Thermal behaviour of pure and mixed ammonium, molybdate tetrahydrate and aluminum hydroxide

The thermal behavior of pure and mixed ammonium molybdate tetrahydrate and aluminum hydroxide has been studied by thermal analysis (DTA & TG) techniqu e. A series of pure and mixed solids were clacined in air at 250-1000 degre es C. X-ray diffraction analysis was used to identify the solid products of calcination at different temperatures. The results obtained revealed that, ammonium molybdate tetrahydrate decomposes to MoO3 at about 340 degrees C and then melts at about 790 degrees C. The intensities of diffraction patte rns of MoO3 changed with temperature of treatment pointing to a noticeable preferred orientation process. On the other hand, AI(OH)(3) transformed int o oxyhydroxide compound at about 225 degrees C after which amorphous Al2O3 could be formed. The crystalline phase Al-2(MoO4)(3) is formed at 750 degre es C as a result of solid-solid interaction between the produced oxides. Th e increase of temperature of treatment up to 1000 degrees C led to the deco mposition of the formed compound Al-2(MoO4)(3) The presence of MoO3 enhance d the crystallization of Al2O3 in alpha phase upon heating at 1000 degrees C.