| Porous mullite ceramics were fabricated with flyash, aluminium source （alumina and aluminium hydroxide） as starting materials through starch consolidation method. The bending strength, apparent porosity was tested. Microstructure of the samples was observed by scanning electron microscopy （SEM）. X-ray patterns of the samples were tested on X-ray diffractometer using CuKαradiation. The study indicated that Al （OH） 3 is more suitable to be used to prepare high strength mullite ceramics.AlF3 as additive is helpful to form mullite whisker in a lower temperature. The whiskers constructed an interlocking structure, which enhanced the bending strength of the porous mullite ceramics. As a source of aluminium, Al（OH）3 was more suitable to fabricate needle-like mullite than A12O3.The result shows that the strength of the porous mullite ceramics produced with Al（OH）3 and AlF3 were enhanced from 70MPa to 120MPa.For to reduce the sintering temperature of the porose mullite ceramics produced with flyash, La2O3, Y2O3 and MgO were added in to promote the densification （at 1400℃）of the mullite ceramics fabricated by flyash-Al（OH）3-AlF3 system, respectively. The research indicated that all the additives （La2O3, Y2O3, MgO） can made the samples densification at 1400℃. The mechanism of promote densification of the additives is that La2O3 and Y2O3 formed liquid phase in a low temperature with reactants respectively, and MgO formed solid solution promoted densification. The mullitization process was restrained while added overmuch MgO（10wt%）. With bauxite as alumina source and added MgO（3wt% or 5wt%） can’t produced mullite ceramics at 1400℃. The main phase in ceramics is corundum and quartz.In this paper, porous mullite ceramics with strength increased were produced with flyash as raw materials at 1400℃by added additives and aluminium sources, and the bending strength were enhanced successfully. And then increase the industrious application of the porous mullite ceramics prepared from flyash. |
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