Fabrication and catalytic growth mechanism of mullite ceramic whiskers using molybdenum oxide as catalyst

Abstract Mullite ceramic whiskers are successfully synthesized by a facile solid-state reaction process, using kaolin and Al(OH) 3 as raw materials and MoO 3 as catalyst of mullite whisker growth. The effect of MoO 3 catalyst on mullitization reaction and mullite morphology is investigated by XRD analysis and SEM observation. XRD results indicate that the addition of MoO 3 alters the mullitization reaction path, which leads to a decrease by 200 °C in the initial temperature of mullitization reaction, accelerates the reaction process and raises the reaction extent. SEM images demonstrate that MoO 3 encourages growth of mullite whiskers. The average aspect ratio of mullite whiskers increases from 4.7 to 18.4 with the increase of firing temperature from 1100 to 1500 °C. The combined results from TG-DSC and XRD suggest that the formation of Al 2 (MoO 4 ) 3 delays the sublimation temperature of MoO 3 from 600 to 800 °C. Through analyzing the experimental results, the MoO 3 -assisted catalytic growth mechanism of mullite whiskers is proposed based on the “dissolution-precipitation” process. The MoO 3 decreases the viscosity of Si-rich liquid and thus promote alumina solubility, resulting the mullite nucleation and growth. The assumption that MoO 3 containing MoO 6 octahedral chains acts as the role of template agent inducing mullite whisker growth is proposed.