Production - purification

Purification of Graphite

The graphitising process is also accompanied by a purification of the material treated, normally reducing the content of impurities to considerably less than 1000 ppm. For many applications, this purity is insufficient, so that a thermal purification at higher temperatures up to 3100C with longer residence times is carried out to reduce the impurities to a concentration of less than 200 ppm. If still lower ash values are required, a thermo-chemical purification is necessary.

Thermo-chemical purification

Event after graphitisation at around 3000C most graphites contain small amounts of metallic impurities. If the ash values in the materials have to be below 200 ppm, thermal purification is applied. By adding gaseous halogens or halogen compounds, all hetero-atoms forming stable carbides are transferred into volatile halogen compounds and thus removed. By means of this procedure, impurities may be lowered to less than 1 pm.