Reaction mechanism of initial dehydration of zirconium oxide chloride octahydrate in its thermal decomposition

Mechanism of initial dehydration of ZrOCl2.8H2O was investigated by isothermal heating and X-ray diffraction studies. In the range of 500C to 66.50C, two molecules of three-coordinated lattice water are lost in the first step of dehydration and subsequently one molecule of four-coordinated lattice water is lost. After the loss of three molecules of lattice water, the rate of thermal decomposition become slow and the crystal structure changes. It seems that above 66.50C, both dehydration and chemical reaction which produces HCl presumably occur competitively. Activation energy of the initial dehydration is estimated to be 12.9 kcal-mol. (author)