Virtual Impact Fractionation of Superconductor Precursor Powders in Inert Gas Atmosphere

Virtual impactor fractionation has been used to remove all particles over a selectable micron-sized threshold in samples of precursor powders for MgB₂ and Nb₃Sn superconductors. In a virtual impactor the powder is dispersed in an aerosol stream and passed through a vane geometry in which particles less than a critical size follow the gas streamlines which turn abruptly into a collection chamber, while particles larger than the critical size pass undeflected into a reject chamber. The aerosol dispersion was made in an inert gas flow in order to prevent degradation of the powder by exposure to oxygen or moisture.