MILLING AND MECHANICAL ALLOYING OF INORGANIC NONMETALLICS

The versatility of mechanochemical processing was investigated in a number of nonmetallic inorganic systems. It is shown that high energy grinding can be used to produce amorphous carbon from synthetic graphite and some forms of natural graphite. Elemental sulfur can likewise be amorphized by prolonged high energy grinding. Phase transformations of alpha-Fe2O3 (hematite) and mechanochemical reactions of this phase with ZnO and NiO are strongly influenced by the presence of iron resulting from wear of the grinding media. Thus spinel type ferrites were obtained by grinding of such mixtures for short times (1-3 h in a Spex mill); however, longer grinding times resulted in the formation of FeO or (Fe, Zn)O (when grinding ZnO) or FeO or (Fe, Ni)O (when grinding NiO), presumably as a result of the reaction of mill wear debris with the mill charge. The suspected (Fe, Zn)O phase is most likely a nonequilibrium solid solution. Negligible wear accompanied the mechanochemical synthesis of NiS and ZnS from elemental powders. These sulfides were formed for short milling times. In contrast, sulfides of tungsten were not formed even when rather long milling times were employed. The survey of mechanochemical reactions presented here further reinforces the concept that this low temperature synthesis method is a robust process route for production of a wide range of materials.