Effect Of Nano-scale Particles On Pore Structure Modification And Properties Of Corundum-based Refractory Castables

Refractory castables are easy to install,environmentally friendly and cost-effective,which make it a popular material widely used in high-temperature applications,including metallurgy,petroleum,cements and glass industry.Pores,as among the important parts of the matrix of castables,are helpful to prevent the instant propagation of cracks and are closely related to properties of castables,including strength,thermal conductivity,thermal shock resistance and corrosion resistance.Therefore,in this paper,the filling and refining effect of nano particles on pores was utilized to form a large number of sub-micron or nano-scale pores in castables and the influence mechanism of pores on the microstructure and properties were also explored.Firstly,Al₂O₃-SiO₂ gel powder was used as an additive in this paper to explore the effect of sol particles on the microstructure and properties of ultra-low cement bonded castables.The results showed that the apparent porosity of the castable gradually increased with the addition of Al₂O₃-Si O₂ gel powder.In addition,the castable with 6%Al₂O₃-Si O₂ gel powder had the highest mechanical strength,the best fracture toughness and excellent thermal shock resistance.However,the hot temperature flexural strength of castables did not change significantly.Based on the study above,a new type of Al₂O₃-SiO₂ gel powder was introduced and its influence on the pore structure and performance of castables was explored.The results showed that as the heat treatment temperature increased from 110°C to 1100°C and finally reached 1500°C,the pore size of castables increased from 72 nm to 550 nm and finally to 8?m.And the shape of pores also changed from slender to circular.In the meantime,after firing at 1500°C,the apparent porosity of castables with Al₂O₃-SiO₂gel powder were higher than those without.Moreover,the castables had higher mechanical strength,better fracture toughness and more excellent slag resistance than the blank group.In order to further improve the high temperature performance of castables,the refining effect to the pores and in-situ reaction with Al₂O₃ of nano Si O₂ powder were used to form submicron/nano pores and mullite in castables.The results indicated that the addition of nano silica was beneficial to form nano pores at 110°C.However,after firing at 1100°C,a large number of nano pores in the castables disappeared,leaving only micro pores.In the meantime,the apparent porosity of castables increased with the addition of nano silica.Moreover,the HMOR of castables increased by about 110%,the residual flexural strength retention rate increased by about 200%and the penetration index also decreased by 11%,which indicated that the addition of nano SiO₂ was beneficial to improve the hot temperature properties and slag resistance properties of castables.