Development and testing of composite refractory bricks (a case study of selected Kenyan clays)

Abstract

Refractory bricks (refractories) are used in the construction of furnaces and kiln internal linings that hold, melt and transfer raw materials being processed. Kenya imports refractories mainly for its cement, metal smelting and sugar processing industries. Kaolin, bauxite, salama, soapstone and ball clays exhibited Loss of Ignition of 7-15%, silica of 46-55% and alumina of 25-34%. Soapstone and salama clays exhibited high values of potassium (5.6%) and iron oxide (16%), while salama clay had low alumina of 20% disqualified as refractory clay material. Alumina, silica and iron oxides in kaolin, bauxite and ball clays made them suitable as composite refractory clays. The properties of the developed composite bricks were determined at different mix ratios and particle sizes and their results compared with American Society of Testing Materials (ASTM) standards. Kaolin and bauxite clays were mixed at different ratios with 10% binder (ball clay). Developed bricks were moulded to volumes of (70x70x70) mm, subjected to a pressure of 4.1N/m2 and dried at 110℃. The bricks were fired in the furnace at 200°C for 6 hours, 650°C for 3 hours, 950°C for 4 hours and 1250°C for 8 hours and left to cool to room temperature. They were then subjected to physical and thermal tests and data obtained analysed using Statistical Analysis Software at 5% level of significance. Cold crushing strength, thermal shock resistance and bulk density were directly proportional to the increase in kaolin ratio. Decrease in linear shrinkage and apparent porosity was directly proportional to bauxite ratio. As kaolin to bauxite ratio increased from 2:7:1 to 7:2:1, apparent porosity decreased from 38% to 29% and bulk density increased from 1.45g/cm3 to 1.61g/cm3, cold crushing strength increased from 2.2 to 3.3KN/m2, linear shrinkage decreased from 8.89% to 3.69%, and thermal shock resistance increased from 14 to 27 cycles. Bulk density, cold crushing strength, linear shrinkage and thermal shock resistance decreased with increase in particle sizes but apparent porosity increased with increase in particle size. As particle sizes increased from 150µm to 600µm, apparent porosity increased from 29% to 36%, bulk density decreased from 2.23g/cm3 to 1.166g/cm3, cold crushing strength decreased from 3.3 to 2.64MN/m2, linear shrinkage from 3.69% to 2.0%, and thermal shock resistance from 27 to 19 cycles. Particle sizes of 150µm at a mix ratio of 7:2:1 produced apparent porosity of 29%, bulk density of 2.23g/cm3, cold crushing strength of 3.3MN/m2, linear shrinkage of 3.69% and thermal shock resistance of 27 cycles which was suitable for commercial production. This study adds knowledge to existing literature on refractories local clays