Validity of Smectite Clays as a Binding Material for the Production of Refractory Bricks

Abstract

This study aims to evaluate the suitability of local clays rich in smectite for the manufacture of refractory bricks by characterizing their chemical, mineralogical, physical, and thermal properties at high temperatures. Two raw materials were used: local bauxite as the main source of alumina, and local smectite clay as the main source of silica and as a binding agent, added at proportions of 10%, 15%, and 20%. The bricks were formed using a semidry pressing method with 15% water content by weight, and pressed at 10 tons. The bricks were pressed to the required dimensions according to standard specifications. After complete drying, the brick samples were fired at 1400°C for 2 h. The investigation included chemical analyses to determine major oxide proportions, as well as physical, mechanical, and thermal tests to evaluate industrial performance, in addition to X-ray diffraction analysis and scanning electron microscopy. The results showed a relative decrease in Al₂O₃ content when smectite content increased, which negatively reflects on the melting resistance. X-ray diffraction analysis confirmed the formation of the mullite phase after firing, accompanied by tridymite, corundum, and occasionally sillimanite. Scanning Electron Microscope observations revealed a microstructure characterized by an interlocking network of mullite fibers of varying lengths, which enhances thermal and mechanical stability. In addition, a silica phase and distributed angular corundum grains were identified. Increasing the smectite content lead to a decrease the bulk density and a relative decrease in thermal shock resistance and refractoriness, while improving the mechanical resistance. In contrast, high smectite content resulted in increased volumetric and linear shrinkage due to crystal rearrangement during heating. The results indicate the possibility of using local clays rich in smectite at rates 10% and 15% with local bauxite to produce refractory bricks that conform to Iraqi standard specifications, thereby supporting the economic viability of the local industry.