微波熔盐氮化法合成α-Si3N4粉体及反应机理研究

Silicon nitride and its composite materials with excellent properties are widely used in mechanical, electrical/optical devices, refractory materials and other fields. The synthesis of α-Si3N4 with single phase and fine grain is the key process for fabricating high quality and high performance silicon nitride ceramics. The conventional methods for the preparation of Si3N4 powders suffer from several disadvantages, such as low alpha phase content, large particle size and uneven distribution, which play great negativing effects on the enhancement of the properties of silicon nitride ceramics. To overcome these drawbacks, a novel low temperature microwave-assisted molten salt nitridation technique was developed in this project to prepare single-phase α-Si3N4 superfine powders. The project will focus on: 1) microwave-assisted molten salt synthesis of α-Si3N4 powders and preparation conditions optimization; 2) clarification of nucleation and growth mechanism of α-Si3N4 in the molten salt mediate; 3) establishment of the relationship between microstructure and physical properties of alkali metal molten salts systems, and the influence of dissolution behavior of reactants on the preparation of α-Si3N4; 4) simulation of the microstructure model of molten salt reaction system by first-principles molecular dynamics and illumination of the reaction mechanism of α-Si3N4. Based on the research work, the basic theory on the formation of theoretical bases for selection of molten salt and precise control of product phase composition and microstructure will be elucidated. And the work will not only have important academic but also industrial significance.

氮化硅陶瓷及其复合材料作为一种性能优异的功能材料，在机械、电学/光学器件、耐火材料等多种领域内有广泛的应用。单相、细晶α-Si3N4粉体的合成是制备高性能的氮化硅陶瓷的关键，而目前合成方法制备的α-Si3N4粉体普遍存在着纯度低、α相含量不高、粒径大、且粒度分布不均匀等的缺点，严重制约了氮化硅陶瓷制品性能的提升。鉴于此，本课题拟采用微波熔盐氮化法低温合成单相α-Si3N4超细粉体。重点研究，1) 微波熔盐氮化法合成α-Si3N4的工艺因素；2) 熔盐条件下α-Si3N4形核与生长机理；3) 碱金属熔盐体系的微观结构、熔盐物性与反应物溶解行为的相关性；4) 熔盐反应体系微观结构模型的建立及α-Si3N4的反应生成机理等。相关研究成果对熔盐法低温合成非氧化物陶瓷粉体技术的发展及非氧化物陶瓷粉体显微结构的控制具有理论指导及借鉴意义。

氮化硅及非金属氮化物材料作为一类性能优异的功能材料，在机械、电学/光学器件、耐火材料等多种领域内有广泛的应用。然而，目前的氮化物制备方法普遍存在着操作过程复杂、反应温度高及产物纯度低等难以克服的缺点。熔盐法是一种简单易行、重复性高的无机材料粉体制备方法，具有合成温度低、反应时间短、合成粉体的纯度高及粒径小等优点。鉴于此，项目采用熔盐法制备氮化碳、氮化铝、氮化硼和硼碳氮粉体，研究了熔盐种类、反应温度及反应时间等工艺条件对粉体合成过程的影响。研究结果表明，熔盐提供了液相反应介质，有利于反应物的扩散和氮化反应的进行，同时作为模板调控产物形貌。熔盐氮化法合成的氮化硅为单相六方状α-Si3N4纳米片，粒径约170 nm，厚度1~4 nm；采用熔盐法合成了四方管状氮化碳（TCNTs）粉体，其长度约为2~20 μm，宽度及高度约为50~2000 nm，具有较高的杂质氮含量、独特的一维中空结构和较大的比表面积，与体相的氮化碳相比，所制备的TCNTs的光催化性能和吸附性能更加优异；熔盐法合成氮化硼的粒径随熔盐/反应物质量比的增加而减小，当熔盐/反应物质量比增加至15:1时，产物为几层厚的氮化硼纳米片，厚度约为1 nm；熔盐中合成了纳米片状BCN，BC0.4N试样的片状厚度约为10 nm，其比表面积最高为484 m2/g，对亚甲基蓝具有优良的吸附性能。相关研究成果为熔盐法合成非金属氮化物陶瓷粉体在熔盐的选择、产物相组成和显微结构的精确控制方面奠定理论基础，对低温合成粉体技术的成分结构设计、生产工艺的优化以及应用技术具有理论指导及借鉴意义。