Effect of different atmospheres on the microstructure and fracture properties of a phosphate bonded high-alumina refractory

Phosphate-bonded refractories are widely used in high-temperature applications, including direct reduction reactors of the steel and petrochemical industries. This work explores the effects of air, CO, H2, CO+H2, and coke-breeze embedding on the microstructure and fracture properties of a phosphate-bonded high alumina refractory. Samples were exposed at 900°C for 96 h, followed by mechanical and microstructural characterization using Miniaturized Wedge Splitting Test (MWST), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Reducing atmospheres induces microstructural transformations, including changes in mullite, corundum formation, and an increase in the glassy phase. The untreated material shows a specific fracture energy (Gf) of 108 J.m−2 and lower brittleness. H2 exposure yields the most pronounced changes, with the highest Gf (228 J.m−2) and increased brittleness. CO exposure increases brittleness, giving Gf = 148 J.m−2. The CO+H2 atmosphere mitigates degradation, lowers brittleness, and limits microstructural changes.