Modeling the charge compensation effect in silica-rich Na2O-K2O-Al2O3-SiO2melts

At high SiO2 contents, a model of Na2O-K2O-Al2O3-SiO2 melts must take into account the "charge compensation effect" whereby the replacement of a tetra valent Si4+ by a trivalent Al3+ in the silicate network is facilitated by t he formation of (NaAl)(4+) or (KAl)(4+) associates. This effect has been ta ken into account in the quasichemical model by treating the (NaAl)(4+) and (KAl)(4+) associates as separate species in the melt, which is then formall y treated as consisting of the components NaO1/2, KO1/2, AlO3/2, SiO2, (NaA l)O-2 and (KAl)O-2. Optimizations of the Na2O-Al2O3-SiO2, K2O-Al2O3. SiO2 a nd NaAlSiO4-KAlSiO4-SiO2 systems at high SiO2 contents are reported.