Effect Of Different Supports Of Iron And Alumina On Properties Of Magnesia-hercynite Material

Because of its unique nature and excellent performance, magnesia-hercynite brick becomes the most promising substitutes of the magnesia chrome brick used in the burning zone of cement rotary kilns, which achieve the chrome-free of refractories used in cement rotary kilns. At present the main raw materials of preparing magnesia-hercynite are sintered, fused hercynite or sintered, fused magnesia-iron clinker with fused magnesia alumina spinel. The four magnesia-hercynite bricks still possess some differences which may not only existed in the production costs but also in the performance, although they have the similar chemical composition, phase composition or structure. In this research, based on controlling the similar chemical composition and ensuring the same condition of specimen preparing, the specimens were prepared using sintered hercynite, fused hercynite, sintered magnesia-iron clinker, fused magnesia-iron clinker and fused magnesia alumina spinel as iron and alumina supports, respectively. The physical properties, performance of forming a coating, thermal shock resistance and structure flexibility were tested in the same measuring conditions to evaluate the difference of the four materials’ use of performance accurately.1. Specimens with sintered hercynite and fused hercynite have the similar phase composition and microstructure. The mutual diffusion reaction occurs between periclase and hercynite, forming(Mg,Fe2+)Al2O4, spinel and magnesia-iron solid solution under high temperature,which leads to loose structure of the hercynite particles. And combination between hercynite and periclase is looser relatively, with much porous in the structure. Three phase regions existed in the specimens coming from the oxidation and diffusion of ion: firstly, ferrous ion dissolves into the crystal structure generating magnesia-iron solid solution. Secondly, the mutual diffusion between periclase and hercynite generates(Mg,Fe2+)Al2O4 phase. The third is the magnesium iron spinel and magnesia spinel phase region.2. Specimens with sintered magnesia-iron clinker and fused magnesia-iron clinker have the similar phase composition and microstructure. The iron is widely distributed in the structure. The diffusion reaction occurs between magnesia-iron clinker and magnesia alumina spinel, generating Mg(Fe3+,Al)2O4 compound and continuous solid solution AlFe2O4. Large part of iron existed in the edge of magnesia-iron clinker particles diffuse into the crystal structure of magnesia alumina spinel, while the spinel possesses good stability and the alumina is diffused little into the magnesia-iron clinker. Combination between magnesia-iron clinker grain and magnesia alumina spinel is tight.3. Specimens with sintered and fused magnesia-iron clinker have higher bulk density, cold comprehensive stress and lower apparent porosity and thermal expansion. Specimens with fused hercynite and magnesia-iron clinker possess higher refractoriness under load. Comprehensively, among the four kinds of magnesia-hercynite, the specimen with sintered hercynite as iron and alumina support possesses weak physical properties at room temperature and high temperature strength, while the specimen with fused magnesia-iron clinker and magnesia alumina spinel as iron and alumina supports possesses good physical properties at room temperature and high temperature strength.4. The specimen with sintered hercynite possesses suitable elastic modulus and good structure flexibility. The retention rate of elastic modulus is relatively higher after thermal shock, which means that the specimen has good properties of thermal shock resistance. While the specimen with fused magnesia-iron clinker and spinel has higher elastic modulus and poor structure flexibility. The retention rate of elastic modulus is relatively lower after thermal shock, which means that the specimen possesses poor property of thermal shock resistance. Comprehensively, specimens with the fused hercynite and sintered magnesia-iron clinker as iron and alumina supports respectively have the property of thermal shock resistance between the above two.5. The specimen with sintered hercynite has better property of forming coating, while the specimens’ property of forming coating with magnesia-iron and spinel is not very well. The specimen with fused hercynite possesses poor property of forming coating. Through preparing coating on the working face of magnesia-hercynite brick, it can improve the property of forming coating significantly. The coating materials contain iron and alumina which can react with the brick and cement respectively at high temperature, which strengthen the reaction between the brick and cement and speed up the forming of coating.