Melt-textured high temperature superconductor production

摘要

Production of optimised melt-textured bulk specimens of YBa2Cu3O7 (Y-123) high temperature superconductor involves (a) preparing a starting material of various component powders (of nm to 80 mu particle size) which result in a melt-textured body of - 50 wt.% Y-123 containing 5-50 wt.% Y-211, 0-45 wt.% Sm-211 and/or 0-45 wt.% Nd-422; (b) mixing (with an acceptable carbon uptake of up to 0.18 wt.%), optionally together with an organic binder or aid; (c) forming a green body; and then melt-texturing by either (d) contacting with a seed crystal of decomposition temperature higher than the maximum temperature (Tmax), heating at 200-400 K/hr. to T1 = 1020 deg C to Tmax, holding for up to 60 mins., furnace cooling at up to 400K/hr. to T2 = 1015 to 960 deg C (undercooling of the melt), slowly cooling at 0.5-2.0 K/hr. down to T3 =930 deg C, further cooling at 50 K/hr. or by furnace cooling to 450-400 deg C, holding for -80 hrs. while oxygen flooding the furnace and then cooling naturally or at 50 K/hr. to room temperature or (d') heating at 200-400 K/hr. to T1 = 1020 deg C to Tmax, holding for up to 60 mins., furnace cooling at up to 400K/hr. down to the seed crystal decomposition temperature (lower than the maximum temperature), placing the seed crystal on the molten green body, furnace cooling at up to 400 K/hr. to T2 = 1015 to 960 deg C, slowly cooling at 0.5-2.0 K/hr. down to T3 =930 deg C, further cooling at 50 K/hr. or by furnace cooling to 450-400 deg C, holding for - 80 hrs. while oxygen flooding the furnace and then cooling naturally or at 50 K/hr. to room temperature. Preferably, the powder mixture is mixed with a binder selected from shellac, PMMA, wax, a thermoplastic, polyvinylbutyral, polyvinyl alcohol (derivative), a polyacrylate derivative or a polymethacrylate derivative.