Preparation of metallic powders and alloys in polyol media: A thermodynamic approach

Through simple thermodynamic considerations, the metal oxides reduction rea ction in polyol medium (ethylene glycol) has been addressed with the assump tions that the reaction takes place at the boiling point of the alcohol, an d that the polyol is totally oxidized with formation of CO2 and H2O. By con sidering the initial (MOx + ethylene glycol) and final (M + CO2 + H2O) stat es, we estimated the Gibbs free energies (DeltaG(red)) for the reduction of numerous oxides, and found a good correlation with the experimental result s. Without any exception, oxides leading to metallic powder when reacted in boiling polyol medium have a negative calculated DeltaG(red). However, a f ew oxides with negative calculated DeltaG(red) could not be reduced to meta l, likely for kinetics limitations and/or solubility issues. This strategy has been extended with similar success to both hydroxide precursors and oth er alcohols having longer backbones (e.g., glycerol). Finally, we show that this basic thermodynamic approach opens new insights for the synthesis of alloys, obviously represents a useful prediction tool for the preparation o f metals, and could be easily extended to the preparation of oxides. (C) 20 00 Academic Press.