Obtenção de mulita a partir do resíduo do caulim.

Abstract

In the process of kaolin improvement two types of residue are generated and disposable in the environment. The first residue, about 70%, is generated from the washing of the kaolin and the second is generated from the improvement in a sieve ABNT N° 200 (0.074mm), of the remaining washed kaolin (30%). These residues present excellent qualities to be used as raw materials, rich in quartz. Kaolinite when is submitted to a high temperature produce two stable phases: mullite and crystobalite. Mullite is a stable phase at high temperature of the silicaalumina system and appears from the solid reaction between Al203 and Si02. The properties of mullite, such as, low thermal expansion, low dielectric constant and high shear strength, make this material as a good candidate to be applied in electronic products and in structural high temperature uses. The residue from the kaolin with such oxides mentioned before can be improved and transformed into usable products. In this work, compositions with residue from kaolin, alumina and ball-clay, passed in sieve (aperture of 0,15mm) were studied to obtain mullite. The compositions were established by using a REFORMIX 2.0 computing program, developed by the Federal University of Sao Carlos - Brazil. The specimens were made by uniaxial pressing process with 27 MPa and sintering at temperatures from 1350 to 1500°C/1h and 1500°C/3h, with heating rate of 10°C / min. Through the results of the chemical analysis of the formulated masses, it can be verified that the proportions of the oxides are close to the stoichiometric composition of mullite and that the sintering, at studied temperatures, give the formation of mullite, and confirmed by the XRD analysis. The results showed that the compositions with low alumina content and submitted to a high temperatures and time sintering, presented the best results.