For viscosity measurements in CaO-FeO-Fe₂O₃SiO₂ slags at temperatures up to 1700°C a viscosimeter with high accuracy was constructed and built. Measurements were undertaken mainly at 1600°C under air and carbon dioxide atmospheres at CaO/SiO₂-ratios of 0.66, 1.00 and 1.50. Additional measurements were carried out at 1500 and 1700°C under air. The results are:
(1) At low iron oxide contents the viscosity strongly depends on the basicity. The highest viscosities are found in acid slags.
(2) Increasing iron oxide content decreases the viscosity. The decrease is stronger in acid than in basic slags since at high iron oxide contents the viscosity values approach each other.
(3) The degree of oxidation influences the viscosity only a little.
(4) At Fe₂O₃/(FeO+CaO)=0.5 the viscosity changes due to a change in the atomic structure of the slag.
The results could be interpreted by the slag structure. The viscosity depends on the size and the concentration of the atomic structural units of viscous flow. These units are the silicate and the ferrite anions. Their size and concentration are influenced by the slag composition.