Energy Efficiency in the Microwave-Assisted Solid-State Synthesis of Cobalt Aluminate Pigment

Due to their rapid, selective, and volumetric heating, microwaves have been widely used in the past to enhance solid-state reactions as well as the synthesis of ceramic pigments. The aim of this work is to present a case study involving the preparation of blue CoAl2O4 pigment using different microwave applicators and generator frequencies, showing the advantages which can derive from a properly designed microwave reactor for the solid-state synthesis of such pigment. The results show that, when using a properly designed microwave applicator, the specific energy consumption can be significantly lowered compared to conventional heating techniques. Consistently with the data on the dielectric properties of precursors found in literature, the microwave processing of cobalt oxide and aluminum hydroxide mixtures resulted more favorable at 2.45 GHz than at 5.8 GHz microwave frequency.