Studies on Preparation of Gypsum Plaster by Special Hydrothermal Method, (IV): Direct Crystallization Tests of Hemihydrate (CaSO4⋅1/2H2O) from Gypsum Crystal in Various Electrolyte Solution

In continuing the previous studies, it is the main point to studing, in the present paper, on the special hydrothermal method for making gypsum hemihydrate CaSO4⋅1/2H2O by directly crystallizing out from gypsum crystal in the solution of various electrolyte of organic and inorganic salts, as following: (1) Sodium salts of oxalic, acetic, citric and tartaricacids, and Rochelle salt or potassium and sodium tartarate, and gelatine, and (2) Sulphates as Na2SO4, K2SO4, ZnSO4, MgSO4, Al2(SO4)3, Cr2(SO4)3, Fe2(SO4)3, K2Al2(SO4)4, (NH4)2Al2(SO4)4, K2Cr2(SO4)4 and (NH4)2Fe2(SO4)4, phosphate as NaH2PO4, and borate as Na2B4O7. In the former case of organic acid salt, sodium salt of citric acid was proved to be the most suitable electrolyte in water solution of 0.1-0.01%, to obtain good crystallized tabuilar or prismatic crystal of gypsum hemihydrate. In the latter case of various inorganic salts, Al2(SO4)3 was observed to be most effective in its 5% or more concentrated solution. to obtain the hemihydrate above described.