Synthesis Of Galaxite And Its Effect On The Properties Of Magnesia Refractory

With the rapid development of China’s cement industry,cement production is increasing and the demand for refractories for cement kiln burning zones is growing.Magnesia-chromite bricks are easily oxidized to toxic water-soluble Cr⁶⁺in the service environment,causing serious environmental pollution.At present,the periclase-hercynite refractories used in the burning zone of cement kiln have high fracture work,good flexibility and cement coating adherence.However,the hercynite has strict requirements on the atmosphere in the production process,and the process is complex.In use,Fe²⁺（?）Fe³⁺will produce volume effect,form cracks,and eventually induce structural damage and affect service life.Based on this,this subject synthesized galaxite and prepared periclase-galaxite refractories,and studied its high temperature performance and microstructure,reactivity with cement clinker and cement coating adherence.The main studies and results are as follows:1.Galaxite was synthesised by sintering and the effects of temperature,different sources of manganese and aluminium,atmosphere and additives on the synthesis of galaxite were investigated.（1）Compared to MnO₂ and MnCO₃,the galaxite synthesised using MnO as the manganese source has the highest synthesis rate,a larger grain size,a lower apparent porosity of 1.5%,a higher bulk density of 3.88 g/cm³ and a denser structure.Compared to Al（OH）₃,the galaxite synthesised usingα-Al₂O₃ as the aluminium source has less cracking,lower apparent porosity and a denser structure.Therefore,MnO andα-Al₂O₃ are more suitable as raw materials for the synthesis of galaxite.（2）In air atmosphere,galaxite began to form at 1500℃,but there were some Al₂O₃existed,and with the increase of temperature to 1600℃,galaxite was completely formed,galaxite grains were interconnected and sintered more densely,and the bulk density reached3.88 g/cm³.This indicates that 1600℃ is the ideal temperature for synthesis galaxite.（3）In reducing and nitrogen atmosphere,galaxite was completely formed at 1550℃,the apparent porosity was 0.8%,the highest bulk density was 3.91 g/cm³,and the grain development was good.This shows that the protective atmosphere is more conducive to the synthesis of galaxite and can reduce the synthesis temperature.Compared to air atmosphere,protective atmospheres have lower oxygen partial pressures,creating oxygen vacancies,accelerating oxygen ion diffusion transfer and promoting sintering.（4）The addition of ZrO₂ can obviously promote the sintering of galaxite,but when too much is added,it will hinder the growth of galaxite grains,and the optimum addition amount is 3 wt.%.The addition of Ti O₂ will promote the crystallization and growth of galaxite.If too much is added,impurities such as Al₂Ti O₅ and MnO₂ will be generated.Considering comprehensively,the optimum addition amount is 1 wt.%.2.The periclase-galaxite refractories were prepared by using magnesia and galaxite as raw materials,and the effects of the addition amount and introduction form of galaxite on properties and microstructure were investigated.（1）With the increase of the amount of galaxite fine powder,the apparent porosity of the specimens showed a tendency to decrease and then increase,the hot modulus of rupture of the specimens increased gradually.With the addition of 12 wt.%of galaxite,the specimen has a maximum hot modulus of rupture of 29.6 MPa,which is 19.6 MPa higher than that of pure magnesia refractories.Compared to periclase-hercynite refractories,it has better high temperature strength.（2）The addition of galaxite improves the thermal shock resistance of the material due to the thermal mismatch with periclase,the presence of microcracks within the material.With the same amount of galaxite added,the improvement effect of particles on thermal shock resistance is more obvious.With the addition of 8 wt.%galaxite particles,the residual strength ratio of the specimen after thermal shock is up to 81.3%,which is 32.4%higher than that of pure magnesia refractories.（3）At high temperature,due to the interdiffusion of Mn²⁺and Mg²⁺,composite spinel is formed near periclase,which promotes the bonding and improves the strength.The formation of composite spinel is accompanied by volume expansion to produce microcracks,and due to the interdiffusion of Mn²⁺and Mg²⁺,the material has higher toughness and improved thermal shock resistance.3.Static crucible and interlayer method were used to study the corrosion resistance and cement coating adherence of periclase-galaxite refractories.（1）The cement clinker reacts with galaxite to form more low melting point mineral phases,such as Mn₃Al₂Si₃O₁₂ and Mn₂Al₄Si₅O₁₈,and penetrates into the material.With the increase of galaxite,more liquid phases are formed,and the corrosion resistance of the material is gradually reduced.（2）The liquid phase of the cement clinker penetrates into the material,forming C₄AM as the main binding material for the kiln coating,while the Mnions inside the material diffuse to the surface to produce more C₄AM with the cement clinker,forming a stable kiln coating.A transition layer is formed between the material and the cement clinker,and the cement clinker and the material are bonded.The adhesion strength of the kiln coating is 3.4 MPa,which is higher than that of periclase-hercynite material.