Inert-Gas Buffering for Particle Size Separation of Superconductor Precursor Powders

The removal of all particles over a desired micron-scale size threshold from a powder sample is critical to the development of fine-filament, powder-in-tube superconducting wires, for which the final filament size is limited by the largest particles in the precursor powder filling. This project will develop a particle-removal technology that disperses the powder in an aerosol suspension and then passes the dispersed powder through a Stokes-flow geometry, in which the powder particles are separated. The basic approach has been used for several decades for size classification, but never for separation of bulk quantities of powder. In previous work, a slot-geometry impactor was developed and evaluated for bulk separation applications. Phase I improved the earlier process in three respects: (1) dry nitrogen gas was used as the buffer gas rather than air, in order to eliminate contamination of the precursor powders; (2) a fluidized-bed dispersal system was developed to increase mass loading without aggregation; and (3) a boundary-sheet flow of powder-free gas was introduced along the walls of the impactor structure, in order to suppress particle wall interactions that limit large mass loadings. In Phase II, an electron-beam-assisted precipitator will be developed to remove the separated fines from the aerosol flow. The present pressurized inert-gas flow will be converted into a recirculating closed-circuit flow. The slot impactor vane structure will be rebuilt with 1-m-long vanes, and manifolds for supply, exhaust, and boundary flow along the vane structure will be pressure-equalized to assure a uniform Stokes threshold along the extended geometry. Commercial Applications and other Benefits as described by the awardee: In addition to high-performance superconductors, the technology also should be applicable to the separation of particles used in specialty sintered metal and ceramic materials for aerospace and defense, and in consumer products. For ceramics, large particles cause stress concentrations, which cause brittle fracture. For sunscreen, powders utilize Ti2O3, the most effective UV absorber; however, Ti2O3 is also the pigment for white paint, and makes skin appear pasty. By reducing particle size, the powder becomes invisible, while retaining its UV protection capability