Sublimation behavior of molybdenum oxides

The sublimation and decomposition of Mo oxides, such as MoO/sub 2/, MoO/sub 3/, and Mo/sub 4/O/sub 11/, were studied by high temperature mass spectrometry. Partial pressures of various vapor species including polymeric molecules were reinvestigated for MoO/sub 2/ and MoO/sub 3/, and newly studied for Mo/sub 4/O/sub 11/ by this technique. Heats of reactions over these oxides at measured temperatures T were obtained by the Second Law method and compared with previous data. In this work, estimated thermodynamic functions for the gaseous polymeric species were used to obtain heats of reactions at 298 K. For MoO/sub 2/ and MoO/sub 3/, reasonable partial pressures and heats of reactions for various species were obtained. The heats of sublimation for polymeric (MoO/sub 3/)/sub 2/ and (MoO/sub 3/)/sub 3/ obtained by the Second and Third Law methods at 298 K were in good agreement. The vapor species over Mo/sub 4/O/sub 11/ were the same as those over MoO/sub 3/, but the magnitudes of the various partial pressures were appreciably lower for Mo/sub 4/O/sub 11/ than for MoO/sub 3/.