The Study On Preparing The Porous Mullite With Al Powder And Fly Ash

The Al powder and fly ash used to synthesize the porous mullite and the mechanism and influencing factors were also studied. Because the excessive impurities in fly ash had negative effect on the properties of samples, the new impurity removal method using hydrochloric acid and Al powder was further investigated. Then the pore-forming mechanism and influencing factors were also discussed. The conclusions were listed as follows.The activity of Al powder could reduce the sintering temperature by 100oC and then save the synthesis cost. The oxidation reaction of Al powder made the samples expand when the temperature rose. The expansion could compensate the shrinkage at 1500oC, which produced the pores. The study showed that the mass ratio of fly ash/Al metal was 89.5:10.5, the samples sintered at 1300oC/30min then 1500oC/4h performed the best properties and pore microstructures. Because the Mg addition(2wt%) was beneficial to the formation of rod-like mullite which improved the pore stability, the addition made the samples properties(porosity 30.7%, flexural strength 47.9MPa) better than those of no Mg addition.The new method of impurity removal is more beneficial for the properties of sintered samples than traditional method. The application temperature was enhanced to 1600oC after removing Fe elements. The samples at high temperature could produce gas and pores in the sintered samples were formed.By studying the new method of impurity removal by using 40ml hydrochloric acid, it's found that the green body after dry-pressing(10KN) were sintered at 1500oC/4h, which made the properties (porosity 51.9%, flexural strength 38.5MPa) of porous mullite best. And the mullite amount, porosity and flexural strength in sintered samples after tempering treatment at 1400oC/4h sample didn't change largely. It showed that the samples after impurity removal performed better than before and could satisfy requirement in the low temperature(1400 oC).