Influência do tipo de solvente na síntese de mulita por sol-gel.

Abstract

Mullite is a synthetic material that has received particular attention due to their chemical, physical and mechanical properties, which are correlated with the synthesis method used. The sol-gel method stands out compared to the other chemical methods due to the possibility of obtaining materials with high purity and low temperatures for synthesis. Therefore, this study aims to analyze the influence of the solvent to obtain mullite via different sol-gel routes: Pechini route, route by route by slow gelation and rapid gelation. Studied for each route was examined the influence of the solvents water, ethyl alcohol, isopropyl alcohol and tetrahydrofuran (THF), to obtain mullite. The samples were characterized by X-ray diffraction (XRD), thermal analysis (TG and DTA), nitrogen adsorption (BET), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed the influence of different routes and solvents in obtaining the mullite. By the Pechini Route mullite was formed when it used only ethanol as a solvent. In the slow and fast gelling all solvents studied crystallized mullite depending on the control of other process variables, such as solvent used, the solution concentration, temperature, etc. Comparatively, the Pechini Route mullite obtained with lower crystallinity than all other routes, has the largest surface area and a more porous morphology. In the slow gelation mullite was synthesized in almost all synthesis conditions and all solvents, however, the use of alcohols as solvent gave obtaining the most crystalline samples with high reactivity, having the smaller surface areas, with a morphology formed by aggregates and individual particles. In the fast gelation of the solution at low concentration with the use of alcohols as solvent, was indicated condition. However, this route showed more heterogeneities having lower crystallinity, and thus superficias larger areas, for the slow gelation morphology being formed by large aggregates and considerable amount of glassy phase.