Influence of Activity of CaSO4•2H2O on Hydrothermal Formation of CaSO4•0.5H2O Whiskers

The influence of the activity of calcium sulfate dihydrate (CaSO4 center dot 2H(2)O) on the hydrothermal formation of CaSO4 center dot 0.5H(2)O whiskers was investigated in this paper, using commercial CaSO4 center dot 2H(2)O as the raw material. The experimental results indicated that the activity of CaSO4 center dot 2H(2)O was improved after calcination of the commercial CaSO4 center dot 2H(2)O at 150 degrees C for 6.0 h followed by hydration at room temperature for 1.0 h, corresponding to the decrease of the agglomerated particle sizes from 29.7 mu m to 15.1 mu m, the increase of the specific surface areas (BET) from 4.75 m(2).g(-1) to 19.12 m(2).g(-1) and the grain sizes from 95 nm to 40 nm. The active CaSO4 center dot 2H(2)O produced by the calcination-hydration treatment favored the hydrothermal dissolution of CaSO4 center dot 2H(2)O, promoting the formation of hemihydrate calcium sulfate (CaSO4 center dot 0.5H(2)O) whiskers with high aspect ratios.