LI Fengyou ¹, ZHANG Ling ¹, CHANG Yanan ², SU Xin ³, ZHANG Zhihao ², ZHANG Huan ¹

(1. School of materials and metallurgy, Liaoning University of Science and Technology, Anshan 114051, Liaoning, China; 2. Shandong Refractories Group Lunai Kiln Refractories Co., Zibo 255200, Shandong, China; 3. Research Institute of Refractories, Yingkou Qinghua Group, Yingkou 115100, Liaoning, China)

Abstract: Mullite materials were in-situ synthesized by solid state reaction sintering using nano-η-Al₂O₃ powder as aluminum source, quartz powder, silica fume, white mud (soft clay) and composite powder (white mud︰quartz powder=25︰75) as silica source. The effects of different silicon sources and temperatures on the sintering properties, phase composition and microstructure of the samples were investigated, and the synthesis mechanism of mullite was analyzed. The results show that the sample with white mud as silicon source has the best properties at 1550 ℃ for 3 hours. Its bulk density is 2.86 g/cm³, the apparent porosity is 3.5 %, and the flexural strength is 135.6 MPa. The samples prepared by nano-η-Al₂O₃ powder and other three silicon sources except white mud are all mullite phase diffraction peaks. The sample mullite crystals prepared from quartz powder and silica fume are short columnar with relatively low flexural strength, while the sample mullite crystals prepared from white mud and composite powder are long columnar with relatively high flexural strength. Nano-η-Al₂O₃ reacts with amorphous SiO₂ separated from white mud to form mullite, and then reacts with SiO₂ in quartz powder and silica fume to synthesize mullite.
Key words: nano-η-Al₂O₃; in situ synthesis; mullite; flexural strength