Metakaolin-based geopolymer as an alternative binder in semi-insulating refractories

Abstract

Semi-insulating refractories are recognized for their capability to minimize thermal losses and potentially save energy. Encouraging the advancement of cement-free compositions, cold-setting binders like geopolymers have emerged as captivating alternatives. This study focused on evaluating the incorporation of a metakaolin-based geopolymer binder in semi-insulating fused silica-containing castables. As reference materials, calcium aluminate cement (CAC)-bonded compositions with and without polymeric microspheres were also investigated. Three refractory castables were processed, and the prepared samples underwent characterization, including mechanical strength, apparent density and porosity, thermal shock resistance, thermal conductivity measurements, and SEM analysis. The geopolymer-bonded castable presented improved performance, exhibiting a thermal conductivity of 0.735 W/m.K at 800 °C, flexural strength of 6.24 MPa and apparent density of 1.68 g/cm3 after firing at 815 °C. The results underscore that utilizing geopolymer as a replacement for CAC enabled the design of a semi-insulating castable with enhanced properties and without the need for using porogenic agents.