Abstract: To assess the effects of modified SiO₂ sources on the structure and properties of high-purity mullite materials by reactive sintering method, the modified SiO₂ source was fabricated by doping 8% (mass fraction) γ-Al₂O₃ into natural quartz and heating at 1 550 ℃. Subsequently, mullite samples were prepared by using different SiO₂ sources and γ-Al₂O₃ as raw materials. The results show thatthe melting temperature of SiO₂ decreases after adding a small amount of γ-Al₂O₃. The modified SiO₂ sources are transformed into a large amount of SiO₂-rich liquid phase in a narrow temperature range (1 570 ℃ to 1 580 ℃). The formation of a large amount of SiO₂-rich liquid phase promotes the mulliteization reaction, accelerates the particle rearrangement, increases the density of materials, and improves the reaction sintering property of high-purity mullite materials. During the calcination process, the SiO₂-rich liquid phase is gradually consumed by the reaction and converted into high-temperature mullite. Meanwhile, the liquid phase environment provided by the melting of modified SiO₂ source promotes the anisotropic crystal growth of mullite. After calcination at 1 700 ℃ for 3 h, the obtained mullite grains morphology exhibits columnar shape and forms a cross network structure, which enhances the degree of bonding between crystals. Therefore, high-purity mullite materials with the modified SiO₂ sources exhibit higher density and better mechanical properties.

Key words: modified SiO₂ source, γ-Al₂O₃, high-purity mullite, SiO₂-rich liquid phase, sintering property, compressive strength