Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – With melting
Patent
1995-11-27
1998-11-03
Kunemund, Robert
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
With melting
505729, 117 83, 117 84, 117 85, C30B 2306
Patent
active
058308296
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing textured high-temperature superconducting solid parts.
Oxide-ceramic high-temperature superconductors are regarded as promising materials for components or workpieces in the field of electrical engineering and electronics, since their high transition temperatures permit operation in liquid nitrogen, and cooling with liquid helium is unnecessary. A precondition for their wide cost effective use, however, is a high critical current density j.sub.c.
Processes for producing superconducting components having high critical current densities already exist. Thus, superconducting layers of the compounds YBa.sub.2 Cu.sub.3 O.sub.x (YBCO 123) and Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.x (BSCCO 2212) can be deposited on monocrystalline substrates made of SrTiO.sub.3 or MgO and there permit current densities j.sub.c of .gtoreq.10.sup.6 A/cm.sup.2. The components thus obtained however have the drawback of limited conductor length and small absolute currents. With the "powder-in-tube" method, high current densities in the range of .gtoreq.5.multidot.10.sup.4 A/cm.sup.2 are likewise achieved. This process has been carried out successfully with compounds of the type BSCCO 2212 and BSCCO 2223 (see B. Hensel et al. in Physica C 205 (1993) 329-337). The resulting specimens likewise only have relatively low absolute currents and in addition inevitably carry a silver sheath around the superconducting core. For a number of engineering applications such as supply leads or current limiters, the said silver sheath is undesirable or causes problems.
If components are fabricated in accordance with shaping processes conventional in industrial ceramics, so far only low critical transport current densities of not more than 1000 A/cm.sup.2 are achieved. The cause of this are the weak links between the individual superconducting grains. Within the scope of the invention, the term c axis refers to the crystallographic axis perpendicular to the CuO planes in the superconducting crystals, whereas a and b designate the axes in the CuO planes. According to the studies by Dimos et al. in Physical Review B, Vol. 41, (1990), 4038-4049, the critical transport current density in oxide-ceramic superconducting material of the substance class YBCO depends sensitively on the angles between the crystallographic axes of individual crystallites. The smaller the angles, the larger the critical transport current density. The most favorable arrangement is a so-called "two-axes texture", i.e. the respective crystallographic axes of all the crystallites are parallel to one another, while at the same time the (a, b) planes are aligned along the superconducting current direction.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide a suitable process by means of which the crystallites of a component can be oriented as parallel as possible with respect to one another and along the current direction, and by which it is therefore possible to produce solid shaped parts made of oxide-ceramic superconducting material, which permit critical transport current densities of more than 10,000 A/cm.sup.2.
This object is achieved by a process of the generic type mentioned in the preamble, whose distinguishing features should be seen in solid shaped parts, which comprises solid shaped parts made of oxide-ceramic superconducting material of a phase mixture of the substance class YBCO first being molded, pressed and sintered, a zonewise thermal treatment then being carried out along their longitudinal axis, heating first being carried out, in a first zone, to a temperature in the range of from 50 to 200 K below the peritectic melting temperature of the phase mixture initially present in the shaped part, the temperature then being raised, in a second zone having a temperature gradient in the range of from 10 to 250 K/cm, then, in a third zone, a temperature of up to 50 K above the peritectic melting temperature of the phase mixture initially present in the shaped p
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patent: 5409892 (1995-04-01), Hayashi et al.
patent: 5444040 (1995-08-01), Kojima et al.
Park, "Microstructural Properties of PF doped YBa.sub.2 Cu.sub.3 O.sub.7-x, High Tc Superconductor Prepared by Melting Method", J. of Materials Science: Mat. in Electronics (Mar. 1993) vol. 4, No. 1, pp. 77-82 abs only .
Assmus Wolf
Brand Markus
Brommer Gunter
Elschner Steffen
Gauss Stephan
Hoechst Aktiengesellschaft
Kunemund Robert
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