Molybdenum oxide catalyzed low temperature preparation of mullite whisker from silica-alumina gel slag

Abstract

Catalyzed by MoO3, mullite whiskers were synthesized through a molten salt method. This study comprehensively explored the impact of reaction temperature, MoO3 mass fraction, and calcination temperature on the morphology of mullite whiskers. Employing analytical techniques such as XRD and SEM, the phase composition and morphology of the samples were meticulously scrutinized. The results unveiled that at a MoO3 mass fraction of 7–8% (molar fraction) and a calcination temperature of 800 °C, mullite whiskers demonstrated a heightened level of purity. Building on these observations, the study delved into the mechanistic underpinnings of MoO3 as a catalyst in mullite whisker synthesis. It is proved that the metal oxides contained in the silica-alumina glue slag can also form a local liquid phase at low temperatures, reducing the viscosity of the reaction system and liquefaction temperature. The addition of molybdenum oxide makes the reaction process of mullite whisker growth shorter. At the same time, the addition of molybdenum oxide can effectively reduce the viscosity of the reaction system, thus lowering the reaction temperature and increasing the reaction efficiency. In addition molybdenum oxide can be used as a templating agent to induce the growth of mullite whiskers along specific crystal planes. Compared with aluminum fluoride catalysis, molybdenum oxide does not produce the hazardous gas HF, the sublimated molybdenum oxide gas can be recycled, and the molybdenum oxide attached to the whiskers can also be dissolved in water. These theories provide experience in the large-scale preparation of mullite whiskers.