MECHANICAL AND MICROWAVE ACTIVATION OF SOLID-PHASE SYNTHESIS OF ZINC-CHROMITE SPINEL

The reactivity of zinc and chromium (III) oxides, hydroxides and salts (nitrates), as well as the xerogel combustion product (XCP) obtained from a solution of zinc and chromium (III) nitrates with the addition of citric acid, in the reaction of ZnCr2O4 spinel formation was analyzed. Reaction mixtures were prepared by simple mixing of components, as well as under conditions of mechanical activation or microwave processing. Effective constants of reaction rate and product yield were used to estimate the reactivity. A higher rate of the reaction involving hydroxides and salts compared to oxides is shown due to the activation of reagents during thermolysis. It has been established the increased activity of zinc and chromium (III) nitrates and XCP, which was a pre-prepared substance in which the main part of the gases (water vapor, CO2, N2, partially nitrogen oxides) was removed during combustion, leaving the oxide components in an active form, which were subsequently brought into close contact by compression. This distinguished XCP from a mixture of zinc and chromium (III) nitrates, in which gas emission during burning occurred in previously pressed tablets, which reduced the contact area of the reagents. The effect of mechanical activation and microwave treatment of reagents, during which a significant part of the precursors thermolysis took place, was analyzed. The newly formed oxide components actively interacted, and at the final stage of firing, a significant portion of the defects had time to heal. The spinel yield at different temperatures from mixtures consisting of zinc and chromium oxides/hydroxides without machining and after treatment in a planetary mill (PM) was compared, as well as the yield of ZnCr2O4 from mixtures with different preparation methods before burning at a constant temperature (1000 °C, 1 h). The maximum yield was observed when XCP or a mixture of zinc and chromium nitrates were used as precursors. A high reactivity of XCP was noted in the spinel formation without additional pretreatment. With an increase in the burning temperature, the spinel lattice was naturally ordered, which was confirmed by a decrease in the cell parameter and an increase in the size of crystallites. For citation: Filatova N.V., Kosenko N.F., Pavlova K.A., Fedorova G.S. Mechanical and microwave activation of solid-phase synthesis of zinc-chromite spinel. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2026. V. 69. N 3. P. 48-56. DOI: 10.6060/ivkkt.20266903.6885.