Abstract: The effect of soluble phosphorus on CaSO₄·2H₂O (DH) dehydration to α-calcium sulfate hemihydrate gypsum (α-HH) in hydrothermal CaCl₂ solutions and the crystal shape regulation were investigated. The action mechanism of soluble phosphorus was studied by means of growth of hemihydrate crystal. The system pH was the main factor to determine whether DH could be dehydrated to α-HH in 24% CaCl₂ solution at 98℃. Acicular a-HH crystal could be obtained when pH was less than 2.0. High-strength α-HH crystal with aspect ratios from 0.5 to 3.0 could be observed when polycarboxylic crystal habit modifier NS was added. The corresponding compressive strength was more than 20 MPa. The presence of soluble phosphorus was favorable for α-HH formation by lowering system pH, increasing supersaturation degree and reducing interfacial energy. On the other hand, acid radical ions affected α-HH crystallization behavior and adsorption results of medium crystal agent NS.

Key words: soluble phosphorus, hydrothermal, phase change, preparation, high-strength a-hemihydrates gypsum

摘要： 研究了水热CaCl₂溶液中可溶磷对CaSO₄·2H₂O脱水形成α-半水石膏相以及晶形调控的影响,并从高强α-半水石膏相的晶体生长角度探讨了可溶磷的作用机理。结果表明:在98℃ 24%的水热CaCl₂溶液中,pH 的大小是决定二水石膏能否发生脱水相变反应形成α-半水石膏的主要因素;当pH不超过2.0时,可以得到针状的α-半水石膏,加入多元羧酸类媒晶剂NS后,可以得到长径比0.5～3.0的短柱状高强α-半水石膏,抗压强度超过20 MPa;可溶磷的存在可以降低体系的pH,增大α-半水石膏的过饱和度,降低晶体与液相界面的表面自由能,有利于α-HH相的形成;另一方面,酸根离子会影响到α-HH的结晶习性,减弱羧酸类媒晶剂的吸附效果。

关键词: 可溶磷, 水热, 相变, 制备, 高强a-半水石膏