杂质缺陷诱导阿利特晶胞常数的改变及多晶转变

阿利特或硅酸三钙,(C3S)固溶体是水泥熟料中最重要的矿物,某些杂质离子可以稳定其多晶型中的三方R型,具有较高的水化活性.杂质离子固溶进入C3S晶格,形成杂质缺陷,这些缺陷引起C3S晶格常数的变化.研究显示:C3S晶格常数的变化与其对称性有关,从而提出了-种由杂质缺陷引起晶格常数相对变化的计算方法,用于预测C3S固溶体和阿利特可能的稳定晶型.在实验室合成了不同掺杂的C3S固溶体单矿物,并从实验熟料中萃取了阿利特.对样品晶型进行X射线衍射(X-ray diffraction,XRD)测定及晶格常数相对变化计算的预测.计算预测结果和XRD分析结果之间较好相符.XRD分析表明:纯C3S的对称性最差,属于三斜晶系.当C3S中P2O5固溶量在0.4%(质量分数,下同)时,C3S固溶体为单斜M1型.当CaF2掺量在1.0%时,C3S固溶体也为M1型.当CaF2掺量提高到2.0%时,C3S固溶体是R型.复合掺加氟磷对改变C3S固溶体对称性有显著作用,只要掺杂0.4%的P2O5和0.7%的CaF2即可使R型C3S固溶体在室温下稳定.对熟料中萃取阿利特的分析表明:普通熟料中萃取阿利特的稳定晶型属于Mi型;含氟磷的熟料中阿利特是以R型为主的R型和M3型的混合体.分析结果验证了计算预测结果.

CRYSTAL LATTICE CONSTANT CHANGE AND POLYMORPH OF ALITE CAUSED BY IMPURITY DEFECTS

Alite or solid solution of Ca_3SiO_3 (C_3S) is a very important mineral in portland clinker. The rhombohedral pattern R of alite stabilized by certain impure ions is more hydrated. The impure ions form defects in the C_3S crystal lattice. The defects can induce change in the crystal lattice constant. Calculations and tests indicate that the symmetry of C_3S is related to the change in crystal lattice constant. Thus, a method for calculating the crystal lattice constant change brought about by doping ions was suggested. With the calculation results, the possible polymorphs of C_3S solid solution can be estimated. Pure C_3S was synthesized and C_3S solid solutions that contain certain ions were prepared. Alites were extracted from experimental clinkers. The polymorphs of the samples were examined by X-ray diffraction (XRD) and deduced with the calculations of the crystal lattice constant changes. The calculation results are coordinated with the XRD testing results. The results show that pure C_3S had the lowest symmetry and had a triclinic form. The polymorph of C_3S solid solution has a monoclinic M_1 form when doped with P_2O_5 0.4% (in mass fraction, the same below). If the contents of CaF_2 in C_3S are 1.0%, the crystal form of C_3S is also M_1. And the rhombohedral form R of C_ 3S solid solution is stabilized with 2.0% CaF_2 doping. With complex doping of P_2O_5 and CaF_2, the symmetry of C_3S solid solution can be improved remarkably. By adding 0.4% P_2O_5 and 0.7% CaF_2 into C_3S, the R form is stabilized. The extracted alite from the experimental clinker doped with P_2O_5 and CaF_2 is an admixture of R and M_3 form, and the alite from the ordinary clinker is M_1 polymorph. The XRD results conform to the predictions from calculations.