硫酸中における二水セッコウの準安定性

抄録

The metastability of CaSO₄·2H₂O in 20-55% H₂SO₄ was studied by wet DTA method. The solid phase precipitated was also examined by means of DTA, X-ray diffraction analysis and microscopic observation.
In the CaSO₄·2 H₂0→α CaSO₄·1/2 H₂O reaction, the upper limit temperature (Y) for metastability of CaSO₄·2 H₂O in the case of 1 minute induction period for dehydration lowered markedly as the concentration of H₂SO₄ (Z) increased, and these relation was represented as follows :
Log (110-Y) =0.0226Z+0.620
From above results, it was confirmed that the metastable zone for CaSO₄·2 H₂O in H₂SO₄ aqueous solution existed in the wide range of higher temperature than those reported by Zdanovskii on metastable equilibrium for CaSO₄· 2 H₂O_??_ α CaSO₄·1/2 H₂O in H₂SO₄ aqueous solution.
The shape of crystals of α CaSO₄·1/2 H₂O precipitated in H₂SO₄ aqueous solution varied markedly from wiskerlike to short prismoidal as the concentration of H₂SO₄ increased, and the crystals precipitated in the H₂SO₄ concentration of 20 and 30% had the L/D ratio of 60-100.