The present invention provides a process for the deposition of particulate material of a desired substance on a surface, which includes: (i) charging a vessel with a compressed liquid; (ii) introducing into the vessel a first feed stream comprising a solvent and said substance dissolved therein and a second feed stream comprising the compressed fluid, wherein said substance is less soluble in the compressed fluid relative to its solubility in the solvent and the solvent is soluble in the compressed fluid, and wherein the first feed stream is dispersed in the compressed fluid, allowing extraction of the solvent into the compressed fluid and precipitation of particles of said substance; (iii) exhausting compressed fluid, solvent and said substance from the vessel at a rate substantially equal to the rate of addition of such components to the vessel in step (ii) through a restrictive passage, and then a flow of particles of said substance is formed; and (iv) exposing a receiver surface to the exhausted flow of particles of said substance. |