溶胶-凝胶、微波熔盐法低温制备ZrB2-SiC超细复合粉体

With the development of aerospace and energy, ultra-high temperature ceramics (UHTCs) are urgently required. ZrB2-SiC ceramics are thought as one of the most potential strategic ultra-high temperature materials with the excellent performances of high melting point, high thermal conductivity and high oxidation resistance in high temperature range. However, SiC was generally introduced to ZrB2 powders by mechanical mixing before sintering process. Therefore, the distribution of SiC in the matrix is restricted. Additionally, the big grain sizes of ZrB2-SiC and high content of impurity reduce the sintering activity. Subsequently, it is difficult to prepare ZrB2-SiC composites with high mechanical performance at a relatively low temperature. The best way to solve the problem is using the ultrafine ZrB2-SiC composite powders with high purity and uniform dispersion as raw material. Therefore, the present research project aims to fabricate ultrafine ZrB2-SiC mixture powders with small particle size, good dispersion property and high oxidation resistance in high temperature by microwave-assisted molten salt method in low temperature. The following investigations will be carried out in the project: (1) The effect of preparation parameters on the fabrication of ultrafine ZrB2-SiC composite powders; (2) The investigation of the synthesis mechanism of the ultrafine ZrB2-SiC composite powders, the tailor of the crystalline phases, the particle morphology and the particle size distribution in final products, and the relationship between the viscosity and surface tension of molten salt and the morphology and dispersion of the resulted ultrafine ZrB2-SiC composite powders; (3) The study of the microstructure characterizing, sintering ability and oxide resistance of the final ultrafine ZrB2-SiC composite powders. The results of this investigation will provide theoretical basis for low temperature and high efficiency preparation of ZrB2-SiC composite powders using microwave-assisted molten salt method.

航空航天、能源等高科技领域的发展对超高温陶瓷材料提出了迫切要求。ZrB2-SiC复相陶瓷具有高熔点、高热导率和优良的高温抗氧化性，是最具前途的超高温材料之一。通常采用机械混合ZrB2、SiC两种粉体再经高温烧结制备ZrB2-SiC复相陶瓷，该方法存在粉体混合不均的缺点，影响粉体的烧结性能及复相陶瓷的高温使用性能。鉴于此，本项目拟采用溶胶-凝胶法制备前驱体、再经微波加热熔盐（微波熔盐）法在低温下制备高纯、均匀的ZrB2-SiC超细复合粉体。主要研究：1）微波熔盐法制备ZrB2-SiC超细复合粉体的方法；2）微波熔盐法制备ZrB2-SiC超细复合粉体的合成机理，相成分、形貌及粒度分布的调控，熔盐的表面张力及粘度对复合粉体微观形貌等的影响等；3）ZrB2-SiC超细复合粉体的结构表征、烧结性能及抗氧化性的研究。通过本项目的研究为ZrB2-SiC超细复合粉体的低温、高效制备提供应用基础理论依据。

航空航天、能源等高科技领域的发展对超高温陶瓷材料提出了迫切要求。ZrB2-SiC复相陶瓷具有高熔点、高热导率和优良的高温抗氧化性，是超高温材料领域最具前途的材料之一。通常采用机械混合ZrB2、SiC两种粉体再经高温烧结制备ZrB2-SiC复相陶瓷，该方法易在前期的机械混合过程中引入杂质且混合不均匀，严重影响粉体的烧结性能及复相陶瓷的高温使用性能。鉴于此，本项目开展了如下研究：1）熔盐法低温合成ZrB2-SiC复合粉体； 2）溶胶-凝胶、熔盐法常规加热制备ZrB2-SiC复合粉体；3）溶胶-凝胶、微波熔盐法制备ZrB2-SiC复合粉体；4）ZrB2-SiC复合粉体抗氧化性能研究。得到如下结论：1）采用熔盐法合成ZrB2-SiC复合粉体的最佳配方条件是锆/硅摩尔比为1:1，B2O3加入量为120 wt%、活性炭加入量为120 wt%以及Mg粉加入量为150 wt%，最佳热处理条件是1200℃保温1 h，制备的ZrB2-SiC复合粉体颗粒细小，粒径在0.5μm左右，但粉体颗粒易团聚；2）采用溶胶-凝胶、熔盐结合常规加热的方法很难制备纯相的ZrB2-SiC复合粉体；3）采用溶胶-凝胶、微波熔盐法合成ZrB2-SiC复合粉体的最佳配方条件是硼加入量为180 wt%、炭加入量为100 wt%、熔盐/反应物质量比为1:1、Mg粉加入量与（ZrO2+SiO2）质量相同，最佳热处理条件是1250℃保温0.5 h，合成的纯相ZrB2-SiC复合粉体粒径在10μm左右，但易团聚；4）在ZrB2中引入第二项SiC使其表观氧化活化能由326 kJ•mol-1提高到380 kJ•mol-1。本项目制备的纯相ZrB2-SiC复合粉体颗粒细小，ZrB2、SiC两相分布均匀，有利于后续制备性能优良的ZrB2-SiC复合陶瓷材料。