Vaporization behavior of Ir 4 (CO) 12 and Re 2 (CO) 10 measured by torsion effusion gravimetric method
Metal carbonyls are of great importance in chemical vapor deposition (CVD), composite materials fabrication, and other near-net shape technologies. Carbonyl CVD is used for deposition of high-purity metallic and alloy coatings for which vapor pressure data is essential. In this study, we report vapor pressures of solid Ir 4 (CO) 12 and Re 2 (CO) 10 carbonyls measured by using the Knudsen Cell methodology using a torsion effusion thermogravimetric system. The vapor pressure of the Ir 4 (CO) 12 exhibited incongruent vaporization, as the molecular weight (MW) of the effusing species was determined as 128 g/mol as compared to the theoretical MW of 1105 g/mol. It is proposed that the Ir 4 (CO) 12 (s) partially decomposed (~66%) to Ir 4 (CO) 12 (g), Ir(s), and CO(g). The Re 2 (CO) 10 on the other hand, showed congruent behavior with Re 2 (CO) 10 (s) vaporizing to Re 2 (CO) 10 (g) in the measured temperature range. The raw data for vapor pressures was measured using two sets of Knudsen cells with different orifice sizes, and the equilibrium vapor pressures were calculated using Whitman-Motzfeldt methodology. The equilibrium vapor pressures of these carbonyls, partial pressures of gaseous species in case of decomposition, average molecular weights of the effusing gasses were determined. The vapor pressures and Gibbs energies of vaporization reactions of the two above mentioned carbonyls, as well as comparison of vaporization thermodynamics these two carbonyls with other carbonyls from Group VIB to VIIIB are presented in this work.