Influence Of Melting Process On The Structure And Properties Of Fused Magnesia And MA Spinel

With the development of modern high temperature industry,the excellent properties of electrically fused magnesium materials are becoming more and more concerned.It has high melting point（2800℃）,large crystals,compact structure,strong slag resistance,high temperature resistant,chemical stability,compression strength,insulation performance is strong,scouring resistance,corrosion resistance,crystal at about 2300℃chemical remained stable performance,etc.Based on the excellent characteristics of fused magnesia shows,it is widely applied in high temperature electrical insulation materials,is also the production of high-grade magnesia brick,magnesia carbon brick and monolithic refractories important raw materials,in addition,single crystal,poly crystal,high purity fused magnesia,used in the manufacture of high and ultra high temperature resistant,compression,high-frequency insulation resistance,thermoelectric pair material,electronic ceramics,rockets,nuclear furnace,and other fields have broad application prospects.However,the high energy consumption of the electric melting magnesium oxide industry has become a bottleneck to the development of the industry,and it has been an urgent task to reduce the single consumption of smelting.At the same time,it is urgent to control environmental pollution in production,recycle and utilize energy resource waste,and improve the taste of magnesium oxide.Therefore,it is necessary to melt the melting process of magnesium oxide and the crystallization process of magnesium oxide and the transfer of impurities in the process of smelting and cooling.But thermal expansion coefficient of the fused magnesium is higher(14.6×10^-6℃),poor thermal shock resistance.Magnesium aluminum spinel（MgAl₂O₄）is a composite mineral composed of MgO and Al₂O₃,whose theoretical chemical composition is MgO 28.33%,Al₂O₃ 71.67%.It has high temperature resistance,low thermal expansion rate,good thermal shock stability,corrosion resistance and other excellent high temperature performance.But the electric melting process is large and costly.To improve this defect,studies have shown that adding ZrO₂,ZnO,TiO₂ can reduce the synthesis temperature of magnesium alumina spinel.In order to improve its sintering performance,it is not obvious to reduce the high temperature performance of spinel.This study focus on the composition of titanium dioxide additives on the composition,cell parameters and microstructure of magnesium aluminum spinel and its mechanism of action.This study light burned magnesia powder,industrial aluminum oxide as raw material to synthesis of fused magnesium aluminate spinel material,titanium dioxide is the main research of additives for electric fusion magnesium aluminium spinel phase composition,microstructure,the effect of using XRD,SEM analysis of the sample phase composition,crystal cell parameters and microstructure of the fracture.Research shows:（1）.The fused magnesia,which is fused by different technology,has the best crystallization in the position of close to the sand,and the crystal development is complete;The fused magnesia stone products of the direct current electrode are dense with the structure of the ac electrode,and the crystallization particles are large and the purity is high;In the process of fusion,the hollow electrode is well ventilating,and the fused products are dense in structure and large in grain size.（2）.Due to the electromagnetic stirring of the direct current electrode,the impurities of the fused products are evenly distributed;During the direct current melting process,the network is stable and the noise generated is relatively small.（3）.Titanium dioxide is an admixture that can increase the crystal cell parameters of magnesium-alumina spinel and cell volume,increase the volume density of materials and improve the sintering properties of materials.（4）.With the increment of titanium dioxide to join magnesium aluminate spinel,crystal cell parameters and cell size decreases after increasing first.Because the titanium dioxide,and magnesium titanate solid solution to the magnesium aluminate spinel,excessive amounts of magnesium titanate located in the grain boundary will hinder the growth of magnesium aluminate.The amount of titanium dioxide should not exceed 5wt%when the magnesium alumina spinel is prepared by electrofusion.