Inorganic wire insulation for super-conducting wire

Abstract

The need for high current, high field, low loss, stable superconductors has led to the development of multifilamentary Nb.sub.3 Sn as the most promising candidate for use in superconducting machines. However, the brittle nature of Nb.sub.3 Sn and the high reaction temperature (.about.700.degree. C.) required to form it preclude the use of standard organic insulation systems. A recently developed class of high temperature dielectric materials which are characterized by unusually large specific heats and thermal conductivities at cryogenic temperatures offers the opportunity of providing increased enthalpy stabilization in a superconducting winding, as well as the required dielectric strength. The inorganic insulation system consists of a composite glass and ceramic powder vitrified at a temperature which coincides with the superconducting formation temperature of 600.degree.-800.degree. C. The glass and the ceramic is chosen in such a way that the vitrification temperature of the composite coincides with the reaction temperature of 600.degree.-800.degree. C. The most successful glasses meeting this criterion are two Westinghouse glasses designated A-508 and M3072. Suitable ceramic fillers are Al.sub.2 O.sub.3 and the Ceram Physics, Inc. ceramics SClC and SClA. Organic binders and solvents are used. Cladding with, e.g., nickel is preferable for the copper layer of Nb.sub.3 Sn wire.