"The study of constitution and properties of high alumina insulating refractories made of some local and imported raw materials."

Abstract

The present thesis aims to prepare high alumina insulating refractories from some local and imported raw materials and also, study their phase constitution, microstructure and different physical properties. This type of refractories is demanded in Egypt for the thermal insulation of industrial furnaces. The employed starting raw materials are calcined alumina, bauxite and polystyrene as imported materials and Klabsha kaolin, Aswan ball clay and coked rice hulls as local ones. Their chemical and phase constitution were first investigated. Porous bodies were prepared from kaolin or clay mixtures using calcined alumina or I and bauxite materials. The plastic shaping processes, besides the semi-dry pressing process were used. Coked rice hulls and polystyrene were employed as combustible materials. The green bodies were dried and fired up to 1500°C. Then, their physical properties were determined and their phase constitution was identified. Through this work, the reaction between kaolin or clay with aluminum oxide derived from the two sources (bauxite and calcined alumina) was studied. This reaction was nearly completed at 1500oC forming mullite and corundum. Also, there are two processes acting in an opposite direction and determine the volume change of porous bodies; the densification of fired bodies causing a decrease in volume and mullite formation accompanied with a volume increase. The chemical composition, impurities level and firing temperature affect the degree of densification and mullite formation and consequently the volume change.