Mullite-based composites can be made by an in situ reaction process using silica-coated alumina (SCA) powder as a mullite precursor. In this paper we present the combined effects of zirconia and premullite seeds on the crystallization process and microstructure development. When zirconia is added without seeding, mullite formation proceeds through the formation of transient zircon. This phase provides a lower energy barrier for mullite nucleation and thus lowers the mullitization temperature. The presence of yttria as a stabilizer in zirconia reduces the activation energy for zircon formation and thus promotes the transient reaction. The addition of premullite seeds results in the nucleation of mullite from alumina and silica, and zircon does not form. At low seeding levels mullitization remains nucleation-controlled; however, once the seeding level exceeds 1–2%, this is no longer the case.
莫来石基复合材料可通过使用硅包覆氧化铝(SCA)粉末作为莫来石前驱体的原位反应过程制成。本文介绍了氧化锆和莫来石种子对结晶过程和微观结构发展的综合影响。在不添加锆石种子的情况下,莫来石的形成是通过瞬态锆石的形成进行的。这一阶段为莫来石成核提供了较低的能量障碍,从而降低了莫来石化温度。氧化锆中作为稳定剂的钇的存在降低了锆石形成的活化能,从而促进了瞬态反应。添加前莫来石种子会导致氧化铝和二氧化硅形成莫来石晶核,而锆石不会形成。在低添加量时,莫来石化仍受成核控制;但一旦添加量超过 1-2%,情况就不再如此。