The activity of cobalt and silicon in the Co - Si system with special focus on the α-Co solid solution

The activities of cobalt and silicon at 1190 deg C have been determined in the Co-Si system by simple and reactive Knudsen effusion mass spectroscopy. This work constitutes the first measurement of activities in the alpha -Co solid solution. The composition dependence of the activities within the alpha -Co solid solution region was used to calculate the self-interaction coefficients of silicon in alpha -Co: ln gamma sub Si exp infinity =-10.4plus/minus0.2 and epsilon sub Si exp (Si) =18.6plus /minus0.8. The regular solution model was shown to be a fairly good description of the alpha -Co solid solution with an energy parameter Z omega sub CoSi =-120plus/minus5 kJmol exp -1 . These results compare well with literature data on similar systems (Fe-Si and Ni-Si).