Physical properties of FeO-Fe2O3-SiO2-CaO melt systems

Ferritic slags are characteristic for steel production processes but mainly for processes of non-ferrous metals, e.g. copper or lead production. Iron partly oxidizes in the process of its refining or during concentration melt ing of concentrates in non-ferrous metals production and oxides of iron pas s into the slag. CaO and SiO2 are the main components of such slag systems but certain amount of iron may be in the form of FeO and Fe2O3. Stags, whic h due to their composition after solidification spontaneously decay, i.e. t hey undergo a volume change during re-crystallization of dicalcium silicate (2CaO.SiO2) are used preferrentially. In real slag systems these main comp onents are accompanied with other oxides - MgO, MnO, Al2O3, P2O5 or ZnO. Our work was aimed at observation of density, molar volume, surface tension and viscosity in the basic slag system consisting of FeO - Fe2O3-CaO-SiO2. We had obtained the knowledge during the study of physical properties of f ayalittic (FeO - Fe2O3 - SiO2) or calcium ferrite (FeO - Fe2O3 - CaO) slag at 1300 degreesC. The density of melts was measured by maximum gas pressure in bubble method. The molar volume of the melt at a given temperature was calculated from experimental results of its density and chemical compositio n. It is evident that silica decreases the density of FeO - Fe2O3 - CaO - S iO2 melt system and on the contrary it increases its molar volume. The surf ace tension was measured by ring method and maximum gas pressure in bubble method. Increasing content of silica in slag melt causes decreasing of its surface tension which proves the knowledge about surface activity in such m elt systems. Viscosity of FeO - Fe2O3 - SiO2 - CaO slags was measured by ro tating method. Addition of calcium oxide into FeO - Fe2O3 - SiO2 melt showed a decrease of its viscosity while addition of silica into FeO - Fe2O3 - CaO melt caused an increase of its viscosity. Due to those facts we have also made an idea on the structure of such melt systems. From presented results of density, s urface tension and viscosity measurements appears that silica in FeO - Fe2O 3 - SiO2 - CaO stabilizes Fe2+ ions and calcium oxide supports the existenc e of Fe3+ ions. Ions of three valent iron behave in that slag system as com plexation able cations transiting from a prevailingly octahedral into a pre vailingly tetrahedral coordination. We assume that the structure of FeO - F e2O3 - SiO2 - CaO melt system in an observed interval of chemical compositi on might be made of Fe2+ and Ca2+ cations or FeO2-, Fe2O4-, FeO45- and SiO4 4- anions.