The term high-alumina brick refers to refractory brick having an alumina (AI2O3) content of 47.5% or higher. This descriptive title distinguishes them from brick made predominantly of clay or other aluminosilicates which have an alumina content below 47.5%.
High-alumina brick are classified by their alumina content according to the following ASTM convention. The 50%, 60%, 70% and 80% alumina classes contain their respective alumina contents with an allowable range of plus or minus 2.5% from the respective nominal values. The 85% and 90% alumina classes differ in that their allowable range is plus or minus 2% from nominal.
