Effect Of Pore Structure On High Temperature Performance Of Alumina Thermal Insulation Materials

The pore structure parameters have a great influence on the high-temperature performance of thermal insulation materials.In order to solve the problems of large pores and black core residue inherent by the method of adding pore forming agent,the research group used the inorganic sol impregnation method to retain the original texture of the pore forming agent,and the room temperature performance of alumina thermal insulation materials was deeply studied,but the high temperature performance of materials with optimized pore struture was not discussed.Therefore based on the preparation of alumina thermal insulation material by adding pore forming agent,the plant pore forming agent was pretreated by sol-gel impregnation method,and the plant woven pores were introduced into alumina thermal insulation material to refine the pore structure and study its high temperature performance.The main research contents are as follows: walnut shell,rice husk and sawdust impregnation with SiO₂ sol,Al2O3 sol and ZrO₂ sol are used as pore forming agents to prepare alumina insulation materials,and the effects of sol type and concentration on high temperature performance of alumina thermal insulation material are studied;in addition,using flake graphite,corn starch and carbon fiber as pore-forming agents to prepare alumina thermal insulation materials,and the effect of pore shape on the high-temperature performance of alumina thermal insulation materials was stuied;based on the image analysis method and fractal geometry to study the pore structure parameters of the material,and used the "critical stress fracture theory" and "thermal shock damage theory" to analyze thermal shock resistance of the material;finally,the relationship between mean pore size,fractal dimension and thermal shock resistance factor is comparatively analyzed.The following results can be obtained:（1）The high temperature volume stability,normal temperature flexural strength,elastic modulus and load softening temperature of the alumina heat insulation material prepared by impregnating walnut husk,rice husk and sawdust with different sols have been improved,but the high temperature performance of the material is quite different.Among them,the alumina thermal insulation materials prepared with 5 wt.% ZrO₂ sol impregnation walnut shell,5 wt.% ZrO₂ sol impregnation rice husk,7 wt.%Al₂O₃ sol impregnation sawdust and three sol（3wt.%SiO₂、7wt.%Al₂O₃ and 5wt.% ZrO₂ sols）impregnation walnut shell as poreforming agents have better comprehensive high temperature performance.（2）When flake graphite,corn starch and carbon fiber are used as pore formers,the internal pore shapes of the alumina thermal insulation material are flaky,spherical and striped,respectively.Using carbon fiber as the pore-forming agent,the material has good comprehensive properties,with a flexural strength of 47.10 MPa,a retention rate of elastic modulus of 85.8%,and a higher softening temperature under load.（3）By means of image analysis and fractal geometry analysis of pore structure parameters of alumina insulation materials prepared with different pore-forming agents,it is found that the number of pores increases and the mean pore size decreases after pore-forming agents with sol impregnation,which can improve the mechanical properties of the samples.The calculated results of the thermal shock resistance parameters of the samples are consistent with the experimental results,which further proves that the sol-impregnated pore former can improve the thermal shock resistance of the material.The samples prepared by impregnating walnut shells with three sols have better thermal shock resistance,and their thermal shock fracture resistance and thermal shock resistance performance are better.