Production of powders and films by the rapid expansion of supercritical solutions

A new process utilizing the rapid expansion of supercritical fluid solutions (RESS) is described for the production of fine powders and thin films by the rapid nonequilibrium precipitation of nonvolatile compounds from dense gas solutions upon expansion. A variety of the fluid solution expansion parameters, including solute and solvent identity, solute concentration, expansion temperature, and expansion nozzle configuration, has been shown to affect the product characteristics of materials formed during the RESS process. Conditions favouring thin film formation include very dilute solutions and short nozzles minimizing residence time during expansion. Particle formation is favoured by more concentrated solutions. The process has been demonstrated to produce products of widely varying morphology by the adjustment of RESS parameters, and examples of SiO₂ GeO₂ and various polymeric materials are presented. Unique features of the RESS process relevant to other powder and film production methods are described and potential applications are discussed.