Influence of disodium hydrogen phosphate dodecahydrate on hydrothermal formation of hemihydrate calcium sulfate whiskers

The influence of Na2HPO4 center dot 12H(2)O on the hydrothermal formation of hemihydrate calcium sulfate (CaSO4-0.5H(2)O) whiskers from dihydrate calcium sulfate (CaSO4 center dot 2H(2)O) at 135 degrees C was investigated. Experimental results indicate that the addition of phosphorus accelerates the hydrothermal conversion of CaSO4 center dot 2H(2)O to CaSO4 center dot 0.5H(2)O via the formation of Ca-3(PO4)(2) and produces CaSO4 center dot 0.5H(2)O whiskers with thinner diameters and shorter lengths. Compared with the blank experiment without Na2HPO4 center dot 12H(2)O, the existence of minor amounts (8.65 x 10(-4)-4.36 x 10(-3) mol/L) of Na2HPO4 center dot 12H(2)O led to a decrease in the diameter of CaSO4 center dot 0.5H(2)O whiskers from 1.0-10.0 to 0.5-2.0 mu m and lengths from 70-300 to 50-200 mu m. (C) 2013 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.