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Exploring new applications of negative thermal expansion (NTE) materials is a recent research hotspot. In this work, the IV A element Sn was used to tailor the thermal expansion and dielectric properties of NTE material ZrMgMo 3 O 12 , and the samples Zr 1–x Sn x MgMo 3 O 12 (x = 0.05, 0.10, 0.15, 0.20, 0.25) can be used in the field of high-frequency dielectric ceramics. Both the substitution amount of Sn and sintering temperature have a certain effect on the properties of Zr 1-x Sn x MgMo 3 O 12. The coefficients of thermal expansion (CTE) can be adjusted between near zero thermal expansion (ZTE) (−0.24 × 10−6/K−1) and NTE (−8.16 × 10−6/K−1) and become larger toward negative as the amount of Sn increased under the same sintering temperature. The dielectric constants of Zr 1-x Sn x MgMo 3 O 12 can be adjusted in the range of 130∼155, which are about 25 times than ZrMgMo 3 O 12. The dissipation factors of Zr 1-x Sn x MgMo 3 O 12 were adjustable between 4.37 × 10−4 and 5.54 × 10−4, meeting the application requirements of high-frequency dielectric ceramics. This research shows that Sn can adjust the thermal expansion properties and significantly improves the dielectric properties of ZrMgMo 3 O 12 , so that Zr 1-x Sn x MgMo 3 O 12 materials have high value in the field of high-frequency dielectric ceramics. [ABSTRACT FROM AUTHOR]

This work investigates the behavior and properties of corundum and mullite ceramics at high temperatures and during very long exposures in a controlled atmosphere. The motivation of the work lies primarily in advanced applications in nuclear energy technology, specifically in the search for materials for helium-cooled reactors of the 4th generation. The studied ceramic samples Al63, Al70, Al76, Al96, Al100, where the number indicates the mass percentage of Al 2 O 3 , were exposed for 1000 h at a temperature of 900 °C in gaseous atmospheres of helium, nitrogen and air. The properties of the exposed and unexposed samples were evaluated by measuring the bending strength at room temperature (CMOR), hot modulus of rupture at high temperature (HMOR), and isothermal creep, BET method, and using electron microscopy. The color changes induced by the reducing atmosphere and temperature were also interpreted using a simple thermochemical model. The CMOR measurement results show that all ceramic samples do not significantly change their properties due to long-term exposure. The detected deviations in the exposed samples from the unexposed ones can be considered random caused by the inherent heterogeneous structure. A similar conclusion also applies in the case of the HMOR measurement results, except for the results for the Al63 sample, where the drop in the strength of the exposed samples by approx. 37 MPa (20 %) may be related with the highest proportion of polyvalent oxide admixtures of all studied ceramics, i.e. 1.01 wt % Fe 2 O 3 and 0.52 wt % TiO 2. The change in color indicates that the iron and titanium present are being reduced. However, none of the conducted experiments indicate that changes in the redox state associated with the formation of oxygen vacancies would significantly reduce strength at high temperatures or increase creep in mullite ceramics. [ABSTRACT FROM AUTHOR]

Si3N4 ceramics with high mechanical properties and thermal conductivity, exhibiting fine and bimodal microstructure, were prepared by adjusting the Er2O3/MgO ratio and hot‐pressing sintering at 1800°C for 4 h. The microstructure, grain distribution, lattice oxygen content, mechanical properties, and crack propagation process of the sintered bulk samples were systematically investigated. It was found that a low Er2O3/MgO ratio contributed to the densification of Si3N4 ceramics, whereas a high Er2O3/MgO ratio favored the grain growth of Si3N4 ceramics. In this research, the grain size distribution and average diameters as well as their impact on mechanical properties were examined. When the ratio of Er2O3/MgO was 3:1, Si3N4 had a larger average diameter and higher thermal conductivity, but the mechanical properties were somewhat reduced. When the ratio of Er2O3/MgO was 2:2, the sample displayed enhanced mechanical performance, which can be explained by the formation of a bimodal structure. The research indicates that it is feasible to control the microstructure and optimize the mechanical properties of Si3N4 ceramics by tailoring the sintering additives. [ABSTRACT FROM AUTHOR]

Porous SiC ceramics with three different pore sizes (∼7, ∼45, and ∼98 μm) and two different porosities (∼54% and ∼63%) were prepared to investigate the effects of pore size on electrical and thermal properties of the porous ceramics. With an increase in pore size from ∼7 to ∼98 μm at the same porosity (∼54%), the electrical and thermal conductivities of the porous ceramics increased from ∼1.01 to ∼2.30 Ω−1·cm−1 and ∼14.3 to ∼26.2 W·m−1K−1, respectively. Similar trends have been obtained in the ceramics with ∼63% porosity. The porous SiC ceramic with larger pore size has smaller pore/strut interface area at the same porosity, which leads to less carrier scattering and phonon‐pore scattering at the pore/strut interfaces, resulting in higher electrical and thermal conductivities, respectively. These results suggest that the electrical and thermal properties of porous SiC ceramics can be successfully tuned by adjusting the pore size and porosity depending on the application. [ABSTRACT FROM AUTHOR]

Alumina‐based porous ceramics were fabricated via the starch consolidation casting route, using titanium oxide as a sintering additive. Alumina‐titania‐starch slurries with starch contents of 2.5, 5, 7.5, and 10 wt% relative to the alumina‐titania system were prepared. Titania was added to the slurries in proportions of 0, 1, 3, and 5 wt%, relative to alumina. The effects of starch and titania contents in the green bodies on the linear and volumetric shrinkage, as well as the total and open porosities of the sintered alumina product, were investigated. The effect of titania addition on mechanical, electrical, and thermal properties of the obtained porous alumina ceramics was studied. Microstructure and pores morphology were characterized by SEM. The alumina‐based ceramics obtained had external porosities that varied between 54 and 76 vol%. Thermal conductivities as low as 0.06–0.1 W/m.K were achieved and the volume electrical resistivity ranged from 3.6 to 600 GΩ·m, while compressive strengths up to 2.8 MPa for a titania ratio of 1 wt% were attained. [ABSTRACT FROM AUTHOR]

(KMg)3+ co-doped Sc 2 W 3 O 12 ceramics have been prepared via co-precipitation method. Effects of (KMg)3+ co-doping amount and sintering temperature on the phase constitution, microstructure, morphology, and negative thermal expansion (NTE) performance of K x Mg x Sc 2- x W 3 O 12 (0 ≤ x ≤ 1.25) ceramics were studied. Results indicate that: Sc3+ cations can be substituted by (KMg)3+ dual-cations and a composition-induced structural phase transition was observed in K x Mg x Sc 2- x W 3 O 12. For x ≤ 0.25, orthorhombic Sc 2 W 3 O 12 gradually changed into hexagonal K x Mg x Sc 2- x W 3 O 12 and coexisted. Single phase K x Mg x Sc 2- x W 3 O 12 with hexagonal symmetry can be prepared for 0.25 < x ≤ 1. When x ≥ 1.25, (KMg)3+ substitution reaches its solid solution limit in Sc 2 W 3 O 12 , and impurity MgWO 4 formed in the samples. As co-doping amount x increased, the NTE performance of the K x Mg x Sc 2- x W 3 O 12 (0 ≤ x ≤ 1) ceramics gradually enhanced. The coefficient of thermal expansion (CTE) of K x Mg x Sc 2- x W 3 O 12 (0 ≤ x ≤ 1) ceramics enhanced from −2.14 × 10−6 °C−1 to −19.68 × 10−6 °C−1 in 30–700 °C. With the increase of sintering temperature from 800 to 1100 °C, the grains grew up and the density of the K 0.75 Mg 0.75 Sc 1.25 W 3 O 12 ceramics increased as well, and the NTE performance was also improved. The linear CTE of K 0.75 Mg 0.75 Sc 1.25 W 3 O 12 ceramics enhances from −2.15 × 10−6 °C−1 to −14.70 × 10−6 °C−1 in 30–700 °C. [ABSTRACT FROM AUTHOR]

Lightweight phenolic matrix composites are highly potential in ablative thermal protective materials for future aerospace vehicles, and hybrid modification is considered as one of effective ways to improve the oxidation and ablation resistance of phenolic matrix. Herein, the co-continuous silica zirconium hybrid phenolic resin (SZRx) was synthesized, which can be used to prepare lightweight ablation resistant aerogel composites by the sol-gel method. The SZRx aerogel showed stable porous structure and excellent hydrophobicity, and the silicon zirconium hybrid greatly improved the high temperature carbon residue and oxidation resistance of phenolic resin. The SZRx aerogel composites also possessed excellent integrated characteristics of heat protection and insulation, with a linear ablation rate as low as 0.032 mm/s and a back temperature below 200 °C. The synergistic effect of silicon and zirconium formed the multiphase ceramic layer (C, SiO 2 , SiC and ZrO 2) with the sea-island-like structure on the surface of the composite material, which can effectively resist high-temperature ablation and aerodynamic exfoliation. This can indicate that silicon zirconium dual element hybrid phenolic resin is the highly competitive matrix for lightweight and ablation resistant composite materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Ceramic thermal barrier coatings (TBCs) with high toughness and low thermal conductivity are important for developing aero engines with high thrust‐to‐weight ratio and thermal efficiency. In this work, the properties of tantalate Y1/6Yb5/6TaO4 (YYT) were optimized by introducing 8 wt.% yttria‐stabilized zirconia (8YSZ), synthesized using spark plasma sintering, as a second‐phase ceramic. The highest toughness (3.57 MPa m1/2) of the YYT/8YSZ composite ceramics was due to multiple toughening mechanisms. The underlying mechanisms of these processes were revealed based on the microstructures and residual stress of the YYT/8YSZ composite ceramics. A shift from an intergranular fracture to a transgranular fracture was caused by the difference between soft‐grain YYT and hard‐grain 8YSZ, which consumed the fracture energy. Furthermore, the formation of microcracks, crack deflection, bridging, and branching were analyzed based on the differences in Young's moduli and thermal expansion coefficients of YYT and 8YSZ. Internal defects and weak connections between the YYT and 8YSZ grains reduced the thermal conductivity of the composites until it reached its lowest value at 1.4 W m−1 K−1. The studied toughening mechanisms could be applied to various composites. Moreover, herein, we provide a new strategy to design and synthesize TBCs with enhanced performance. [ABSTRACT FROM AUTHOR]

This study utilizes modulation of ionic disorder and electronegativity differences for targeted component design of high-entropy ceramic compositions. A series of novel multicomponent ceramics with the general formula (LaGdYSm) x 2 Yb x 1 Zr 2 O 7 (x 1 +4x 2 = 2, x 1 = 0.6,0.4,0.2,0) were prepared by solid-state reaction. The evolution patterns of their microstructures were analyzed using XRD and TEM, and the anti-sintering ability and thermophysical properties were evaluated. The results confirm that the multicomponent ceramics gradually transform from the coexistence of pyrochlore/fluorite dual-phase structure to pyrochlore structure with the tuning of the size disorder degree. After 50h of exposure to air at 1500 °C, the ceramics retained excellent phase stability. Segregation of La and Yb elements with large differences in radius size occurs, forming a mixture of the La-rich pyrochlore and the Yb-rich fluorite phases. The specimen with the maximum size disorder exhibits the lowest grain growth rate and the greatest thermal insulation properties. Large lattice distortions and sluggish diffusion effects are responsible for the mutual inhibition of grain growth in the two-phase coexistence zone. The thermal insulation properties of the ceramics show well correlated with the degree of the size disorder, further validating the effectiveness of the component design. Meanwhile, the thermal expansion coefficients of prepared ceramic can reach 11.49 × ∼11.58 × 10−6 K−1 at 1000–1100 °C. The customization principles used in this work fill a gap in the compositional design methodology for multicomponent lanthanum zirconate-based high-entropy ceramics. It is essential for developing rare-earth zirconates with tunable thermophysical properties in the area of thermal barrier coatings. [ABSTRACT FROM AUTHOR]

Zirconium carbide (ZrC) ceramics have a high melting point, low neutron absorption cross section, and excellent resistance to the impact of fission products and are considered to be one of the best candidate materials for fourth-generation nuclear energy systems. ZrC ceramics with a high relative density of 99.1% were successfully prepared via pressureless sintering using a small amount of MoSi2 as an additive. The influence of the MoSi2 content on the densification behavior, microstructure, mechanical properties, and thermal properties of ZrC ceramics was systematically investigated. The results show that the densification of ZrC was significantly enhanced by the introduction of MoSi2 due to the formation of a liquid phase during sintering. In addition, the ZrC grains were refined due to the pinning effect of the generated silicon carbide. The flexural strength and Vickers hardness of ZrC ceramics with 2.5 vol% MoSi2 sintered at 1850 °C were 408 ± 12 MPa and 17.1 GPa, respectively, which were approximately 30% and 10% higher compared to the samples without the addition of MoSi2. The improved mechanical properties were mainly attributed to the high relative density (99.1%) and refined microstructure. [ABSTRACT FROM AUTHOR]

Al 2 O 3 /B 2 O 3 powder mixtures prepared at various ratios from 10.7 to 54.1 wt% B 2 O 3 were used to synthesize Al 18 B 4 O 33 powders by solid state calcination at 1300 °C for 1 h. Al 18 B 4 O 33 formation was completed at 44 wt% B 2 O 3 instead of stoichiometric ratio of 13.17 wt% B 2 O 3. In other words, B 2 O 3 -rich liquid phase accelerated Al 18 B 4 O 33 crystallization. Al 18 B 4 O 33 particles were not acicular in shape when first formed, but they were fully acicular for the 44 wt% and the 54.1 wt% B 2 O 3 mixtures. Anorthite-based glass and CaO were selected to induce liquid phase sintering. CaO considerably improved densification to 95.4 % relative density at 1350 °C. Both glass and mullite also enhanced densification to 94.8 %. Epitaxial nucleation of mullite on Al 18 B 4 O 33 particles resulted in a solid solution as well. Dielectric, mechanical and thermal properties of the samples were investigated and evaluated for possible applications. [ABSTRACT FROM AUTHOR]

An additively manufactured reaction‐bonded silicon carbide ceramic composite is fabricated using a bimodal powder feedstock and the binder‐jetting printing technique. On fabricating, the ceramic is investigated to report its composition, mechanical, and thermal properties at room temperature and high temperatures (up to 750∘C$^{\circ }C$). The ceramic has a density of 2.76 g/cc, and shows a hardness of 21.74 GPa, and a flexure strength of 207.5 MPa at room temperature. The mechanical property of flexure strength is used to estimate its failure probability under applied stress, using a Weibull distribution. The mechanical properties and failure probabilities are compared with those of conventionally fabricated reaction‐bonded silicon carbide ceramics reported in the literature. These ceramics were fabricated using methods such as slip‐casting, compacting, and tape‐casting. The comparison is used to elucidate the advantages and areas of improvement of the present additive manufacturing technique for reaction‐bonded ceramics. [ABSTRACT FROM AUTHOR]

Recently, CaO‐doped (≤4 mol.%) tetragonal zirconia (CaSZ) ceramic was recommended as a potential alternative to yttria‐stabilized ZrO2 (YSZ). Here, we investigate the limits of starting particle sizes on the stability of tetragonal (t) phase and other associated benefits on measured properties. Synthesized CaSZ powders calcined with different temperatures were used as a mono‐sized or mixed (i.e., two different calcination temperatures) batch fraction for making dense CaSZ ceramic. The mixed‐batch powders were found to be far more efficient in stabilizing the t‐phase in ceramic. Compared to YSZ, CaSZ recorded remarkable enhancement in toughness (up to 8.3 MPa m$\sqrt {\mathrm{m}} $). Contrary to YSZ, CaSZ ceramic demonstrated outstanding thermal stability. [ABSTRACT FROM AUTHOR]

The (1−x)CaO-B2O3-SiO2(CBS)/xMg2SiO4 composites were prepared and the influence of CBS crystallizable glass content on the sintering properties, dielectric properties, and thermal properties of the composites were investigated. The primary crystal phases in the CBS/Mg2SiO4 composites were CaMgSi2O6 and CaB2O4. An appropriate amount of Mg2SiO4 reduced the crystallization temperature of the composite. For x = 0.30, a sintering temperature of 890°C with a holding time of 60 min resulted in a bulk density of 2.645 g/cm3, dielectric constant of 6.6, and dielectric loss of 2.54 × 10−3 at 10 kHz. Prolonged holding time promotes grain growth; when extended from 60 min to 180 min for x = 0.30, the permittivity increased from 6.5 to 6.6 and Q×f increased from 10,100 GHz to 15,700 GHz when x = 0.30 at 13 GHz. The CTE of 70 wt.% CBS + 30 wt.% Mg2SiO4 composite was 9.5 ppm/°C, which approached the value of a circuit board for a ceramic ball grid array package (CBGA). [ABSTRACT FROM AUTHOR]

Reduced graphene oxide, due to its structure, exhibits anisotropic properties, which are particularly evident in electrical and thermal conductivity. This study focuses on examining the influence of reduced graphene oxide in silicon carbide on these properties in directions perpendicular and parallel to the direction of the aligned rGO flakes in produced composites. Reduced graphene oxide is characterized by very high in-plane thermal and electrical conductivity. It was observed that the addition of rGO increases thermal conductivity from 64 W/mK (reference sample) up to 98 W/mK for a SiC–3 wt.% rGO composite in the direction parallel to the rGO flakes. In the perpendicular direction, the values were slightly lower, reaching up to 84 W/mK. The difference observed in electrical conductivity values is more significant and is 1–2 orders of magnitude higher for the flakes' alignment direction. The measured electrical conductivity increased from 1.2710−8 S/m for the reference SiC sinter up to 1.55 × 10−5 S/m and 1.2410−4 S/m for the composites with 3 wt.% rGO for the perpendicular and parallel directions, respectively. This represents an enhancement of four orders of magnitude, with a clearly visible influence of the anisotropy of the rGO. The composite's enhanced electrical and thermal conductivity make it particularly attractive for electronic devices and high-power applications. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of (1-x)K 0.5 Bi 0.5 TiO 3 - xBaTiO 3 [(1-x)KBT - xBT] were synthesized using a solid-state reaction pathway. X-ray diffraction analysis confirmed the presence of a single-phase perovskite structure. To explore relaxation and conduction mechanisms, complex impedance spectroscopy was employed. Reduction in Curie temperature was observed as BT content increased. The grain and grain boundary contributions to relaxation was examined through complex impedance and modulus plots and quantified via fitting experimental data to an equivalent circuit model. Examination of the Complex impedance spectra uncovered the existence of dielectric relaxation characteristic of a non-Debye nature. Furthermore, the activation energy determined suggests commonalities in governing the conduction and relaxation processes in relation to temperature-dependent conductivity and relaxation time. A negative temperature coefficient of resistance behaviour was obtained from the temperature-dependent conductive study. Dielectric spectra revealed that these ceramic capacitors are useful in reduction of signal interference, signal attenuation and impedance matching circuits applications. [ABSTRACT FROM AUTHOR]

Mullite fiber-based porous ceramics is one of the most commonly used high-temperature insulation materials. However, how to further reduce the thermal conductivity and improve the strength of such materials has been a challenge in the field of high-temperature insulation. In this paper, mullite micro/nano fiber-based porous ceramic was prepared by introducing mullite nanofibers into mullite microfiber-based porous ceramics and the effect of microfiber/nanofiber weight ratio on the samples properties were characterized and analyzed. Results showed that the compressive strength and high-temperature thermal insulation properties of the porous ceramics increased significantly with an increase in the nanofiber content. For the porous ceramics with similar density (about 0.50 g/cm3), the compressive strength of the sample with a microfibers/nanofibers weight ratio of 1:2 was 1.43 MPa, which was much higher than that of the porous ceramics prepared with only microfibers (0.26 MPa). Meanwhile, the backside thermal equilibrium temperature of the sample with a microfiber/nanofiber weight ratio of 1:2 at 900 °C environment was 355.8 °C, which was much lower than that of the porous ceramic prepared with only microfibers (476.5 °C). In addition, in order to investigate the temperature resistance of mullite micro/nano fiber-based porous ceramics, the sintering temperatures was increased from 1400 °C to 1500 °C. Results shows that the high-temperature thermal insulation performance of mullite micro/nano fiber-based porous ceramics with high mullite nanofiber content decays more seriously. The back-temperature test showed that the thermal equilibrium temperature of the samples with a mullite micron/nanofiber weight ratio of 1:1 in 900 °C environment increased rapidly from 386.3 °C to 454.2 °C when the sintering temperature was increased from 1400 °C to 1500 °C. The preparation of mullite micro/nanofiber-based porous ceramics provides a new strategy to improve the performance of fiber-based porous ceramics. [ABSTRACT FROM AUTHOR]

Ni-containing SiOC bulk ceramics have been prepared by spark plasma sintering at 1300 °C from polysiloxane at Ar atmosphere in the present work. The microstructure and properties of SiOC ceramics with different Ni content were studied. The resultant Ni-containing SiOC ceramics consists of in situ formed turbostractic layer carbon, CNTs (C nanotubes) and SiC crystals which dispersed in the SiOC matrix. With increasing content of Ni, the Ni-containing SiOC ceramics displayed less porosity. And the increasing Ni improved the mechanical, thermal and friction properties of SiOC ceramics. Ni-containing SiOC ceramics developed a carbon friction layer, which enhanced abrasion resistance to provide friction materials with stable friction coefficients and low abrasion values. A decrease in wear mass, from 2.06 to 0.18 mg was observed as the Ni content increasing from 0 to 2 wt%. The primary wear mechanisms of SiOC ceramics were recognized as abrasive wear, fatigue wear, and adhesion wear. [ABSTRACT FROM AUTHOR]

Piezoelectric ceramics with excellent piezoelectric properties and a high Curie temperature are important for numerous electromechanical devices in a broad range of temperature environments. In this work, the relaxor ferroelectric Pb(Yb1/2Nb1/2)O3 end member was selected to be introduced into a BiScO3-PbTiO3 high-temperature piezoelectric ceramic to reduce the dielectric loss and improve the piezoelectric properties while slightly reducing the Curie temperature. The phase structure and dielectric, ferroelectric and piezoelectric properties of 0.025Pb(Yb1/2Nb1/2)O3-(0.975 − x)BiScO3-xPbTiO3 (0.60 ≤ x ≤ 0.63) ceramics were systematically analyzed, and the best electrical properties were observed in the morphotropic phase boundary region x = 0.61 with d33 = 370 pC/N, kp = 44%, Pr = 33.9 μC/cm2. Importantly, no significant depolarization was observed in the x = 0.61 ceramic from room temperature to 290 °C, demonstrating its good thermal stability and potential applications in a wide range of temperature environments. [ABSTRACT FROM AUTHOR]

In this study, according to the Dinger model, aqueous Si 3 N 4 slurries with a solid loading of 63 vol% and a viscosity lower than 1.0 Pa s were successfully prepared using two-grade Si 3 N 4 powders with D 50 = 7.2 μm and 9.4 μm as starting materials. These resulting slurries exhibited good rheological properties and suspension stability. Notably, the presence of β-Si 3 N 4 seeds existed in the starting materials effectively reduced the nucleation barrier by transforming homogeneous nucleation into heterogeneous nucleation. Consequently, it facilitated the reconstructive phase transformation of α-Si 3 N 4 to β-Si 3 N 4 , promoted the anisotropic growth of β-Si 3 N 4 nucleation, and resulted in the final formation of the bimodal microstructure. This unique microstructure significantly enhanced the mechanical properties of Si 3 N 4 ceramics, resulting in a high flexural strength of 1011.4 MPa and a fracture toughness of 14.8 MPa m1/2. These excellent properties were achieved through the combination of gelcasting and gas pressure sintering. Simultaneously, the Si 3 N 4 ceramics exhibited a low thermal conductivity of 47.7 W m−1 K−1, mainly owing to the low density of 95.3 %, the presence of low-thermal-conductivity silicate-based noncrystalline substances, and the possible existence of lattice oxygen in Si 3 N 4 crystals. [ABSTRACT FROM AUTHOR]

Lightweight ablative materials owing to their low density, high efficiency heat insulation and excellent designability, which are considered as the most promising candidate materials in the field of aerospace ablative thermal protection. In this work, a polycarbosilane (PCS) in-situ reinforced carbon felt/phenolic (PR/C f) aerogel composite is reported. The surface of aerogel and carbon fiber was coated with PCS protective layer by sol gel method and secondary vacuum impregnation process. The aerogel composite material possesses low density (0.264–0.307 g/cm3), hydrophobic, low thermal conductivity (0.121–0.178 W/(m·K)) and significant high compressive strength (12.89 MPa). When the oxygen acetylene flame with high heat flow density ablates for 20 s, it shows high efficiency in heat protection and insulation, and the linear ablation rate is as low as 0.089 mm/s. The PL/PR/C f aerogel composite shows competitive and broad application prospects in the field of ablation heat protection in the future. [ABSTRACT FROM AUTHOR]

To date, the restricted capability to fabricate ceramics with independently tailored nano‐ and macroscopic features has hindered their implementation in a wide range of crucial technological areas, including aeronautics, defense, and microelectronics. In this study, a novel approach that combines self‐ and digital assembly to create polymer‐derived ceramics with highly controlled structures spanning from the nano‐ to macroscale is introduced. Polymerization‐induced microphase separation of a resin during digital light processing generates materials with nanoscale morphologies, with the distinct phases consisting of either a preceramic precursor or a sacrificial polymer. By precisely controlling the molecular weight of the sacrificial polymer, the domain size of the resulting material phases can be finely tuned. Pyrolysis of the printed objects yields ceramics with complex macroscale geometries and nanoscale porosity, which display excellent thermal and oxidation resistance, and morphology‐dependent thermal conduction properties. This method offers a valuable technological platform for the simplified fabrication of nanostructured ceramics with complex shapes. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of the influence of the sintering additive ratio on the microstructure evolution of silicon nitride (Si 3 N 4) ceramics, Si 3 N 4 ceramics were prepared by gas pressure sintering using different ratios of Y 2 O 3 /MgSiN 2 as additives. Varying the ratio of Y 2 O 3 /MgSiN 2 changed the composition of the liquid phase, thereby affecting the densification process and phase transformation rate of Si 3 N 4 ceramics, and ultimately changing their microstructure. The reduction in the Y 2 O 3 /MgSiN 2 ratio raised the N/O and Si/O ratios in the system, which increased the liquid phase viscosity. The Si 3 N 4 grain distribution varied from "normal to bimodal". In the case of increasing the proportion of MgSiN 2 and prolonging the sintering time, more of the glass phase evaporated, which reduced the content of the low thermal conductivity phase and increased the continuity of Si 3 N 4 /Si 3 N 4. Therefore, Si 3 N 4 ceramics with 1 wt% Y 2 O 3 and 5 wt% MgSiN 2 exhibited excellent properties after sintering at 1900 °C for 12 h, with thermal conductivity, bending strength, and fracture toughness of 106.7 Wm−1K−1, 776 MPa, and 11.66 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

In recent years, the MgO-Nd 2 Zr 2 O 7 composite ceramics inert matrix (IM) was proposed as a candidate for the transmutation of Pu and minor actinides (MA) in light water reactors (LWR) or accelerator driven sub-critical system (ADS). To take full advantage of the pyrochlore structure of Nd 2 Zr 2 O 7 to accommodate different types of MA and Pu, in this work, Y and Ce co-doped ω MgO-(1- ω)(Nd 1- x Y x) 2 (Zr 1- x Ce x) 2 O 7 (M-NYZC) composite ceramics used as a candidate IM for inert matrix fuel were prepared by solid-state one-step sintering method at 1500 °C for 3 h. The phase structure and microstructure of M-NYZC composite ceramics were characterized by XRD and SEM-EDS. Also, the thermal physical properties of M-NYZC composite ceramics including the thermal expansion coefficient and thermal conductivity were investigated systematically. Results from XRD and SEM-EDS showed that the magnesium oxide and NYZC pyrochlore solid solution are intermixed well with each other, and the M-NYZC samples present uniform element distribution with a grain size of about 1 μm. Also, the as-prepared samples possessed well densified microstructure, and the average relative density of all samples could exceed 95 %. Moreover, the thermal expansion coefficient and thermal conductivity of 0.5M-0.5NYZC (x = 0, 0.15, 0.2, 0.5, 0.9) samples were located in the range of 13.4 × 10-6–14.4 × 10-6 K-1 and 16.34–3.70 W·m-1·K-1 respectively. By comparison, the thermal physical properties of 0.5M-0.5NYZC samples are superior to that of traditional UO 2 and MOX fuels. It is suggested that the M-NYZC composite ceramics prepared in this study can meet the thermal physical performances of inert matrix fuel. [ABSTRACT FROM AUTHOR]

The porous SiC-Mullite porous ceramics with different pore size were prepared by SiC particles, kaolin, Al(OH) 3 , and flake graphite, V 2 O 5 and AlF 3 were used as mineralizers, the pore size was controllable by adjusting the size of flake graphite. Then the improved empirical formula and grey theory were used to study the effect of the change in pore size on the material properties. The results showed that with the increase of mean pore size from 1.1 μm to 8.5 μm, the cold modulus of rupture and cold crushing strength decreased by 20.8 MPa and 13.7 MPa, respectively. And the thermal conductivity increased from 1.213 W⋅m−1⋅K−1 to 1.721 W⋅m−1⋅K−1 at 800 °C. The <5 μm pores were helped enhance the strength and decreased the thermal conductivity. [ABSTRACT FROM AUTHOR]

Reaction-bonded SiC is a ceramic with excellent thermal properties, good corrosion resistance and the characteristic of near-net-shape manufacturing. However, the poor fracture toughness of free Si limits the applications of reaction-bonded SiC. In this study, TiC was added to reaction-bonded SiC and reacted with free Si to form Ti 3 SiC 2. The effects of TiC and carbon black on the mechanical properties of reaction-bonded SiC were investigated. The results demonstrated that the in-situ formation of Ti 3 SiC 2 and decrease in the content and size of free Si improved the mechanical properties of reaction-bonded SiC ceramics. The mechanical properties of TiC-added reaction-bonded SiC with 17.5 wt% carbon black were superior to those of TiC-added reaction-bonded SiC with 15 wt% carbon black. Moreover, increasing the TiC content of reaction-bonded SiC with 17.5 wt% carbon black from 0 to 7.5 wt% caused an increase in its bending strength from 183.92 to 424.43 MPa and an increase in fracture toughness from 3.7 to 5.24 MPa m1/2. [ABSTRACT FROM AUTHOR]

In Part 1 of this study, we investigated the macrokinetic parameters and phase formation mechanism in the combustion front of Zr–Nb–B mixtures. In the second part, we produced consolidated samples of solid solutions NbB 2 -(0.100%)ZrB 2 by hot pressing the combustion-derived powders at 1900 °C. By measuring the crystallographic parameters, mechanical and thermophysical properties of the produced bulk samples, we obtained valuable insights into the behavior of the solid solutions. Our results pave the way for the application-specific fine-tuning of the mechanical properties and thermal conductivity of diboride solid solutions in the Zr–Nb–B system for ultra-high temperature applications. Our findings have significant implications for the development of advanced materials with outstanding performance in extreme environments. [ABSTRACT FROM AUTHOR]

In this work, (20- x)MgO–20Al 2 O 3 –56SiO 2 –4B 2 O 3 - x CuO (x = 0, 0.25, 0.5, 0.75, 1, 1.25 mol%) glass-ceramics were synthesized by solid-state reaction method. The crystallization, microstructure, thermal and dielectric properties of (20- x)MgO–20Al 2 O 3 –56SiO 2 –4B 2 O 3 - x CuO glass-ceramics was discussed in detail. It was demonstrated that the CuO lowers the crystallization temperature of α-cordierite and promotes the crystallization process of MgO–Al 2 O 3 –SiO–B 2 O 3 glass-ceramics. Thus, the crystallization showed a substantial influence on the dielectric properties, as evidenced by an elevation in dielectric constant and a decrease in dielectric loss. Specifically, with the addition of 0.5 mol% CuO, the MgO–Al 2 O 3 –SiO–B 2 O 3 glass-ceramics sintered at 1050 °C shows excellent properties of: ε r = 5.04, tan δ = 2.2 × 10-4, κ = 3.4 W/mK and α = 1.75 × 10-6/°C. These works provide valuable insights into the design and development of (20- x)MgO–20Al 2 O 3 –56SiO 2 –4B 2 O 3 - x CuO glass-ceramics with tailored properties for structure/function integration in the electronics industry. [ABSTRACT FROM AUTHOR]

Herein, Nd 2 O 3 -doped 0.11PIN-0.89PHT (PIN-PHT) single-phase tetragonal piezoelectric ceramics are prepared by traditional solid-phase method. In addition, impacts of Nd-doping on crystal structure and electrical performance for 0.11PIN-0.89PHT ceramics are systematically investigated. Based on Landau theory, we propose a novel strategy for obtaining high-performance ceramics by combining tetragonal phase and relaxor ferroelectrics. Results reveal that the introduction of polar nano-regions in tetragonal phase ceramics by doping with rare-earth ions to convert normal ferroelectrics into relaxed ferroelectrics is responsible for excellent properties of 0.11PIN-0.89PHT- x Nd ceramics. The optimized comprehensive performance is obtained at x = 0.9 mol%, where d 33 = 670 pC/N, S max = 0.29% (45 kV/cm), strain hysteresis = 8.68% (45 kV/cm), d 33 * = 736 p.m./V (30 kV/cm), T C = 312.6 °C, ε r = 3234, k p = 0.62, tan δ = 0.014, and excellent high-temperature stability in temperature range of 20–240 °C. After 106 cycles, electrical properties and strain remain unchanged, showing excellent anti-fatigue behavior. This work provides a novel approach for the development of ceramics with outstanding piezoelectric response, high strain, low strain hysteresis, excellent anti-fatigue resistance and thermal stability, and is expected to realize practical applications of piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Currently, Faraday isolators and rotators for high‐power lasers are popular research topics; therefore, finding magneto‐optical materials with excellent Verdet constants and thermal properties is crucial. In this study, novel holmium scandium aluminum garnet (HoSAG) magneto‐optical ceramics were fabricated using vacuum sintering. This study improved the traditional ball milling method and pre‐synthesized powders with great sinterability after secondary ball milling and sieving. Different pre‐synthesis temperatures were found to have significant effects on the particle size and micromorphology of the synthesized powders. HoSAG ceramics with 0.05 wt% MgO sintering aid and held at 1700°C for 30 h reached a transmittance of 76.7% at 1550 nm. Meanwhile, HoSAG transparent ceramics maintain higher transmittance in the infrared region (>1500 nm) than terbium gallium garnet (TGG) crystals, indicating better application prospects. The Verdet constants of HoSAG magneto‐optical ceramics at 405, 532, 808, and 1064 nm were −421.5, −181.2, −65, and −32.3 rad T−1 m−1, respectively, which are slightly less than those of TGG magneto‐optical ceramics. Moreover, the thermal conductivity of HoSAG ceramics at 300.00 K was 4.89 W m−1 K−1, which is comparable to that of the TGG ceramics. [ABSTRACT FROM AUTHOR]

In this work, the cold sintering assisted process was utilized to fabricate dense 0–3 type (1- x)BaTiO 3 - x CaTiO 3 :Pr3+ ((1- x)BT- x CT:Pr3+, x = 0.1, 0.2 and 0.3) binary composite ceramics. Under the combined action of uniaxial pressure and temperature, CT:Pr3+ has been successfully integrated with BT to form the preliminary BT-CT:Pr3+ composites during cold sintering. It is found that the cold sintering could increase the grain size a little, and annealing at 900 °C significantly promotes the grain size. The prepared (1- x)BT- x CT:Pr3+ composite ceramics have a pure phase of CT:Pr3+, which is difficult to prepare using high temperature solid reaction method when x < 0.23. It is found that all the composite ceramics exhibit excellent ferroelectric properties. Furthermore, a strong photoluminescence, photo-stimulated luminescence and thermal luminescence properties have been obtained. Present study illustrates a potential approach to combine luminescent and piezoelectric properties into the ferroelectric-based composite ceramics by the cold sintering assisted sintering. [ABSTRACT FROM AUTHOR]

SiO2‐Al2O3‐CaO‐based glass (10–60 wt%)/mullite composites were investigated for the LTCC and radome applications. The optimum densification temperatures decreased from 1550°C (10 wt% glass) to 1400°C (30 wt% glass) by means of liquid‐phase sintering, and to 850°C–825°C (50–60 wt% glass) by means of viscous phase sintering. XRD analysis showed that mullite was the main phase as well as in situ crystallized anorthite after 825°C. The composite with 20 wt% glass was a suitable candidate for the radome applications (bulk density = 2.86 g/cm3 after sintering at 1450°C, dielectric constant (loss) = 7.12 (0.0025) at 5 MHz, thermal expansion coefficient = 4.27 ppm/°C between 25°C and 800°C, thermal shock resistance parameter = 162°C), and the composite with 50 wt% glass was a suitable candidate for the low‐temperature cofired ceramic applications (bulk density = 2.64 g/cm3 after sintering at 850°C, dielectric constant (loss) = 6.79 (0.0043) at 5 MHz, thermal conductivity = 2.11 W/m⋅K at 25°C, and thermal expansion coefficient = 3.93 ppm/°C between 25°C and 300°C). [ABSTRACT FROM AUTHOR]

To expand the application of zirconia ceramics in thermal insulation, this study proposes a method to prepare Yttria-stabilized tetragonal zirconia polycrystal ceramics (3Y-TZP ceramics) with fine and complex triply periodic minimal surface (TPMS structures) using digital light processing (DLP) 3D printing technology. The 3Y-TZP ceramic green body was sintered using a two-step method. When sintered at 1450 °C for 3 h, 3Y-TZP ceramics with a relative density of 98.6 ± 0.2% and a flexural strength of 937 ± 24 MPa were finally obtained. Three types of TPMS 3Y-TZP ceramic structures were successfully prepared. A finite element method was employed to validate the mechanical and thermal insulation properties through in-depth experimental studies. The results demonstrate that the diamond structure exhibited the lowest thermal conductivity of 0.93 ± 0.035 W/(mK) and the highest compressive strength of 166.5 ± 27.3 MPa at 67% porosity. The TPMS-type porous 3Y-TZP ceramics prepared by DLP technology have both load-bearing and thermal insulation properties, making them potentially promising for thermal insulation applications. [ABSTRACT FROM AUTHOR]

The hierarchically porous La 2 Zr 2 O 7 (LZO) microsphere fabricated by the electro-spraying assisted phase inversion (ESP) method is a promising feedstock for thermal barrier coatings (TBCs), due to its low thermal conductivity, quite high near-infrared reflectivity and high temperature structure stability. However, the thermal properties of hierarchically porous LZO ceramics above 1000 K are still unclear, limiting its application in TBCs. The effect of hierarchical structure on thermal conduction and thermal radiation was investigated in comparison with mono-sized pores, using the ESP microspheres (LZO-ESP) and other two carbon fillers to modulate the pores. The results showed that LZO-ESP samples exhibited ultra-low thermal conductivity (1.28 W m−1 K−1 at 1173 K), which was 30% lower than that of the reference samples of similar porosity. Heat flux simulation revealed that hierarchical structure can induce more disorder domains than the randomly distributed mono-sized pores. The disorder domains with high tortuosity of heat flux played a predominant role in the reduction of thermal conductivity. Additionally, the hierarchical structure significantly reduced thermal radiation by 36% compared with dense sample due to the decrease in transmissivity. [ABSTRACT FROM AUTHOR]

Mullite/glass/nano aluminum nitride (AlN) filler (1–10 wt% AlN) composites were successfully fabricated for the low‐temperature co‐fired ceramics applications that require densification temperatures lower than 950°C, high thermal conductivity to dissipate heat and thermal expansion coefficient matched to Si for reliability, and low dielectric constant for high signal transmission speed. Densification temperatures were ≤825°C for all composites due to the viscous sintering of the glass matrix. X‐ray diffraction proved that AlN neither chemically reacted with other phases nor decomposed with temperature. The number of closed pores increased with the AlN content, which limited the property improvement expected. A dense mullite/glass/AlN (10 wt%) composite had a thermal expansion coefficient of 4.44 ppm/°C between 25 and 300°C, thermal conductivity of 1.76 W/m.K at 25°C, dielectric constant (loss) of 6.42 (0.0017) at 5 MHz, flexural strength of 88 MPa and elastic modulus of 82 GPa, that are comparable to the commercial low temperature co‐fired ceramics products. [ABSTRACT FROM AUTHOR]

The phase composition, microstructure, electrical and thermal properties of hot-pressed AlN-2 wt% Yb 2 O 3 -4 wt% Sm 2 O 3 - x wt% TiN (x = 0, 0.4, 0.8, 1, 2, 3, 4) ceramics were systematically investigated. Yb 2 O 3 and Sm 2 O 3 were used to react with Al 2 O 3 in AlN to form Yb 3 Al 5 O 12 , SmAlO 3 and SmAl 11 O 18 , which made the samples densely sintered. When sintered at higher than 1700 °C, the electrical resistivity of AlN ceramics with 2 wt% Yb 2 O 3 -4 wt% Sm 2 O 3 decreased significantly to 1010 Ω·cm. This decrease in resistivity was probably caused by the continuity of the secondary phase, which encasing the AlN grains and deteriorating the thermal conductivity. When sintered at 1650 °C, the addition of 0.4–4.0 wt% TiN reduces the electrical resistivity from 8.9 × 1012 to 2 × 1010 Ω·cm while maintaining thermal conductivity at around 90 W/m·K with high compactness. Finally, a series of high performance AlN ceramics, with adjustable electrical/thermal properties, could be obtained for modern semiconductor industry. [ABSTRACT FROM AUTHOR]

Rare-earth (RE) oxide-doped La 2 (Zr 0.7 Ce 0.3) 2 O 7 (LZC) has attracted great interest in thermal barrier coatings (TBCs) because of its lower thermal conductivity. However, studies on the laws governing the effect of different types of RE oxide doping on the performance of LZC ceramics are limited. Therefore, in this study, different types of RE (Sc, Y, Gd and Eu) doped LZC ceramic bulks have been prepared using solid phase reaction method. The effects of RE doping on the crystal structure, mechanical properties and thermal properties of the LZC ceramics were investigated. The results indicated that all five ceramics exhibited a single pyrochlore phase structure, whereas their lattice constants were reduced after doping, with (La 0.85 Sc 0.15) 2 (Zr 0.7 Ce 0.3) 2 O 7 having the lowest lattice constant. The effect of rare earth doping on the grain growth of LZC was not evident; however, it could significantly improve the hardness of LZC. In addition, doping with all four RE ions significantly reduced the thermal conductivity of the LZC ceramics, and the most significant reduction was observed for Gd3+ doping. [ABSTRACT FROM AUTHOR]

Six rare‐earth tantalate high‐entropy ceramics of (5RE.2)Ta3O9 (RE represents any five elements selected from La, Ce, Nd, Sm, Eu, Gd) were designed and prepared by spark plasma sintering process at 1400°C in this study. The (5RE.2)Ta3O9 ceramics only consist of a single‐phase solid solution with perovskite structure. Their relative densities are all above 90%, and the average grain size is in the range of 1.47–2.92 μm. The thermal conductivity of (5RE.2)Ta3O9 ceramics is in 2.24–1.90 W m−1 K−1 (25°C–500°C), which is much lower than that of yttria‐stabilized zirconia. In six samples, (La.2Nd.2Sm.2Gd.2Eu.2)Ta3O9 possesses a thermal conductivity of 1.90 W m−1 K−1, a thermal expansion coefficient of 3.47 × 10−6 K−1 (500°C), a Vickers hardness of about 7.33 GPa, and a fracture toughness of about 5.20 MPa m1/2, which are suitable for its application as thermal barrier coatings. [ABSTRACT FROM AUTHOR]

Dy 2 TiO 5 ceramics with small grain size range of 1.5–3 μm were successfully prepared by microwave sintering method. The phase composition, microstructure, thermal expansion, stability, corrosion resistance and neutron absorption properties of Dy 2 TiO 5 ceramics were investigated. The results show that Dy 2 TiO 5 ceramics possess high mechanical properties due to the small grain size, with a microhardness of 12.26 GPa. The addition of Mo significantly reduces the thermal expansion phenomenon of the sample. The oxide film formed on the surface of the Dy 2 TiO 5 ceramic enhances its excellent corrosion resistance. In addition, the Dy 2 TiO 5 ceramic shows excellent neutron absorption with 87.34% neutron absorption and over 94% thermal neutron absorption in 8 cm thick particles. [ABSTRACT FROM AUTHOR]

This work reports the effect of tin (Sn) doping on the infrared (IR) and terahertz (THz) properties of vanadium dioxide (VO 2 ) films. The films were grown by hydrothermal synthesis with a post-annealing process and then fully characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and temperature-controlled electrical resistivity as well as IR and THz spectroscopy techniques. Utilizing (NH 4 ) 2 SnF 6 as a Sn precursor allows the preparation of homogeneous Sn-doped VO 2 films. Doping of VO 2 films with Sn led to an increase in the thermal hysteresis width while conserving the high modulation depth in the mid-IR regime, which would be beneficial for the applications of VO 2 films in IR memory devices. A further analysis shows that Sn doping of VO 2 films significantly affects the temperature-dependent THz optical properties, in particular leading to the suppression of the temperature-driven THz transmission modulation. These results indicate Sn-doped VO 2 films as a promising material for the development of switchable IR/THz dichroic components. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the mechanisms of polymorphic transformations in ZrO2 ceramics doped with MgO with different concentrations during thermal isochronous annealing, as well as the effect of the phase composition of ceramics on the change in strength properties and resistance to mechanical stress. Solving the problem of polymorphic transformations in zirconium dioxide by doping them with MgO will increase the resistance of ceramics to external influences, as well as increase the mechanical strength of ceramics. According to the data of X-ray phase analysis, it was found that the addition of the MgO dopant to the composition of ceramics at the chosen thermal annealing temperature leads to the initialization of polymorphic transformation processes, while changing the dopant concentration leads to significant differences in the types of polymorphic transformations. In the case of an undoped ZrO2 ceramic sample, thermal annealing at a temperature of 1500 °C leads to structural ordering due to the partial removal of deformation distortions of the crystal lattice caused by mechanochemical grinding. During the study of the effect of MgO doping and polymorphic transformations in ZrO2 ceramics on the strength properties, it was found that the main hardening effect is due to a change in the dislocation density during the formation of a ZrO2/MgO type structure. At the same time, polymorphic transformations of the m—ZrO2 → t—ZrO2 type have a greater effect on hardening at low dopant concentrations than t—ZrO2 → c—ZrO2 type transformations. [ABSTRACT FROM AUTHOR]

The Raman polymerization index (or IP value) is often used as a positive indicator of the firing temperature of the glazes of ancient ceramics. Previous studies have also reported that the IP value was negatively correlated with the chemical composition of the glaze. However, these findings were derived from data on the potential integrative effects of temperature and composition. To explore their individual effects, we prepared celadon glaze samples with controlled composition and firing temperatures. Particularly, according to the typical content of K2O and CaO in celadon glaze, four categories, or, in total, fifteen compositional formulations, were designed, and each formulation was fired at multiple temperatures (from 1180 to 1250 °C by 10 °C). The chemical compositions and the glassy matrix of samples were analyzed by an energy-dispersive X-ray fluorescence spectrometer and Raman spectroscopy, respectively. A positive correlation between firing temperature and IP value (correlation coefficient = 0.56) was detected only in the samples with low contents of K2O and CaO. However, no significant correlation was found when combining the samples with broad variation in chemical composition. Additionally, both the K2O content and CaO content were negatively related to the IP value, with regression coefficients of −9.645 and −5.332, respectively. Our results help to clarify the technology of ancient ceramic production and to improve its preservation. [ABSTRACT FROM AUTHOR]

The tailored physical properties of TiO2 are of significant importance in various fields and, as such, numerous methods for modifying these properties have been introduced. In this study, we present a novel method for doping Fe into TiO2 via the anodic dissolution of iron. The optimal conditions were determined to be an application of 200 V to acetylacetone (acac)/EtOH medium for 10 min, followed by the addition of TiO2 to the solution, sonication for 30 min, stirring at 80 °C, and drying. The resulting powder was calcined at 400 °C for 3 h, and characterization was conducted using XRD, FTIR, TEM, and UV-vis. The synthesized powder revealed the successful doping of Fe into the TiO2 structure, resulting in a decrease in the optical band gap from 3.22 to 2.92 eV. The Fe-TiO2 was then deposited on a metal substrate via the electrophoretic (EPD) technique, and the weight of the deposited layer was measured as a function of the applied voltage and exposure time. FESEM images and EDX analysis confirmed that the deposited layer was nanostructured, with Fe evenly distributed throughout the structure. [ABSTRACT FROM AUTHOR]

Analysis of the microstructure of electro-porcelain is important to better understand its influence on mechanical, electrical and aging behavior. The microstructures of two electro-porcelain materials with low and high quartz contents were analyzed with respect to the distribution of quartz. Using an adequate evaluation of EDS (energy dispersive spectroscopy) mapping data, a reproducible analysis of the size distribution and quantity of quartz was achieved. The method allows the analysis of large areas (12.5 mm2). Therefore, the probability of occurrence for a few large quartz grains could be determined. Independent of the overall amount of quartz in the materials, a wide distribution of the grain size was observed. The size of the large detected quartz grains in both materials was very similar. Around the large quartz particles, microcrack systems with lengths of several 100 µm were observed. They are linearly correlated with the equivalent circle diameter of the quartz grains. The evaluation of the cracks allowed us to determine the critical size below which no cracks around the quartz particles are formed. This size is approximately 10 µm. [ABSTRACT FROM AUTHOR]

To increase the thermocyclic resistance of material, multilayer coatings with alternating layers of Zr-Y-O and Si-Al-N were obtained via magnetron sputtering. It was established that a coating layer based on Zr-Y-O has a columnar structure; the height of the columns is determined by the thickness of the layer. The Si-Al-N-based layer is amorphous. There were monoclinic and tetragonal phases with a large lattice parameter in the composition of the Zr-Y-O-based coating layer. After high-temperature annealing, a tetragonal phase with a small lattice parameter appeared in the microscope column. In the "in situ" mode, a change in the structural state of the Zr-Y-O coating layer was detected in the temperature range of 450–500 °C; namely, a change in the grain size and coherent scattering regions, and an increase in internal elastic stresses. It was found that the thermocyclic resistance increased by more than two times for multilayer samples compared to the single-layer ones we studied earlier. [ABSTRACT FROM AUTHOR]

The objective of this study is to explore and compare the mechanical response of AlCrSiN coatings deposited on two different substrates, namely, WC-Co and cBN. Nano-indentation was used to measure the hardness and elastic modulus of the coatings, and micro-indentation was used for observing the contact damage under Hertzian contact with monotonic and cyclic (fatigue) loads. Microscratch and contact damage tests were also used to evaluate the strength of adhesion between the AlCrSiN coatings and the two substrates under progressive and constant loads, respectively. The surface damages induced via different mechanical tests were observed using scanning electron microscopy (SEM). A focused ion beam (FIB) was used to produce a cross-section of the coating–substrate system in order to further detect the mode and extent of failure that was induced. The results show that the AlCrSiN coating deposited on the WC-Co substrate performed better in regard to adhesion strength and contact damage response than the same coating deposited on the cBN substrate; this is attributed to the lower plasticity of the cBN substrate as well as its less powerful adhesion to the coating. [ABSTRACT FROM AUTHOR]

Finely dispersed (CeO2)1−x(Sm2O3)x (x = 0.05, 0.10, 0.20) and (CeO2)1−x(Nd2O3)x (x = 0.05, 0.10, 0.15, 0.20, 0.25) powders were synthesized via liquid-phase techniques based on the co-precipitation of hydroxides and were used to obtain ceramic materials comprising fluorite-like solid solutions with CSR in the range 69–88 nm (upon annealing at 1300 °C) and open porosity in the range 0.6–6.2%. The physicochemical properties of the synthesized materials were comparatively characterized. In general, the prepared materials were found to possess a mixed type of electrical conductivity, but in the medium-temperature range, the ionic component was predominant (ion transfer numbers ti = 0.93–0.73 at 300–700 °C). The highest ionic conductivity was observed for CeO2-based samples containing 20 mol.% Sm2O3 (σ700°C = 3.3 × 10−2 S/cm) and 15 mol.% Nd2O3 (σ700°C = 0.48 × 10−2 S/cm) was in the temperature range 500–700 °C. The physicochemical properties (density, open porosity, type and mechanism of electrical conductivity) of the obtained ceramic materials make them promising as solid oxide electrolytes for medium temperature fuel cells. [ABSTRACT FROM AUTHOR]

The possibility of obtaining building foamed glass-ceramic using the diamond concentration tailings of the Lomonosov deposit in Arkhangelsk Region, Russia, is demonstrated here. The effect of the tailings' particle size distribution, feed temperature, the addition of a foaming agent, and the content of oxidizer on the feed charge foaming is established. The process conditions for obtaining foamed glass-ceramic materials are described. The specifications of the materials with the optimal composition (tailings 50 wt.%, glass waste 50 wt.%, SiC 0.5 wt.%, Fe2O3 1 wt.%) foamed at 1020–1050 °C were as follows: apparent density 0.23–0.51 g/cm3, compression strength 0.58–2.40 MPa, water absorption (by volume) 8.7–19.0%. Based on the combination of the measured properties when used in dry conditions, the obtained materials can be considered heat-insulating foam materials. The thermal conductivity was 0.060–0.066 W/m·K. [ABSTRACT FROM AUTHOR]

Nanostructured single-phase hafnium-zirconium carbonitride powders were synthesized using a simple and fast mechanochemical synthesis approach. The critical milling duration, after which a (Hf,Zr)(C,N) solid solution formation inside a jar occurred via mechanically induced self-sustained reaction (MSR), was 10 min. After 30 min of treatment, a solid-gas reaction was completed, and as a result, a homogeneous (Hf,Zr)(C,N) powder consisting of 10–500 nm submicron particles was obtained. The phase and structure evolution of the powders after different treatment durations allowed for the establishment of possible reaction mechanisms, which included the formation of Hf/Zr/C-layered composite particles, their interaction via MSR, and further grinding and nitridization. Spark plasma sintering (SPS) was used to produce bulk hafnium-zirconium carbonitride ceramics from nanostructured powder. The sample had higher values of relative density, hardness, and fracture toughness than those for binary compounds of a similar composition. [ABSTRACT FROM AUTHOR]

A developing energy-saving approach of cold sintering in a pure aqueous medium was applied to the preparation of α-Al2O3 ceramics and performed on spark plasma sintering equipment. The initial γ-Al(OH)3 and γ-AlOOH powders and the cold-sintered ceramics were studied by X-ray diffraction analysis, infrared spectroscopy, thermal analysis, and scanning electron microscopy to reveal the chemical and structural transformations they experienced during the cold sintering. At 450 °C and 70 MPa, initially γ-AlOOH transformed into a fragile α-Al2O3 material. Porous α-Al2O3 ceramics with about 60% porosity were obtained after cold sintering of γ-Al(OH)3 in the same conditions combined with subsequent annealing at 1250 °C for 3 h. The role of water molecules in the studied processes was considered as the enhancement of structural mobility in the cold-sintered material due to its reversible hydroxylation similar to earlier investigated supercritical water actions on the precursors during α-Al2O3 formation. Further improvement of the cold sintering setup and regimens would open prospects in α-Al2O3 ceramics manufacturing by an ecologically benign route. [ABSTRACT FROM AUTHOR]