Control of particle growth by chemical transformation in supercritical CO2/ethanol mixtures

The purpose of this work is to take advantage of specific properties of supercritical media to develop a new route for elaboration of fine metal powders. The process consists of the thermal decomposition of a copper precursor previously solubilized in a CO2/ethanol supercritical mixture. It has been shown that low initial concentrations of precursor lead to spherical homogeneous nanostructurated particles with a mean size down to below 1 mm, well crystallized, and free from solvent contamination. A decomposition reaction has been performed in a polymer swollen by the supercritical fluid to quench aggregation. Particles sizes in the range 5-20 nm were obtained in polystyrene and in the range 150-250 nm in silicone. Short residence times in a tubular flow reactor (<30 s) allowed non-aggregated nanoparticles to be obtained (particles of size <50 nm were amorphous). The mechanism of particle growth in supercritical media has been examined assuming both total and partial coalescence (aggregation), since those mechanisms dominate the particle synthesis, according to experimental and simulation results.