Determination of the High Temperature Melting Behaviour of Synthetic Ferronickel Slags

The industrial manufacturing of ferronickel in electric furnaces produces large amounts of slag with strong acidic character and high melting points, which seriously stresses the furnace refractory. In this study, measurements by a hot stage microscope served for the determination of melting behaviour of synthetically produced ferronickel slags on magnesia as refractory material. Therefore, 13 different slags comprising the main oxides SiO2 (35 to 70 wt.-%), MgO (15 to 45 wt.-%), Fe2O3 (5 to 35 wt.-%) and Al2O3 (0 to 10 wt.-%) were melted in a graphite crucible and afterwards analysed by a hot stage microscope. The design of experiments, which was created by the statistic software MODDE, included 15 experiments with varying slag compositions as well as atmospheres. The evaluation of the test results occurred at three different characteristic states of the samples like the deformation point according to DIN 51730 and the temperatures, at which the area of residual cross section of the samples amounted to 30 respectively 40 % of the original value in dependence of their SiO2/MgO ratio and iron oxide content. Additionally, the thickness of the zone influenced by the slag was measured and evaluated. The results indicated that the deformation temperature decrease with an increasing content of Al2O3 and SiO2/MgO ratio. Furthermore, a content of 4 respectively 10 wt.-% Al2O3 resulted to the lowest temperature for 40 % residual cross section. In addition, the alumina content showed a changeable influence on the area of influenced zone of the refractory at high and low SiO2/MgO ratios.