Flow stress is one of the most significant plastic mechanical properties of ceramic material at high temperature, and it is crucial to its processing and manufacturing. In the present paper, a novel temperature-dependent flow stress model for ceramic materials is proposed firstly. The model establishes a clear and meaningful relationship between the flow stress and various material parameters including temperature, elastic modulus, Poisson’s ratio, melting point, and particularly, without any fitting parameters. Then, the individual effect of strain rate and the coupling effect of temperature and strain rate on flow stress is investigated. In this way, a new temperature-strain rate-dependent flow stress model for ceramic material is developed. And the model is verified by comparison between its predicted data and the available experimental results of different ceramic materials. So that the variation law of flow stress with temperature and strain rate can be well described by the presented model. In addition, compared with traditional models, the presented model has simpler form, clearer mechanism and fewer fitting parameters. Achievements of this paper can provide a foundation for the service stability and safety evaluation of ceramic materials.

In this study, the high-temperature corrosion behavior was evaluated for (La,Gd)₂Zr₂O₇ (LGZ) used as a promising thermal barrier coatings (TBCs) material. (La,Gd)₂Zr₂O₇ + YSZ multilayer prepared from atmospheric plasma spray (APS) were exposed to calcium-magnesium-alumino-silicate (CMAS) melt at 1300 °C for 2, 12, 48, and 100 h. Molten CMAS and (La,Gd)₂Zr₂O₇ reacted to form reaction layer Ca₂Gd₈(SiO₄)₆O₂ (apatite) at 1300 °C. The thickness of the reaction layer increased with increasing heat-treatment time. A correlation between the hardness and Young’s modulus relationship for the reaction layer of the coating was observed for the microstructure using nanoindentation. It was confirmed that the pores of the coating were reduced through the infiltration of molten CMAS in the initial stage of the corrosion reaction, and the hardness and Young’s modulus were increased due to densification. Fracture toughness increased with heat treatment time in both directions (in-plane and through-thickness). The fracture toughness in the in-plane direction is 0.19–0.23 MPa√m. On the other hand, the fracture resistance in the thickness direction was 0.87–1.26 MPa√m, which was higher than that in the in-plane direction. These results show that the crack propagates in the in-plane direction and causes TBC delamination.

We performed thermodynamic and phase-field (PF) simulations to investigate micropore formation mechanisms in a pseudo-binary system, B₂O₃–UO₂, during the solidification process. In the B₂O₃–UO₂, a solid UO₂ nucleation occurs in liquids below the melting point (T_m). As the temperature decreases further, a monotectic reaction (Liquid → S + Liquid#2) occurs below the monotectic temperature (T_mono ≈ 1845 K). Here, S and Liquid#2 denote the phases of solid UO₂ and second liquid containing low UO₂ concentration. This study calculated that the behaviors of the Liquid and S phases during the cooling process depended strongly on the cooling rates, leading to high vapor pressure of the liquid phase due to the low UO₂ concentration. The vapor pressure of liquid phase showed comparatively high values at high temperatures. In this PF simulation, the UO₂ concentration of the liquid phase decreased rapidly at 1838 K under a low cooling rate (β = 6 K/min). Therefore, the porosity was considered to increase by vaporization of the liquid. On the other hand, under a high cooling rate (β = 120 K/min), the porosity could be lower than under the low cooling rate condition because the UO₂ concentration decreased at lower temperature. The dependency between porosity and a cooling rate is consistent with Yusufu’s experimental results.

ZnO varistors are able to be successfully fabricated containing c-axis oriented fine grains of 2.5–2.8 µm for the first time, by using fine hexagonal templated ZnO. The crystalline orientation is clarified to have significant effects on the electrical behaviors of grain boundaries, even with low orientational degree (e.g., as Lotgering factor of 0.116). Break down voltage per a grain boundary (V_gb) and ε_r decrease by 16 and 5 % in perpendicular direction to the c-axis alignment from those in parallel, respectively. The control of crystal orientation has a possibility of leading to further advance in protection performance of ZnO-based multilayer varistors.

WO₃ epitaxial films with the same thickness and in-plane crystal grain size were prepared using pulsed laser deposition with various Si contents in the target to clarify the effect of Si addition to WO₃ on the gas sensing properties. X-ray diffraction measurements indicated that the films grown on the (1102) face of sapphire had a (001) orientation with in-plane epitaxial relationships of [110]WO₃//[0111] or [110]WO₃//[2110]Al₂O₃, regardless of the Si content. Scanning probe microscopy observations revealed that particles with a diameter of several tens of nanometers grow on the surface of the Si-doped WO₃ film. Measurements of the gas response to ethanol and acetone showed superior gas selectivity towards acetone gas at low temperatures, which is due to the catalytic effect of SiO_x particles on the film surface.

In this study, the gel-cast green bodies of alumina/graphite composites were fabricated using various epoxy monomers. The effects of the molecular structure of the monomers on the carbonization behavior and electrical conductivity of the reductively sintered bodies were systemically investigated. In the case of carbonization behavior under a temperature range of 300–700 °C, the amount of ether group in epoxy monomers exhibited influence on carbon residue amount. Moreover, carbonization of the multifunctional epoxy monomer induced fewer defects in the carbon network than carbonization of the bifunctional monomer. In addition, the graphitization characteristics of sintered bodies under 1600 °C correlated well with carbonization process. The relationship between carbonization/graphitization and the electrical properties of the sintered bodies is discussed in this paper.

Blue copper hydroxide was synthesized by adding aqueous ammonia or sodium hydroxide to copper chloride, copper nitrate, and copper sulfate solutions, and black copper oxide was produced by heat treatment after filtration. When excess sodium hydroxide was added to copper chloride, copper nitrate, and copper sulfate solutions, the precipitated blue copper hydroxide changed to black copper oxide over time. The effects of synthesis temperature, synthesis time, and excess sodium hydroxide on the spectral reflectance of the precipitated copper oxide in the visible and near-infrared regions were determined. Under optimum conditions, it was possible to synthesize black copper oxide (II) with a visible light region reflectance of less than 5 % and a near-infrared region reflectance of more than 70 %. This copper oxide can be applied to high solar reflective paints necessary for heat island measures.

Porous Mo–Al–Si–B ceramics were prepared by activation reaction sintering method utilizing Mo, Al, Si and B elemental particles as starting materials, and the pore forming mechanism of the porous materials with different Si contents was investigated by characterizing the phase constitution, volume expansion rate, pore structure and pore morphology. The results show that the volume expansion, porosity, maximum pore size and permeability of the porous ceramics tended to decrease and then increase with the addition of Si atomic ratio, and the volume expansion, overall porosity, maximum pore size and permeability reached the maximum values of 26.64, 56.21 %, 14.16 µm and 169.48 m³·m⁻²·kPa⁻¹·h⁻¹ at Si atomic ratio of 1.3, respectively. The phase components with different Si contents were characterized by X-ray diffraction (XRD), and the results showed that the phase constitution gradually changed from MoAlB to MoSi₂ as the Si atomic ratio increased. The pore forming mechanism of porous Mo–Al–Si–B was investigated, mainly: interstitial pores generated by the powder pressing process; contraction of the pore structure due to the surface tension of the Al–Si molten liquid phase; and pore forming by the Kirkendall effect caused by the partial diffusion of different solid-state atoms.

We have determined the crystal structure of Gd₈Ba₅Co₄O₂₁ by single-crystal X-ray diffraction and transmission electron microscopy (TEM). Gd₈Ba₅Co₄O₂₁ shows a tetragonal I4/m structure with a = 13.8982(3) Å and c = 5.76510(10) Å. This compound is isostructural with R₈Ba₅Ni₄O₂₁ (R = rare-earth ions) with two types of BaO₁₀, GdO₇ and CoO₅ polyhedra. Using scanning TEM, we directly observed the atomic arrangements of Gd₈Ba₅Co₄O₂₁, which was consistent with crystal structure analysis. Isolated CoO₅ square pyramids are placed with the relationship to 4-fold symmetry about the c-axis. Gd₈Ba₅Co₄O₂₁ has a similar local structure to R₂BaCoO₅ with a Y₂BaNiO₅-type structure. The first neighboring Co–Co atomic distances are shorter than those of R₂BaCoO₅ because of changes in the framework structure composed of RO₇ and CoO₅ polyhedra.