The Liquid-Vapor Phase Transition in a Copper-Calcium System

It is established that 82% of the vapor can condense into the liquid phase when calcium is evaporated from an alloy with copper at low pressures of 0.7-1.33 kPa under nonequilibrium conditions. Based on values of the vapor pressure of calcium and copper determined using the boiling point approach, a complete diagram of state is constructed that includes the condensed and vapor phases at atmospheric pressure and in vacuums of 0.7 and 1.33 kPa. The temperatures of boiling and the composition of the condensate are calculated from the boundaries of the melt-vapor phase transitions. The condensate is represented by calcium with a copper content no greater than 3.95 x 10(-2)wt % and a boiling point 77-129 degrees C higher than the melting point of Ca. It is assumed that the condensate remains in the molten state. The fundamental possibility of a liquid-vapor-liquid process that can be applied to distillation for the production of calcium is thus proved.