Study On Performance Optimization And The Explosive Resistance Of Hydratable Alumina Bonded Corundum Castable During Heating

Hydratable alumina is a kind of high-purity refractory binder.No other impurities are introduced,and low-melting liquid phase is rarely formed at high temperature with hydratable alumina as binder,which is beneficial to improve the thermal strength,volume stability of the castable and the resistance to the formation of cracks.However,the aluminum sol gel produced by the hydration of hydratable alumina can fill the internal pores of castables,resulting in lower air permeability and narrower dehydration temperature range of the hydrated product,which makes the castables easy to explosive spalling during heating.In severe cases,the facilities can be even damaged totally.Therefore,effects of particle size distribution,curing time,addition of ultrafine powder,hydratable alumina,H₂O₂ and polypropylene fiber on physical properties and explosive resistance during heating of alumina based castables bonded by hydratable alumina were investigated in present paper.It was found that addition of microsilica and reactiveα-Al₂O₃ show small influence on explosive temperature with a range of 100℃although they indicate a great influence on the physical properties of the castable.The experimental results showed that the explosive resistance of the specimens increased at first and then decreased with the mass fraction of aggregate gradually increased from 60%to 70%;when the mass ratio of particles to fine powder was 68:22,the explosive resistance reached the best values.With the addition of microsilica gradually increased from 0 to 6%,the explosive resistance increased at first and then decreased;when the microsilica addition was 1%,the explosive resistance reached the best values.When adding 2%microsilica,the addition of showed less impact on the explosive resistance;with the addition ofα-Al₂O₃ gradually increased from 0 to 6%,the explosive resistance decreased at first and then increased,and when no reactiveα-Al₂O₃addition,the explosive resistance reached the best values.The bonding strength,air permeability and moisture content of the specimens,and their relationship with explosive resistance were studied by changing the hydrated alumina addition and curing time.The more hydratable alumina content,the less free water content in the specimens,and the more adsorbed water and bound water content.With 1%hydratable alumina addition,the free water content was as high as 86.9%.When the hydratable alumina content was 9%,the free water content was only 34%.After curing at30℃for 12h,the explosive resistance of the specimens increased with the increase of the hydratable alumina content.With the prolongation of the curing time,the explosive resistance of each group of specimens was gradually improved,but the higher the content of hydratable alumina,the smaller the value of the increase in explosive resistance.After60h of curing,the temperature of anti-explosion of the specimens with 1%hydratable alumina content was as high as 800℃,which was 500℃higher compared with that after12h curing.It is believed that the moisture content,especially the free water content,was an unfavorable factor for the explosive resistance of the specimens,the bonding strength has an important positive effect on the explosive resistance,and the air permeability could have a fundamental improvement effect on the explosive resistance.The addition of H₂O₂ could significantly improve the explosive resistance of the castables,especially when H₂O₂ addition exceeds 0.075%.However,when H₂O₂ addition exceeds 0.075%,the pore amount within 5～20μm in pore diameter increased significantly,which makes the air permeability increase significantly and the mechanical strength decreases drastically.Addition of pore-forming agent polypropylene fiber showed a little effect on the explosive resistance of the castables;when polypropylene fiber addition reached 0.1%,the temperature of anti-explosion increased by 100℃.However,the composite additions of H₂O₂ and polypropylene fiber improved explosion resistance significantly.H₂O₂ generated O₂ by spontaneous decomposition reaction in the castable,formed a series of nearly spherical pores in the castable.These pores were evenly distributed in the castables,but the connected channels between the pores are still relatively narrow and tortuous,and the narrow and long pores formed by the melting and shrinkage of polypropylene fibers could overlap these pores to organically link the pores together,provided high-speed channels for the migration and diffusion of water vapor and moisture,thereby improved the explosive resistance of the castables.Therefore,the composite addition of H₂O₂ and polypropylene fiber is a way to effectively and stably improve the explosive resistance of the castables.