Studies on the non-isothermal decomposition of H3PMo12O40 center dot xH(2)O and H4PVMo11O40 center dot yH(2)O

This paper reports a comparative study of the non-isothermal decompositions of the heteropolyacids HPM and HPVM, with structures consisting of Keggin units (KUs). Non-isothermal analysis at low heating rates demonstrated the existence of 4 crystal hydrate species, depending on the temperature. The s tability domains of the anhydrous forms of HPM and HPVM were found to be 15 0-380 degrees C, respectively. Processing of the TG curves obtained at diff erent heating rates by the Ozawa method revealed that the decomposition of anhydrous HPM takes place according to a unitary mechanism, whilst for anhy drous HPVM two mechanisms are observed. Thus, the first pan of the constitu tion water is lost simultaneously with the departure of vanadium from the K U as VO2+, while the second part is lost at higher temperatures as in the c ase HPM.