Physically and chemically bound H2O in the gyrolite structure

Synthetic pure gyrolite prepared under hydrothermal conditions (32 h, 200 °C) from a stoichiometric composition (CaO/SiO2 = 0.66) of calcium oxide and a fine-grained SiO2onH2O mixture can easily adsorb water vapour. The equilibrium quantity of adsorbed water vapour was estimated from desorption thermograms. It was determined that the thermal effect of desorption is close to the steam-heat of water vapour at temperatures up to 175 °C. This part of water vapour adsorption can be described by a physical adsorption model, only a small quantity of water vapour being chemisorbed. The crystal structure of gyrolite under a pressure of water vapour and at low temperatures (-197 °C) was stable.