Research On The Preparation And Cementitious Behavior Of Barium Aluminate Cement

The hydraulic binder at room temperature can react with water and make the material get strength,which is widely used in unshaped refractory materials,in which calcium aluminate cement is the most widely used.But in the castable of calcium aluminate cement,the physical properties of the material at high temperature are reduced because of the introduction of CaO.Barium aluminate with hydraulicity can also be used as refractory materials.The melting point of BaAl₂Si₂O₈ produced by the reaction of barium aluminate with SiO₂ at high temperature is higher,and BaAl₂Si₂O₈ has good high temperature properties,it is able to solve the problem of low performance of CaAl₂（SiO₄）₂ low melting phase produced by calcium aluminate cement at high temperature.But the research on the preparation of barium aluminate is lack of systematicness.Barium aluminate also has the problem that the hydration speed is too fast,which affects its usage performance.How to slow down its hydration speed is the key factor affecting the usage of barium aluminate.To solve the problems above,this paper using barium aluminate as the research object,studied the effects of different raw materials and different calcination temperatures on the synthesis of barium aluminum;then the hydration characteristics of barium aluminum,the way to slow down the hydration rate of barium aluminate,and the barium aluminate and Al₂O₃ composite slurry rheological activity the characteristics were studied;on this basis,studied the effect of barium aluminate cement on the properties of corundum castable.The conclusions are as follows:（1）Using high temperature solid phase synthesis method,with BaCO₃ or BaSO₄ as the source of barium,Al₂O₃ or Al（OH）₃ as the aluminum source,BaAl₂O₄ can be synthesized by calcining 3h at a certain temperature,and the higher the calcination temperature,the more the BaAl₂O₄ content.The temperature of synthesizing BaAl₂O₄with BaCO₃ and Al（OH）₃ is the lowest,and the BaAl₂O₄ phase with high purity can be synthesized at about 1000℃.（2）BaAl₂O₄ hydration was carried out at 25℃and 90%humidity with the ratio of water to cement（1:1）.The composition of the hydrated phase is complex,including AlO（OH）,Al（OH）₃,Ba（AlO（OH）₂）₂,BaAl₂C₂O₁₃H₁₀ and other phases.The morphologies of the hydrated products of BaAl₂O₄ are mainly long columnar and needle like,and a small amount of granules and flakes..The hydration rate of BaAl₂O₄ is fast,the exothermic peak appears around 9.4min,and then the hydration ends quickly.After 3h,the hydration is close to the end（3）In order to reduce the hydration rate of BaAl₂O₄ and slow down the setting time,the methods of adding active Al₂O₃ micro powder and citric acid were used respectively to slow down the hydration rate.Adding active Al₂O₃ micro powder can reduce the hydration speed of BaAl₂O₄.When the content of Ba Al₂O₄ is 30%,The initial setting time of the composite of Al₂O₃ micro powder and BaAl₂O₄ is 120 minutes,which is similar to the initial setting time of the present commercial calcium aluminate cement.Adding citric acid into BaAl₂O₄,the occurrence time of the exothermic peak of BaAl₂O₄ hydration gradually increased with the increase of added amount.When the addition amount was 2%,the exothermic peak appeared at 14.4 minutes.The hydration weight gain rate of pure BaAl₂O₄ was 34%when it was hydrated after 120 minutes.After adding citric acid of 1%and 2%,the weight gain rate was 8%and 5%.Compared with the commercial calcium aluminate cement Secar71,the viscosity of the slurry of BaAl₂O₄ and the active Al₂O₃ composite is larger,which is a non-Newtonian fluid,and its thixotropy is better.（4）BaAl₂O₄ and active Al₂O₃ micro powder composite or Secar71 cement were used respectively as binder to prepare corundum castable.After heat treatment at 1550℃for3h,in specimens with SiO₂ powder,in the specimen using BaAl₂O₄ and active Al₂O₃micro powder composite as binder,there are barium feldspar（BaAl₂Si₂O₈）phase formation;in the specimen using Secar71 cement as binder,there are calcium feldspar（CaAl₂（SiO₄）₂）phase formation.The high temperature rupture strength of corundum castable with BaAl₂O₄ and active Al₂O₃ composite is higher than that of corundum castable with calcium aluminate cement Secar71,which is more than 80%,and increases with the increase of BaAl₂O₄ content.