外来离子对硅酸三钙原位高温结构相变及性能的影响研究

The total amount of bulk cement in China has consecutively ranked first in the world over the past 20 years. The tricalcium silicate (C3S) solid solutions known as alites are the principle phase of clinker, responsible for strength development. The content of C3S is approximately to 110 million tons in 2012. Therefore, it is important to study the effect of foreign ions doping on the phase transition and property of C3S for the production of hydraulically favorable polymorphs. This is the key to improve the hydraulic property of clinker and realize energy conservation and emission reduction. In our recent study, the stabilization rule of different C3S polymorphs by the incorporation of foreign ions has been established. It is believed that some rule can also be extracted from the effect of foreign ions on the phase transitions. However, the effect of foreign ions on the phase transitions is unclear. Interestingly, maxima reactivity had been reported to be approached corresponding approximately to phase transitions point, which is also not fully understood. In view of the limitation of traditional research methods on experimental techniques and evaluation, in this project, the structural phase transition of C3S and its solid solutions will be studied by real time in-situ technique. The structural changes will be mainly monitored by the in-situ high temperature x-ray diffraction (18kW) we owned, and analysed using Rietveld method. An attempt will be made to study the regular effect of foreign ions on the phase transition and superstructure. The relationship between foreign ions doping,structural phase transition, polymorphism and the property of C3S will be discussed. The method to product hydraulically favorable polymorphs will be established. The results can enrich the basic theory of cement clinker chemistry, and lay a theoretical foundation for improving the quality control of Portland cement clinker production.

我国水泥产量连续20多年稳居世界第一。硅酸三钙(C3S)的固溶体阿利特是硅酸盐水泥熟料的最主要胶凝相，粗略估算仅2012年C3S量就达11亿吨。不同晶型C3S胶凝性能存在差异，并显著影响熟料强度性能。因此，研究掺杂C3S相变过程及性能，对提高熟料性能，实现水泥工业节能减排具有重要意义。近来，申请人发现外来离子对C3S多晶态稳定作用依离子化学结构变化存在规律性，并推测离子对C3S相变过程影响同样存在规律性。但目前，离子对C3S相变过程影响尚不明确，且掺量达晶型转变点时C3S高活性现象，也尚未被理解。本项目针对传统研究方法的不足，采用本室拥有的18kW高温衍射仪结合Rietveld方法等，研究不同离子对结构相变的影响规律及机制，探讨离子固溶、结构相变，C3S晶体结构与性能间相互影响关系，确立获得高胶凝C3S的方法。研究成果有助于丰富水泥熟料化学应用基础理论，为提高水泥熟料强度性能提供理论基础。

我国是世界上水泥产量最多的国家，水泥产量连续20多年稳居世界第一。研究水泥熟料最主要矿相硅酸三钙( C3S)相变过程及性能，对提高熟料性能，实现水泥工业节能减排具有重要意义。项目从研究不同离子掺杂对C3S相变特性及其结构参数变化影响入手，结合不同晶型C3S结构及其差异的研究，理解了不同晶型C3S结构转变关系及机制，阐明了离子固溶对结构相变的影响规律及机制；揭示了离子固溶、C3S晶型与亚稳能量储藏和水化性能之间的相互影响关系，探讨了C3S晶相转变点高活性的本质。研究表明，C3S受热相变过程、晶型转变数目主要取决于其室温所稳定的晶型。不同离子固溶均可以降低C3S相变温度。离子固溶所致的相变潜热的减少主要与其固溶所形成的Ca或O空位有关。在T1和T2晶型硅酸三钙中SiO4四面体结构严重扭曲畸变，偏离正四面体对称性。自T3晶型开始以上的高对称晶型中，SiO4四面体基本达到正四面体对称结构。由R晶型向单斜晶型转变主要通过SiO4四面体的取向改变。由单斜向三斜晶型转变，主要源于SiO4四面体的取向和Ca原子位置的改变。而T3晶型向T2 的转变除与SiO4四面体取向改变有关外，还涵盖了SiO4四面体自身结构的扭曲畸变，另外进一步向T1晶型转变还可能包含了Ca原子位置的变动。离子固溶通过增大C3S晶格扭曲畸变程度，阻碍原子位移型相变，从而实现稳定不同高温晶型。从热力学上看，C3S水化活性取决于结构介稳性（晶型）和其能量介稳性（亚稳储藏能量）。准同型相界适用于C3S。在多离子组合作用下，掺磷有利于稳定高胶凝性R型阿利特，显著提高阿利特强度。项目成果极大丰富了水泥熟料化学应用基础理论，并为通过调控阿利特晶型实现水泥性能提高提供了基础理论依据和技术支撑，同时也可为深入理解水化反应过程提供了重要的科学依据。