Comparing the phase transformation of continuous alumina fiber and xerogels derived from the same precursor

Phase transformation is essentially important for the microstructures and properties of sol-gel prepared alumina fiber and powders. In this study, alumina precursor fiber and xerogels were prepared using the same aluminum carboxylate sol. The phase transformation and microstructure evolution of the precursor fibers and xerogels were investigated using TG-DSC, XRD, TEM, and SEM methods. The alumina precursor fiber and xerogels have similar chemical structures and Al(III) species. After preheated at 600 degrees C, most of the free water molecules, hydroxyl groups, nitrate acid radical, formic acid radicals, and acetic acid radicals are removed from the alumina precursor fiber and xerogels. The preheated fiber and xerogels exhibit amorphous phases. From the TG-DSC curves, the transformation temperature from gamma-Al2O3 to alpha-Al2O3 in the preheated fiber is 30 degrees C lower than that in the preheated xerogels. The TEM results suggest that the fiber calcined at 1000 degrees C for 1 h can be completely transformed into alpha-Al2O3 phase, while the xerogels need to be calcined at 1100 degrees C for 1 h to completely convert into the alpha-Al2O3 phase. The difference in the phase transformation of the alumina fiber and xerogels was discussed in this paper.