Studies On The Structure Mechanism Of Hierarchical Porous Mullite With Different Silicon Sources

Hierarchical porous mullite monoliths have been prepared via sol-gel process accompanied by phase separation. Propylene oxide(PO) acted as an acid scavenger to mediate the gelation, poly(ethylene oxide)(PEO) as the phase-separation inducer and network former, alμminμm chloride hexahydrate(Al Cl3·6H2O) as the alμminμm source. The route was improved by using hypotoxic tetraethylorthosilicate(TEOS) and nontoxic aqueous colloidal silica(Aq) instead of tetramethoxysilane(TMOS). The hierarchical porous mullite monoliths is prepared by adjusting the amount of H2 O, Et OH, Si/Al, PEO, PO and Na F, and aging temperature via sol-gel method. In addition, changing the amount of different relative molecular weight of phase-separation agent is necessary to synthesize hierarchical porous mullite monoliths with controllable macropores. The synthesis mechanism and microstructural development were comparatively investigated by scanning electron microscopy(SEM), thermogravimetry-differential thermal analysis(TG-DTA), X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR) and nitrogen adsorption-desorption. The optimμm amount of PEO, gel times, hardness, shrinkage, transformation temperature and relative crystallinity of mullite phase, and pore size with different silicon sources are not the same. It was found that the mixing degree of precursors and concurrent process of gelation and phase separation are key elements to get well-defined hierarchical porous mullite monoliths. In addition, the monoliths with high relative crystallinity are more likely to be obtained under low transformation temperature in organic silicon sources system. By adjusting the relative molecular weight and the amount of phase separation agent in inorganic silicon source and organic silicon source system, hierarchical porous mullite monoliths with adjustable pore size are successfully prepared. It may provide a broader prospect for this materials.