| Alumina is cheaply available and has good mechanical and thermodynamic properties.The porous ceramics made from alumina has excellent performance such as high temperature resistance,good mechanical properties,large specific surface area and many other unique properties.It has wide application value in many fields such as composites preparation,sound insulation,filtration and aerospace.In this thesis,the foam-freeze casting method is used to prepare porous alumina ceramics with excellent properties using alumina as the raw material.The main research content includes the orthogonal experiments to explore the primary and secondary factors,single factor cycle experiment on the significant factors and discussion of all the experimental results.Using a three-factor and three-level orthogonal experimental design,the main influencing factors（solid content,foaming agent concentration,sintering temperature）of the preparation of porous alumina ceramics by the foam-freeze casting method are experimentally explored,and the orthogonal table L9（34）is selected.The closed porosity of the prepared samples is between 0.01 and 1.29%,and the open porosity lies between77.43 and 86.92%.The specific strength is 18.41-28.69×103 N·m/kg.The results of the experiment were analyzed by range analysis,variance analysis and matrix analysis.In the range analysis,blank column is found that the range is relatively large,indicating that there may be a certain interaction between the factors.The analysis of variance shows that for the indicators determined by the experiment,each factor is not a significant influencing factor,which indirectly proves that each factor is insignificant.There may be interactions between factors.Further use of matrix analysis,the results obtained are consistent with the range analysis,which confirms the accuracy of the orthogonal experimental theoretical analysis.At the same time,through the analysis of the total weight matrix of the orthogonal experiment,it is concluded that the optimal scheme of the orthogonal experiment is A1B2C1,that is,the solid content of 25 vol.%,the foaming agent concentration of 6 g/L,and the sintering temperature of 1550°C.The optimal experimental plan obtained by the orthogonal experiment was verified,and the sample with the specific strength as high as 30.27×103 N·m/kg with the open porosity of 80.94%and the closed porosity of 0.22%.Each group of orthogonal experiments shows that the orthogonal experiment design and statistical analysis are effective,and the orthogonal experiment design is used to obtain better process parameters.Using foam-freeze casting method,under the conditions of solid content of 25 vol.%and sintering temperature of 1550℃,by expanding the range of foaming agent concentration（0.2-24 g/L）,the effect of foaming agent concentration on structure and performance are studied.The prepared alumina porous ceramic preform has an open porosity between 78.42%and 80.45%,and a very low closed porosity only 0.23%to0.71%.The compressive strength is between 16.56 and 27.60 MPa,the permeability is4.963×10-12-1.469×10-11 m2 and the coefficient of thermal expansion is between8.431×10-6-8.264×10-6/℃.The comprehensive performance of porous alumina ceramic is the best when the foaming agent concentration is 1 g/L.By changing the solid content of the slurry in a wide range（10-45 vol.%）,the total porosity is 51.67-93.96%,the compressive strength is 0.58-68.88 MPa,the permeability is 8.790×10-11-7.125×10-12 m2 and the thermal expansion coefficient of 8.334×10-7-8.573×10-7/℃.The solid content has a great influence on the porosity,compressive strength,permeability and pore structure of the prepared material.By adjusting the solid content,porous alumina ceramics with excellent comprehensive performance can be prepared. |
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