Ceramics, Volume 5, Issue 3 (September 2022) – 26 articles

Thin films of Sr_0.98Zr_0.95Y_0.05O_3−δ (SZY) electrolyte were grown on porous supporting SrTi_0.8Fe_0.2O_3−δ electrodes by the chemical solution deposition method from a low-viscous solution of inorganic salts. The films were characterized by X-ray diffraction and scanning electron microscopy. The gas-tightness of the films was evaluated using the differential-pressure method. The across-plane electrical conductivity of 1 mm thick SZY film was measured by impedance spectroscopy and compared to that of a massive ceramic sample. The revealed difference in electrical properties of the film and massive SZY samples indicates that diffusional interaction between the film and the substrate influences the performance of the supported electrolyte. Full article

Porosity is a key feature in dictating the overall performance of biomedical scaffolds, with special relevance to mechanical properties. Usually, compressive strength and elastic modulus are the main parameters used to determine the potential mechanical suitability of porous scaffolds for bone repair. However, their assessment may not be so easy from an experimental viewpoint and, especially if the porosity is high, so reliable for brittle bioceramic foams. Hence, assessing the relationship between porosity and mechanical properties based only on the constitutive parameters of the solid material is a challenging and important task to predict the scaffold performance for optimization during design. In this work, a set of equations was used to predict the compressive strength and elastic modulus of bone-like hydroxyapatite scaffolds produced by digital light processing-based vat photopolymerization (total porosity about 80 vol.%). The compressive strength was found to depend on total porosity, following a power-law approximation. The relationship between porosity and elastic modulus was well fitted by second-order power law, with relative density and computational models obtained by numerical simulations. Full article

Nowadays, humidity sensors are attracting a great deal of attention, and there are many studies focusing on enhancing their performances. Nevertheless, their fabrication through facile methods at reasonable cost is a significant factor. In this article, a new magnesium silicate nanopowder was successfully synthesized using a simple and low-cost sol–gel method. Subsequently, modified sepiolite was achieved by the substitution of iron ions in the synthesized nanopowders. The specimens were then characterized by X-ray diffraction, field emission–scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric–differential thermal analysis, infrared spectroscopy, and nitrogen adsorption. Furthermore, humidity sensors were manufactured by screen printing the prepared powders on alumina substrates with interdigitated Pt electrodes. The results showed that the fabricated sensors with modified sepiolite exhibited interesting characteristics for humidity detection. Full article

Mica is a group of clay minerals that are frequently used to fabricate electrical and thermal insulators and as adsorbents for the treatment of cationic pollutants. However, conventional subtractive manufacturing has the drawback of poor three-dimensional (3D) shape control, which limits its application. In this study, we propose digital light processing (DLP)-based additive manufacturing (AM) as one of the most effective ways to address this drawback. Two major challenges for the ceramic DLP process are the production of a homogeneous and stable slurry with the required rheological properties and the maintenance of printing precision. The mica green body was fabricated using a 53 vol.% solid loading slurry through DLP, which exhibited good dimensional resolution under an exposure energy dose of 10 mJ/cm². The precise, complex 3D structure was maintained without any defects after debinding and sintering at 1000 °C. The use of ceramic AM to overcome the shape-control limitations of mica demonstrated in this study offers great potential for expanding the applications of mica. Full article

The new approach to obtaining ceramic materials in the Na₂O–CaO–SiO₂–P₂O₅ system based on the binder—an aqueous solution of sodium silicate and filler—hydroxyapatite was shown in current research. After heat treatment at 500 °C and 700 °C, the ceramic samples included non-reacted hydroxyapatite Ca₁₀(PO₄)₆(OH)₂, β-rhenanite β-NaCaPO₄ and sodium calcium silicophosphate Na₂Ca₄(PO₄)₂SiO₄. An increase in temperature to 900 °C and 1100 °C allowed to obtain ceramic materials with the following phases: devitrite Na₂Ca₃Si₆O₁₆, β-rhenanite β-NaCaPO₄, β-wollastonite β-CaSiO₃, and silicon dioxide SiO₂. The strength of ceramic samples rose with increasing temperature from ≈7.0 MPa (bending) and ≈7.2 MPa (compression) at 500 °C to ≈9.5 MPa (bending) and ≈31.6 MPa (compression) at 1100 °C. At the same time, the apparent density decreased from 1.71 g/cm³ to 1.15 g/cm³. The top of the compressive strength equal to 31.6 MPa was observed when the apparent density was 1.15 g/cm³. Obtained ceramics consisted of biocompatible phases, widely studied in the literature; thus, it confirms the possibility of using an aqueous solution of sodium silicate in medical materials science. Full article

Y₂O₃ at 3% mol partially stabilized Zr₂O₃ (3YSZ) porous specimens with variable open porosity, from fully dense up to ~47%, and their potential use as anode supports for new solid oxide cell designs were fabricated by tape casting. The stiffness, strength and fracture properties were measured to investigate the influence of porosity on mechanical properties. The evolution of Young’s modulus and characteristic strength was evaluated by ball-on-ring tests. The variation of critical plane stress Mode I stress intensity factor with porosity has also been investigated and modelled from the results obtained from fracture mechanics testing. R-curve behaviour was observed in dense 3YSZ specimens and in porous 3YSZ compositions. The width of the transformation zone after fracture mechanics testing and the variation with porosity were investigated. The phases existing in the fracture zone were determined and quantified by Raman spectroscopy. It was found that the width of the transformation zone increased with increasing porosity. A new general R-curve model for 3YSZ based on the McMeeking–Evans equation is presented, which can be used to predict the behaviour of the R-curve as a function of porosity, simply by knowing the properties of the dense material and introducing in this equation porosity-dependent laws on the key properties that affect fracture toughness. Full article

Biocompatibility of ceramic materials in Ca₂P₂O₇-Ca(PO₃)₂ system was investigated using different methods, including in vitro and in vivo tests. Ceramic materials in the Ca₂P₂O₇-Ca(PO₃)₂ system were obtained by annealing cement-salt stone based on powder mixtures of calcium citrate tet-rahydrate Ca₃(C₆H₅O₇)₂·4H₂O and monocalcium phosphate monohydrate (MCPM) Ca(H₂PO₄)₂·H₂O. The phase composition of cement-salt stone included brushite, monetite as a result of chemical reaction of starting components after adding of water. The presence of citric acid as by-product of chemical reaction, leads to increase the setting time of the cement-salt stone. Highly concentrated aqueous suspensions based on calcium citrate and MCPM powders providing content of calcium polyphosphate Ca(PO₃)₂ up to 20 wt % in ceramics were used for designing bioresorbable materials. The presence of an excess of monocalcium phosphate monohydrate makes it possible to reduce the annealing temperature of ceramics, which is associated with the formation of a lower melting phase of Ca(PO₃)₂. In vivo tests shown that obtained ceramic materials can be recommended for regenerative treatments for bone defects. Full article

Fine powders of mixed gadolinium tantalum niobates doped with Eu, Sm, Tb, and Er were synthesized. Ceramic samples of polycomponent solid solutions of Gd_0.96Eu_0.01Sm_0.01Tb_0.01Er_0.01Nb_0.9Ta_0.1O₄ were obtained from synthesized powders using conventional sintering technology. The phase composition and phase structure characteristics of the Gd_0.96Eu_0.01Sm_0.01Tb_0.01Er_0.01Nb_0.9Ta_0.1O₄ ceramic phases were determined by XRD. The effect of ceramic sintering temperature on the physical characteristics of Gd_0.96Eu_0.01Sm_0.01Tb_0.01Er_0.01Nb_0.9Ta_0.1O₄ solid solutions is shown. The morphological features of the microstructure of the Gd_0.96Eu_0.01Sm_0.01Tb_0.01Er_0.01Nb_0.9Ta_0.1O₄ ceramics were studied in relation to its mechanical characteristics. At the same time, the strength characteristics (Young’s modulus, microhardness) and the critical stress intensity factor for mode I K_IC were evaluated for the first time for the synthesized compounds. Photoluminescence and cathodoluminescence were studied in the visible region. The study confirms the potential application of Gd_0.96Eu_0.01Sm_0.01Tb_0.01Er_0.01Nb_0.9Ta_0.1O₄ ceramic solid solutions as scintillators and radioluminescent light sources. Full article

A mixture of abramis brama (freshwater bream), carassius carassius (crucian carp), and sander lucioperca (pike perch) scales was used for the preparation of fish scale powder containing constituents of organic and inorganic nature. The mixture of the mentioned fish scales was washed, dried, and ground for the preparation of fish scale powder. Vibration sieving was used to prepare fish scale powder enriched with inorganic components. According to thermal analysis data, this fish scale powder enriched with inorganic components included about 36.5 wt.% components removed when heating, primarily those of organic nature, and 63.5 wt.% mineral components. Inorganic powders consisting of hydroxyapatite and magnesium whitlockite were obtained via heat treatment of this fish scale powder at 800–1000 °C. Particles of these inorganic powders consisted of sintered grains with dimensions less than 100 nm after heat treatment at 800 °C, less than 200 nm after heat treatment at 900 °C, and 100–1000 nm after heat treatment at 1000 °C. Fish scale powder enriched with inorganic components as well as heat-treated inorganic powders consisting of hydroxyapatite and magnesium whitlockite can be recommended for the production of different materials, such as ceramics or composites. Full article

Porous yttriastabilized zirconia (YSZ), in a composite with NiO, is widely used as a cermet electrode in solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). Given cycles of high temperature in these energy devices, mechanical integrity of the porous YSZ is critical. Pore morphology, as well as properties of the ceramic, ultimately affect the mechanical properties of the cermet electrode. Here, we fabricated porous YSZ sheets via freezing of an aqueous slurry on a cold thermoelectric plate and quantified their flexural properties, both for as-fabricated samples and samples subjected to thermal shock at 200 °C to 500 °C. Results of this work have implications for the hydrogen economy and global decarbonization efforts, in particular for the manufacturing of SOFCs and SOECs. Full article

Polycrystalline zinc selenide (ZnSe) and Cr²⁺ or Fe²⁺ doped ZnSe are key optical elements in mid-infrared laser systems. The laser-induced damage of the optical elements is the limiting factor for increasing the power and pulse energy of the lasers. In the present work, the optical damage of the ZnSe, Cr²⁺:ZnSe, and Fe²⁺:ZnSe samples induced by a repetitively pulsed Ho³⁺:YAG laser at 2091 nm was studied. The probability of the optical damage and the laser-induced damage threshold (LIDT) were determined for the samples manufactured using different processing techniques. The highest LIDT was found in ZnSe samples annealed in an argon atmosphere. It was also found that the samples annealed in a zinc atmosphere or with hot isostatic pressing resulted in a decrease in the LIDT. The Cr²⁺-doped ZnSe had the lowest LIDT at 2.1 µm compared to Fe²⁺-doped or undoped ZnSe. The LIDT fluence of all tested ZnSe samples decreased with the increase in the pulse repetition rate and the exposure duration. The results obtained may be used to improve the treatment procedures of ZnSe, Cr²⁺:ZnSe, and Fe²⁺:ZnSe polycrystals to further increase their LIDT. Full article

The aim of this work is to study the hydrogenation processes in lithium-containing ceramics under high-temperature irradiation. Irradiation was carried out with protons with an energy of 1 MeV and fluences of 10¹⁵–10¹⁷ ion/cm² at irradiation temperatures of 300–1000 K. The choice of irradiation conditions is due to the possibility of simulation of the radiation damage accumulation processes in the near-surface layer of Li₂TiO₃ ceramics, as well as establishing the dependences of changes in structural parameters during temperature heating of samples during irradiation. It has been established that at irradiation fluences of 10¹⁵–10¹⁶ ion/cm², the formation of dislocation defects is observed, the density of which has a pronounced dependence on the irradiation temperature. At irradiation fluence above 5 × 10¹⁶ ion/cm², an increase in the crystal structure deformation is observed, due to swelling processes as a result of implanted hydrogen accumulation in the near-surface layer structure. At the same time, an increase in the irradiation temperature leads to a decrease in the swelling value, which is due to the accelerated migration of implanted hydrogen in the near-surface layer and its release through the existing pores. Results of mechanical tests showed that the swelling of the crystal structure and its deformation leads to embrittlement and a partial decrease in the strength of the near-surface layer. The obtained research results will further allow us to evaluate the resistance of lithium ceramics to the processes of hydrogenation and destruction as a result of the formation of gas-filled cavities in the structure of the near-surface layer. Full article

The influence of certain factors on the kinetics of the process of obtaining aluminum borides (burning rate, ingot formation, and phase separation) was investigated. In this study, we report the registration of diboride using the SHS protocol. The synthesis of aluminum diboride from boric anhydride occurred by the aluminothermic method. The initial components were boron trioxide and aluminum in the form of powders. Researchers paid special attention to the degree of grinding of the charge fluxing substances. The influence this had on the rate of development of the degree of charge concentration was studied. To calculate the degree of charge, a composition was chosen according to the speed obtained from a number of experiments where melting was carried out with the following charge densities in g/cm³: 0.80; 1.08; 1.18; 1.74. The method of melting was ignition from above. The experimental results allowed us to conclude that the nature of the change in the combustion rate of the system, where there was an excess of the reducing agent in the charge, is the same. An increase in the combustion rate, where there was an excess of aluminum of up to 20%, was likely due to the fact that the reaction area of the charge components increased. In addition, an increase in speed can be explained by a decrease in heat losses due to a reduction in the melting time. With an increase in excess aluminum above 20% of the stoichiometry, the observed decrease in the combustion rate can be explained by a decrease in the specific heat of the process due to the melting of the excess aluminum, which played the role of a ballast. Full article

Nanoscale powders of hydrated Ca₂P₂O₇, CaCO₃, and a product of mixed-anionic composition containing P₂O₇⁴⁻ and CO₃²⁻ anions were synthesized from aqueous solutions of Ca(CH₃COO)₂, pyrophosphoric acid (H₄P₂O₇), and/or (NH₄)₂CO₃. Pyrophosphoric acid was previously obtained on the basis of the ion exchange process from Na₄P₂O₇ solution and H⁺-cationite resin for further introduction into the reactions as an anionic precursor. The phase composition of powders after the syntheses was represented by bioresorbable phases of X-ray amorphous hydrated Ca₂P₂O₇ phase, calcite and vaterite polymorphs of CaCO₃. Based on synthesized powders, simple cylindrical constructions were prepared via mechanical pressing and fired in the temperature range of 600–800 °C. Surface morphology observation showed the presence of bimodal porosity with pore sizes up to 200 nm and 2 μm, which is likely to ensure tight particle packing and roughness of the sample surface required for the differentiation of osteogenic cells. Thus, the prepared ceramic samples can be further examined as model objects for bone tissue repair. Full article

Apatite is widely used in medicine as a biomaterial for bone tissue restoration. Properties of apatite depend on its composition, including the Ca/P ratio. This paper shows what range of Ca/P ratio can be attained in apatite by the mechanochemical method of synthesis, providing fast formation of a single-phase product. The synthesis was carried out from a reaction mixture of CaHPO₄ and CaO at different Ca/P ratios in the range of 1.17–2.10. The products were studied by PXRD, FTIR and NMR spectroscopy, HRTEM, and STA. In mixtures with a low initial Ca/P ratio (1.17–1.48), directly in the mill, the formation of calcium orthophosphate with whitlockite structure containing an HPO₄²⁻ group and structural water is shown for the first time. This phosphate has structure similar to that of whitlockites of hydrothermal origin and differs from high-temperature β-tricalcium phosphate that has composition Ca₃(PO₄)₃. A series of samples of apatite was obtained with varied composition, which depends on the initial Ca/P ratio. At Ca/P < 1.67, the formation of two types of calcium-deficient apatite was documented. At Ca/P > 1.67, the existence of two types of calcium-rich apatite is confirmed. Full article

This work aimed to study the oxidation resistance of γ-TiAl based alloy, doped with small concentrations of carbon, silicon, and yttrium oxide in air at 800 and 1100 °C for 30 h. The TNM-B1 alloy samples were produced via high-energy ball milling, self-propagating high-temperature synthesis, and hot isostatic pressing techniques. The microstructure, oxidation kinetics at 800–1100 °C, scale structure, and oxidation mechanism were studied. The oxidation of alloys modified with carbon and silicon at 1100 °C was characterized by the formation of a three-layer coating. The Y₂O₃ modified alloy performed the greatest oxidation resistance at 1100 °C and promoted the formation of a dense Al₂O₃ interlayer. Full article

In this paper, partial transient liquid phase (PTLP) diffusion bonding between Si₃N₄ ceramics and Ht250 cast iron was carried out by using an Ti/Cu/Kovar/Cu/Ti interlayer. The effects of the heating temperature and holding time on the microstructure, formation mechanism, and mechanical properties of Si₃N₄/Ht250 cast iron joints were studied. The results show that the maximum shear strength of the joint is 112 MPa when the welding temperature is 1000 °C and the holding time is 1 h. In addition, the problems of Ti/Cu/Ti intermetallic compound formation and Cu/Si₃N₄ ceramic residual thermal stress in the joint can be effectively alleviated. Full article

Powders of alkyl phosphoric acids and calcium alkyl phosphates with various alkyl chains (butyl, octyl, and dodecyl) have been synthesized. The resulting powders were characterized by X-ray phase analysis, electron microscopy, and thermal analysis. It was shown that the calcium alkyl phosphates correspond to the composition of acid salts of calcium alkyl phosphates Ca(RPO₄H)₂, data on which are not presented in the literature. The thermal behaviour of calcium alkyl phosphates can be described as a complex phase transformation into biphasic calcium phosphate mixture (of Ca₂P₂O₇ and Ca₃(PO₄)₂) with the increase of the Ca to P ratio in comparison to initial materials. The powders thermally treated in the range of 400–600 °C could be recommended as single precursors of biphasic bioceramics. Full article

Alumina and zirconia thin films modified with colored nano-Fe_xO_y pigments were sintered by the flash-lamp-annealing method. We selected a nano α-Al₂O₃ and micron α-Al₂O₃ bimodal mixture as the base precursor material, and we doped it with 5 vol% of Fe_xO_y red/brown/black/yellow pigments. The coatings were deposited from nanoparticle dispersions both on glass and on flexible metal foil. The characteristics of the thin films obtained with the use of various additives were compared, including the surface morphologies, optical properties, crystallinities, and structures. Flash lamp annealing was applied with the maximum total energy density of 130 J/cm² and an overall annealing time of 7 s. Based on the simulated temperature profiles and electron-microscopy results, a maximum annealing temperature of 1850 °C was reached for the red Al₂O₃: Fe₂O₃ ceramic film. The results show that red α-Fe₂O₃ pigments allow for the achievement of maximum layer absorption, which is effective for flash lamp sintering. It was also possible to use the selected red α-Fe₂O₃ particles for the flash-lamp-assisted sintering of ZrO₂ on a 30 µm-thin flexible stainless-steel substrate. Full article

Local drug delivery systems are an effective approach in the treatment of purulent–septic inflammation of bone tissue. Chemically bonded multiphase ceramics based on calcium-deficient carbonate-substituted hydroxyapatite combine resorbability, osteoconductivity, and the possibility of volumetric incorporation of antibiotics. Macroporosity is regulated by the concentration of polyethylene glycol granules introduced into the initial powder composition, followed by their extraction. The selected conditions for the consolidation of the ceramic matrix and the extraction of PEG granules retain the activity of vancomycin, which is confirmed by the results of microbiological studies. The concentration of vancomycin and the porosity affect the local concentration and release of the antibiotic. The incorporation method provides a prolonged release of the antibiotic for up to 31 days. In vivo experiments with bone implantation have shown that chemically bound macroporous ceramics with incorporated vancomycin are a therapeutically effective carrier of the substance during the healing of bone defects in conditions of surrounding purulent–septic inflammation, and can be considered as a carrier for local antibacterial therapy, at the site of implantation. Full article

Powders of β-tricalcium phosphate (β-TCP, Ca₃PO₄) doped with manganese (Mn²⁺) are comprehensively analyzed with electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) techniques. The modeling of the spectra permitted to calculate the values of zero-field splitting ($B_2^0$ = −904 MHz; $B_4^0$ = −1.41 MHz and $B_4^3$ = 195.2 MHz) and explain the origin of the low-field hyperfine structures as the allowed spin transitions of fine structure. Three structurally inequivalent positions for Mn²⁺ in the β-TCP crystal lattice are identified and their g-factors and hyperfine constants are quantified. The obtained results can serve as fundamental background to the study of structurally disordered matrices with high spin (S ≥ 1) impurities which are important for catalytic systems. Full article

Synthetic 11 Å tobermorite (Ca₅Si₆O₁₆(OH)₂.4H₂O) and its Al-substituted analogue are layer-lattice ion-exchangers with potential applications in nuclear and hazardous wastewater treatment. The present study reports the facile one-pot hydrothermal synthesis of an Al-tobermorite-rich cation-exchanger from a combination of paper recycling ash, post-consumer container glass, and lime, with compositional ratios of [Ca]/[Si + Al] = 0.81 and [Al]/[Si + Al] = 0.18. The reaction products were characterized by powder X-ray diffraction analysis, ²⁹Si magic angle spinning nuclear magnetic resonance spectroscopy, and scanning electron microscopy. Hydrothermal processing in 4 M NaOH_(aq) at 100 °C for 7 days yielded an Al-tobermorite-rich product that also contained katoite (Ca₃Al₂SiO₁₂H₈), portlandite (Ca(OH)₂), calcite (CaCO₃), and amorphous silicate gel. The hydrothermal product was found to have a Cs⁺ cation exchange capacity of 59 ± 4 meq 100 g⁻¹ and selective Cs⁺ distribution coefficients (K_d) of 574 ± 13 and 658 ± 34 cm³ g⁻¹ from solutions with molar ratios [Cs⁺]:[Na⁺] and [Cs⁺]:[Ca²⁺] of 1:100. In a batch sorption study at 20 °C, the uptakes of Pb²⁺, Cd²⁺, and Cs⁺ were determined to be 1.78 ± 0.04, 0.65 ± 0.06, and 0.36 ± 0.03 mmol g⁻¹, respectively. The kinetics of Pb²⁺, Cd²⁺, and Cs⁺ removal were described by the pseudo-second-order rate model, which gave respective rate constants (k₂) of 0.010, 0.027, and 1.635 g mmol⁻¹ min⁻¹, and corresponding correlation coefficients (R²) of 0.997, 0.996, and 0.999. The metal ion sorption properties of the tobermorite-rich product compared favorably with those of other waste-derived tobermorites reported in the literature. Potential strategies to improve the yield, crystallinity, and sorption characteristics of the product are discussed. Full article

In ceramic thin films, choosing an appropriate sample preparation method for transmission electron microscopy (TEM) analyses is of paramount importance to avoid preparation-induced damage and retain nanoscale features that require investigation. Here we compare two methods of TEM thin film sample preparation, namely conventional wedge polishing and focused ion beam (FIB) based lift out preparation applied to ferroelectric barium titanate (BaTiO₃, BT) thin films made by chemical solution deposition (CSD). The aim of the work is to determine the pros and cons of each method considering not only the quality of the TEM specimen, but also aspects such as availability, ease of use, and affordability. Besides some limitations on the selection of visualized area due to thickness constraints on the FIB-made sample, both methods offer the capability to prepare samples with very comparable quality, as indicated by achieving the same thickness, a largely agreeing microstructure, no secondary phases on the diffraction pattern, and good atomic resolution. This last observation is especially important in the current context of material science, where more nanoscale phenomena are becoming the subject of study. The wedge polishing method, however, is deemed more affordable in terms of instrumentation, as it only requires a tripod polisher, a polishing wheel, and a precision ion polishing system, whereas the lift out method requires a scanning electron microscope (SEM) equipped with an FIB system. We believe that this work serves groups working on ferroelectric thin films in preparing TEM samples in a more effective and uncomplicated manner, facilitating progress in understanding this fascinating class of materials. Full article

Post-metal chalcogenides, including InSe, In₂Se₃, and In₄Se₃, have attracted considerable attention as potential thermoelectric materials because of their intrinsically low thermal conductivity, which is attributed to their layered structure with weak van der Waals bonds. In this study, we examined the electrical and thermoelectric properties of Si-doped In₂Se₃ (In_2−xSi_xSe₃, x = 0, 0.005, 0.01, 0.015, and 0.02) polycrystalline samples. Hexagonal α(2H)-In₂Se₃ phase was synthesized without any impurity, and gradual changes in the lattice parameters were observed with Si doping. Drastic changes were observed for the measured electrical and thermal transport properties at 450–500 K, due to the phase transition from α to β at 473 K. The highest power factors were achieved by the sample with x = 0.015 for both α and β phases, exhibiting the values of 0.137 and 0.0884 mW/mK² at 450 and 750 K, respectively. The total thermal conductivities of the α phase samples decreased gradually with increasing Si doping content, which is attributed to the point defect phonon scattering by Si doping. The total thermal conductivities of the β phase samples significantly decreased compared to those of the α phase samples. Therefore, the sample with x = 0.015 (In_1.985Si_0.015Se₃) showed the maximum thermoelectric figure of merit values of 0.100 and 0.154 at 450 and 750 K, which are enhanced by 152 and 48% compared with those of the undoped α- and β-In₂Se₃ samples, respectively. Full article

Freeze foams are novel and innovative cellular structures that are based on a direct foaming process and that can be manufactured using any material that can be processed by powder technology. The foam formation process is characterized by the highly complex interaction of various process and material parameters that were chosen empirically and that have so far been difficult to reproduce. To allow properties to be specifically tailored towards certain applications, it is necessary to examine the phenomena observed during foam formation as well as the impact of the process and material parameters on the structural constitution to deduce guidelines for manufacturing and quality assessment (e.g., mechanical strength, cell and pore sizes, pore size distribution). The variety of possible applications are a result of the wide spectrum of initial suspensions and especially the foam structure properties derived from process parameters such as the cell geometry, pore size distribution, fraction of open and closed porosity, and the textures of the cell struts. Due to earlier findings, the focus of this paper focuses on adjusting and tailoring the macrostructure (homogenization of the pore sizes and their distribution inside foam cells) to create load- and application-adapted ceramic foams. To this end, an experiment was designed using previously identified pore and characteristic influencers (air and water content, temperature of the suspension, pressure reduction rate) as influencing parameters. Their interconnected impacts on selected target values were examined during the freeze foaming process using an in situ freeze foaming device inside an X-ray. Full article

The use of fiber-reinforced composite materials has widely spread in various sectors, including aerospace, defense, and civil industry. The assessment of these heterogeneous material systems is important for safer and risk-free applications and has contributed to the need for self-sensing composites. This work is focused on the development of piezoresistive composites, the prediction of their performance and structural health monitoring (SHM). Additionally, this work unpacks the complexity of carbon nanotubes (CNTs) micro-fabrication and the development of piezoresistive and electromagnetic (EM) waves detection electrodes. Scanning electron microscopy (SEM) was used to characterize the CNTs structure and morphologies. The manufactured CNTs were incorporated in epoxy systems to fabricate glass fiber reinforced polymer (GFRP)-CNTs smart composites with piezoresistive properties. The detection of micro-damage onset and its progression was carried out in mode I, to evaluate the sensitivity of the smart composites to damage development. The change in electrical conductivity of the nanotubes-reinforced composite systems due to localized mechanical strains enabled crack propagation detection. The relationship between crack propagation, fracture toughness, and electrical resistivity of the smart composite was analyzed. Full article