THE ACTIVITY OF COBALT AND SILICON IN THE CO-SI SYSTEM WITH SPECIAL FOCUS ON THE ALPHA-CO SOLID-SOLUTION

The activities of cobalt and silicon at 1190 degrees C have been deter mined in the Co - Si system by simple and reactive Knudsen effusion ma ss spectroscopy. This work constitutes the first measurement of activi ties in the alpha-Co solid solution. The composition dependence of the activities within the alpha-Co solid solution region was used to calc ulate the self-interaction coefficients of silicon in alpha-Co: In gam ma(Si)(infinity) = -10.4 +/- 0.2 and epsilon((Si))(Si) = 18.6 +/- 0.8. The regular solution model was shown to be a fairly good description of the alpha-Co solid solution with an energy parameter Z omega(CoSi) = -120 +/- 5 kJ . mol(-1). These results compare well with literature data on similar systems (Fe - Si and Ni - Si).