Experimental study of ternary Ca-Mg-Si phase equilibria and thermodynamic assessment of Ca-Si and Ca-Mg-Si systems

The Ca-Si phase diagram was modeled by the Calphad method based on experimental data from the literature. A consistent thermodynamic description of the Ca-Si system is presented and used to point out some discrepancies between different sets of activity measurements or in the liquidus temperatures of CaSi. The ternary Ca-Mg-Si phase equilibria were investigated using X-ray diffraction methods, metallography, scanning electron microscope with energy dispersive X-ray microanalysis, and differential thermal analysis on key samples selected by thermodynamic calculations. The complete phase diagram was determined. Two ternary phases, CaMgSi, Ca7Mg6Si14, were found. The phase Ca2Mg3Si could not be confirmed. For the binary phases no remarkable solubility of the third component was observed. The ternary phase Ca7Mg6Si14 was found only in stoichiometric composition. By contrast, the phase CaMgSi dissolves up to 7 at.% Ca. Thermodynamically calculated phase diagrams are shown at 400 degreesC, in three vertical sections and the liquidus surface. They are well supported by the experimental data. (C) 2003 Elsevier Ltd. All rights reserved.