Lowest calcinates
Calcinates in this product group are characterised by the fact that they have a lower Mohs hardness than corundum. They break more easily and differently than classical corundum. They are usually metastable but isolable phases of aluminium oxide with a very high specific surface area.
Low Calcinates
Lowest and low-calcined products are relatively close in their properties, but ultimately differ in BET (specific surface area) and oil absorption. The products have a different history. They are often used in polishes. Despite a lower Mohs hardness of the grain, the angularity of a grain can strongly influence the polishing process.
Medium calcinates
In the case of medium calcinates, the alpha phase of the Al₂O₃ - i.e. the corundum - is preferred. Here one finds low BET values and lower oil absorption. They are found in polishes for hard surfaces such as steel. Nevertheless, they still have a certain activity, which also makes them suitable for use in ceramics and glazes.
Medium-high and high calcinates
Medium-high and high calcinates consist practically only of alpha Al₂O₃ and thus also have the Mohs hardness of corundum. The BET is low here. They provide the highest abrasiveness on hard surfaces and are used in a wide variety of places in refractories, ceramics and sometimes also in polishing.