new modified RESS process, RES suspensions, has been proved successfully to coat ultrafine particles [15] and [16]. Coating or encapsulation of nanoparticles is a major challenge due to the extremely small size, high surface energy, and high surface area of the nanoparticles. The whole equipment consisted on a spray chamber, a supercritical extraction column and a recovery system for the particles. Before entering into the spray room, the ultrafine particles were well dispersed in the supercritical solution of coating materials to form the supercritical suspension. Silica particles of 5 μm were used as core particles. The coating material was paraffin (melting point: 48–50 °C). A nanoscale paraffin layer was deposited on the surface of silica particles. It was found that there was no significant agglomeration during coating process.