Formation and transformation of five different phases in the CaSO4-H2O system:: Crystal structure of the subhydrate β-CaSO4•0.5H2O and soluble anhydrite CaSO4
Formation and transformation of five different phases in the CaSO4-H2O system:: Crystal structure of the subhydrate β-CaSO4•0.5H2O and soluble anhydrite CaSO4
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DOI：
10.1021/cm7027542
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发表时间：
2008-03-25
影响因子：
8.6
通讯作者：
Jensen, Torben R.
中科院分区：
文献类型：
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作者：
Christensen, Axel Norlund;Olesen, Maja;Jensen, Torben R.
在CaSO_4-H_2 O体系中至少存在五种晶相，即石膏型CaSO_4中心点2 H（2）O，亚水化型α-和β-CaSO_4中心点0.5H（2）O，可溶和不溶性硬石膏型CaSO_4。本研究利用同步辐射X射线衍射技术（SR-PXD）原位时间分辨研究了CaSO 4-H2O体系中这五种相的形成及其转变过程。此外，还提出了β-CaSO_4中心点0.5H（2）O和可溶性硬石膏CaSO_4的修正结构模型。在25 ℃下研究了α-CaSO 4中心点0.5H（2）O的水合作用，结果表明，在混合两种反应物后立即开始与H2O反应，CaSO 4中心点2 H（2）O的形成与α-CaSO 4中心点0.5H（2）O的耗尽相关联。在25-500 ℃范围内研究了CaSO_4中心点2 H（2）O的热分解，结果表明，α-CaSO_4中心点0.5H（2）O的形成，随后形成可溶性硬石膏AIII-CaSO_4，其逐渐转化为不溶性硬石膏AII-CaSO_4。在25-500 ℃的温度范围内研究了α-CaSO 4中心点0.5D（2）O的热分解，并显示出连续相变为β-CaSO 4中心点0.5D（2）O、可溶性硬石膏AIII-CaSO 4和不溶性硬石膏AII-CaSO 4。在200-500 ℃的研究温度范围内，硬石膏的两种多晶型物共存。使用1 M HNO 3或1 M LiCl溶液在25-200 ℃的温度范围内研究CaSO 4中心点2 H（2）O的水热分解，并且在两个实验中，CaSO 4中心点2 H（2）O转化为α-CaSO 4中心点0.5H（2）O，并进一步转化为不溶性硬石膏AII-CaSO 4。根据SR-PXD数据，提出了β-CaSO_4中心点0.5H（2）O的结构模型，其晶胞为三角晶系（六方晶系），a = 6.93145（3），c = 12.73617（4），Z = 6，空间群P3（1）.根据粉末中子衍射数据，提出了可溶性硬石膏AIII-CaSO_4的结构模型，其六方晶胞参数为a = 6.9687（1），c = 6.3004（1），Z = 3，空间群为P6（2）22。
At least five crystalline-phases can be found in the CaSO4-H2O system, which are gypsum CaSO4 center dot 2H(2)O, the subhydrates alpha- and beta-CaSO4 center dot 0.5H(2)O, and the soluble and insoluble anhydrite CaSO4. The formation of these five phases in the CaSO4-H2O system and their transformations were investigated by in situ time-resolved synchrotron radiation powder X-ray diffraction (SR-PXD) in this study. Furthermore, revised structural models for beta-CaSO4 center dot 0.5H(2)O and soluble anhydrite CaSO4 are presented. The hydration of alpha-CaSO4 center dot 0.5H(2)O was studied at 25 degrees C and showed that the reaction with H2O started immediately after mixing the two reactants and that the formation of CaSO4 center dot 2H(2)O was coupled to the depletion of alpha-CaSO4 center dot 0.5H(2)O. The thermal decomposition of CaSO4 center dot 2H(2)O was investigated in the temperature range of 25-500 degrees C and showed the fon-nation of alpha-CaSO4 center dot 0.5H(2)O followed by the formation of soluble anhydrite AIII-CaSO4, which was gradually converted to insoluble anhydrite AII-CaSO4. The thermal decomposition of alpha-CaSO4 center dot 0.5D(2)O was investigated in the temperature range of 25-500 degrees C and showed successive phase transformations to beta-CaSO4 center dot 0.5D(2)O, soluble anhydrite AIII-CaSO4, and insoluble anhydrite AII-CaS04. The two polymorphs of anhydrite coexist in the investigated temperature range of 200-500 degrees C. The hydrothermal decomposition of CaSO4 center dot 2H(2)O was investigated in the temperature range of 25-200 degrees C using a 1 M HNO3 or a 1 M LiCl solution, and in both experiments, CaSO4 center dot 2H(2)O was converted to alpha-CaSO4 center dot 0.5H(2)O and further to insoluble anhydrite AII-CaSO4. A structural model for beta-CaSO4 center dot 0.5H(2)O is proposed on the basis of SR-PXD data and a trigonal unit cell (in hexagonal setting) a = 6.93145(3), c = 12.736 17(4) angstrom, Z = 6, and space group P3(1). A structural model for soluble anhydrite AIII-CaSO4 is also proposed on the basis of powder neutron diffraction data, and a hexagonal unit cell parameters are a = 6.9687(1), c = 6.3004(1) angstrom, Z = 3, and space group P6(2)22.