Hongbin Tan

Preparation of mullite fibres by sol-gel processes using aluminium carboxylates and tetraethylorthosilicate

Abstract Mullite fibres were prepared using aluminium carboxylates (ACs) and tetraethylorthosilicate by sol–gel process. ACs were synthesised from dissolution aluminium in a mixture of formic acid and glacial acetic acid using aluminium chloride hexahydrate as catalyst. The optimum condition for obtaining ACs is as follows: the molar ratio of aluminium, formic acid and acetic acid was 1∶3∶2·26 and aluminium chloride hexahydrate was 10 wt-%. All the Al and Si components were mixed at the molecular level and linear molecules were formed in the precursor sol. The dried gel fibres completely transformed to mullite fibres at 1200°C and the calcinated fibres had a smooth surface and uniform diameter.

Synthesis and Characterization of Rich Silica Mullite Fibers by Sol–Gel Method Using Aluminum Lactate and Silica Sol

Rich silica mullite fibers were prepared from an aqueous solution of aluminum lactate and silica sol by the sol–gel method, in which the Al/Si molar ratio of fibers was 0.64. The aluminum lactate was prepared by mixing aluminum nitrate and lactic acid in the molar ratio of 1:3. The fibers sintered at 1200°C presented as an amorphous phase, with a rough surface and uniform diameter. Mullite and silica phases were obtained after the fibers were sintered at 1400°C for 1 h, and the mullite whiskers were observed at the fibers surface, with a high aspect ratio of > 10 (about 0.06 μm in diameter). The diameter of the whiskers reached about 0.5 μm at fibers surface when the fibers were sintered at 1600°C for 1 h.

Activation energy of mullite crystallisation from precursor fibres determined by differential scanning calorimetry

Abstract Mullite fibres were prepared by the sol–gel method using aluminium lactate and tetraethylorthosilicate. The aluminium lactate was prepared by mixing aluminium nitrate and lactic acid with a molar ratio of 1∶3. Thermogravimetry–differential scanning calorimetry, X-ray diffraction and scanning electron microscopy analysis were used to characterise the properties of the gel and ceramic fibres. The gel fibres completely transformed to mullite fibres at 1200°C, with a uniform diameter and dense microstructure. The active energy of mullite crystallisation was 1121·7 kJ mol−1 by the Kissinger equation, which was consistent with most data reported by other authors.