Viscosity models for molten slags

The understanding and optimisation of the metallurgical processes require access to accurate data of the physical properties of slags. Viscosity is one of the most important properties in the case of metallurgical melts, in view of its direct effect on the kinetic conditions of the processes, and is one of the key factors to be taken into consideration in process modeling. The difficulty and high cost of measuring the viscosity of slags has led to development of number of viscosity models. Most of these models employ parameters extracted from experimental data of viscosity, which ensure the validity of the models in viscosity estimation. In this report models developed to estimate the viscosity of fully molten oxide slags were discussed. In addition viscosities of converter slags (Basic Oxygen Furnace, Argon-Oxygen Decarburization furnace) predicted with different models were compered. In the case of BOF-slag the Iida and the modified Urbain models seemed to be more reliable than the other models in predicting the viscosities. The values calculated by KTH model were too high for this high basic slag whereas in the case of NPL model the slag composition was observed to be outside of the working range of the model. Urbain model modified by Forsbacka as well as the modified Iida models takes account of chromium oxide as a separate component in the calculations and are thus assumed to be more reliable than the other models in predicting viscosities of chromium containing slags. However the reliability of these models is debatable in the case of high chromium containing slags e.g. AOD-slag after oxidising period due to existing of solid phases in the slag. Iida as well as the Urbain model modified by Forsbacka are also assumed to be reliable predicting viscosity of slag composition corresponding the AOD-slag after reduction period. Also NPL-model seemed to give reliable viscosity values, since in this case the slag composition is inside the working range of the model. Although there are plenty of experimentally measured viscosity data available for ternary systems, less data in limited ranges are available as the order of the system gets higher. Also lack of experimental data of very basic slag compositions as well as slags containing iron and chromium oxides is apparent. Due to lack of experimental data the performance of these models in predicting viscosities of converter slags was not able to evaluate. Thus more experimental work is necessary to provide the data to test and optimise the models for these very complex slag compositions