Alumina (Al2O3) is a widely used technical ceramic known for its exceptional hardness, wear resistance, and high compressive strength, even under extreme temperatures and corrosive conditions. It is also an excellent electrical insulator and gas-tight material.

To produce alumina, a tightly packed powder form of Al2O3, mixed with a binder, is fired. The commercially available grades of alumina range from 90% to 99.95% purity, with higher purity levels offering greater hardness. Alumina can be machined using diamond grinding techniques and can be polished, although the achievable polish depends on the grain size and whether the alumina was pressed or extruded.

Grades with 90%-97% purity are ideal for metalizing, as their larger grain structure facilitates metal deposition and brazing. The 98%-99.95% purity range is common for isostatically pressed grades, though extruded shapes are also available at a lower cost.

As-fired tolerances of alumina are typically within a few percent of the desired dimensions. Achieving extremely tight tolerances requires precision machining with diamond grinding, which increases costs but allows for tolerances down to millionths of an inch, providing remarkable stability and durability.

Additionally, blending alumina with zirconia or silicon nitride results in a composite material that is tougher than pure alumina, with enhanced hardness, strength, and thermal properties, especially at high temperatures.