Kinetics and formation mechanisms of the nanocomposite powder Ag–SnO2 prepared by reactive milling

A nanocomposite powder Ag–SnO2 was produced at room temperature by reactive ball-milling of mixtures of powders of silver bronze (Ag3Sn) and of silver oxide (Ag2O). Reaction kinetics were investigated for powders ground in air and under vacuum using X-ray diffraction (XRD) analysis, thermal analysis and 119Sn Mössbauer spectrometry. For these two milling conditions, all the results indicate a two-stage reaction path: oxidation of Sn to SnO from the decomposition of Ag2O under milling followed by oxidation of SnO to SnO2. In air, molecular oxygen contributes further to Sn oxidation, particularly to the oxidation of SnO to SnO2. Nevertheless, the reaction is found to be slower in air because of the formation of a surface barrier of silver carbonates from a reaction of Ag2O with the CO2 present in air.