THE COMMON COMPONENT EFFECT IN MULTICOMPONENT, MULTIPHASE EQUILIBRIUM SYSTEMS

For a halide-activated pack cementation process, codeposition of Cr and Si into diffusion coatings on steel surfaces can be achieved by using two halide salts to optimize jointly the partial pressures of CrCl2(v) and SiF2(v). The selection of the second salt is the key point for this process. SOLGASMIX program was used to calculate the equilibrium vapor pressures of different metal halide gas species for different activator salt combinations. Two salts with the same cation develop low partial pressures for CrCl2(v) and SiF2(v), which are not high enough to codeposit Cr and Si into a coating. Two salts with different cations produce a different result. Some combinations, such as NaCl and CaF2, have high and comparable partial pressures of CrCl2(v) and SiF2(v). However, other combinations either have low partial pressures, or the partial pressures of CrCl2(v) and SiF2(v) are not of the same magnitude. The role of the partial pressure for the alkali metal is elucidated.