Patent ID: 7223445

Claim:
A process for the deposition of particulate material of a desired substance on a surface is disclosed, the process comprising: (i) charging a particle formation vessel, the temperature and pressure in which are controlled, with a compressed fluid; (ii) introducing into the particle formation vessel at least a first feed stream comprising at least a solvent and the desired substance dissolved therein through a first feed stream introduction port and a second feed stream comprising the compressed fluid through a second feed stream introduction port, wherein the desired 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 the desired substance, (iii) exhausting compressed fluid, solvent and the desired substance from the particle formation vessel at a rate substantially equal to the rate of addition of such components to the vessel in step (ii) while maintaining temperature and pressure in the vessel at a desired constant level, such that formation of particulate material in the vessel occurs under essentially steady-state conditions, wherein the compressed fluid, solvent and the desired substance are exhausted from the particle formation vessel through a restrictive passage to a lower pressure whereby the compressed fluid is transformed to a gaseous state and a flow of particles of the desired substance is formed, and (iv) exposing a receiver surface to the exhausted flow of particles of the desired substance and depositing a uniform layer of particles on the receiver surface.