High Current-carrying Capability Research Articles

High current-carrying capability in c-axis-oriented superconducting MgB2 thin films.

In high-quality c-axis-oriented MgB2 thin films, we observed high critical current densities ( J(c)) of approximately 16 MA/cm(2) at 15 K under self-fields comparable to those of cuprate high-temperature superconductors. The extrapolated value of J(c) at 5 K was estimated to be approximately 40 MA/cm(2). For a magnetic field of 5 T, a J(c) of approximately 0.1 MA/cm(2) was detected at 15 K, suggesting that this compound would be a very promising candidate for practical applications at high temperature and lower power consumption. The vortex-glass phase is considered to be a possible explanation for the observed high current-carrying capability.

OLIN C197

Abstract Olin C197 is a second-generation high performance alloy developed by Olin Brass. It has a strength and bend formability similar to C194 (see Alloy Digest Cu-360, September 1978), but with 25% higher electrical and thermal conductivity. High conductivity allows C197 to replace brasses and bronzes in applications where high current-carrying capability is required. Also, the strength of C197 provides higher contact forces when substituted for many lower strength coppers. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion and wear resistance as well as forming and joining. Filing Code: CU-627. Producer or source: Olin Brass.

A method to improve grain boundary current-carrying capability in melt-textured YBa2Cu3O7- delta

A major impediment for many applications of bulk high-Tc superconductors is the extremely low current-carrying capability due to grain boundary weak links. A method has been developed to eliminate secondary phases and reduce microcracks at the grain boundaries in YBCO superconductor by removing a fraction of the liquid phase formed during melt texturing. Samples fabricated using this method consist of large domains containing several grains of oriented platelets with grain boundaries free of secondary phases and microcracks. The processing conditions have been tailored to obtain domains extending over a length of 15 to 20 mm, a width of 8 to 10 mm and a thickness of up to 5 mm. The grain boundary misorientation is characterized by optical microscopy as well as X-ray pole figure analysis. These grain boundaries, though having large misorientation angles up to 27.80 degrees , are found to carry high currents at 77 K, both in self-field and in an applied magnetic field of 1.5 T. These results give promise of the manufacture of polycrystalline YBCO superconductors with high current-carrying capability.

I-V characteristics of melt-textured YBa 2Cu 3O 7− x superconductors containing grain boundaries

The current-voltage ( I-V) characteristics of melt-textured YBCO superconductors have been studied in single-grain samples as well as samples containing grain boundaries of high current-carrying capability. The latter samples contained one or more grain boundaries of angles in excess of 20°. The measurements were performed at 77 K using both DC and pulsed currents in self-field. In samples possessing critical current densities in the range of 13 000–63 000 A cm -2, the I-V characteristics exhibit a nearly power-law behavior with a negative curvature in a double-logarithmic plot. The power exponent n is found to be correlated to the value of J c in these samples. On the other hand, the I-V characteristics for samples containing grain boundaries and possessing critical current densities of approximately 10 000 A cm -2 are predominantly of a linear type. It is concluded that a possible J c limiting mechanism for these specimens is flux flow along the grain boundaries due to reduced pinning forces in the grain boundary plane.

High Current Brush Material Development, Part II: Metal- Solid Lubricant Coated Wires

The preparation and testing of an electrical contact material, metal-solid lubricant coated copper wires for fabrication of multielement high current brushes, are described. The composite coating consisted of a metal, copper or silver, and an overall 1-5 weight percent (wt %) of a fine solid lubricant powder (graphite, WS 2, or WSe2) evenly dispersed and well oriented in the metal matrix. The coatings were obtained by an electrolytic codeposition technique. By sliding a bundle of the coated wires against a rotating silver or copper slip ring at constant speed of 16.75 m/s, the sliding characteristics-- contact voltage drop and friction of the testing system-were measured as a function of current density up to 12.4 MA/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in several different gas environments. Several brush life tests were made at 12.4 MA/m 2. Results indicate that the coated wire possesses high currentcarrying capability under a wide range of environmental conditions. The tests also showed that vapor lubrication is applicable to all solid lubricants with lameilar structure for reduction of wear rate. A tribochemical background of the sliding system is discussed.