Journal of the American Ceramic Society最新文献

The K₂O·nSiO₂ laminated anti-fire and thermal-insulation glass was prepared by a new low-temperature in situ pre-reaction method using the high-solid content (55 wt%) and low-viscosity (16.5 ± 0.1 mPa s (500 1/s)) SiO₂ sol. This method favored the preservation of the K₂O·nSiO₂ precursor for a long time at low-temperature environment, which promoted industrialized production. In this article, dynamics of in situ reaction, subsidence kinetics, failure characteristics, and mechanism at low temperatures and anti-fire and thermal-insulation mechanism were analyzed in detail. The curing reaction of the K₂O·nSiO₂ precursor was a first-order reaction with a reaction rate constant k_T = 8.38 × 10⁷ exp(−75.1 × 10³/(RT)). The hardness, low-temperature, ultraviolet-resistance, and thermal-insulation performances were systematically characterized. The steel ball method was used to study the hardness of materials. The differential scanning calorimeter revealed the relationship between the low-temperature performance of materials at the microscopic level and their freezable water content. And combined with liquid nitrogen-assisted cryogenic imaging technology (LNACIT) to observe ice-crystal growth, it revealed the failure characteristics and mechanism at low temperatures. The microporous structure that enhanced thermal-insulation performance by prolonging heat transfer was clearly revealed in SEM. This work provided new approaches to improve reliability and safety of K₂O·nSiO₂ material in extreme environments.

Interdiffusion of Zr and Hf in the diboride system was investigated. High-purity zirconium diboride (ZrB₂) and hafnium diboride (HfB₂) were prepared by a combination of boro-/carbothermal reduction synthesis and densification by spark plasma sintering. The bulk ceramics had relative densities of 99.3% for ZrB₂ and 99.7% for HfB₂, and both ceramics were phase-pure by x-ray diffraction analysis. Diffusion couples of ZrB₂ and HfB₂ were annealed at temperatures ranging from 2000°C to 2200°C for times from 4 to 12 h. Zr and Hf elemental concentration profiles were measured using energy dispersive spectroscopy and analyzed using an algorithm based on a Boltzmann transformation of Fick's second law. The interdiffusion coefficients increased as the annealing temperature elevated, which indicates that the interdiffusion was a thermally activated process. The diffusion rate of Hf in ZrB₂ is smaller than that of Zr in HfB₂ due to the larger atomic mass and stronger bonding strength.

The K₂O·nSiO₂ laminated anti-fire and thermal-insulation glass was prepared by a new low-temperature in situ pre-reaction method using the high-solid content (55 wt%) and low-viscosity (16.5 ± 0.1 mPa s (500 1/s)) SiO₂ sol. This method favored the preservation of the K₂O·nSiO₂ precursor for a long time at low-temperature environment, which promoted industrialized production. In this article, dynamics of in situ reaction, subsidence kinetics, failure characteristics, and mechanism at low temperatures and anti-fire and thermal-insulation mechanism were analyzed in detail. The curing reaction of the K₂O·nSiO₂ precursor was a first-order reaction with a reaction rate constant k_T = 8.38 × 10⁷ exp(−75.1 × 10³/(RT)). The hardness, low-temperature, ultraviolet-resistance, and thermal-insulation performances were systematically characterized. The steel ball method was used to study the hardness of materials. The differential scanning calorimeter revealed the relationship between the low-temperature performance of materials at the microscopic level and their freezable water content. And combined with liquid nitrogen-assisted cryogenic imaging technology (LNACIT) to observe ice-crystal growth, it revealed the failure characteristics and mechanism at low temperatures. The microporous structure that enhanced thermal-insulation performance by prolonging heat transfer was clearly revealed in SEM. This work provided new approaches to improve reliability and safety of K₂O·nSiO₂ material in extreme environments.

Without using any organic additive, zircon-type (space group I4₁/amd) (Lu_1−xSc_x)_0.99VO₄:0.01Bi³⁺ (x = 0−1, 0.1 interval) nano/microcrystals were successfully synthesized via a hydrothermal reaction at 180°C for 24 h. The products were systematically characterized via XRD, FE-SEM, TEM, elemental mapping, and optical spectroscopy to investigate the effects of Sc³⁺ doping on crystal structure, morphology, and luminescent properties. It was found that with the substitution of Lu³⁺ by Sc³⁺, the products gradually transformed from LuVO₄:Bi³⁺ nanocrystals into highly anisotropic ScVO₄:Bi³⁺ microrods preferentially growing up along the [001] direction. The peak wavelength of both excitation and emission almost linearly increased with decreasing cell volume, accompanied by band broadening, which was rationalized by considering crystal field splitting energy (Dq), character of the chemical bond (nephelauxetic effect) and metal to metal charge transfer (MMCT) energy. This finely tunable broadband emission (center wavelength 581−639 nm, FWHM >175 nm) enables the materials to supplement multicolor components, presenting potential for application in phosphor-converted white light-emitting diode (pc-WLED) and others.

High-entropy engineering has emerged as a transformative strategy to enhance the functional properties of ceramic materials. In this study, we synthesized and systematically evaluated high-entropy TiO₂-based ceramics, [Ta_0.5(In_0.2Tm_0.2Gd_0.2Ga_0.2La_0.2)_0.5]_xTi_1‒xO₂ (x = 0.5%, 1%, 2%, 3%), incorporating multiple donor‒acceptor cation pairs to achieve synergistic improvements. The optimized composition exhibited an extraordinary dielectric constant of ∼2.7 × 10⁴, ultra-low dielectric loss of 0.007 at 1 kHz, and exceptional thermal stability across a wide temperature range. These outstanding properties are attributed to the interplay of internal barrier layer capacitance and electron-pinned defect dipole effects. Additionally, high-entropy engineering introduced significant lattice distortions, resulting in a 109% increase in Vickers hardness compared to undoped TiO₂. First-principle calculations demonstrate that high-entropy doping with trivalent–pentavalent ion pairs in rutile TiO₂ stabilizes multiple defect configurations. This work highlights the potential of high-entropy engineering as a robust tool for advancing TiO₂-based dielectric ceramics, while establishing a solid foundation for material innovations.

The simplified regular interface has a significant difference from the actual morphology, and a part of the extracted actual interface has randomness. The simulation results obtained from the above two interface models are difficult to apply to the improvement of thermal barrier coatings (TBCs) preparation technology. To solve the problem, the exponential autocorrelation function, AR digital filtering technique, Johnson transformation system, and Genetic Algorithm are applied to establish TBCs non-Gaussian rough interface model. The submodel method is applied to carry out multi-scale thermal cycling simulations of the TBCs. Non-Gaussian rough interface stress distribution states are analyzed, and the anomalous damage mechanism in which the TBCs’ life increases with increasing roughness is elucidated. Finally, the effects of roughness, contour slope, root mean square, skewness, and kurtosis on the strength and life of TBCs are analyzed. The results show that the stress extremes at the non-Gaussian rough interfaces of TBCs are affected not only by roughness, but also by kurtosis of non-Gaussian morphology parameters. The anomalous damage mechanism can be explained by the decrease in the non-Gaussian rough interface mean equivalent strain range with increasing roughness. The root mean square slope exhibits a more significant impact on TBCs’ life than roughness. Furthermore, a strategy combining increased roughness with decreased kurtosis offers a viable pathway to surpass current fatigue life limits. The conclusions can guide the improvement of preparation techniques to enhance the service life of TBCs.

HfC_xN_y solid solution powders were synthesized by combustion synthesis using Hf and carbon black as reactants, with HfC or HfN as diluents under a nitrogen atmosphere. The effects of processing parameters on phase compositions and microstructures were systematically examined, and the reaction mechanism in the combustion synthesis of HfC_xN_y was elucidated. The results demonstrated that both phase compositions and microstructures were strongly dependent on the processing parameters. For undiluted samples with high Hf/C molar ratio and diluted samples with low HfC content, the microstructure featured HfC_xN_y crystals embedded in the unreacted molten Hf. At moderate HfC contents, HfO₂ formed and replaced molten Hf as the bonding phase. At high HfC contents, the microstructure evolved into agglomerates composed of HfC_xN_y crystals. In contrast, the introduction of HfN as a diluent led to more complex phase compositions. Based on thermodynamic calculations and experimental characterization, four reaction pathways for the formation of the HfC_xN_y solid solution have been proposed. In path 1, HfC_xN_y crystals are directly precipitated from Hf-C-N melt. In path 2, HfC crystals precipitate from Hf-C melt, followed by the formation of HfC_xN_y phase through the reaction between HfC and N₂. In path 3, HfC_xN_y phase forms through a solid-state reaction between HfC and HfN. In path 4, HfC_xN_y phase forms via a solid-state reaction between HfN and C. This study provides mechanistic insight into HfC_xN_y formation in combustion synthesis and offers guidance for tailoring high-quality powder.