Wanli Yang

Growth of Flower-Like AIN by Combustion Synthesis Assisted with Mechanical Activation

Flower-like AlN microstructure with many cone-like petals was prepared by combustion synthesis assisted with a mechanical activation (MA) method using NH4Cl as a reacting additive. The products were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive spectrum (EDS) and transmission electron microscopy (TEM). A possible mechanism for the growth of AlN microflowers was proposed base on several parallel experiments and discussion. It was found that both the MA time and NH4Cl content play crucial roles for the growth of the flower-like microstructure.

Effect of Oxide Additives on Catalysis and Microstructure of RBSN Using Low-Purity Silicon Powder as Raw Materials

The three kind of oxides such as 3Y-ZrO2, Fe2O3 and MgO were used as catalyst in reaction bonded silicon nitride (RBSN) with low-purity silicon powder as raw materials. The oxides can strongly promoted the nitridation ratio of RBSN, and the catalysis effects of these oxides for RBSN were investigated. After 4h nitridation, the degree of nitridation increased from 43% to 96% by adding 10wt% of 3Y-ZrO2 additive comparing with the sample without additive, and the catalystic effects of Fe2O3 and MgO were slightly less than 3Y-ZrO2 additive. XRD patterns revealed that the main phases of the reaction products were α-Si3N4, β-Si3N4 and Si-N-O intermediation. SEM micrographs show that the hexagonal columnar β-Si3N4 separated from acicular α-Si3N4.

Effects of Impregnating and Heat Treatment on the Oxidation and Thermal Shock Properties of Pressureless Sintered SiC/Graphite Composites

SiC/0~20% graphite (volume fraction) composites were successfully fabricated by pressureless sintering at 1700 °C for 2 h in nitrogen atmosphere. The impregnating and heat treatment process for the samples with silica sol/phenolic impregnant was carried out at 1450 °C for 2 h in nitrogen atmosphere. The Vickers hardness, oxidation resistance and thermal shock property of the composites before and after treatment were tested, and the microstructure and phase composition were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results shown that the Vickers hardness of SiC/20% graphite was increased from 3.35 GPa to 4.90 GPa by heat treatment, and the oxidation resistance and thermal shock property of the heat treated samples were also improved significantly. The SEM and XRD results revealed that the formation of new SiC particles by the reaction of silica sol and phenolic was the main reason for the mechanical properties improvements.