Kryomilling

Kryomilling, commonly spelled cryomilling, is a milling technique conducted at cryogenic temperatures, typically using liquid nitrogen, to reduce materials while controlling heat generation and chemical changes. The process embrittles many ductile materials, enabling brittle fracture rather than plastic deformation, which can lead to finer powders, refined microstructures, and reduced oxidation during size reduction.

In practice, a cryogenic mill or a standard ball mill equipped with a cooling system is used. The sample and milling media are cooled to cryogenic temperatures, often around 77 K, and milling is carried out under inert or low-oxygen conditions to minimize oxidation. Milling parameters such as ball-to-powder ratio, milling time, and cooling rate are chosen based on the material and desired outcome. The low temperature also helps suppress diffusion and phase transformations that could occur with heat buildup.

The anticipated outcomes of kryomilling include ultrafine or nanostructured powders, improved dispersion of reinforcements in composites, reduced cold welding of particles, and enhanced stability of volatile components in some systems. It is used with a range of materials, including metals (especially hard-to-mill alloys), ceramics, polymers, and some pharmaceutical powders, to facilitate subsequent consolidation by sintering or additive manufacturing.

Safety and practical considerations are important. Kryomilling requires specialized equipment and handling of liquid nitrogen, which poses risks such as cold burns, asphyxiation hazards, and pressure-related dangers in sealed vessels. The process is energy-intensive and may incur higher equipment costs and maintenance needs compared with conventional milling. Nevertheless, it is valued for enabling finer powder production and improved material properties in various applications.