Preparation of Porous Mullite Ceramics by Fly Ash/Al Compositions

Porous mullite was prepared from a reactive mixture of Al metal powder and the fly ash produced by power plant. The sintering ceramics was characterized for the pore structure and phase identification studies. It was found that the sintered specimen expands at first (1300-1400 degrees C) and then shrinks which was correspondence to the changing of open porosity. The expansion was attributed to the fact that the alumina produced from the oxidation reaction of Al powder made the volume larger than the starting mixtures. At 1550 degrees C, it was inferred that the alkaline element in the fly ash made the mullite decomposed then destroyed the mullite structure. The SEM photographs suggested us that the pore diameter of the sintered ceramics might be adjusted by adding Al powder with different grain sizes. Moreover, because of the rod-like mullite produced in the pores, Mg metal addition could develop the further modification of the pore structure with similar porosity (47% at 1400 degrees C/4h) compared with that (53%) with 0wt % Mg metal powders.