Preparation Of Porous Cordierite Ceramics By Environmentally Friendly Foam Gel-casting Method

Cordierite porous ceramics are often used as filter of molten metal,hot gas,automobile exhaust and diesel particulates due to their high permeability,good thermal stability,corrosion resistance and high temperature resistance etc.At present,the cordierite porous ceramics used in casting have a contradiction between high porosity and high strength,so it is meaningful to develop a new green process to prepare materials with high porosity,high permeability and high strength.In this thesis,single-phase cordierite porous ceramics were prepared using Mg O,?-Al₂O₃and Si O₂ as the main raw materials,by a process combining environmentally friendly foam gel-casting method with vacuum freeze-drying technique.The effects of solid content?15?25 vol.%?,the amounts of gelatin?6?8 wt.%?and foaming agent concentration?2?6 g/L?have been investigated by orthogonal experiment and single factor experiment individually.At last,a mathematical model of the relationship between compressive strength and porosity was established based on the experimental results and related theory.The results of range analysis and variance analysis of the orthogonal experimental show that the factors affecting the total shrinkage,open porosity and specific strength of the material are solid content,the amount of gelatin and foaming agent concentration from main to secondary.In a given factor level,solid content has significant influence on total shrinkage,open porosity and specific strength.The effects of amount of gelatin on total shrinkage and specific strength are relatively significant,but the influences on open porosity are not obvious.For total shrinkage,foaming agent concentration is relatively significant.but it has insignificant effects on the open porosity and specific strength.The optimal solution to determine the specific strength is 25 vol.%?solid content?,10 wt.%?amounts of gelatin?,2 g/L?foaming agent concentration?.The result is verified by subsequent experiments.The total shrinkage of the sample is-0.79%,the open porosity is 83.07%,and the specific strength is 9.06×10³ N·m/kg.The results of single variable experiments on the significant influencing-content show that the solid content has no effect on the composition of the material and has a small effect on the total shrinkage rate,but it has an obvious effect on the porosity,compressive strength,permeability and thermal expansion coefficients.In the scale of?0.05?0.15 g/m L?,gelatin concentration has a significant effect on the total shrinkage rate,pore structure,pore rate,bulk density and compressive strength of the prepared material.Considering its filtration application,the samples prepared with solid content 20 vol.%,amount of gelatin 8 wt.%,foaming agent concentration 2 g/L have the best overall performance.The open porosity is 87.85%,the compressive strength is 1.90 MPa,the permeability is 1.69×10^-11 m²,and the coefficient of thermal expansion is 1.96×10^-6/?.According to the Gibson-Ashby model and the MSA model,all the experimental data in this paper were fitted,and two expressions??28?1212??1-P?^3.21?r=0.958?and?_f?28?5067460exp?-17.05P??r=0.912?were obtained.In contrast,the Gibson-Ashby model is more suitable for fitting the cordierite porous ceramics prepared by this method.The formula can be used to predict and design the mechanical properties of cordierite porous ceramics prepared by the environmentally friendly foam coagulation method.The preparation method developed in this thesis is a green preparation technology,and the prepared material has higher porosity and higher strength,which is guiding significance for other porous ceramics.