Vacuum Vaporization in the System MgO‐Cr2O3

The vaporization of the system MgO‐Cr 2 O 3 was studied in a vacuum of 10 −5 torr (10 −3 N/m 2 ) at 1500° to 1700°C using the Langmuir and Knudsen methods. It was found that the phases in the system vaporize nearly congruently and the logarithm of the vaporization coefficient, α, of MgCr 2 O 4 increases linearly with increasing reciprocal temperature. Alpha tends to unity at a temperature near the melting point (2525±23°C). The additivity rule can be applied to the Langmuir vaporization rates on the basis of the surface area ratios of the phases in the 2‐phase system MgO‐Cr 2 O 3 . The enthalpies of vaporization of MgCr 2 O 4 were 695.0 and 549.2 kcaVmol for activated and equilibrium processes, respectively.