Effect of Cobalt Oxide Addition on the Microstructure and Sinterability of Mullite Synthesized by Sol-gel Method

Mullite precursor powders were prepared by a sol-gel method by using aluminum nitrate nonahydrate and ethyl orthosilicate as raw materials, as pH value of reaction solution is about 8. The effect of cobalt oxide addition on the phase compositions and densification of mullite cera-mics obtained by sintering of mullite precursor were investigated. The results show that the formation temperature of mullite was significantly reduced, and it was about 100℃ lower than that of the sample without cobalt oxide addition. The sinterability of mullite precursors prepared by sol-gel method shows that the densification rate of the sample with cobalt oxide is faster than that of the sample without cobalt oxide. The maximum bulk density of the sample can reach to 2.912 g/cm3, as the mullite precursors with 10wt% cobalt oxide addition were sintered at the temperature of 1 400℃ for 2 h. And a large number of needle-like mullite grains with the ratio of length to diameter of ~14 were obtained in the sample. Needle-like mullite grains interweave with each other to form a dense network structure. The effect of cobalt oxide addition on the phase compositions and densification behavior of mullite ceramics maybe attributed to Al3+ in mullite [AlO6] octahedron structure may be replaced by Co2+, which cause its grain lattice distortion and activate its grain lattice. And mullite was formed and sintered at the lower sintering temperature. © 2020, Materials Review Magazine. All right reserved.