Abstract
Statistical thermodynamics was applied to the quantitative interpretation of the immiscibility of the binary silicate systems. The author has established the model of molten MO-SiO2 systems composed of c mol MO and (1−c) mol SiO2, as follows: (1) When c mol MO dissolves into (1−c) mol SiO2, Nc in the 2(1−c)N Si-O-Si chains decompose into Si-O* *O-Si by the following reaction: MO+Si-O-Si→Si-O* MO*-Si. (2) The binding energies of Si-O, Si-O*, M-O and M-O*. vary in proportion to the Si-O-Si decomposition ratio c⁄2(1−c). From this model, the Gibbs’ free energy of the molten system Gl can be written, as follows: G_l=(1-c)G_Sio_2^l+Ac+Bc^2/1-c+Cc^3/(1-c)^2+RT{c lnc+(2-3c) ln(2-3c)-2(1-c) ln2(1-c)}where GSio2l is the Gibbs’ free energy of SiO2 liquid and A, B and C are constants. From this formula, the immiscibility of MO-SiO2 systems can be explained systematically and the activities of SiO2 in molten binary silicate systems have been calculated.
