Thermodynamic constraints arising from the polymeric approach to silicate slags: the system CaO–FeO–SiO2 as an example

Systematization of mixing properties in the system CaO–FeO–SiO2 in the liquid state is carried out in the framework of some simplifying assumptions arising from polymer theory. The Gibbs free energy of mixing is conceived as composed of a chemical interaction term and a mechanical strain energy term arising from chain elasticity of polymeric units. The chemical interaction is resolved adopting a modified Toop–Samis approach. The polymerization path is shown to be compositionally dependent upon the local polymerization constant, Kp that, in its turn is exponentially related to the values attained at the limiting binaries, i.e.:Kp,CaO–FeO–SiO2=Kp,CaO–SiO2XCaXCa+XFeKp,FeO–SiO2XFeXCa+XFe.The mechanical strain energy is shown to be satisfactorily reproduced by the equationGstrain=3RT2ν̄Sixa2,where νSi is the local mean polymerization extent and x/a is a bending term taking into account the relative arrangement of monomers in the chain. The model reproduces fairly well the experimentally observed thermodynamic activities of the components along the limiting binaries and within the ternary field.