Enhancing thermal performance of flint refractories through Iraqi bauxite additions: A study on porosity, density and thermal properties

Flint-based refractory bricks were produced from Iraqi ores of the Husseiniyat region in western Iraq and improved through the formation of non-dense mullite. Results showed that increasing the coarse Bauxite addition rate in the mix led to a simultaneous rise in bulk density and porosity, highlighting the importance of coarse fraction engineering. Porosity decreased markedly from 27.8% in pure flint to 9.18% at 20% bauxite, while density increased from 2.08 g/cm³ to 3.0 g/cm³ at 40%, due to the development of an interconnected of mullite phase at 20% with minor corundum formation at 40%. At higher bauxite additions (30–40%), porosity increased again. Water absorption followed the same trend, decreasing sharply at 20% and rising at higher contents. Thermal expansion reached its maximum at 20% bauxite, then gradually decreased at 10%, 30%, 40%, and pure flint compositions. This trend is attributed to mullite formation from bauxite particles, which enhances dimensional stability at high temperatures. Specific heat capacity was highest in more porous samples (pure flint and 30–40% bauxite), indicating greater thermal energy storage, while the lowest value occurred at 20% due to its denser structure. Overall, controlling bauxite content enables precise tuning of refractory properties for high-temperature applications.