Synthesis of oxides, oxocarbides and carbides of molybdenum by thermal decomposition of diethylenetriamine oxomolybdenum compounds

Abstract

Thermal decompositions of four diethylenetriamine oxomolybdenum compounds, the oxocomplex diethylenetriaminetrioxomolybdenum(VI), [MoO 3(dien)] (DIENMO1), two polymorphs of bis(diethylenetriammonium) heptamolybdate(VI) tetrahydrate, (H 3dien) 2[Mo 7O 24] · 4H 2O (DIENMO7-I) and (DIENMO7-II), and the bis(3-aza-l,5-penta- methylenediammonium) octamolybdate(VI) hexahydrate, (H 2dien) 2[Mo 8O 26] · 6H 2O (DIENMO8), have been studied using TG, DTA and DTG techniques under an argon atmosphere from room temperature to 600°C. Whereas the themal decompositions of the three polyoxomolybdate salts DIEMNO7-I, DIENMO7-II, and DIENMO8 lead to a mixture of MoO 2 and Mo 2C, the final residue from the oxycomplex is a mixture of Mo 2C and the mixed valence molybdenum(V, VI) oxide Mo 4O 11. The results show that the molybdenum oxide/molybdenum carbide ratio depends on the starting material. An increase in the formation of molybdenum oxide is observed as the ratio Mo/C increases. The ulterior oxidation of the final mixtures yields Mo 4O 11 and MoOC as intermediate solid products, and MoO 3 as the final product above 535° C. The final solid residues in an argon atmosphere and the intermediate products in the oxidative atmosphere were analysed by elemental analysis and X-ray powder diffractometry.