Abstract
The thermal decomposition of pure ammonium heptamolybdate tetrahydrate (AHMT), and doped with Li+, Na+ and K+ ions was investigated using thermogravimetry, differential thermal analysis, infrared and X-ray diffraction techniques. Results obtained revealed that the decomposition of AHMT proceeded in three decomposition stages in which both NH3 and H2O were released in all stages. The presence of 0.5 mol % alkali metal ions enhances the formation of the intermediateb (NH4)2MO7O22·2H2O while the decomposition of this intermediate into MoO3 is slightly affected in the presence of all dopant concentrations used. The infrared absorption spectra of the thermal products of AHMT treated with 10 mol% alkali metal ions (AMI) at 350°C indicated a reduction of some Mo6+ ions. By heating of AHMT above 500°C in presence of 5 or 10 mol % of AMI, a solid-solid interaction between alkali metal oxides and MoO3 giving rise to well crystallized alkali metal molybdates. finally the activation energies accompanied various decomposition stages were calculated.
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