Activity Measurement of the Constituents in Liquid Cu-Mg and Cu-Ca Alloys with Mass Spectrometry

A mass spectrometer has been used to study activities of the constituents in liquid Cu-Mg and Cu-Ca alloys. Activities and heats of mixing have been determined from a series of measurements of the ratios of the ion current intensity of the solution components according to the Belton-Fruehan treatment. The activities in both systems exhibit negative deviation from ideali ty and tend to approach an ideal behavior at higher temperatures. The terms of RT ln ?Cu and RT ln ?Mg show very small temperature dependence within the present experimental range and agree well with the values reported by Garg et al. for the CuMg system. The terms of RT ln ?Ca and RT ln ?Cu ar e independent of temperature and in excellent agreement with the values assessed by Risold et al. for the Cu-Ca system. Relative partial molar enthalpy and integral heat of mixing in the liquid Cu-Mg and Cu-Ca systems were also estimated.