Abstract:DTA/TGA and XRD were employed to study the thermal decomposition of three commercial polyphase ammonium molybdate mixtures. Aseries of intermediate phases of ammonium molybdates, in which the content of molybdenum increases with the raise of temperature, were identified during the course of heating. The main decomposition reactions occurred in steps as follows: (1) at 110℃, (NH4)₆Mo₇O₂₄·4H₂O decomposed into (NH₄)₄Mo₅O₁₇; (2) at 220℃,(NH₄)₄Mo₅O₁₇decomposed into (NH₄)₂Mo₄O₁₃; (3) at 290℃, (NH₄)₂Mo₄O₁₃orβ-(NH₄)₂Mo₄O₁₃decomposed into MoO₃.

Key words: ammonium molybdate　thermal decomposition　metallic molybdenum