Effects of Basicity and FeO Content on the Softening and Melting Temperatures of the CaO-SiO<SUB>2</SUB>-MgO-Al<SUB>2</SUB>O<SUB>3</SUB> Slag System

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Abstract

The effects of basicity (the ratio between CaO and SiO2) and FeO content on softening and melting temperatures of direct reduced iron (DRI) residual, otherwise known as slag, were investigated.Sample slag pellets were prepared for two target compositions, CaO-SiO2-10%MgO-5%Al2O3 and CaO-SiO2-5%MgO-10%Al2O3. Two sets of experiments were conducted on the pellets: one varied basicity values between 1.83 and 0.55, and the other varied the FeO contents between 10% and 50% at constant basicity. The softening and melting process under elevated temperature was recorded using an optical softening-melting temperature measuring device and the temperature points were recorded at the four distinct shape changes of the sample pellets: initial deformation, sphere and hemisphere formation, and complete melting.The lowest softening and melting temperatures of the CaO-SiO2-5%MgO-10%Al2O3 samples occurred at a basicity of 0.55 while for the CaO-SiO2-10%MgO-5%Al2O3 samples it occurred at 0.70. This corresponds to the liquidus temperatures on the CaO-SiO2-MgO-Al2O3 quaternary phase diagram. At constant basicity, the deformation temperature of CaO-SiO2-10%MgO-5%Al2O3 samples was found to be higher than that of CaO-SiO2-5%MgO-10%Al2O3 samples. Lastly, the addition of FeO below 20% to the CaO-SiO2-MgO-Al2O3 system significantly decreased the softening and melting temperatures of the slag samples. However, further addition of FeO beyond 20% produced inconclusive results.

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