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 ideality and tend to approach an ideal behavior at higher temperatures. The terms of RT ln γ_Cu and RT ln γ_Mg show very small temperature dependence within the present experimental range and agree well with the values reported by Garg et al. for the Cu-Mg system. The terms of RT ln γ_Ca and RT ln γ_Cu are 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.