Kinetics of physico-chemical processes during intensive mechanical processing of ZnO–MnO2 powder mixture

Experimental results of electron paramagnetic resonance spectra, X-ray diffraction, scanning electron microscopy and infrared spectroscopy demonstrate that the kinetic of the physical and chemical processes that takes place during prolonged intensive mechanical processing (MP, 03120min) of powder mixtures of 50%wt ZnO+50%wt MnO2 can be described as a three stage process. (1) 030min, particles destruction, formation of superficial defects, fast increment of sample average temperature (from 290 to ∼600K) and annealing of defects with the lowest energy of activation Eac. (2) 30390min, further particle destruction, slow increment of sample average temperature (from ∼600∼600 to ∼700K), formation and growth of a very disordered layer of β‐MnO2β‐MnO2 around ZnO particles, dehydration of MnO2, formation of solid solution of Mn2+ ions in ZnO, formation of nano-quasiamorphous states in the ZnO–MnO2 mixture and onset of the formation of the ZnMnO3 phase. (3) 3903120min, the sample average temperature remains constant (∼700K), the reaction is completed and the spinel ZnMnO3 phase with a unit cell a=8.431(1) Å and space group Fd3¯m is the only phase present in the sample. No ferromagnetism at room temperature was detected in this study.

► The kinetics during mechanical processing of ZnO–MnO2 samples is a three stage process. ► First stage, reduction of crystallites size and accumulation of defects. ► Second stage, nano-quasiamorphous states formation and onset of the ZnMnO3 phase. ► Third stage, complete reaction to the spinel ZnMnO3 phase.