Study On Magnesia-Zirconia Brick For RH Refining Furnace

The traditional magnesia-chrome brick used in RH refining furnace causes environmental pollution.In order to produce substitute for magnesia-chromite brick of RH refining furnace,magnesia-zirconia brick for RH refining furnace was studied in this thesis.The effects of direct and indirect addition of zirconia on the properties of magnesia-zirconia bricks were investigated.The effect of calcium zirconate with different cerium oxide content on the properties of magnesia-zirconia brick was discussed.The main conclusions are shown as follows.（1）The magnesia zirconia brick samples were prepared by directly adding desiliconized zirconium.The distribution of ZrO₂ is not uniform in the samples.The phase transformation of m-ZrO₂and the shrinkage of light burned magnesia powder in the sintering process produce cracks.The thermal shock resistance of samples are decreased.（2）ZrO₂ is evenly distributed in the magnesia-zirconia brick prepared with pre-synthesized magnesia-zirconia sand.The c-ZrO₂ is formed by solid solution reaction of ZrO₂ with Mg O and Ca O in the samples.The phase transformation of ZrO₂ and the mismatch of thermal expansion coefficient between c-ZrO₂ and Mg O resultes in microcracks in the sample,which consumed the energy of the main crack.The thermal shock resistance of samples is improved.（3）The sintering performance and thermal shock resistance of samples are improved with the sintering temperature increase due to the atom diffusion rate is accelerated,and the solid solution reaction is promted.（4）The sintering properties and thermal shock resistance of magnesia zirconia brick prepared with pre-synthesized calcium zirconate are both impreved with the increase of calcium zirconate adding amount.The thermal expansion coefficient mismatch between CaZrO₃ and Mg O leads to microcracks in the samples,hence the thermal shock resistance of the samples is improved due to the microcracks toughening effect.（5）The magnesia zirconia brick prepared with pre-synthesized calcium zirconate.The solid solution reaction of CeO₂ and ZrO₂ promotes the sintering of the sample.The excess CeO₂ can not be fully dissolved into ZrO₂,and CeO₂ is partially dissolved into Mg O which resultes in the lattice distortion of Mg O.The lattice of Mg O is activated and changed,which reduce the lattice constant and interplanar spacing of Mg O.As a result,the grain of Mg O contracte greatly in the sintering process,cracks appeare in the sample,the sintering performance,the thermal shock resistance and slag resistance of the sample are reduced.（6）The comparison results of slag resistance between magnesia-zirconia brick prepared with different type zirconia and magnesia-chromite is shown as follows.The slag resistance of magnesia-zirconia brick prepared with pre-synthesized magnesia-zirconia sand has the excellent performance to high alkalinity RH slag,which is better than magnesia-chromite brick.The analysis shows that the molar ratio of Ca O/SiO₂>2,ZrO₂ in magnesia-zirconia brick reactes with Ca O in slag to form CaZrO₃,and Mg O in magnesia-zirconia brick reacted with Fe₂O₃ and Al₂O₃ in slag to form high melting point magnesia-alumina spinel（Mg Al₂O₄）and Mg（Al,Fe）₂O₄ composite spinel.The formation of CaZrO₃ and composite spinel is accompanied by volume expansion,which block the way of slag penetration.The ZrO₂absorbs Ca O in slag,which improve slag viscosity,decrease the slag penetration rate,the slag resistance of the sample is improved.The low melting point calcium ferric aluminate（C₄AF）is formed by the iron oxide,alumina in the magnesia-chromite brick working layer and the calcium oxide in the slag which lead to the poor slag resistance of magnesia-chrome brick.