Synthesis and encapsulation of yttria stabilized zirconia particles in supercritical carbon dioxide

Nanocrystalline oxide powders synthesized in supercritical CO2 (SC-CO2) generally consist in nanoparticle agglomerates, which are difficult to handle. In this work a particle encapsulation method in SC-CO2 was developed to overcome this problem. By performing both the synthesis and encapsulation steps in the supercritical fluid, the agglomeration of particles can be limited, their handling can be improved and the powder behavior can be modified depending on the selected encapsulation agent. Poly(dimethylsiloxane)-graft-polyacrylate (PDMS-g-PA) phase separation method and methylmethacrylate (MMA) polymerization on particle surface are typical encapsulation processes usable in batch mode, with SC-CO2 as a solvent, for ceramic powder encapsulation. This paper describes preliminary results concerning the synthesis of yttrium stabilized zirconia (YSZ) in SC-CO2 and its encapsulation with PDMS-g-PA or PMMA in SC-CO2. It has been shown that both phase separation and polymerization allow coating of the oxide particles, and clearly modify their properties. On the other hand, the use of a surfactant like PDMS-g-PA allows anchoring of MMA monomer and promotes polymerization on the particle surface. The choice of the surfactant is considered as a key parameter for a successful encapsulation process. This preliminary work offers new perspectives for synthesis and encapsulation of ceramic powders in SC-CO2.