field on the pressure behavior of the investigated structures was studied, revealing different pressure dependences of the PL energy in non-polar and polar MQWs. Non-polar MQWs generally follow the pressure dependence of the GaN bandgap. In contrast, the pressure coefficients of the PL energy in polar QWs are highly reduced with respect to those of the bulk GaN, which is due to the hydrostatic-pressure-induced increase in the piezoelectric field in quantum structures and the nonlinear behavior of the piezoelectric constant. Full article
(This article belongs to the Special Issue Growth and Characteristics of Nitride Semiconductor Layers)
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31 pages, 3624 KiB  
Review
Electrical Resistivity Measurements for Nondestructive Evaluation of Chloride-Induced Deterioration of Reinforced Concrete—A Review
by Kevin Paolo V. Robles, Jurng-Jae Yee and Seong-Hoon Kee
Materials 2022, 15(8), 2725; https://doi.org/10.3390/ma15082725 - 7 Apr 2022
Cited by 37 | Viewed by 6336
Abstract
The objective of this study is to review, evaluate, and compare the existing research and practices on electrical resistivity as a nondestructive technique in evaluating chloride-induced deterioration of reinforced concrete elements in buildings and civil infrastructure systems. First, this paper summarizes the different [...] Read more.
The objective of this study is to review, evaluate, and compare the existing research and practices on electrical resistivity as a nondestructive technique in evaluating chloride-induced deterioration of reinforced concrete elements in buildings and civil infrastructure systems. First, this paper summarizes the different measurement techniques for gathering electrical resistivity (ER) values on concrete. Second, comparison analyses are performed to review the correlation of ER to different parameters representing corrosive environment and activity of steel corrosion in concrete, such as degree of water saturation, chloride penetration and diffusivity, and corrosion rate. In addition, this research enumerates and individually discusses the different environmental and interference factors that are not related to the electrochemical process of steel corrosion in concrete but directly affect the ER measurements, including temperature, the presence of steel reinforcement, cracks and delamination defects, specimen geometry, and concrete composition. Lastly and most importantly, discussions are made to determine the current gap of knowledge, to improve the utilization of this method in field and laboratory measurements, and future research. Full article
(This article belongs to the Section Construction and Building Materials)
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10 pages, 3682 KiB  
Communication
Photoluminescence and Energy Transfer in Double- and Triple-Lanthanide-Doped YVO4 Nanoparticles
by Vassiliy A. Medvedev, Ilya E. Kolesnikov, Pavel K. Olshin, Mikhail D. Mikhailov, Alina A. Manshina and Daria V. Mamonova
Materials 2022, 15(7), 2637; https://doi.org/10.3390/ma15072637 - 3 Apr 2022
Cited by 4 | Viewed by 2407
Abstract
Optical materials doped with several lanthanides are unique in their properties and are widely used in various fields of science and technology. The study of these systems provides solutions for noncontact thermometry, bioimaging, sensing technology, and others. In this paper, we report on [...] Read more.
Optical materials doped with several lanthanides are unique in their properties and are widely used in various fields of science and technology. The study of these systems provides solutions for noncontact thermometry, bioimaging, sensing technology, and others. In this paper, we report on the demonstration of YVO4 nanoparticles doped with one, two, and three different rare earth ions (Tm3+, Er3+, and Nd3+). We discuss the morphology, structural properties, and luminescence behavior of particles. Luminescence decay kinetics reveal the energy transfer efficiency (up to 78%) for different ions under the selective excitation of individual ions. Thus, we found that the energy transition from Tm3+ is more favorable than from Er3+ while we did not observe any significant energy rearrangement in the samples under the excitation of Nd3+. The observed strong variation of REI lifetimes makes the suggested nanoparticles promising for luminescent labeling, anticounterfeiting, development of data storage systems, etc. Full article
(This article belongs to the Special Issue Optical Properties and Applications of Nanocrystals)
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14 pages, 845 KiB  
Article
Role of Different Material Amendments in Shaping the Content of Heavy Metals in Maize (Zea mays L.) on Soil Polluted with Petrol
by Mirosław Wyszkowski and Natalia Kordala
Materials 2022, 15(7), 2623; https://doi.org/10.3390/ma15072623 - 2 Apr 2022
Cited by 9 | Viewed by 2061
Abstract
Petroleum substances are among the xenobiotics that most often contaminate the natural environment. They have a strong effect on soil, water, and other components of the environment. The aim of this pot experiment has been to determine the effect of different soil material [...] Read more.
Petroleum substances are among the xenobiotics that most often contaminate the natural environment. They have a strong effect on soil, water, and other components of the environment. The aim of this pot experiment has been to determine the effect of different soil material amendments (compost, 3%; bentonite, 2% relative to the soil mass or calcium oxide, in amounts corresponding to one full hydrolytic acidity) on the content of heavy metals in aerial parts of maize (Zea mays L.) grown on soil polluted with petrol (0, 2.5, 5, and 10 cm3 kg−1 of soil). The content of all heavy metals, except copper, in the aerial biomass of maize was positively correlated, but biomass yield negatively correlated, with the increasing doses of petrol. The highest increase in the content of heavy metals was noted for chromium and manganese. Materials used for phytostabilisation (compost, bentonite, and calcium oxide) had a significant effect on the content of heavy metals and biomass yield of maize. They contributed to the modified accumulation of elements, especially chromium, copper, and cobalt in the aerial biomass of maize. In comparison with the control series (without material amendments), the application of calcium oxide proved to be most effective. It had the most evident influence on the chemical composition of maize, limiting the accumulation of lead, zinc, manganese, and iron and increasing biomass yield. Full article
(This article belongs to the Special Issue Advances in Eco-Friendly Adsorbent Materials for Removal of Inorganic and Organic Pollutants)
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34 pages, 6077 KiB  
Review
Magnetite Nanoparticles: Synthesis and Applications in Optics and Nanophotonics
by Nataliia Dudchenko, Shweta Pawar, Ilana Perelshtein and Dror Fixler
Materials 2022, 15(7), 2601; https://doi.org/10.3390/ma15072601 - 1 Apr 2022
Cited by 64 | Viewed by 13481
Abstract
Magnetite nanoparticles with different surface coverages are of great interest for many applications due to their intrinsic magnetic properties, nanometer size, and definite surface morphology. Magnetite nanoparticles are widely used for different medical-biological applications while their usage in optics is not as widespread. [...] Read more.
Magnetite nanoparticles with different surface coverages are of great interest for many applications due to their intrinsic magnetic properties, nanometer size, and definite surface morphology. Magnetite nanoparticles are widely used for different medical-biological applications while their usage in optics is not as widespread. In recent years, nanomagnetite suspensions, so-called magnetic ferrofluids, are applied in optics due to their magneto-optical properties. This review gives an overview of nanomagnetite synthesis and its properties. In addition, the preparation and application of magnetic nanofluids in optics, nanophotonics, and magnetic imaging are described. Full article
(This article belongs to the Special Issue Feature Paper in Optical and Photonic Materials)
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14 pages, 3900 KiB  
Article
Magnetic Properties of A2Ni2TeO6 (A = K, Li): Zigzag Order in the Honeycomb Layers of Ni2+ Ions Induced by First and Third Nearest-Neighbor Spin Exchanges
by Tatyana Vasilchikova, Alexander Vasiliev, Maria Evstigneeva, Vladimir Nalbandyan, Ji-Sun Lee, Hyun-Joo Koo and Myung-Hwan Whangbo
Materials 2022, 15(7), 2563; https://doi.org/10.3390/ma15072563 - 31 Mar 2022
Cited by 14 | Viewed by 2468
Abstract
The static and dynamic magnetic properties and the specific heat of K2Ni2TeO6 and Li2Ni2TeO6 were examined and it was found that they undergo a long-range ordering at TN = 22.8 and 24.4 [...] Read more.
The static and dynamic magnetic properties and the specific heat of K2Ni2TeO6 and Li2Ni2TeO6 were examined and it was found that they undergo a long-range ordering at TN = 22.8 and 24.4 K, respectively, but exhibit a strong short-range order. At high temperature, the magnetic susceptibilities of K2Ni2TeO6 and Li2Ni2TeO6 are described by a Curie–Weiss law, with Curie-Weiss temperatures Θ of approximately −13 and −20 K, respectively, leading to the effective magnetic moment of about 4.46 ± 0.01 μB per formula unit, as expected for Ni2+ (S = 1) ions. In the paramagnetic region, the ESR spectra of K2Ni2TeO6 and Li2Ni2TeO6 show a single Lorentzian-shaped line characterized by the isotropic effective g-factor, g = 2.19 ± 0.01. The energy-mapping analysis shows that the honeycomb layers of A2Ni2TeO6 (A = K, Li) and Li3Ni2SbO6 adopt a zigzag order, in which zigzag ferromagnetic chains are antiferromagnetically coupled, because the third nearest-neighbor spin exchanges are strongly antiferromagnetic while the first nearest-neighbor spin exchanges are strongly ferromagnetic, and that adjacent zigzag-ordered honeycomb layers prefer to be ferromagnetically coupled. The short-range order of the zigzag-ordered honeycomb lattices of K2Ni2TeO6 and Li2Ni2TeO6 is equivalent to that of an antiferromagnetic uniform chain, and is related to the short-range order of the ferromagnetic chains along the direction perpendicular to the chains. Full article
(This article belongs to the Section Quantum Materials)
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18 pages, 12375 KiB  
Article
In Vitro Hydrolytic Degradation of Polyester-Based Scaffolds under Static and Dynamic Conditions in a Customized Perfusion Bioreactor
by Pilar Alamán-Díez, Elena García-Gareta, Pedro Francisco Napal, Manuel Arruebo and María Ángeles Pérez
Materials 2022, 15(7), 2572; https://doi.org/10.3390/ma15072572 - 31 Mar 2022
Cited by 18 | Viewed by 2896
Abstract
Creating biofunctional artificial scaffolds could potentially meet the demand of patients suffering from bone defects without having to rely on donors or autologous transplantation. Three-dimensional (3D) printing has emerged as a promising tool to fabricate, by computer design, biodegradable polymeric scaffolds with high [...] Read more.
Creating biofunctional artificial scaffolds could potentially meet the demand of patients suffering from bone defects without having to rely on donors or autologous transplantation. Three-dimensional (3D) printing has emerged as a promising tool to fabricate, by computer design, biodegradable polymeric scaffolds with high precision and accuracy, using patient-specific anatomical data. Achieving controlled degradation profiles of 3D printed polymeric scaffolds is an essential feature to consider to match them with the tissue regeneration rate. Thus, achieving a thorough characterization of the biomaterial degradation kinetics in physiological conditions is needed. Here, 50:50 blends made of poly(ε-caprolactone)–Poly(D,L-lactic-co-glycolic acid (PCL-PLGA) were used to fabricate cylindrical scaffolds by 3D printing (⌀ 7 × 2 mm). Their hydrolytic degradation under static and dynamic conditions was characterized and quantified. For this purpose, we designed and in-house fabricated a customized bioreactor. Several techniques were used to characterize the degradation of the parent polymers: X-ray Photoelectron Spectroscopy (XPS), Gel Permeation Chromatography (GPC), Scanning Electron Microscopy (SEM), evaluation of the mechanical properties, weigh loss measurements as well as the monitoring of the degradation media pH. Our results showed that flow perfusion is critical in the degradation process of PCL-PLGA based scaffolds implying an accelerated hydrolysis compared to the ones studied under static conditions, and up to 4 weeks are needed to observe significant degradation in polyester scaffolds of this size and chemical composition. Our degradation study and characterization methodology are relevant for an accurate design and to tailor the physicochemical properties of polyester-based scaffolds for bone tissue engineering. Full article
(This article belongs to the Special Issue Advanced Functional Materials for Biomedicinal Applications)
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23 pages, 7989 KiB  
Article
Characterization of the Thermal Behavior of a Complex Composite (Clutch Facing) Combining Digital Image Stereo Correlation and Numerical Approach
by Camille Flament, Bruno Berthel, Michelle Salvia, Gérard Grosland and Isabelle Alix
Materials 2022, 15(7), 2582; https://doi.org/10.3390/ma15072582 - 31 Mar 2022
Cited by 2 | Viewed by 1933
Abstract
Car clutch facings are complex fiber-reinforced composites. The coefficient of thermal expansion (CTE) of the composite is one of the main thermal properties, which affects dry clutch engagement process due to heat associated with friction. In the case of clutch facing, which only [...] Read more.
Car clutch facings are complex fiber-reinforced composites. The coefficient of thermal expansion (CTE) of the composite is one of the main thermal properties, which affects dry clutch engagement process due to heat associated with friction. In the case of clutch facing, which only exists in its final form as a non-planar annular disc, it is difficult to define an elementary representative volume. The objective of this work was to develop a method for identifying the CTE distributions on the entire part. A device allowing measuring the strain fields by digital image correlation (DIC) under homogeneous thermal loading (up to 300 °C) was developed. The experimental results highlight the heterogeneity and the orthotropic nature of the material behavior and the influence of the angle between the fibers on the CTE. To take into account that the measured strain fields are related to the CTE, but also to the shape of the part, different approaches to identify the CTE were considered: direct measurements, classical laminate theory (CLT) and finite element method updating (FEMU). Only the FEMU allows an accurate identification of the CTE distributions. Nevertheless, the CLT respects the orders of magnitude and remains a useful tool for the design of clutches. Full article
(This article belongs to the Special Issue Organic Matrix Composites and Multifunctional Materials)
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28 pages, 4061 KiB  
Review
Porphyrins and Phthalocyanines on Solid-State Mesoporous Matrices as Catalysts in Oxidation Reactions
by Joanna Szymczak and Michal Kryjewski
Materials 2022, 15(7), 2532; https://doi.org/10.3390/ma15072532 - 30 Mar 2022
Cited by 24 | Viewed by 3465
Abstract
The review presents recent examples of heterogenic catalysts based on porphyrins and phthalocyanines loaded on mesoporous materials, such as MCM-41, SBA-15, MCM-48, SBA-16 or Al-MCM-41. Heterogenic approach to catalysis eases recovery, reuse and prevent macrocycle aggregation. In this application, mesoporous silica is a [...] Read more.
The review presents recent examples of heterogenic catalysts based on porphyrins and phthalocyanines loaded on mesoporous materials, such as MCM-41, SBA-15, MCM-48, SBA-16 or Al-MCM-41. Heterogenic approach to catalysis eases recovery, reuse and prevent macrocycle aggregation. In this application, mesoporous silica is a promising candidate for anchoring macrocycle and obtaining a new catalyst. Introduction of porphyrin or phthalocyanine into the mesoporous material may be performed through adsorption of the macrocycle, or by its in situ formation—by reaction of substrates introduced to the pores of the catalytic material. Catalytic reactions studied are oxidation processes, focused on alkane, alkene or arene as substrates. The products obtained are usually epoxides, alcohols, ketones, aldehydes or acids. The greatest interest lies in oxidation of cyclohexane and cyclohexene, as a source of adypic acid and derivatives. Some of the reactions may be viewed as biomimetic processes, resembling processes that occur in vivo and are catalyzed by cytochrome P450 enzyme family. Full article
(This article belongs to the Special Issue Solid State-Supported Porphyrins and Phthalocyanines as Catalysts and Photocatalysts)
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11 pages, 3632 KiB  
Article
Fabry-Perot Interference Fiber Acoustic Wave Sensor Based on Laser Welding All-Silica Glass
by Wenhua Wang
Materials 2022, 15(7), 2484; https://doi.org/10.3390/ma15072484 - 28 Mar 2022
Cited by 15 | Viewed by 2874
Abstract
Due to the small difference between the thermal expansion coefficients of silica optical fiber and silica glass, they are used as probe materials of optical fiber acoustic wave sensors. According to the light absorption characteristics of a pressure-sensitive silica diaphragm and silica glass, [...] Read more.
Due to the small difference between the thermal expansion coefficients of silica optical fiber and silica glass, they are used as probe materials of optical fiber acoustic wave sensors. According to the light absorption characteristics of a pressure-sensitive silica diaphragm and silica glass, the laser welding of an all-silica Fabry–Perot (FP) interference optical fiber acoustic wave sensor with a CO2 laser is proposed. For understanding the influence of thermal expansion of sealing air in an FP cavity and the drift of interference-intensity demodulation working point of a FP interference acoustic wave sensor, we designed a process for the laser welding of an ultra-thin silica diaphragm and sleeve and optical fiber and sleeve. The exhaust hole of the FP cavity is reserved in the preparation process, and an amplified spontaneous emission light source and a tunable optical-fiber FP filter are introduced to stabilize the working point. The sensor is tested with a 40 kHz sound vibration signal. The results show that the sound pressure sensitivity of the sensor to an acoustic source of 0.02–0.1 W/cm2 is 6.59 mV/kPa. The linearity coefficient is 0.99975, indicating good linearity. Full article
(This article belongs to the Special Issue Advanced Optical Methods for Materials Sciences)
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26 pages, 3011 KiB  
Review
Effects of Shot Peening and Cavitation Peening on Properties of Surface Layer of Metallic Materials—A Short Review
by Aleksander Świetlicki, Mirosław Szala and Mariusz Walczak
Materials 2022, 15(7), 2476; https://doi.org/10.3390/ma15072476 - 27 Mar 2022
Cited by 38 | Viewed by 6364
Abstract
Shot peening is a dynamically developing surface treatment used to improve the surface properties modified by tool, impact, microblasting, or shot action. This paper reviews the basic information regarding shot peening methods. The peening processes and effects of the shot peening and cavitation [...] Read more.
Shot peening is a dynamically developing surface treatment used to improve the surface properties modified by tool, impact, microblasting, or shot action. This paper reviews the basic information regarding shot peening methods. The peening processes and effects of the shot peening and cavitation peening treatments on the surface layer properties of metallic components are analysed. Moreover, the effects of peening on the operational performance of metallic materials are summarized. Shot peening is generally applied to reduce the surface roughness, increase the hardness, and densify the surface layer microstructure, which leads to work hardening effects. In addition, the residual compressive stresses introduced into the material have a beneficial effect on the performance of the surface layer. Therefore, peening can be beneficial for metallic structures prone to fatigue, corrosion, and wear. Recently, cavitation peening has been increasingly developed. This review paper suggests that most research on cavitation peening omits the treatment of additively manufactured metallic materials. Furthermore, no published studies combine shot peening and cavitation peening in one hybrid process, which could synthesize the benefits of both peening processes. Moreover, there is a need to investigate the effects of peening, especially cavitation peening and hybrid peening, on the anti-wear and corrosion performance of additively manufactured metallic materials. Therefore, the literature gap leading to the scope of future work is also included. Full article
(This article belongs to the Special Issue Metallic and Ceramic Materials Integrity – Surface Engineering for Wear, Corrosion and Erosion Prevention)
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12 pages, 5505 KiB  
Article
Photoaligned Liquid Crystal Devices with Switchable Hexagonal Diffraction Patterns
by Inge Nys, Brecht Berteloot and Kristiaan Neyts
Materials 2022, 15(7), 2453; https://doi.org/10.3390/ma15072453 - 26 Mar 2022
Cited by 6 | Viewed by 2364
Abstract
Highly efficient optical diffraction can be realized with the help of micrometer-thin liquid crystal (LC) layers with a periodic modulation of the director orientation. Electrical tunability is easily accessible due to the strong stimuli-responsiveness in the LC phase. By using well-designed photoalignment patterns [...] Read more.
Highly efficient optical diffraction can be realized with the help of micrometer-thin liquid crystal (LC) layers with a periodic modulation of the director orientation. Electrical tunability is easily accessible due to the strong stimuli-responsiveness in the LC phase. By using well-designed photoalignment patterns at the surfaces, we experimentally stabilize two dimensional periodic LC configurations with switchable hexagonal diffraction patterns. The alignment direction follows a one-dimensional periodic rotation at both substrates, but with a 60° or 120° rotation between both grating vectors. The resulting LC configuration is studied with the help of polarizing optical microscopy images and the diffraction properties are measured as a function of the voltage. The intricate bulk director configuration is revealed with the help of finite element Q-tensor simulations. Twist conflicts induced by the surface anchoring are resolved by introducing regions with an out-of-plane tilt in the bulk. This avoids the need for singular disclinations in the structures and gives rise to voltage induced tuning without hysteretic behavior. Full article
(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)
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11 pages, 2876 KiB  
Article
Eu-Doped Pyrochlore Crystal Nano-Powders as Fluorescent Solid for Fingerprint Visualization and for Anti-Counterfeiting Applications
by Layla Brini, Ines Bennour, Alessandra Toncelli, Ramzi Maalej and Mohamed Abdelhedi
Materials 2022, 15(7), 2423; https://doi.org/10.3390/ma15072423 - 25 Mar 2022
Cited by 6 | Viewed by 2450
Abstract
Undoped Y2Sn2O7 and Eu3+ doped Y2Sn2O7 samples with doping concentrations 7%, 8%, 9%, and 10% are successfully synthesized by the co-precipitation method. A complete structural, morphological, and spectroscopic characterization is carried out. [...] Read more.
Undoped Y2Sn2O7 and Eu3+ doped Y2Sn2O7 samples with doping concentrations 7%, 8%, 9%, and 10% are successfully synthesized by the co-precipitation method. A complete structural, morphological, and spectroscopic characterization is carried out. XRD measurements reveal that samples crystallize in the pure single pyrochlore phase and Eu3+ ions occupy sites with D3d symmetry. After mechanical grinding, the average crystallite size is less than 100 nm for all compositions. Optical characterization shows emission from the 5D0 level towards the lower lying 7F0,1,2,3,4 levels. The CIE color coordinates of all the pyrochlore phosphors are very close to those of the ideal red light. For the visualization of latent fingerprints, different surfaces are tested, including difficult ones (wood and ceramic), with excellent results. All three levels of fingerprint ridge patterns are visualized: core (Level 1), bifurcation and termination (Level 2), and sweat pores (Level 3). Moreover, our nano-powders are used to prepare a stable fluorescent ink. Full article
(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)
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18 pages, 6243 KiB  
Review
Metal Marking Behavior and Testing of Porcelain Tableware
by Luc Hennetier, Ana Moura and Manuel Ribeiro
Materials 2022, 15(7), 2442; https://doi.org/10.3390/ma15072442 - 25 Mar 2022
Cited by 2 | Viewed by 3430
Abstract
The term “metal marking” is widely used to define the common phenomenon of tableware glazes being damaged by metallic cutlery. Appearing as unaesthetic gray marks and scratches resulting from normal conditions of use, these defects deeply affect the performance of ceramic products, especially [...] Read more.
The term “metal marking” is widely used to define the common phenomenon of tableware glazes being damaged by metallic cutlery. Appearing as unaesthetic gray marks and scratches resulting from normal conditions of use, these defects deeply affect the performance of ceramic products, especially in intensive environments, such as in the hospitality industry. The scope of this article is to establish a comprehensive review of the phenomenon, focusing on the physical and chemical mechanisms involved in the process, and their interactions and consequences. It also intends to list the different methods normally followed to avoid or at least reduce this defect, in order to enhance the durability of porcelain dishware. This manuscript also provides a review of the different testing methods developed and used by the tableware industry and technical centers to quantify the ability of porcelain tableware to produce metal marks. To face the current lack of any international or at least national standard testing procedure that would permit a reliable comparison of products, a new metal marking test developed at the Technological Center for Ceramic and Glass (CTCV) is presented as an alternative to common tests normally based on knives as a marking tool. Full article
(This article belongs to the Special Issue Science and Technology of Porcelain: History, Processing, Structure and Properties)
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18 pages, 5022 KiB  
Review
Programming Soft Shape-Morphing Systems by Harnessing Strain Mismatch and Snap-Through Bistability: A Review
by Yi Wu, Gang Guo, Zhuxuan Wei and Jin Qian
Materials 2022, 15(7), 2397; https://doi.org/10.3390/ma15072397 - 24 Mar 2022
Cited by 10 | Viewed by 4459
Abstract
Multi-modal and controllable shape-morphing constitutes the cornerstone of the functionalization of soft actuators/robots. Involving heterogeneity through material layout is a widely used strategy to generate internal mismatches in active morphing structures. Once triggered by external stimuli, the entire structure undergoes cooperative deformation by [...] Read more.
Multi-modal and controllable shape-morphing constitutes the cornerstone of the functionalization of soft actuators/robots. Involving heterogeneity through material layout is a widely used strategy to generate internal mismatches in active morphing structures. Once triggered by external stimuli, the entire structure undergoes cooperative deformation by minimizing the potential energy. However, the intrinsic limitation of soft materials emerges when it comes to applications such as soft actuators or load-bearing structures that require fast response and large output force. Many researchers have explored the use of the structural principle of snap-through bistability as the morphing mechanisms. Bistable or multi-stable mechanical systems possess more than one local energy minimum and are capable of resting in any of these equilibrium states without external forces. The snap-through motion could overcome energy barriers to switch among these stable or metastable states with dramatically distinct geometries. Attributed to the energy storage and release mechanism, such snap-through transition is quite highly efficient, accompanied by fast response speed, large displacement magnitude, high manipulation strength, and moderate driving force. For example, the shape-morphing timescale of conventional hydrogel systems is usually tens of minutes, while the activation time of hydrogel actuators using the elastic snapping instability strategy can be reduced to below 1 s. By rationally embedding stimuli-responsive inclusions to offer the required trigger energy, various controllable snap-through actuations could be achieved. This review summarizes the current shape-morphing programming strategies based on mismatch strain induced by material heterogeneity, with emphasis on how to leverage snap-through bistability to broaden the applications of the shape-morphing structures in soft robotics and mechanical metamaterials. Full article
(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)
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11 pages, 35271 KiB  
Article
Grain Growth Behavior and Electrical Properties of 0.96(K0.46−xNa0.54−x)Nb0.95Sb0.05O3–0.04Bi0.5(Na0.82K0.18)0.5ZrO3 Ceramics
by Yeon-Ju Park, Il-Ryeol Yoo, Seong-Hui Choi, Jiung Cho and Kyung-Hoon Cho
Materials 2022, 15(7), 2357; https://doi.org/10.3390/ma15072357 - 22 Mar 2022
Cited by 2 | Viewed by 1884
Abstract
This study investigated the causes of microstructural changes and the resultant electrical properties according to the sintering temperature of 0.96(K0.46−xNa0.54−x)Nb0.95Sb0.05O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 lead-free ceramics by analyzing [...] Read more.
This study investigated the causes of microstructural changes and the resultant electrical properties according to the sintering temperature of 0.96(K0.46−xNa0.54−x)Nb0.95Sb0.05O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 lead-free ceramics by analyzing the correlation between vacancy concentrations and 2D nucleation. When sintered for 4 h, no grain growth occurred for the x = 0.000 composition over a wide temperature range, demonstrating that the existence of initial vacancies is essential for grain growth. As x increased, that is, as the vacancy concentration increased, the critical driving force (ΔGC) for 2D nucleation decreased, and abnormal grain growth was promoted. The number and size of these abnormal grains increased as the sintering temperature increased, but at sintering temperatures above 1100 °C, they decreased again owing to a large drop in ΔGC. The x = 0.005 specimen sintered at 1085 °C exhibited excellent piezoelectric properties of d33 = 498 pC/N and kp = 0.45 due to the large number of large abnormal grains with an 83% tetragonal phase fraction. The x = 0.000 specimen sintered at 1130 °C with suppressed grain growth exhibited good energy storage properties because of its very high relative density and small grain size of 300 to 400 nm. Full article
(This article belongs to the Special Issue Ferromagnetic and Ferroelectric Materials: Synthesis, Applications, and Techniques)
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19 pages, 8672 KiB  
Article
Numerical Simulation of Damage Evolution and Electrode Deformation of X100 Pipeline Steel during Crevice Corrosion
by Wenxian Su and Zhikuo Liu
Materials 2022, 15(6), 2329; https://doi.org/10.3390/ma15062329 - 21 Mar 2022
Cited by 5 | Viewed by 2560
Abstract
In this paper, the spatial and temporal damage evolution was described during crevice corrosion through developing a two-dimensional (2-D) model. COMSOL code was used to simulate the crevice corrosion regulated by the I∙R voltage of nickel (Ni) metal in sulfuric acidic. The electrode [...] Read more.
In this paper, the spatial and temporal damage evolution was described during crevice corrosion through developing a two-dimensional (2-D) model. COMSOL code was used to simulate the crevice corrosion regulated by the I∙R voltage of nickel (Ni) metal in sulfuric acidic. The electrode deformation, potential and current curves, and other typical characteristics were predicted during crevice corrosion, where results were consistent with published experimental results. Then, based on the Ni model, the damage evolution of X100 crevice corrosion in CO2 solution was simulated, assuming uniform distribution of solution inside and outside the crevice. The results showed that over time, the surface damage of Ni electrode increased under a constant applied potential. As the gap increased, the critical point of corrosion (CPC) inside the crevice moved into a deeper location, and the corrosion damage area (CDA) gradually expanded, but the threshold value of corrosion damage remained almost unchanged. The CDA inside the crevice extended toward the opening and the tip of crevice. Since the potential drop in this region increases with increasing current, the passivation potential point moved towards the opening. As the gap increased and the electrolyte resistance decreased, the critical potential for reaching the maximum corrosion rate moved into a deeper location. It is significant for predicting the initial damage location and the occurrence time of surface damage of crevice corrosion through the 2-D model that is not available through the one-dimensional simplified model. Full article
(This article belongs to the Special Issue Structural Strength, Corrosion and Failure Analysis of Pressure Vessel and Pipeline System)
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10 pages, 1327 KiB  
Article
Fabrication of Type-Variable Electronic Paper Using Electrophoretic Particle Loading with Multiple Bottom Electrode Structure
by Sang Il Lee, Dongjin Lee and Kunsik An
Materials 2022, 15(6), 2289; https://doi.org/10.3390/ma15062289 - 20 Mar 2022
Viewed by 2282
Abstract
This study suggested the design of type-variable electronic paper with multiple bottom electrode structures and experimentally investigated the process mechanism of the electrophoretic particle loading method (EPLM) as an electronic ink injection method. The type-variable electronic paper was achieved by constructing the multi-electrode [...] Read more.
This study suggested the design of type-variable electronic paper with multiple bottom electrode structures and experimentally investigated the process mechanism of the electrophoretic particle loading method (EPLM) as an electronic ink injection method. The type-variable electronic paper was achieved by constructing the multi-electrode structure that had a structure of four electrodes that can independently apply voltage to one cell. By injecting electronic ink that mixes two types of particles with opposite charges into an electrically neutral color (blue) fluid, we realized electronic paper with a single color, and we then measured the optical characteristics of the panel. We used the EPLM to prevent charged particles that have lost their charge from being injected into the e-paper by using an electric field. In order to confirm the color expression and transmittance control effect using the multi-electrode structure, we conducted reflectance measurement and transmittance measurement experiments. Our experiments confirmed that the expression of more than five colors was possible and that the transmittance was controllable to a minimum of 13.50% and a maximum of 71.18%. This study provides an attractive method to create e-paper as a new form outside the framework of existing e-paper technology. Full article
(This article belongs to the Special Issue Feature Paper in Section Smart Materials)
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9 pages, 2579 KiB  
Article
A Simple Structure for an Independently Tunable Infrared Absorber Based on a Non-Concentric Graphene Nanodisk
by Kun Yu, Peng Shen, Wei Zhang, Xicheng Xiong, Jun Zhang and Yufang Liu
Materials 2022, 15(6), 2296; https://doi.org/10.3390/ma15062296 - 20 Mar 2022
Cited by 7 | Viewed by 2279
Abstract
Due to its unique electronic and optical properties, graphene has been used to design tunable optical absorbers. In this paper, we propose a plasmonic absorber consisting of non-concentric graphene nanodisk arrays, which is designed to operate in the mid-infrared spectral range and is [...] Read more.
Due to its unique electronic and optical properties, graphene has been used to design tunable optical absorbers. In this paper, we propose a plasmonic absorber consisting of non-concentric graphene nanodisk arrays, which is designed to operate in the mid-infrared spectral range and is capable of achieving nearly perfect absorption. Two perfect absorption peaks are produced due to the impedance of the structure, which matches that of the free space. The influences of the thicknesses of the dielectric layer, the size of graphene nanodisk, and the incident conditions on the absorption are studied. Moreover, the absorption intensity can be independently tuned by varying the Fermi levels of two graphene nanodisks. Furthermore, the polarization-independent absorbance of the absorber exceeds 95% under oblique incidence, and remains very high over a wide angle. This proposed absorber has potential applications in optical detectors, tunable sensors, and band-pass filters. Full article
(This article belongs to the Special Issue Nano and Advanced Material Engineering)
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18 pages, 22175 KiB  
Article
Oxidation Behaviour of Microstructurally Highly Metastable Ag-La Alloy
by Andraž Jug, Mihael Brunčko, Rebeka Rudolf and Ivan Anžel
Materials 2022, 15(6), 2295; https://doi.org/10.3390/ma15062295 - 20 Mar 2022
Cited by 3 | Viewed by 1879
Abstract
A new silver-based alloy with 2 wt.% of lanthanum (La) was studied as a potential candidate for electric contact material. The alloy was prepared by rapid solidification, performed by the melt spinning technique. Microstructural examination of the rapidly solidified ribbons revealed very fine [...] Read more.
A new silver-based alloy with 2 wt.% of lanthanum (La) was studied as a potential candidate for electric contact material. The alloy was prepared by rapid solidification, performed by the melt spinning technique. Microstructural examination of the rapidly solidified ribbons revealed very fine grains of αAg and intermetallic Ag5La particles, which appear in the volume of the grains, as well as on the grain boundaries. Rapid solidification enabled high microstructural refinement and provided a suitable starting microstructure for the subsequent internal oxidation, resulting in fine submicron-sized La2O3 oxide nanoparticle formation throughout the volume of the silver matrix (αAg). The resulting nanostructured Ag-La2O3 microstructure was characterised by high-resolution FESEM and STEM, both equipped with EDX. High-temperature internal oxidation of the rapidly solidified ribbons essentially changed the microstructure. Mostly homogeneously dispersed nano-sized La2O3 were formed within the grains, as well as on the grain boundaries. Three mechanisms of internal oxidation were identified: (i) the oxidation of La from the solid solution; (ii) partial dissolution of finer Ag5La particles before the internal oxidation front and oxidation of La from the solid solution; and (iii) direct oxidation of coarser Ag5La intermetallic particles. Full article
(This article belongs to the Special Issue Advanced Properties of Engineering Thin Films and Materials)
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10 pages, 2452 KiB  
Article
Si-Doped HfO2-Based Ferroelectric Tunnel Junctions with a Composite Energy Barrier for Non-Volatile Memory Applications
by Yoseop Lee, Sungmun Song, Woori Ham and Seung-Eon Ahn
Materials 2022, 15(6), 2251; https://doi.org/10.3390/ma15062251 - 18 Mar 2022
Cited by 23 | Viewed by 4612
Abstract
Ferroelectric tunnel junctions (FTJs) have attracted attention as devices for advanced memory applications owing to their high operating speed, low operating energy, and excellent scalability. In particular, hafnia ferroelectric materials are very promising because of their high remanent polarization (below 10 nm) and [...] Read more.
Ferroelectric tunnel junctions (FTJs) have attracted attention as devices for advanced memory applications owing to their high operating speed, low operating energy, and excellent scalability. In particular, hafnia ferroelectric materials are very promising because of their high remanent polarization (below 10 nm) and high compatibility with complementary metal-oxide-semiconductor (CMOS) processes. In this study, a Si-doped HfO2-based FTJ device with a metal-ferroelectric-insulator-semiconductor (MFIS) structure was proposed to maximize the tunneling electro-resistance (TER) effect. The potential barrier modulation effect under applied varying voltage was analyzed, and the possibility of its application as a non-volatile memory device was presented through stability assessments such as endurance and retention tests. Full article
(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)
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9 pages, 29383 KiB  
Article
Plasmonically Enhanced Colloidal Quantum Dot/Graphene Doped Polymer Random Lasers
by Mingxuan Cao, Min Wang, Zhiwen Wang, Luhao Zang, Hao Liu, Shuping Xiao, Matthew M. F. Yuen, Ying Wang, Yating Zhang and Jianquan Yao
Materials 2022, 15(6), 2213; https://doi.org/10.3390/ma15062213 - 17 Mar 2022
Cited by 4 | Viewed by 2001
Abstract
An improvement in random lasers based on a colloidal quantum dot (QD)/graphene-doped polymer was observed and attributed to multiple light-scattering and graphene surface plasmon resonance. The emission characteristics of quantum dots doped with graphene oxide and reduced graphene oxide were compared. The QD/reduced [...] Read more.
An improvement in random lasers based on a colloidal quantum dot (QD)/graphene-doped polymer was observed and attributed to multiple light-scattering and graphene surface plasmon resonance. The emission characteristics of quantum dots doped with graphene oxide and reduced graphene oxide were compared. The QD/reduced graphene oxide hybrid exhibited a lower laser emission threshold (~460 μJ/cm2). The emission modes and thresholds were strongly dependent on both the graphene doping concentration and the external temperature. Decreased plasmon coupling was the primary reason for lower QD/graphene laser emission with increasing temperature. The optimum reduced graphene oxide concentration was 0.2 wt.%. This work provides a practical approach to optimizing the threshold and stability of random laser devices, with potential applications in displays, sensors, and anti-counterfeiting labels. Full article
(This article belongs to the Section Optical and Photonic Materials)
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37 pages, 23480 KiB  
Review
Engineering 2D Materials for Photocatalytic Water-Splitting from a Theoretical Perspective
by Mukesh Jakhar, Ashok Kumar, Pradeep K. Ahluwalia, Kumar Tankeshwar and Ravindra Pandey
Materials 2022, 15(6), 2221; https://doi.org/10.3390/ma15062221 - 17 Mar 2022
Cited by 66 | Viewed by 6455
Abstract
Splitting of water with the help of photocatalysts has gained a strong interest in the scientific community for producing clean energy, thus requiring novel semiconductor materials to achieve high-yield hydrogen production. The emergence of 2D nanoscale materials with remarkable electronic and optical properties [...] Read more.
Splitting of water with the help of photocatalysts has gained a strong interest in the scientific community for producing clean energy, thus requiring novel semiconductor materials to achieve high-yield hydrogen production. The emergence of 2D nanoscale materials with remarkable electronic and optical properties has received much attention in this field. Owing to the recent developments in high-end computation and advanced electronic structure theories, first principles studies offer powerful tools to screen photocatalytic systems reliably and efficiently. This review is organized to highlight the essential properties of 2D photocatalysts and the recent advances in the theoretical engineering of 2D materials for the improvement in photocatalytic overall water-splitting. The advancement in the strategies including (i) single-atom catalysts, (ii) defect engineering, (iii) strain engineering, (iv) Janus structures, (v) type-II heterostructures (vi) Z-scheme heterostructures (vii) multilayer configurations (viii) edge-modification in nanoribbons and (ix) the effect of pH in overall water-splitting are summarized to improve the existing problems for a photocatalytic catalytic reaction such as overcoming large overpotential to trigger the water-splitting reactions without using cocatalysts. This review could serve as a bridge between theoretical and experimental research on next-generation 2D photocatalysts. Full article
(This article belongs to the Special Issue Electronic Structure Theory of Low Dimensional Materials)
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23 pages, 7382 KiB  
Article
Combined Electrochemical, Raman Analysis and Machine Learning Assessments of the Inhibitive Properties of an 1,3,4-Oxadiazole-2-Thiol Derivative against Carbon Steel Corrosion in HCl Solution
by Simona Varvara, Camelia Berghian-Grosan, Gianina Damian, Maria Popa and Florin Popa
Materials 2022, 15(6), 2224; https://doi.org/10.3390/ma15062224 - 17 Mar 2022
Cited by 6 | Viewed by 2151
Abstract
The inhibiting properties of 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol (PyODT) on the corrosion of carbon steel in 1.0 M HCl solution were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, Raman spectroscopy, and SEM-EDX analysis. An approach based on machine learning algorithms and Raman data was also applied [...] Read more.
The inhibiting properties of 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol (PyODT) on the corrosion of carbon steel in 1.0 M HCl solution were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, Raman spectroscopy, and SEM-EDX analysis. An approach based on machine learning algorithms and Raman data was also applied to follow the carbon steel degradation in different experimental conditions. The electrochemical measurements revealed that PyODT behaves as a mixed-type corrosion inhibitor, reaching an efficiency of about 93.1% at a concentration of 5 mM, after 1 h exposure to 1.0 M HCl solution. Due to the molecular adsorption and structural organization of PyODT molecules on the C-steel surface, higher inhibitive effectiveness of about 97% was obtained at 24 h immersion. The surface analysis showed a significantly reduced degradation state of the carbon steel surface in the presence of PyODT due to the inhibitor adsorption revealed by Raman spectroscopy and the presence of N and S atoms in the EDX spectra. The combination of Raman spectroscopy and machine learning algorithms was proved to be a facile and reliable tool for an incipient identification of the corrosion sites on a metallic surface exposed to corrosive environments. Full article
(This article belongs to the Special Issue Corrosion and Corrosion Inhibition of Metals and Their Alloys)
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31 pages, 4478 KiB  
Review
Exploring the Journey of Zinc Oxide Nanoparticles (ZnO-NPs) toward Biomedical Applications
by Fahadul Islam, Sheikh Shohag, Md. Jalal Uddin, Md. Rezaul Islam, Mohamed H. Nafady, Aklima Akter, Saikat Mitra, Arpita Roy, Talha Bin Emran and Simona Cavalu
Materials 2022, 15(6), 2160; https://doi.org/10.3390/ma15062160 - 15 Mar 2022
Cited by 229 | Viewed by 12454
Abstract
The field of nanotechnology is concerned with the creation and application of materials having a nanoscale spatial dimensioning. Having a considerable surface area to volume ratio, nanoparticles have particularly unique properties. Several chemical and physical strategies have been used to prepare zinc oxide [...] Read more.
The field of nanotechnology is concerned with the creation and application of materials having a nanoscale spatial dimensioning. Having a considerable surface area to volume ratio, nanoparticles have particularly unique properties. Several chemical and physical strategies have been used to prepare zinc oxide nanoparticles (ZnO-NPs). Still, biological methods using green or natural routes in various underlying substances (e.g., plant extracts, enzymes, and microorganisms) can be more environmentally friendly and cost-effective than chemical and/or physical methods in the long run. ZnO-NPs are now being studied as antibacterial agents in nanoscale and microscale formulations. The purpose of this study is to analyze the prevalent traditional method of generating ZnO-NPs, as well as its harmful side effects, and how it might be addressed utilizing an eco-friendly green approach. The study’s primary focus is on the potential biomedical applications of green synthesized ZnO-NPs. Biocompatibility and biomedical qualities have been improved in green-synthesized ZnO-NPs over their traditionally produced counterparts, making them excellent antibacterial and cancer-fighting drugs. Additionally, these ZnO-NPs are beneficial when combined with the healing processes of wounds and biosensing components to trace small portions of biomarkers linked with various disorders. It has also been discovered that ZnO-NPs can distribute and sense drugs. Green-synthesized ZnO-NPs are compared to traditionally synthesized ones in this review, which shows that they have outstanding potential as a potent biological agent, as well as related hazardous properties. Full article
(This article belongs to the Special Issue Preparation, Physico-Chemical Properties and Biomedical Applications of Nanoparticles)
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11 pages, 5776 KiB  
Article
The Effects of 3-Dimensional Bioprinting Calcium Silicate Cement/Methacrylated Gelatin Scaffold on the Proliferation and Differentiation of Human Dental Pulp Stem Cells
by Dakyung Choi, Manfei Qiu, Yun-Chan Hwang, Won-Mann Oh, Jeong-Tae Koh, Chan Park and Bin-Na Lee
Materials 2022, 15(6), 2170; https://doi.org/10.3390/ma15062170 - 15 Mar 2022
Cited by 17 | Viewed by 3523
Abstract
A calcium silicate cement/methacrylated gelatin (GelMa) scaffold has been applied in tissue engineering; however, the research on its applications in dental tissue regeneration remains lacking. We investigate the effect of this scaffold on human dental pulp stem cells (hDPSCs). hDPSCs were cultured in [...] Read more.
A calcium silicate cement/methacrylated gelatin (GelMa) scaffold has been applied in tissue engineering; however, the research on its applications in dental tissue regeneration remains lacking. We investigate the effect of this scaffold on human dental pulp stem cells (hDPSCs). hDPSCs were cultured in 3D-printed GelMa and MTA-GelMa scaffolds. Cell adhesion was evaluated using scanning electron microscopy images. Cells were cultured in an osteogenic differentiation medium, which contained a complete medium or α-MEM containing aqueous extracts of the 3D-printd GelMa or MTA-GelMa scaffold with 2% FBS, 10 mM β-glycerophosphate, 50 μg/mL ascorbic acid, and 10 nM dexamethasone; cell viability and differentiation were shown by WST-1 assay, Alizarin Red S staining, and alkaline phosphatase staining. Quantitative real-time PCR was used to measure the mRNA expression of DSPP and DMP-1. One-way analysis of variance followed by Tukey’s post hoc test was used to determine statistically significant differences, identified at p < 0.05. hDPSCs adhered to both the 3D-printed GelMa and MTA-GelMa scaffolds. There was no statistically significant difference between the GelMa and MTA-GelMa groups and the control group in the cell viability test. Compared with the control group, the 3D-printed MTA-GelMa scaffold promoted the odontogenic differentiation of hDPSCs. The 3D-printed MTA-GelMa scaffold is suitable for the growth of hDPSCs, and the scaffold extracts can better promote odontoblastic differentiation. Full article
(This article belongs to the Special Issue Hydrogel Biomaterials: Present and Future Challenges)
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19 pages, 5743 KiB  
Article
Polyester and Epoxy Resins with Increased Thermal Conductivity and Reduced Surface Resistivity for Applications in Explosion-Proof Enclosures of Electrical Devices
by Małgorzata Szymiczek and Dawid Buła
Materials 2022, 15(6), 2171; https://doi.org/10.3390/ma15062171 - 15 Mar 2022
Cited by 4 | Viewed by 2409
Abstract
Composite materials are still finding new applications that require the modification of various properties and are characterized by the summary impact on selected operational features. Due to the operating conditions of electrical equipment enclosures in potentially explosive atmospheres, the surface resistivity ensuring anti-electrostatic [...] Read more.
Composite materials are still finding new applications that require the modification of various properties and are characterized by the summary impact on selected operational features. Due to the operating conditions of electrical equipment enclosures in potentially explosive atmospheres, the surface resistivity ensuring anti-electrostatic properties, i.e., below 109 Ω and resistance to the flame while maintaining appropriate operational enclosure properties is very important. It is also crucial to dissipate heat while reducing weight. Currently metal or cast-iron enclosures are used for various types of electrical devices. As part of the work, a material that can be used for a composite matrix for the enclosure was developed. The study aimed to assess the influence of selected fillers and chemical modifications on the thermal conductivity coefficient, resistivity, and strength properties of matrix materials for the production of electrical device enclosures used in the mining industry. Selected resins were modified with graphite, copper, and carbon black. Tests were carried out on the coefficient of thermal conductivity, surface resistivity, flammability, and flexural strength. At the final stage of the work, a multi-criteria analysis was carried out, which allowed the selection of a composite that meets the assumed characteristics to the highest degree. It is a vinyl ester composite modified with 15 wt.% MG394 and 5 wt.% MG1596 graphite (W2). The thermal conductivity of composite W2 is 5.64 W/mK, the surface resistivity is 5.2 × 103 Ω, the flexural strength is 50.61 MPa, and the flammability class is V0. Full article
(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)
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19 pages, 5911 KiB  
Article
Activated Carbon Preparation from Sugarcane Leaf via a Low Temperature Hydrothermal Process for Aquaponic Treatment
by Kanyanat Tawatbundit and Sumrit Mopoung
Materials 2022, 15(6), 2133; https://doi.org/10.3390/ma15062133 - 14 Mar 2022
Cited by 5 | Viewed by 3648
Abstract
The effects of hydrothermal treatment, 0–5% KMnO4 content, and 300–400 °C pyrolysis temperature, were studied for activated carbon preparation from sugar cane leaves in comparison with non-hydrothermal treatment. The percent yield of activated carbon prepared by the hydrothermal method (20.33–36.23%) was higher [...] Read more.
The effects of hydrothermal treatment, 0–5% KMnO4 content, and 300–400 °C pyrolysis temperature, were studied for activated carbon preparation from sugar cane leaves in comparison with non-hydrothermal treatment. The percent yield of activated carbon prepared by the hydrothermal method (20.33–36.23%) was higher than that prepared by the non-hydrothermal method (16.40–36.50%) and was higher with conditions employing the same content of KMnO4 (22.08–42.14%). The hydrothermal and pyrolysis temperatures have the effect of increasing the carbon content and aromatic nature of the synthesized activated carbons. In addition, KMnO4 utilization increased the O/C ratio and the content of C-O, Mn-OH, O-Mn-O, and Mn-O surface functional groups. KMnO4 also decreases zeta potential values throughout the pH range of 3 to 11 and the surface area and porosity of the pre-hydrothermal activated carbons. The use of the pre-hydrothermal activated carbon prepared with 3% KMnO4 and pyrolyzed at 350 °C as a filter in an aquaponic system could improve the quality of water with pH of 7.2–7.4, DO of 9.6–13.3 mg/L, and the turbidity of 2.35–2.90 NTU. It could also reduce the content of ammonia, nitrite, and phosphate with relative removal rates of 86.84%, 73.17%, and 53.33%, respectively. These results promoted a good growth of catfish and red oak lettuce. Full article
(This article belongs to the Collection Advanced Biomass-Derived Carbon Materials)
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12 pages, 4733 KiB  
Article
High-Frequency and High-Power Performance of n-Type GaN Epilayers with Low Electron Density Grown on Native Substrate
by Roman M. Balagula, Liudvikas Subačius, Justinas Jorudas, Vytautas Janonis, Pawel Prystawko, Mikolaj Grabowski and Irmantas Kašalynas
Materials 2022, 15(6), 2066; https://doi.org/10.3390/ma15062066 - 11 Mar 2022
Cited by 7 | Viewed by 2795
Abstract
The n-type GaN epilayers with low electron density were developed on a native substrate using the metalorganic vapour phase epitaxy method and investigated under pulsed electric fields until material breakdown and optically in the spectrum range from 0.1 THz to 60 THz [...] Read more.
The n-type GaN epilayers with low electron density were developed on a native substrate using the metalorganic vapour phase epitaxy method and investigated under pulsed electric fields until material breakdown and optically in the spectrum range from 0.1 THz to 60 THz at two temperatures of 77 K and 300 K. The epilayers demonstrated the low-field electron mobility and density values reaching up to 1021 cm2/V·s and 1.06 × 1016 cm−3 (at 300 K) and 2652 cm2/V·s and 0.21 × 1016 cm−3 (at 77 K), respectively. Maximum injected electric power value till the damage of the GaN epilayer was found to be up to 1.8 GW/cm3 and 5.1 GW/cm3 at 77 K and 300 K, respectively. The results indicate new practical possibilities of the GaN material controlled by an external electric field. Full article
(This article belongs to the Special Issue Wide and Ultra-Wide Bandgap Semiconductor Materials for Power Devices)
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20 pages, 2045 KiB  
Review
Achievements and Future Perspectives of the Trivalent Thulium-Ion-Doped Mixed-Sesquioxide Ceramics for Laser Applications
by Angela Pirri, Roman N. Maksimov, Jiang Li, Matteo Vannini and Guido Toci
Materials 2022, 15(6), 2084; https://doi.org/10.3390/ma15062084 - 11 Mar 2022
Cited by 28 | Viewed by 3254
Abstract
This paper is devoted to reviewing the latest results achieved in solid-state lasers based on thulium-doped mixed-sesquioxide ceramics, i.e., (Lu,Sc,Y)2O3. The near- and mid-infrared regions are of interest for many applications, from medicine to remote sensing, as they match [...] Read more.
This paper is devoted to reviewing the latest results achieved in solid-state lasers based on thulium-doped mixed-sesquioxide ceramics, i.e., (Lu,Sc,Y)2O3. The near- and mid-infrared regions are of interest for many applications, from medicine to remote sensing, as they match molecular fingerprints and cover several atmospheric transparency windows. These matrices are characterized by a strong electron–phonon interaction—which results in a large splitting of the ground state—and by a spectral broadening of the optical transition suitable for developing tunable and short-pulse lasers. In particular, the manuscript reports on the trivalent thulium laser transitions at 1.5, 1.9, and 2.3 µm, along with the thermal and optical characteristics of the (Lu,Sc,Y)2O3 ceramics, including the fabrication techniques, spectroscopic and optical properties, and laser performances achieved in different pumping regimes, such as continuous-wave (CW), quasi-CW, and pulsed modes. A comparison of the performance obtained with these mixed-sesquioxide ceramics and with the corresponding crystals is reported. Full article
(This article belongs to the Special Issue Multiple Applications for Ceramic Materials)
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29 pages, 4254 KiB  
Review
Current Research and Challenges in Bitumen Emulsion Manufacturing and Its Properties
by Ahmed Al-Mohammedawi and Konrad Mollenhauer
Materials 2022, 15(6), 2026; https://doi.org/10.3390/ma15062026 - 9 Mar 2022
Cited by 19 | Viewed by 8950
Abstract
The global increase of road infrastructure and its impact on the environment requires serious attention to develop sustainable and environmentally friendly road materials. One group of those materials is produced by using bitumen emulsion. However, there are still scientific and technical obstacles standing [...] Read more.
The global increase of road infrastructure and its impact on the environment requires serious attention to develop sustainable and environmentally friendly road materials. One group of those materials is produced by using bitumen emulsion. However, there are still scientific and technical obstacles standing against its regular application. The bitumen emulsion formulation process and compositional optimization are subjected to a high number of degrees of freedom. Consequently, obtaining the desired product is mostly based on a series of random and tedious trials because of the enormous number of tests that are carried out to meet the required properties, such as emulsion stability, viscosity, droplet size (and distribution), and bitumen emulsion chemistry. Several pre-established formulation procedures have been presented in the literature. Some of them have technical limitations to be utilized for practical industrial application, whereas others are still not understood enough to be applied in bitumen emulsion formulation. Therefore, discussing some important issues in this field could be useful to offer a practical guide for bitumen emulsion manufacturers when trying to formulate a well-defined bitumen emulsion to best fit its use in pavement infrastructure rather than to simply to meet standard specifications. This review paper aims to enable the ultimate potential of bitumen emulsion by further reviewing the research progress of bitumen emulsion manufacturing and discussing the literature available up to now on this topic, in the realm of bitumen emulsion manufacturing and emulsion chemistry. Full article
(This article belongs to the Special Issue Feature Papers in Construction and Building Materials)
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19 pages, 4390 KiB  
Review
Production and Upgrading of Recovered Carbon Black from the Pyrolysis of End-of-Life Tires
by Sebastião M. R. Costa, David Fowler, Germano A. Carreira, Inês Portugal and Carlos M. Silva
Materials 2022, 15(6), 2030; https://doi.org/10.3390/ma15062030 - 9 Mar 2022
Cited by 38 | Viewed by 9715
Abstract
Increasing awareness regarding fossil fuel dependence, waste valorization, and greenhouse gas emissions have prompted the emergence of new solutions for numerous markets over the last decades. The tire industry is no exception to this, with a global production of more than 1.5 billion [...] Read more.
Increasing awareness regarding fossil fuel dependence, waste valorization, and greenhouse gas emissions have prompted the emergence of new solutions for numerous markets over the last decades. The tire industry is no exception to this, with a global production of more than 1.5 billion tires per year raising environmental concerns about their end-of-life recycling or disposal. Pyrolysis enables the recovery of both energy and material from end-of-life tires, yielding valuable gas, liquid, and solid fractions. The latter, known as recovered carbon black (rCB), has been extensively researched in the last few years to ensure its quality for market applications. These studies have shown that rCB quality depends on the feedstock composition and pyrolysis conditions such as type of reactor, temperature range, heating rate, and residence time. Recent developments of activation and demineralization techniques target the production of rCB with specific chemical, physical, and morphological properties for singular applications. The automotive industry, which is the highest consumer of carbon black, has set specific targets to incorporate recycled materials (such as rCB) following the principles of sustainability and a circular economy. This review summarizes the pyrolysis of end-of-life tires for the production of syngas, oil, and rCB, focusing on the process conditions and product yield and composition. A further analysis of the characteristics of the solid material is performed, including their influence on the rCB application as a substitute of commercial CB in the tire industry. Purification and modification post-treatment processes for rCB upgrading are also inspected. Full article
(This article belongs to the Special Issue Advance in Environmentally Friendly Materials)
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13 pages, 5794 KiB  
Article
Acoustic Characteristics of Microcellular Foamed Ceramic Urethane
by Jin Hong and Sung Woon Cha
Materials 2022, 15(6), 2007; https://doi.org/10.3390/ma15062007 - 8 Mar 2022
Cited by 4 | Viewed by 2709
Abstract
Noise pollution critically degrades the quality of human life, and its effects are becoming more severe due to rapid population growth and the development of industry and transportation. Acoustic wave aggregation in the 30–8000 Hz band can have a negative impact on human [...] Read more.
Noise pollution critically degrades the quality of human life, and its effects are becoming more severe due to rapid population growth and the development of industry and transportation. Acoustic wave aggregation in the 30–8000 Hz band can have a negative impact on human health, especially following continuous exposure to low-frequency noise. This study investigates the acoustic performance of microcellular foams made of a mixture of brittle and soft materials and their potential use as absorption materials. It is common to use porous materials to improve acoustic properties. Specimens prepared by mixing ceramic and urethane were made into microcellular foamed ceramic urethane by a batch process using carbon dioxide. The specimens were expected to exhibit characteristics of porous sound-absorbing materials. After measuring the acoustic characteristics using an impedance tube, a significant sound-absorption coefficient at a specific frequency was noted, a characteristic of a resonance-type sound-absorbing material. However, the sound-absorption properties were generally worse than those before foaming. Differences based on the size, shape, and structure of the pores were also noted. It will be necessary to check the effects of cellular morphological differences on the absorption properties by controlling the variables of the microcellular foaming process in a future study. Full article
(This article belongs to the Special Issue Polymer Foams: Materials, Processing and Properties)
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14 pages, 3178 KiB  
Article
Antimicrobial TiN-Ag Coatings in Leather Insole for Diabetic Foot
by Sandra M. Marques, Isabel Carvalho, Teófilo R. Leite, Mariana Henriques and Sandra Carvalho
Materials 2022, 15(6), 2009; https://doi.org/10.3390/ma15062009 - 8 Mar 2022
Cited by 7 | Viewed by 3004
Abstract
This work reports on TiN-Ag antimicrobial coatings deposited by d.c. magnetron sputtering on leather used for insoles on the footwear industry, studies involving the antimicrobial properties of Ag-based functionalized leathers by sputtering techniques are shown. The X-ray diffraction (XRD) results suggested the presence [...] Read more.
This work reports on TiN-Ag antimicrobial coatings deposited by d.c. magnetron sputtering on leather used for insoles on the footwear industry, studies involving the antimicrobial properties of Ag-based functionalized leathers by sputtering techniques are shown. The X-ray diffraction (XRD) results suggested the presence of crystalline fcc-TiN phase for the sample without silver, and also a fcc-Ag phase in the samples containing silver. According to the Scanning Electron Microscopy (SEM) analysis, the coatings were homogeneous and dispersed Ag clusters were detected on the surface of samples with silver content above 8 at. %. The Inductively coupled plasma—optical emission spectrometry (ICP-OES) analysis showed that the ionization of silver over time depends on the morphology of the coatings. The samples did not present cytotoxicity and only samples with incorporated silver presented antibacterial and antifungal activity, highlighting the potential of the TiN-Ag insole coatings for diseases such as diabetic foot. Full article
(This article belongs to the Special Issue Fabrication, Characterization, and Application of Coatings and Thin Films)
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16 pages, 5817 KiB  
Article
Biocompatibility of a New Calcium Silicate-Based Root Canal Sealer Mediated via the Modulation of Macrophage Polarization in a Rat Model
by Xiaoqian Yang, Jun Tian, Mengjie Li, Weiyang Chen, He Liu, Zhejun Wang, Markus Haapasalo, Ya Shen and Xi Wei
Materials 2022, 15(5), 1962; https://doi.org/10.3390/ma15051962 - 7 Mar 2022
Cited by 15 | Viewed by 3312
Abstract
(1) Background: The EndoSequence BC Sealer HiFlow (Brasseler, Savannah, GA, USA) has recently been introduced in clinical applications. Thus, the aims of the present study are to determine its biocompatibility in vivo and to examine its ability to drive macrophage polarization in vitro [...] Read more.
(1) Background: The EndoSequence BC Sealer HiFlow (Brasseler, Savannah, GA, USA) has recently been introduced in clinical applications. Thus, the aims of the present study are to determine its biocompatibility in vivo and to examine its ability to drive macrophage polarization in vitro and in vivo. (2) Methods: HiFlow was implanted into rat connective tissue for 7, 30 and 150 days. The microstructures and elemental compositions were determined by scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX). Hematoxylin–eosin, immunofluorescence, RT–qPCR and flow cytometry were used to elucidate the effects on inflammatory responses and macrophage polarization. (3) Results: SEM-EDX revealed the formation of surface hydroxyapatite crystal layers. Histological evaluation showed that HiFlow exhibited long-term biocompatibility because it decreased inflammatory responses and reduced the number of macrophages over time; however, tissue necrosis was observed in all the groups. RT–qPCR verified that HiFlow regulated the expression of inflammatory factors to inhibit the inflammatory response. Immunofluorescence analysis performed on in vivo samples revealed that HiFlow promoted M2-like macrophage polarization, and these results were confirmed by flow cytometry in vitro. (4) Conclusion: After 150 days of investigation, HiFlow was considered biologically acceptable, and the formation of apatite crystal layers and the promotion of M2-like macrophage polarization may contribute to its favorable biocompatibility. Full article
(This article belongs to the Special Issue Endodontics)
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12 pages, 2780 KiB  
Communication
Carbon Nanotube-Based Thermoelectric Modules Enhanced by ZnO Nanowires
by Patrycja Taborowska, Tomasz Wasiak, Mika Sahlman, Mari Lundström and Dawid Janas
Materials 2022, 15(5), 1924; https://doi.org/10.3390/ma15051924 - 4 Mar 2022
Cited by 8 | Viewed by 2370
Abstract
Carbon nanotubes (CNTs) have a wide range of unique properties, which have kept them at the forefront of research in recent decades. Due to their electrical and thermal characteristics, they are often evaluated as key components of thermogenerators. One can create thermogenerators exclusively [...] Read more.
Carbon nanotubes (CNTs) have a wide range of unique properties, which have kept them at the forefront of research in recent decades. Due to their electrical and thermal characteristics, they are often evaluated as key components of thermogenerators. One can create thermogenerators exclusively from CNTs, without any metal counterpart, by properly selecting dopants to obtain n- and p-doped CNTs. However, the performance of CNT thermogenerators remains insufficient to reach wide commercial implementation. This study shows that molecular doping and the inclusion of ZnO nanowires (NWs) can greatly increase their application potential. Moreover, prototype modules, based on single-walled CNTs (SWCNTs), ZnO NWs, polyethyleneimine, and triazole, reveal notable capabilities for generating electrical energy, while ensuring fully scalable performance. Upon doping and the addition of ZnO nanowires, the electrical conductivity of pure SWCNTs (211 S/cm) was increased by a factor of three. Moreover, the proposed strategy enhanced the Power Factor values from 18.99 (unmodified SWCNTs) to 34.9 and 42.91 µW/m∙K2 for CNTs triazole and polyethyleneimine + ZnO NWs inclusion, respectively. Full article
(This article belongs to the Special Issue Synthesis, Characterization and Applications of Thermoelectric Materials)
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20 pages, 4929 KiB  
Article
Decellularized Pig Kidney with a Micro-Nano Secondary Structure Contributes to Tumor Progression in 3D Tumor Model
by Shuangjia Yang, Le Zheng, Zilong Chen, Zeren Jiao, Tianqing Liu, Yi Nie, Yue Kang, Bo Pan and Kedong Song
Materials 2022, 15(5), 1935; https://doi.org/10.3390/ma15051935 - 4 Mar 2022
Cited by 8 | Viewed by 2937
Abstract
In spite of many anti-cancer drugs utilized in clinical treatment, cancer is still one of the diseases with the highest morbidity and mortality worldwide, owing to the complexity and heterogeneity of the tumor microenvironment. Compared with conventional 2D tumor models, 3D scaffolds could [...] Read more.
In spite of many anti-cancer drugs utilized in clinical treatment, cancer is still one of the diseases with the highest morbidity and mortality worldwide, owing to the complexity and heterogeneity of the tumor microenvironment. Compared with conventional 2D tumor models, 3D scaffolds could provide structures and a microenvironment which stimulate native tumor tissues more accurately. The extracellular matrix (ECM) is the main component of the cell in the microenvironment that is mainly composed of three-dimensional nanofibers, which can form nanoscale fiber networks, while the decellularized extracellular matrix (dECM) has been widely applied to engineered scaffolds. In this study, pig kidney was used as the source material to prepare dECM scaffolds. A chemical crosslinking method was used to improve the mechanical properties and other physical characteristics of the decellularized pig kidney-derived scaffold. Furthermore, a human breast cancer cell line (MCF-7) was used to further investigate the biocompatibility of the scaffold to fabricate a tumor model. The results showed that the existence of nanostructures in the scaffold plays an important role in cell adhesion, proliferation, and differentiation. Therefore, the pig kidney-derived matrix scaffold prepared by decellularization could provide more cell attachment sites, which is conducive to cell adhesion and proliferation, physiological activities, and tumor model construction. Full article
(This article belongs to the Special Issue Biofunctionalized Scaffold in Regenerative Medicine-Series II)
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9 pages, 4130 KiB  
Article
Band Structure of Organic-Ion-Intercalated (EMIM)xFeSe Superconductor
by Lyudmila V. Begunovich and Maxim M. Korshunov
Materials 2022, 15(5), 1856; https://doi.org/10.3390/ma15051856 - 2 Mar 2022
Cited by 1 | Viewed by 2212
Abstract
The band structure and the Fermi surface of the recently discovered superconductor (EMIM)xFeSe are studied within the density functional theory in the generalized gradient approximation. We show that the bands near the Fermi level are formed primarily by Fe-d orbitals. [...] Read more.
The band structure and the Fermi surface of the recently discovered superconductor (EMIM)xFeSe are studied within the density functional theory in the generalized gradient approximation. We show that the bands near the Fermi level are formed primarily by Fe-d orbitals. Although there is no direct contribution of EMIM orbitals to the near-Fermi level states, the presence of organic cations leads to a shift of the chemical potential. It results in the appearance of small electron pockets in the quasi-two-dimensional Fermi surface of (EMIM)xFeSe. Full article
(This article belongs to the Special Issue Structure and Electronic Properties of Emerging Superconductor and Related Materials)
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14 pages, 2282 KiB  
Article
Simple Strategies to Modulate the pH-Responsiveness of Lignosulfonate-Based Delivery Systems
by Massimo Sgarzi, Matteo Gigli, Charlotte Giuriato and Claudia Crestini
Materials 2022, 15(5), 1857; https://doi.org/10.3390/ma15051857 - 2 Mar 2022
Cited by 8 | Viewed by 2879
Abstract
The extensive use of non-degradable microplastics in a wide plethora of daily life products is causing serious pollution problems. More ecofriendly solutions are therefore urgently needed. In this context, the use of lignin, a largely available aromatic polymer, may represent a viable option. [...] Read more.
The extensive use of non-degradable microplastics in a wide plethora of daily life products is causing serious pollution problems. More ecofriendly solutions are therefore urgently needed. In this context, the use of lignin, a largely available aromatic polymer, may represent a viable option. Due to the self-assembly ability of its molecules, lignin is in fact an ideal matrix for the fabrication of nanostructures. In this study, lignosulfonate microcapsules containing a limonene core were prepared and characterized in terms of their dimensions and of the physicochemical characteristics of the capsule-forming lignosulfonate molecules. The main purpose is to elucidate the key properties governing the pH-responsive behavior of the capsules to be able to achieve better control over the release kinetics of the entrapped compound(s). The results demonstrate that both the molecular weight and the concentration of sulfonate groups are the most important factors in this respect. Based on these findings, two strategies were followed to further tailor the capsules’ behavior: (i) fractionation of the starting lignosulfonate by solvent extraction and (ii) introduction of a specific additive in the formulation. The first approach permitted to fabricate highly resistant capsules both in acidic, as well as in alkaline conditions, while in the second case the chemical structure of the additive, the diester diveratryl sebacate, allowed for fast kinetics of release, as values above 70% were reached after 24 h of incubation at pH 4 and pH 12. Full article
(This article belongs to the Special Issue Sustainable Polymers: From Synthesis to Functional Properties)
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11 pages, 5081 KiB  
Review
Eu3+ as a Powerful Structural and Spectroscopic Tool for Glass Photonics
by Thi Ngoc Lam Tran, Alessandro Chiasera, Anna Lukowiak and Maurizio Ferrari
Materials 2022, 15(5), 1847; https://doi.org/10.3390/ma15051847 - 1 Mar 2022
Cited by 13 | Viewed by 2686
Abstract
The unique properties of the Eu3+ ion make it a powerful spectroscopic tool to investigate structure or follow processes and mechanisms in several high-tech application areas such as biology and health, structural engineering, environment monitoring systems and quantum technology, mainly concerning photonics. [...] Read more.
The unique properties of the Eu3+ ion make it a powerful spectroscopic tool to investigate structure or follow processes and mechanisms in several high-tech application areas such as biology and health, structural engineering, environment monitoring systems and quantum technology, mainly concerning photonics. The traditional method is to exploit the unique photoluminescent properties of Eu3+ ions to understand complex dynamical processes and obtain information useful to develop materials with specific characteristics. The objective of this review is to focus on the use of Eu3+ optical spectroscopy in some condensed matter issues. After a short presentation of the more significant properties of the Eu3+ ion, some examples regarding its use as a probe of the local structure in sol–gel systems are presented. Another section is devoted to dynamical processes such as the important technological role of nanocrystals as rare-earth sensitizers. The appealing effect of the site-selection memory, observed when exciting different sites into the 5D1 state, which the 5D0 → 7F0 emission band reflects following the sites’ distribution, is also mentioned. Finally, a section is devoted to the use of Eu3+ in the development of a rare-earth-based platform for quantum technologies. Full article
(This article belongs to the Special Issue Structural and Optical Studies of Eu3+ Doped Materials)
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10 pages, 1920 KiB  
Article
Structure and Electrical Properties of Microwave Sintered BTS-BCT-xBF Lead-Free Piezoelectric Ceramics
by Tao Wang, Jian Ma, Bo Wu, Fenghua Wang, Shiyu Wang, Min Chen and Wenjuan Wu
Materials 2022, 15(5), 1789; https://doi.org/10.3390/ma15051789 - 27 Feb 2022
Cited by 3 | Viewed by 2275
Abstract
Barium titanate (BT)-based ceramics are one of the promising piezoelectric materials for environment-friendly electro-mechanical transformation. However, high performance materials are often sintered at high temperatures, resulting in volatile components and increased energy consumption. Here, 0.82Ba(Ti0.89Sn0.11)O3-(0.18-x)(Ba [...] Read more.
Barium titanate (BT)-based ceramics are one of the promising piezoelectric materials for environment-friendly electro-mechanical transformation. However, high performance materials are often sintered at high temperatures, resulting in volatile components and increased energy consumption. Here, 0.82Ba(Ti0.89Sn0.11)O3-(0.18-x)(Ba0.7Ca0.3)TiO3-xBiFeO3 (BTS-BCT-xBF) piezoelectric ceramics were prepared by microwave sintering (MWS) method, and the structure and properties were emphatically studied, aiming to reveal the regulatory mechanism of MWS on the structure and properties. Compared with conventional solid sintering (CS), the phase structure presents a similar evolution in MWS ceramics as a function of BF, while the more refined grain size and the denser structure are observed in MWS ceramics. The electrical properties (e.g., d33, εr, tan δ, etc.) of MWS ceramics are superior to the CS ceramics owing to the refined grain size and denser microstructure. It is worth noting that the energy storage performance (e.g., energy storage density, energy storage efficiency) significantly outperformed expectations due to the slender hysteresis loop resulting from the smaller grain and high cubic phase. Therefore, the MWS sintering mechanism can further drive practical application of BT-based ceramics. Full article
(This article belongs to the Special Issue Electronic Functional Materials: Synthesis, Structure, Property, Mechanism and Application)
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11 pages, 2867 KiB  
Article
Evaluation of Acoustic Waves in Acousto-Optical Devices by Ultrasonic Imaging
by Sergey A. Titov, Alexander S. Machikhin and Vitold Ed. Pozhar
Materials 2022, 15(5), 1792; https://doi.org/10.3390/ma15051792 - 27 Feb 2022
Cited by 6 | Viewed by 2423
Abstract
The structure of the acoustic field defines the key parameters of acousto-optical (AO) devices. To confirm their compliance with the expected values in the presence of multiple real factors, AO crystalline cells require accurate experimental investigation of the acoustic field after being totally [...] Read more.
The structure of the acoustic field defines the key parameters of acousto-optical (AO) devices. To confirm their compliance with the expected values in the presence of multiple real factors, AO crystalline cells require accurate experimental investigation of the acoustic field after being totally assembled. For this purpose, we propose to detect and quantify all the acoustic waves propagating in AO cells using an impulse acoustic microscopy technique. To validate this approach, we have analyzed both theoretically and experimentally the modes, amplitudes, propagation trajectories, and other features of the ultrasonic waves generated inside an AO modulator made of fused quartz. Good correspondence between theoretical and experimental data confirms the effectiveness of the proposed technique. Full article
(This article belongs to the Special Issue Acousto-Optical Spectral Technologies)
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13 pages, 3559 KiB  
Article
Atomic Layer Deposition of Ultrathin La2O3/Al2O3 Nanolaminates on MoS2 with Ultraviolet Ozone Treatment
by Jibin Fan, Yimeng Shi, Hongxia Liu, Shulong Wang, Lijun Luan, Li Duan, Yan Zhang and Xing Wei
Materials 2022, 15(5), 1794; https://doi.org/10.3390/ma15051794 - 27 Feb 2022
Cited by 4 | Viewed by 2177
Abstract
Due to the chemically inert surface of MoS2, uniform deposition of ultrathin high-κ dielectric using atomic layer deposition (ALD) is difficult. However, this is crucial for the fabrication of field-effect transistors (FETs). In this work, the atomic layer deposition growth of [...] Read more.
Due to the chemically inert surface of MoS2, uniform deposition of ultrathin high-κ dielectric using atomic layer deposition (ALD) is difficult. However, this is crucial for the fabrication of field-effect transistors (FETs). In this work, the atomic layer deposition growth of sub-5 nm La2O3/Al2O3 nanolaminates on MoS2 using different oxidants (H2O and O3) was investigated. To improve the deposition, the effects of ultraviolet ozone treatment on MoS2 surface are also evaluated. It is found that the physical properties and electrical characteristics of La2O3/Al2O3 nanolaminates change greatly for different oxidants and treatment processes. These changes are found to be associated with the residual of metal carbide caused by the insufficient interface reactions. Ultraviolet ozone pretreatment can substantially improve the initial growth of sub-5 nm H2O-based or O3-based La2O3/Al2O3 nanolaminates, resulting in a reduction of residual metal carbide. All results indicate that O3-based La2O3/Al2O3 nanolaminates on MoS2 with ultraviolet ozone treatment yielded good electrical performance with low leakage current and no leakage dot, revealing a straightforward approach for realizing sub-5 nm uniform La2O3/Al2O3 nanolaminates on MoS2. Full article
(This article belongs to the Section Thin Films and Interfaces)
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