Effects of Dry Ball Milling on the Catalitic Activation Energy of NiO and ZnO Powder

Abstract

The crystallite dimension and the lattice distortion of the ground NiO and ZnO powder were measured by X-ray diffraction method, and the effects of dry ballmilling on the catalitic activation energy of the NiO and ZnO powder were studied by the catalitic decomposition of H₂O₂.
The following results have been obtained:
(1) During the grinding process, the catalitic activation energy of the NiO powder increased as the crystallite dimension decreased. It decreased as the crystallite dimension remained as it was. This phenomenon shows that the stoichiometric anion rich surface layer exfoliates as the crystallite dimension decreases, but that it remains intact as the crystallite dimension remains unchanged.
(2) The frequency factor of the N₁O powder shows the same behavior as that of activation energy by the change in the crystallite dimension. This shows that the density of active center on the surface of the paricle increases exceedingly by removal of the surface layer.
(3) The catalitic activation energy of the ZnO powder decreases as the crystallite dimension decreases, and increases as the crystallite dimension increases. This behavior is different from that of NiO. It seems that the difference is due to the difference of p type semiconductor (NiO) from n type semiconductor (ZnO).