HIGH-GRADIENT MAGNETIC SEPARATION OF YBCO PARTICLES IN A GAS-FLUIDIZED BED

High gradient magnetic separation of copper-oxide superconducting particles in a gas-fluidized bed has been studied experimentally. Particles over the size range 45-105-mu-m exhibit classical behavior when fluidized with He gas at 77 K, whereas the more cohesive, smaller particles were difficult to fluidize. Separation experiments on a uniform mixture of tetragonal and orthorhombic phases have shown that 30 min of exposure to the field gradient is sufficient to equilibrate the superconductor concentration profile. In addition, the equilibrium separation data reveal that best separation is achieved at three times the minimum fluidization gas velocity (U(mf)). This is consistent with the behavior of fine powders where the interparticle frictional forces are minimized at 3 U(mf). Observed results are discussed in terms of a collective effect of Meissner and interparticle frictional forces.