Study On The Preparation Of Mullite Lightweight Aggregate And Its Properties

As an important high temperature component in the continuous casting process,the tundish is required to have the functions of heat insulation,improving the composition of molten steel and improving the purity of steel.The permanent lining of tundish inside the working lining,which plays the role of supporting,buffering and heat insulation.Mullite is often used as permanent lining castable in tundish because of its low thermal conductivity.However,the synthesis temperature of mullite is as high as 1500℃,and the kyanite with the highest conversion rate of mullite in mineral of sillimanite group is only 78%.The mullite conversion rate of kyanite is fast,so too high synthesis temperature will lead to rapid volume expansion and reduce the performance of the material.In order to reduce the production cost of mullite,some raw materials can be replaced by industrial waste coal gangue with similar composition.However,the microstructure of coal gangue after high temperature calcination will present a fluffy porous structure,which will reduce the performance of the material.In view of the above problems,this thesis takes kyanite and coal gangue fine powder as raw materials,and uses silica sol and aluminum sol as binders respectively.The research includes three aspects: preparation process of mullite aggregate,selection of binder and raw material ratio.(1)The optimum calcination temperature and holding time of lightweight mullite aggregate containing aluminum sol or silica sol were investigated,and the mechanism was expounded in combination with microstructure and phase composition.(2)The effects of silica sol or aluminum sol content on the physical properties,thermal shock stability and volume stability of aggregates were studied,and the mechanism of the two sols was explained by combining the microstructure and phase composition.(3)The effects of coal gangue addition on the microstructure and phase composition of lightweight mullite aggregates were studied,and the physical properties,thermal shock stability and volume stability of aggregates were studied.And reached the following conclusions:1.When silica sol or alumina sol was used as a binder,the optimum synthesis conditions were 1500℃ for 60 min and 120 min,respectively.At this time,the secondary mullite and recrystallization sintering were almost finished.Mullitization expansion and sintering shrinkage offset each other.The mullite grains were well developed and interspersed with each other to form a close network microstructure.2.Sol as a binder can reduce the synthesis temperature of mullite.Sol improves the physical properties,thermal shock stability and volume stability of mullite aggregates.Silica sol is better than aluminum sol.The surface energy and activity of the sol particles are higher,which can increase the nucleation probability of mullite.This improves the conversion rate of mullite,and also makes the shape and distribution of mullite grains more uniform.The formed network structure improves the cold compressive strength and volume stability of the sample.The sintering driving force provided by the sol particles makes the sample have higher thermal shock stability.3.Coal gangue reduces the cost of synthesizing mullite.When the content is too high,the network microstructure of mullite will be destroyed.The nucleation of nanoparticles can connect the loose structure of coal gangue and form a closely connected polycrystalline crystal structure.The columnar mullite will be wrapped by a small amount of amorphous silica,which improves the cold compressive strength and thermal shock stability.When the amount of coal gangue is too much,it is difficult to form a network structure between the grains,and the performance of the sample decreases sharply.