The increasing interest in supercritical fluids for synthesizing inorganic materials stimulated the development of new processes for production of nanophased powders/layers with controlled characteristics. Original processes based on sol-gel synthesis assisted by supercritical CO2 have been developed. Unusual powder structures/morphologies have been evidenced and cosolvent characteristics have been proved to influence powder specific surface area and crystallite sizes. The development of a new semi-continuous process also enabled to tailor powder morphology by controlling hydrodynamic parameters (injection speed and stirring rate). Especially, yttria-stabilized zirconia prepared with this method are composed of 5-7 nm crystallites aggregated in spherical nanoparticles (<100nm) and yielding particularly high specific surface areas (up to 250 m2/g). These YSZ powders can be compacted/deposited and sintered to prepare nanosized dense membranes for ionic conduction. Finally, SC-CO2 sol-gel processes can also be adapted to directly prepare gas separation membranes. In particular, an innovative process has been developed to coat tubular porous ceramic substrates with porous silica-based layer.