THE APPLICATION OF THE HOCH-ARPSHOFEN MODEL TO LIQUID-SYSTEMS WITH COMPOUND-FORMING TENDENCIES AND A MISCIBILITY GAP

The complex model of Hoch and Arpshofen was applied to the MgO-SiO//2, CaO-SiO//2, Sio-SiO//2, BaO-SiO//2, and Fe-FeO//1//. //5 system. In the liquid, the excess Gibbs energy of mixing equals Wn(x minus x**n) plus M2n(y minus y**2**n), where W is the attractive energy term, M is the repulsive energy term, n is the size (number of atoms) in the complex, x is the atom mole fraction of the component toward which compound formation tendencies are shown, and y is the mole fraction of the component toward which the miscibility gap exists. To represent data in the liquid within the temperature and composition range of interest, such as activity of MgO, CaO, or SiO//2 in the silicate systems or oxygen pressure in the Fe-FeO// 1//. //5 system, the temperature independents W and M are adequate. To represent the critical mixing temperature, however, a temperature-dependent M is required of the form M equals M//0(1 minus alpha T).