Ceramics-Silikáty 29, (4) 291 - 299 (1985)

The viscosity of melts in the syatem CaO-FeO-Fe₂O₃-SiO₂ decreases with increasing content of calcium oxide and iron oxides. The viscosity of the melts in question was found to be a linear function of the mean mole mass of the polyanions calculated on the basis of a statistical model, and an exponential function of the reciprocal value of thermodynamic temperature. The coordination of iron atoms in the melt is genetrally low. The Fe³⁺ cations were not proved to participate in the formation of the polyanionic network. Complex anions of the type FeO₄^5- or Fe₂O₅^4- can be assumed to be present. Their content decreases with increasing temperature while a larger portion of larger silicate polyanions is formed. In this way, the Fe³⁺ cation takes over the function of the tetrahedral network modifier. The phenomenon results in an increase of the mole mass of polyanions with increasing temperature.