低濃度懸濁水状態での半水セッコウの水和反応 Hydration of Calcium Sulfate Hemihydrate in Dilute Aqueous Suspension
In order to explore the setting and hardening characteristics of calcium sulfate hemihydrate, CaSO<SUB>4</SUB>·1/2H<SUB>2</SUB>O, simultaneous measurement of calorimetry and conductimetry at 25°C was carried out during successive addition of three portions of the hemihydrate into water. In addition, the duratiorn of the constant-concentration period as a function of the amount of the hemihydrate was examined by chemical analysis of liquid phase. The results obtained are summerized as follows : <BR>1) The initial concentration increases with the mass of the hemihydrate reaching up to ca. 50 mmol/<I>l</I> but the progress of transformation to the dihydrate from the supersaturated solution causes the reduction of the concentration.<BR>2) Tentative solubility and heat of dissolution in water with respect to the hemihydrate are estimated to be ca. 22 mmol/<I>l</I> and 13.2 kJ/mol, respectively.<BR>3) By mixing the hemihydrate in water, the dissolution and hydration processes occurr successively which are accomlpanied with distinct exothermal double peaks and variation in eletrical conductivity due to the difference in solubility between the hemihydrate and the dihydrate.<BR>4) The thermal flow curves at hydration process of the hemihydrate in water, in dihydrate saturated solution and in an aqueous suspension containing the anhydrite are almost identical, whereas the double thermal peaks are tend to change to single peak with shoulder in the presence of the dihydrate grain. The nucleation and crystal growth of hydration product onto the dihydrate surface as a seed crystal is cleared by SEM observation.
- 無機マテリアル : セッコウ・石灰・セメント・地球環境の科学 = Inorganic materials
無機マテリアル : セッコウ・石灰・セメント・地球環境の科学 = Inorganic materials 3(260), 10-16, 1996-01-01
The Society of Inorganic Materials, Japan