The Research On Improving Spalling Resistance Of Al₂O₃-MgO-CaO System Castables

Al₂O₃-MgO-CaO system castables are widely used in well blocks,porous plug,lining castables and RH snorkel of refining ladle,and it is developing to high purity system nowadays.The tabular alumina,the aluminum-rich spinel（sintered or fused）and the pure calcium aluminate cement are used in the Al₂O₃-MgO-CaO system castables as the main starting materials.Through a large number of application observation and the analysis of residual bricks,spalling is the main damaging reason of this system’s products.Therefore,improving the spalling resistance of this kind of material is the key method to improve its service life.It is proved that Al2O3-MgO-CaO system castables with 4-6%MgO has better applicating effect according to the previous research results and experience.The aim of the study is to find the optimum process route to improve the spalling resistance of Al2O3-MgO-CaO system castable through the adjusting the proportion of alumina and calcium oxide,adding the different type SiO₂,changing the structure and fixing MgO content of 4%.The main contents of the study are as follows:1.The effect of the in-situ CA₆ amount on Al₂O₃-MgO-CaO system castable’s spalling resistance;2.The effect of the different type SiO₂ on Al₂O₃-MgO-CaO system castable’s spalling resistance;3.Effect of structure on Al₂O₃-MgO-CaO system castable’s spalling resistance;The spalling resistance of Al₂O₃-MgO-CaO castables can not be evaluated scientifically and accurately by the current testing method of thermal shock resistance of refractories.The spalling resistance of Al₂O₃-MgO-CaO castables was comprehensively investigated by testing performances related with its thermal shock resistance.The results are as follows:1.The in-situ CA₆ amount and the hot modulus of rupture gradually increase in specimens with the increase of CaO amount.The DSC curve shows a rapid CA₆formation in the specimen when the sintering temperature is higher than 1500℃,and at the same time,the high temperature modulus of elasticity of the specimen sharply decrease.It reflects that rapid expansion of the CA₆ generation causes the obvious structure change in specimens,which is the main reason for its spalling.2.The hot modulus of rupture of the specimen with adding 0.5%wt different type of SiO₂ greatly decreases,which can’t meet the requirement of application.The high temperature modulus of elasticity of the specimen with fused quartz at different temperatures is relatively gentle,and the residual strength of the specimens is the highest after the 5 times thermal cycling.It can be included that the introduction of the appropriate amount of fused quartz can meet the application strength requirements under high temperature and reduce the material dramatic expansion caused by the rapid formation of CA₆ at high temperature,thus the material’s spalling resistance is improved.3.the high temperature strength and other performance of Al₂O₃-MgO-CaO system castables less change by the introduction of chemical fiber and changing the proportion of grain and matrix.The porosity of the specimen increased,and the elastic modulus decreased with the increasing of chemical fiber and the 1-0mm corundum.It can be indicated that the spalling resistance could be improved by adjusting the structure of the specimen,giving CA₆ enough growth space,making its crystal preferentially grow along the base plane,and forming the flake shape.