Liquid or gaseous nitrogen
Liquid nitrogen has three main functions
- Rapidly cools materials to brittle temperature before introduction into the mill
- Maintains a constant working temperature by absorbing heat produced during the grinding process
- Produces an inert, extremely dry and non-toxic atmosphere in the milling plant.
Substances ground cryogenically are physically different from those ground using traditional methods, because of the way in which the material’s structure is broken down.
Substances which have been made brittle cryogenically display homogeneous, crystalline cubic grains: milling at ambient temperature, however, results in powders whose physical properties are non-uniform, because the initial matrix is continually damaged by the flow of crystal planes or the reticular structure of the material.