Study On Modification Of Magnesia In Reducing Nitriding Atmosphere

In this work,In order to improve the practical performance of low grade magnesia,the influence factors of four kinds of magnesia on the properties of their products were explored,and the phase modification of low-grade magnesia was studied by reductive nitrization method with elemental powder（Al,Si）as additive at1500℃and N₂ atmosphere.At the same time,three kinds of magnesia with good phase optimization effect and one of four kinds of magnesia with good quality were selected to prepare Mg O-C brick samples,and the erosion resistance of the samples was characterized.The results are as follows:（1）The grain size of magnesite,the content of high temperature liquid phase and high melting point phase are three factors affecting the performance of Mg O-C brick.The larger the grain size of magnesite,the better the performance of Mg O-C brick.The content of high temperature liquid phase is one of the main factors that reduce the high temperature performance of Mg O-C brick.The high melting point in the magnesia system has obvious hindering effect relative to the molten slag,but the bulk density of the magnesia aggregate products with high melting point is lower,which reduces the room temperature performance of the products.Magnesia containing high melting point phase is more suitable to be added to the product as a matrix.（2）The reaction of Al powder can react with Si O₂ in low melting point CMS and C₂MS₂ of 95 fused magnesia system makes most of the low melting point impurity phases CMS and C₂MS₂ in the fused magnesia system transform into the MgAlON phase with excellent corrosion resistance.And the generated MgAlON has a certain strength.Elemental Si powder can react with Si O₂ in low melting point CMS and C₂MS₂ of 95 fused magnesia system,and then react with N₂ to generate Si₂N₂O.At the same time,the addition of Si can promote the generation of 2Mg O·Si O₂,so as to achieve the purpose of phase optimization.Similar to the modified 95 fused magnesia,MgAlON phase and 2Mg O·Si O₂ phase are also formed in the medium sintered magnesia sample system with Al powder and Si powder,but the development degree of MgAlON phase is lower than that of MgAlON phase in 95 fused magnesia system.The Mg Al₂O₄ phase and 2Mg O·Si O₂ phase are formed by adding Al powder and Si powder in the high-silicon light fired powder system.（3）Among the MgO-C brick samples prepared with Al powder as additive,modified magnesia at 1500℃and N₂ gas atmosphere as the substrate and 97 fused magnesia as the substrate,the modified 95 fused magnesia sample showed the best corrosion resistance to alkaline slag.Followed by 97 fused magnesia sample,modified high silicon sintered magnesia sample,modified medium sintered magnesia sample.The development degree of MgAlON phase is the main factor affecting the corrosion resistance of the sample to alkaline slag.Mg Al₂O₄ phase can also improve the corrosion resistance of the sample.