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

78953 In the fabrication of powder-in-tube (PIT) Nb3Sn superconductors, needed for high energy physics applications, the particle size distribution limits the final filament size to which the strand can be drawn. In previous work, a virtual impactor (VI) aerosol particle sizing process was developed to process powders with near-zero-defect removal of all particles larger than a desired threshold size. The process currently operates with ambient air as the suspension fluid for the aerosol process. However, an inert gas would be preferred because, in recent developments by PIT manufacturers, explosions have occurred during the jet-milling to micron particle size. This project will upgrade previously developed particle sizing technology so that powders can be processed in an inert gas atmosphere. In addition, a novel technique will be introduced to suppress limitations to mass loading that arise from particles flowing in the boundary layers. In Phase I, the boundary flow bypass and an inert-gas buffer flow system will be built and integrated with the VI processor. Separation performance will be evaluated and the maximum mass throughput will be determined. The system will be used to process PIT precursor powders, which will be processed into superconducting wire, and performance will be evaluated. Commercial Applications and Other Benefits as described by the awardee: VI processing addresses an important issue for powder metallurgy and ceramics: how to remove particles with larger than nominal size from a grinding process. Applications include powders for ceramics and sunscreen. For ceramics, large particles cause stress concentrations, which cause brittle fracture. Sunscreen powders utilize Ti2O3, the most effective UV absorber, but it is also the pigment for white paint, and makes skin appear pasty. By reducing the particle size, the powder become invisible, while retaining its UV protection capability. Finally, with respect to the revolution in nanoscale materials, the VI technology should face no fundamental barriers in extending down to sizes as small as ~200 Angstroms.