Effect of Precursor pH on One-dimensional Growth of Mullite Prepared by Sol-Gel Method with WO3 Catalyst

One-dimensional mullite particles were synthesized by sol-gel method from hydrous aluminum chloride (AlCl3 ¤6H2O) and tetraethoxysilane (TEOS) as raw materials and WO3 as catalyst. WO3 had a desired effect on the anisotropic growth of mullite particles by forming aluminum tungstate (AlWO4) as growth template at low temperature, which was greatly dependent on the precursor pH. NMR results indicate that the pH during gelation can highly influence the homogeneity of precursor, mullite formation and microstructural features. One-dimensional mullite particles are significant only when the precursor pH is lower than 7. Morphology of the mullite particles synthesized with pH transforms from anisotropy to isotropy and platelike.