Plasma dynamic synthesis of dispersed metal oxide materials in CO2 medium

Abstract

The steadily high interest in metal oxides, including in the form of fine powders, has led to a rapid increase in their production, the search for new synthetic methods and the expansion of possible applications. CO2 has proven itself as a cheap and abundant source of mild oxidant, which can potentially be used for oxidation reactions. However, the key problem of CO2 application is the necessity to break the bonds of the CO2 molecule that requires a large amount of energy. This work presents a fundamentally new approach for metal oxide synthesis, when applying CO2 as a gaseous precursor and oxidant, based on application of a pulsed arc discharge plasma of the electroerosion type. The implementation of the proposed method called plasma dynamic synthesis results in obtaining dispersed metal oxides that is demonstrated by the examples of Cu–O, Fe–O, Ti–O and Al–O systems. The influence of the metal-containing plasma type and operation modes on the formation of metal-oxide dispersed materials is studied. The multi-pulse operation mode in the considered system with titanium and aluminum electrodes provides obtaining almost completely oxidized products that is found to depend on the electronegativity of the initial metals. When applying aluminum electrodes, the process not only provides a high productivity of obtaining dispersed materials (up to 15 g per cycle), but also allows the CO2 conversion rate of up to 14.5%. Moreover, the electroerosion plasma demonstrates the energy efficiency of CO2 decomposition exceeding other plasma-based methods due to ongoing exothermic reactions of metal oxide formation. The as-synthesized products can be used to obtain bulk ceramic materials that is shown by the example of aluminum oxide powders. The hardness of the obtained ceramic specimens produced by SPS method is found to be ∼22 GPa and correlates with the best samples for aluminum oxides.