Structural transformations preparing the dehydration of Ca(OH)2

Abstract The mechanism of the thermal decomposition of earth alkaline hydroxides has been extensively studied (Niepce, 1976). It results from the formation of water molecules preceding the decomposition. Prereactional effects have been evidenced by different experimental techniques, in a large temperature range before the dehydration temperature (570 K with PH2O = 1.73 torr) (Freund and Wengeler, 1980; Freund, Scheikh-Ol-Eslami and Gentsch, 1975). In particular, X-ray and neutron diffraction studies on powders and single crystals of Ca(OH)2 and Ca(OD)2 have already revealed structural discontinuities at different temperatures which depend on the water pressure conditons (Chaix-Pluchery, 1986; Chaix-Pluchery, Bouillot, Ciosmak, Niepce and Freund, 1983; Chaix-Pluchery, Pannetier, Bouillot and Niepce, 1987).