Raschig rings made from borosilicate glass
In a distillation alumina ball, the reflux or condensed vapour runs down the column, covering the surfaces of the rings, while vapour from the reboiler goes up the column. As the vapour and liquid pass each other countercurrently in a small space, they tend towards equilibrium. Thus less volatile material tends to go downwards, more volatile material upwards.
They are also used for devices where gas and liquid are put in contact for purposes of gas absorption, stripping or chemical reaction, and as a support for biofilms in biological reactors.
Raschig rings made from borosilicate glass are sometimes employed in the handling of nuclear materials, where they are used inside vessels and tanks containing solutions of fissile material, for example solutions of enriched uranyl nitrate, acting as neutron absorbers and preventing a potential criticality accident.