The easy-going oxidation of silicon nitride (Si₃N₄) at high temperature greatly hampers its potential applications. Here, we explored the reaction mechanism between β-Si₃N₄ and O₂ via density functional theory (DFT) calculation, which discloses that O atoms are preferentially adsorbed on the top of Si atoms and N₂ starts to be generated as the dominant gas product at 2/3 monolayer (ML) O coverage. The vacancies formed by N₂ removal attract the O adatoms to transfer to the site of the N vacancy, which accelerates the adsorption of O and the formation of Si–O bonds toward the growth of SiO₂ product. The surface oxidation of β-Si₃N₄ (0001) has been clarified by the unambiguous evolution of [SiN_{4 -n}O_n] (n = 0-4) tetrahedrons going through from [SiN₄] tetrahedron to [SiO₄] tetrahedron, providing a deep insight into intrinsic oxidation process of Si₃N₄ ceramic.

Aluminum nitride (AlN) with a combination of very high thermal conductivity and excellent electrical insulation properties exhibits wide applications. However, it is quite sensitive to a moist environment and hydrolyzes slowly in water. In this work, density functional theory was adopted to examine the atomistic reaction mechanism on the wurtzite AlN(0001) surface. The results indicate that water molecules are preferentially adsorbed at the top site of the AlN(0001) surface. The decomposition of adsorbed H ₂ O into OH and H on the AlN(0001) surface occurs spontaneously without any energy barrier. However, a further dissociation reaction of OH into O and H has an energy barrier of 22.046 kcal/mol. The dissociation of H ₂ O is strongly dependent on the H ₂ O coverage when more water molecules are adsorbed. Ammonia (NH ₃ ) is determined as the dominant gas product at 4/9 monolayer H ₂ O coverage, which will induce N vacancy (V _N ) formation in AlN ceramic. The V _N will be occupied by O ^2- after geometry optimization and plays an acceleration role in the degradation of AlN by water. H ₂ O adsorption and the formation of NH ₃ occur alternately with the H ₂ O coverage increasing. An OH-Al-O layer is formed as a precursor of AlOOH after the first AlN bilayer is fully degraded. This work can guide the manufacture and application of AlN from the theoretical viewpoint.

In this paper, the fabrication and thermal conductivity (TC) of water-based nanofluids using boron (B)-doped SiC as dispersions are reported. Doping B into the β-SiC phase leads to the shrinkage of the SiC lattice due to the substitution of Si atoms (0.134 nm radius) by smaller B atoms (0.095 nm radius). The presence of B in the SiC phase also promotes crystallization and grain growth of obtained particles. The tailored crystal structure and morphology of B-doped SiC nanoparticles are beneficial for the TC improvement of the nanofluids by using them as dispersions. Using B-doped SiC nanoparticles as dispersions for nanofluids, a remarkable improvement in stability was achieved in SiC-B6 nanofluid at pH 11 by means of the Zeta potential measurement. By dispersing B-doped SiC nanoparticles in water-based fluids, the TC of the as-prepared nanofluids containing only 0.3 vol.% SiC-B6 nanoparticles is remarkably raised to 39.3% at 30 °C compared to the base fluids, and is further enhanced with the increased temperature. The main reasons for the improvement in TC of SiC-B6 nanofluids are more stable dispersion and intensive charge ions vibration around the surface of nanoparticles as well as the enhanced TC of the SiC-B dispersions.

Highly pure Al₄SiC₄ powders were prepared by carbothermic reduction at 2173 K using Al₂O₃, SiO₂, and graphite as raw materials. The obtained Al₄SiC₄ powders owned hexagonal plate-like grains with a diameter of about 200–300 μm and a thickness of about 2–6 μm. Based on the experimental results, the reaction of Al₄SiC₄ formation and grain evolution mechanisms were determined from thermodynamic and first-principles calculations. The results indicated that the synthesis of Al₄SiC₄ by the carbothermic reduction consisted of two parts, i.e., solid–solid reactions initially followed by complex gas–solid and gas–gas reactions. The grain growth mechanism of Al₄SiC₄ featured a two-dimensional nucleation and growth mechanism. The gas phases formed during the sintering process favored the preferential grain growth of (0010) and (1 ī0) planes resulting in formation of hexagonal plate-like Al₄SiC₄ grains.