Molybdenum and Chlorine

Abstract

Using the available experimental observations and the results of thermodynamic calculations, a phase diagram of the molybdenum-chlorine system for a pressure of the gaseous phase of 1 atm in the temperature region 0 to 1100°C has been constructed as shown in Fig. 61 [1]. The diagram gives the existence regions of solid MoCl_n, n= 2 to 6. The figure indicates at 950 ± 10°C the disproportionate of MoCl₂(s) to Mo(s) and essentially pure MoCl₄(g). At 2000 K gaseous MoCl₄ is in equilibrium with Mo(s) and the gas phase, for a total pressure of 1 atm, is calculated to consist of (in atm) 0.91 MoCl₄, 0.04 MoCl₃, 0.04 Cl, 0.007 MoCl₂, 0.003 Cl₂, 10^-4 MoCl₅, and 10^-6 MoCl. At 650 ± 10°C the diagram indicates disproportionate of MoCl₃(s) to a-MoCl₂(s) and 1 atm MoCl₄(g). MoCl₄ has a peritectic point at 277 ± 10°C forming MoCl₃(s) and MoCl_4.5(l). The phase transitions of MoCl₄ are not indicated. A eutectic at 183±3°C is observed between MoCl₄ and MoCl₅; the MoCl₄ liquidus (determined by [8]) is given by In x(MoCl₄) = 4.28-[2580+ 455 x²(MoCl₅)]/T±0.04 between 456 and 550 K, where the mole fractions are based on the MoCl₄ and MoCl₅ components [1].

Older data are given in “Molybdän”, 1935, pp. 153/75