Yusheng Ding

Effect of glycerine addition on the synthesis of boron carbide from condensed boric acid–polyvinyl alcohol precursor

Boron carbide (B4C) powder was synthesized by heating a gel precursor with pyrolysis and carbothermal processes. The gel precursor was prepared by the condensation reaction of boric acid (H3BO3) and polyvinyl alcohol (PVA) at a weight ratio of 1/2 with the addition of various amounts of glycerine. The effects of glycerine addition on the synthesis of B4C powder were studied. It was observed that glycerine could promote the condensation reaction and resulted in a pyrolyzed precursor with a much finer distribution of B2O3 in the carbon matrix. This led to a significant reduction of residual free carbon in the B4C powder. Moreover, the morphology of the B4C powder was also found to be closely related to the glycerine addition.

Preparation and Property of SiC/(ZrB 2 -SiC/SiC) 4 Anti-oxidation Coatings for C f /SiC Composites: Preparation and Property of SiC/(ZrB 2 -SiC/SiC) 4 Anti-oxidation Coatings for C f /SiC Composites

以Cf/SiC复合材料为基体,采用浆料浸涂法和脉冲CVD法制备了SiC/（ZrB2-SiC/SiC）4涂层,借助XRD、扫描电镜及能谱对涂层的结构及组成进行了分析研究,并初步考查了其高温抗氧化性能.结果表明,涂层总厚度约100μm,主要由ZrB2-SiC涂层与脉冲CVD SiC涂层交替覆盖而成.在1500℃空气中氧化25h,未涂层试样失重明显; 脉冲CVD SiC涂层试样氧化失重率为5.1%; 而SiC/（ZrB2-SiC/SiC）4涂层试样出现增重现象,增重率达2.5%,表现出优异的抗氧化性能.

Fabrication and Properties of Boron Carbide/Graphite Ceramic Pellets

Boron carbide (B4C)/graphite (C) ceramic pellets containing 25 wt% B4C as an ideal structural component in Chinese 10 MW high temperature gas-cooled test reactor (HTR-10) were successfully prepared by a two-stage operation method at low temperature. Initially, the samples were pressurelessly sintered at 1373 K and subsequently infiltrated with phenolic resin, pyrolysed at 1473 K, then coated with carbon by chemical vapour deposition at 1273 K. Morphology and structure of the samples were analysed by SEM and X-ray diffraction. The mechanical properties of the sintered bodies were also investigated. Superior properties were obtained due to the formation of pyrolytic carbon during the two-stage operation process. Density and compression strength of the samples were 1.94 g.cm–3 and 620 N, respectively. In addition, the rate of abrasion and moisture resistance were near zero for the samples.

Preparation of MoSi 2 -SiC-Si Coatings for C f /SiC Composites by in situ Reaction Method: Preparation of MoSi 2 -SiC-Si Coatings for C f /SiC Composites by in situ Reaction Method

以Cf/SiC复合材料为基体, 采用原位反应法制备了MoSi2-SiC-Si涂层, 借助XRD、扫描电镜及能谱对涂层的结构及组成进行了分析研究, 并考查了其高温抗氧化性能. 结果表明, 涂层总厚度约120μm, 主要由MoSi2、SiC和Si组成. MoSi2-SiC-Si涂层具有优异的高温抗氧化性能, 在1500℃静态空气中氧化96h, 涂层试样失重仅1.8%. 涂层试样失重的主要原因是由于氧气通过涂层中的贯穿性裂纹与Cf/SiC复合材料基体发生了反应.