Strip-form superconductors

摘要

Superconductor strip comprising a binary intermetallic compound such as Nb3 Sn is produced by assembling at least three strips of the higher melting point element with the lower melting point element therebetween and at least one face of each adjacent pair being recessed whereby the lower melting point element is retained in place by capillary action during heat-treatment to form the compound. The compounds may consist of oneof Nb, Ta, V in combination with Al, Ga or Sn. Fig. 1 shows 10m thick strips 9, 10 and 6 of Nb with interleaved strips 7, 8 of Sn being fed through a cooled stopper 12 into a tubular continuous furnace 15 fed with an argon atmosphere. The Nb strip 6 has been previously rolled by a coarse grinding roller to provide recesses on both faces up to 7.5m deep. In the furnace, a slotted rod 18 of aluminium oxide acts as a guide for the strips which are also weighed down lightly by aluminium oxide bars. The strips are pulled through by roller 20 and after passing over pulley 26 for tension control are subjected to a second similar heat-treatment in furnace 23; the finished strip is wound on roller 25. Heat-treatment is at 1000 DEG C. for 15-30 minutes and the finished product is shown in Fig.4 where superconducting layers 56, 57, 58, 59 of Nb3Sn each about 2m thick are formed between Nb layers 51, 53, 52 and Sn layers 54, 55; the size of the tin strip is predetermined to ensure that it is just sufficient to fill the interstices in the niobium layer. The tin may alternatively be provided as a coating, electrolytically deposited or evaporated on to the niobium before or after the recessing treatment.