Alpha calcium sulfate hemihydrate and a method of making alpha calcium sulfate hemihydrate

摘要

A method is provided for making alpha calcium sulfate hemihydrate by heating a solution containing (1) calcium sulfate dihydrate having an average particle size of 1 to 80 micrometers; (2) an inorganic salt, such as NaCl, KCl, NaNO3, Ca(NO3)2, MgCl2, CaCl2 and mixture thereof, and (3) an organic acid, such as succinic acid, maleic acid, mellitic acid, phthalic acid, tartaric acid and mixtures thereof at a temperature in the range of 85 DEG C to 98 DEG C so that the calcium sulfate dihydrate is converted into alpha calcium sulfate hemihydrate. The alpha calcium sulfate hemihydrate has a compressive strength of about 20 MPa to about 30 MPa and a purity of at least 99 %.