Synthesis of Complex Aluminum–Cobalt Systems Using a Thermoactivated Gibbsite Product

Abstract

The authors explore the possibility of synthesizing highly loaded mixed aluminum–cobalt spinels via the hydrochemical treatment of suspensions of a powder of the product of the centrifugal thermal activation of gibbsite in aqueous solutions of cobalt nitrate under room-temperature or hydrothermal conditions via X-ray diffraction, thermal, microscopic, adsorption, and chemical analysis. It is found that the heat treatment of products of hydrochemical interaction (xerogels) in the range of 350–850°C produces Co₃O₄ and CoAl₂O₄ spinel phases with different phase ratios, depending on the conditions of synthesis. The hydrochemical treatment of suspensions at room temperature ensures the dominant formation of a Co₃O₄ phase after calcination, while hydrothermal treatment at 150°C results in deeper interaction between the suspension components during treatment, ensuring the formation of CoAl₂O₄ after heat treatment. It is shown that the maximum content of CoAl₂O₄ spinel (90%, according to H₂-TPR) is observed for the hydrothermal product calcined at a temperature 850°C. The considered technique yields complex aluminum–cobalt compounds with different phase ratios, allowing the complete elimination of effluents. It also reduces the number of stages of synthesis, the amount of initial reagents, and 75 wt % of the total amount of nitrates, relative to using classical nitrate coprecipitation.