Synthesis of Nanoscale Powders In Supercritical Fluids

Nanoscale powders with narrow particle-size distributions significantly reduce sintering time and temperature during the processing of high performance coatings and structural ceramics; their superplastic behavior can be exploited to net-shape form structures. Nanoscale powders can be made by a variety of methods but production scale, cost effective, environmentally sound methods are required. A supercritical C02 process is proposed for the synthesis of nanoscale zirconia (ZrO2) and yttria stabilized ZrO2 powders. During Phase II the process will be extended to non-oxides such as c-BN and TiN. Supercritical C02 is a novel solvent that enable precise control of primary crystallite size, aggregate size and distribution, and interface chemistry. The process will operate in a closed-loop configuration; C02 is abundant, environmentally benign, inexpensive ($ 0.05/lb.), and has reasonable critical parameters that enable this process to be economically scaled to produce large quantities of powder. Reactants will be introduced into the C02 feed stream. Nucleation and particle growth will be controlled by adjusting the reaction conditions Of C02. This process will benefit from increased polymerization kinetics at elevated temperatures and pressures. Powder interfaces will be controlled to prevent aggregate formation and powders will be collected by controlled expansion . Nanophase Technologies Corporation is a commercial producer of nanoscale powders by the GPC process and has made significant progress in superplastic net-shaping of nanophase ceramics.