PREPARATION AND CHARACTERIZATION OF POROUS ALUMINO-SILICATE BONDED SILICON CARBIDE REFRACTORIES

Abstract

Porous SiC products are found in many areas of application such as filter for hot gas cleaning and liquid metal purification, in heat exchangers, acoustic absorbers, catalysis supports, gas burners and heat-insulation. Based on previous literature and demand of porous SiC products in Egyptian industry, this thesis was directed to study the preparation and characterization of porous alumino-silicate bonded SiC refractories. The alumino-silicate bond with high alumina content was used in order to improve the product quality. To fulfill the aim, the main starting materials, silicon carbide, Klabsha kaolin and calcined alumina, were chemically and mineralogically analyzed using XRF and XRD technique. Their surface area and particle size distribution were determined. As sacrificial template, saw-dust and corn and potato starch were also used in the present thesis. They were thermal gravitation analyzed by heating them in air up to 1000 °C. Their particle size distribution and surface area were also determined. Then, the study deals with investigation of preparing porous alumino-silicate bonded SiC specimens. These specimens were prepared from mixtures containing silicon carbide, calcined alumina and Klabsha kaolin through either of two methods, foaming technique or sacrificial template method. These mixtures contain 40 to 80 mass% SiC while the alumina contents of their bonding materials are 60 to 80 mass%. The employed technique of foaming introduces pores into SiC specimens as a result of chemical reaction between aluminum powder and calcium carbide in presence of water which liberates acetylene and hydrogen gases. The reaction and process are assisted by adding sodium meta-silicate and a stabilizer. The shaped specimens were dried and then fired up to 1450 °C for 2hrs. Some preparation variables affecting