Reactive milling with metals for environmentally benign sustainable production

Abstract

A systematic survey over the varied use of milling with metals according to reaction types is presented. After the mechanistic distinction of the brittle milling and ductile kneading also for large-scale industrial processes, the consequences for improved applications are exemplified. This covers milling of metals with infinitely covalent non-metals, with metal salts, molecular crystals and carbon, with metal hydrides, with gases (H₂, N₂, O₂), with semi-metals (As, B, Ge, Se, Si, Te), with organic halides and ketones, and with other metals for mechanical alloying. Homogeneous alloys and nanocomposites are distinguished. Metal-metal mechanical alloying is subdivided under solid solutions of immiscible metals, metal-metal nanocomposites, and intermetallics (crystalline and amorphous). The latter is further subdivided into brittle–brittle, brittle–ductile, and ductile–ductile combinations and followed by superalloy composites. Binary alloys are primarily used for the exemplification in order to limit the already enormous field. Various techniques for the decreasing of unduly long milling times become evident from the mechanistic considerations. Optimal choice of the temperature in heat-controlled mills featuring upgrading and adjustable milling conditions is substantial. This is equally important for milling and for ductile kneading. Essential parameters are the selected temperature and optimal (not maximal) milling impact (for example ball mass, size and speed, ball to powder ratio, chamber filling level) for avoiding clogging or lumping instead of generating the maximal number of collisions. Further tools are cycle operation and semi-continuous processing in closed systems for milling and easy collection under vacuum or with pressurized gases.