Thermal dehydration of (C 6H 5NH 3) 4Mo 8O 26 · 2H 2O. Isothermal kinetic analysis

Abstract

The thermal dehydration of (C 6H 5NH 3) 4 Mo 8O 26 · 2 H 2O in powder and pellet form has been studied by thermogravimetry. The dehydration takes place as first reaction for the isothermal and non-isothermal runs. In the powder samples the final mass loss of water gives a non-stoichiometric amount near 3 2 H 2O. A stoichiometric decomposition takes place in the pellet samples. Non-stoichiometric runs are explained as a result of premature pore closure at the surface of the reacting particles, by the influence of structural effects in the dehydration,which can be avoided in the pellet runs. The reaction kinetic model of the isothermal dehydration between 348 and 373 K was found to be the topo-chemical KEKAM equation and the temperature was found to have an influence on the limiting stages of the transformation 1 < n < 3 2 . The values of the frequency factor and activation energy were A = 2.93 × 10 13 min −1 and E = 101.20 kJ mol −1, respectively.