Thermal polycondensation of ammonium paratungstate, (NH4)10[W12O40(OH)2].4H2O

Abstract

Connected with the examination of the thermal polycondensation of ammonium paratungstate pentahydrate the chemical and morphological properties of intermediate phases formed during the thermal decomposition of APT have been investigated. We have studied the pH and the turbidity of the aqueous solutions of the intermediate phases, the solubility of the phases, and their rehydratation capability as well as the morphology of the crystallite granules and the grain size distribution. These properties of the original APT have been related to the same properties of the products of decomposition formed between different temperature ranges. The results obtained show unambiguously that each of the above mentioned properties suddenly changes in the temperature range 225 to 250 ~ C. This temperature range coincides with the formation temperature of a new phase called APT II. The most probable formula of APT II is (NH4) 8[H2 W13 043 (OH)2 ] "H20.

Reaction scheme in the non-isothermal decomposition of (C6H5NH3)4Mo8O26 · 2 H2O

“…) 8 MoO 3 This process has bean studied by Kiss [2] on the ammonium salt, and it involves structural changes with Mo-O bond rupture near 550 K. Thus, extraction with ethyl acetate and quinoline has been carried out on samples from thermogravimetric decomposition under non-isothermal conditions, stopped at 573 K, in order to study the inorganic anion evolution in the first decomposition step by means of X-ray powder diffraction.…”