X-ray Diffraction Phase Analyses of Mullite Derived from Rice Husk Silica

In this study, mullite synthesized from aluminum nitrate hydrate [(Al(NO3)3.9H2O] and silica sol from rice husk was subjected to sintering treatment at temperatures of 900, 1000, 1100, 1200, and 1300 °C, and characterized using x-ray diffraction (XRD), followed by Rietveld refinement, and differential thermal analysis (DTA). The results indicated that in the sample sintered at 900 °C, no mullite phase was identified, but crystoballite and alumina were well detected. The formation of mullite started at temperature of 1000 °C and continued to grow at higher temperatures, resulted in increased weight percentage (wt%) from 62.62 to 92.29%, while crystoballite and alumina decreased from 22.42 to 1.25% and from 77.58 to 6.46 % respectively. A good correlation was found between the calculated and observed unit cells. For mullite phase, the unit cell dimensions are a = 7.545 nm, b = 7.689 nm and c = 2.884 nm, for crystoballite a = b = 0.5531 nm and c = 0.6923 nm, and for alumina a = b = 0.5026 nm, and c = 1.2808 nm. The DTA analyses revealed that in the untreated sample, only alumina and silica were detected, while in the sintered samples we found the existence of mullite, alumina, and crystoballite.