Journal of Advanced Ceramics

Spherical AlN powders with micrometer size have attracted great attention owing to their good fluidity and dispersity. However, the industrial preparation methods usually require high temperature and long soaking time, which lead to the high cost and limit the wide application of the products. Herein, nearly spherical AlN particles with the average size of 2.5 µm were successfully synthesized via anin-situcombustion synthesis method. The effect of N₂pressure, NH₄Cl content, and Al particle size on the combustion reaction procedure, phase composition, and microstructure of the products was systematically investigated. The results showed that the decreased N₂pressure, increased NH₄Cl content, and Al particle size led to the decreasing of combustion temperature and speed, which further affected the morphology of the products. As a result, low N₂pressure (0.2 MPa), a small amount of NH₄Cl (0.5 wt%), and fine Al particles (∼2.5 µm) contributed to a moderate combustion temperature and facilitated the formation of nearly spherical AlN particles. In addition, based on the gas-releasing assisted quenching experiments and thermo-kinetic analysis, a two-step growth mechanism for the nearly spherical AlN particles was rationally proposed. The present method shows the advantages of low cost and high efficiency for preparing nearly spherical AlN particles, which can be used as raw materials for electronic substrates and fillers for packaging materials.

A novel single-source-precursor for SiC-TaC-C nanocomposites was successfully synthesized by the chemical reaction between a polycarbosilane (allylhydridopolycarbosilane, AHPCS) and tantalum(V) chloride (TaCl₅), which was confirmed by Fourier transform infrared spectra (FTIR) measurement. After pyrolysis of the resultant single-source-precursors at 900 °C, amorphous ceramic powders were obtained. The 900 °C ceramics were annealed at different temperatures in the range of 1200–1600 °C to gain SiC-TaC-C nanocomposites. The phase evolution of ceramic nanocomposites was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results indicate that the TaC starts to crystallize at lower temperature than the β-SiC. It is particularly worth pointing out that the unique core-shell structured TaC@C nanoparticles werein-situformed and homogeneously distributed in the ceramic matrix after annealing at 1400 °C. Even at a high temperature of 1600 °C, the grain sizes of β-SiC and TaC are smaller than 30 nm, fulfilling the definition of nanocomposites. The present study related to SiC-TaC-C nanocomposites paves a new road for enriching ultra-high temperature ceramic family suitable for structural/functional applications in harsh environment.

Severe volume expansion and inherently poor lithium ion transmission are two major problems of silicon anodes. To address these issues, we proposed a pomegranate-type Si/C composite anode with highly dispersed tiny silicon particles as the core assisted by small amount of SiC. Skillfully exploiting the high heat from magnesiothermic reduction, SiC can assist the good dispersion of silicon and provide good interface compatibility and chemical stability. The silicon anchored to the carbon shell provides multipoint contact mode, that together with the carbon shell frame, significantly promoting the transfer of dual charge. Besides, the pomegranate-type microcluster structure also improves the tap density of the electrode, reduces the direct contact area between active material and electrolyte, and enhances the electrochemical performance.

Multi-walled carbon nanotubes (MWCNTs) reinforced Si₂BC₃N ceramics were prepared through mechanical alloying (MA) and following spark plasma sintering (SPS). The thermal shock resistance of Si₂BC₃N ceramics was evaluated comparatively through ice water quenching test and theoretical prediction. Furthermore, the oxidation resistance of MWCNTs incorporated Si₂BC₃N ceramics was evaluated under high temperature. The results show that the calculated parameters such as the critical thermal shock temperature (R) and the thermal stresses resistance (R _st), as well as the toughness (R″″) are improved with addition of 1 vol% MWCNTs. In addition, the crack propagation resistance of 1 vol% MWCNTs incorporated Si₂BC₃N ceramics is obviously improved through generating more tortuous crack propagation paths attributing to the “crack bridging”, “pull-out”, and “crack deflection” mechanisms of MWCNTs. Therefore, the residual strengths of 1 vol% MWCNTs containing specimens remained the highest after the thermal shock tests. Besides, the present work also reveals that the oxidation resistance is more sensitive to relative density than MWCNTs addition.