镶嵌微晶镁铝尖晶石的铝酸钙水泥结合刚玉浇注料水化-脱水动力学和高温性能研究

As a key constituent part of refractory castables, the bonding system of calcium aluminate cement determines the physicochemical properties and service performance of refractory castables. Through optimizing design on phase composition and microstructure of calcium aluminate cement, the high temperature properties of refractory castables could be significantly improved. This project will study the synthesis and mosaic structure of calcium aluminate cements with microcrystal MgAl2O4 spinels. This accompanying mosaic microstructure between MgAl2O4 spinels and calcium aluminates will result in a homogeneous phase distribution in the micrometer region. During researching works, the corundum-based castables will be selected as the research sample template; the dynamics of hydration-dehydration for castables bonded by the new cement will be studied. The intrinsic relationships along the phase composition as well as their homogeneous distribution characteristics in micrometer region on castable rheological behavior, volume stability and strength will be investigated. The influence mechanism of phase reaction among dehydration products of castables matrix and mosaic structure of microcrystal MgAl2O4 spinels on hot strength and thermal shock resistance of castables will be revealed by theoretic analysis and tests. Furthermore, its effect regulation on crack's self-repairing mechanism of castables will also be illustrated. The significant improvement mechanism of corrosion resistance for castables due to the mosaic structure formation of MgAl2O4 spinels and its homogeneous distribution characteristics within cement phases in micrometer region will be explained. The relativity among cement with mosaic structure, microstructure evolution of castables and their high temperature properties will be established. The results of this research work will enrich the theory of microstructure design and performance optimization for refractory castables.

铝酸钙水泥作为耐火浇注料的结合系统决定着浇注料的物理、化学及服役性能，是浇注料的关键组成部分。通过对铝酸钙水泥相组成和微结构的优化设计，可显著改善耐火浇注料的高温性能。本项目将研究具有镶嵌状微晶镁铝尖晶石的铝酸钙水泥的合成，得到尖晶石和铝酸钙物相的伴生镶嵌结构，实现微米区域上物相间的均匀分布。项目将以刚玉浇注料为研究对象，通过这种新型水泥结合浇注料水化-脱水动力学研究，构建水泥相组成和物相间微区均匀分布与浇注料流变学行为、体积稳定性、强度等性能的内在联系；探明浇注料基质中脱水产物间物相反应和镶嵌状微晶尖晶石对浇注料高温强度和热震稳定性的影响机制，揭示其对浇注料中裂纹自修复机理的作用规律；阐明高温下具有镶嵌结构的镁铝尖晶石和物相间微区均匀分布对浇注料抗渣侵蚀性的显著改善机理；在水泥镶嵌状结构、浇注料显微结构演化和高温性能之间建立相关性。相关研究成果可丰富耐火浇注料的微结构设计和性能优化理论。

刚玉尖晶石浇注料以其优良的抗热震性及抗渣性能而得到广泛应用。然而，刚玉尖晶石浇注料在实际应用过程中仍存在一些问题，例如外加尖晶石价格较高且难以分散、原位尖晶石的形成伴随较大体积膨胀等。本项目合成了含有微晶尖晶石的SP-CA水泥，并作为结合剂在浇注料中引入尖晶石，研究了微晶尖晶石的存在对浇注料高温性能的影响，取得以下结论：（1）SP-CA水泥中所含有的尖晶石可以促进水泥的水化，且尖晶石晶粒越小，对水化的促进作用越明显。其促进水化的主要作用机理为亚微米尺寸的尖晶石因为表面电离而带有正电荷，可以促进带有负电荷的水泥水化产物晶核在尖晶石表面的产生，从而促进水泥的水化进程。（2）SP-CA水泥水化机理遵循晶核长大-扩散(NG-D)机制。水化前期由成核结晶与晶体长大过程(NG)控制，随着水化程度提高，逐渐转由扩散过程(D)控制。与CAC水泥相比，SP-CA水泥水化加速期反应速率较快，减速期及稳定期反应速率较慢。（3）经1500℃热处理后，亚微米尺寸的尖晶石颗粒可以连接Al2O3颗粒和CA6，增强了基质的强度，使得浇注料试样经1500℃热处理后试样强度显著增加；亚微米尖晶石的存在会细化浇注料的孔隙，使平均气孔从2μm降低至0.5μm，XFEM分析显示较小的孔隙可以有效预防应力集中，同时可以阻碍裂纹的扩展从而可以提高材料的抗热震性能。（4）亚微米尺寸的尖晶石可均匀分散在基质中，形成一个可以有效吸收钢渣中金属离子的三维尖晶石网络结构，提高了试样的抗渣侵蚀性能。（5）探究了高温热处理过程中试样弹性模量与显微结构之间的相互关系。浇注料试样的弹性模量随温度变化的趋势可分为七个阶段。依次为轻微脱水阶段、C3AH6分解阶段、平稳阶段、CA生成阶段、CA2生成阶段、致密化阶段、CA6生成阶段。