| abstract |
A superconductive element containing magnesiumdiboride (=MgB 2 ), comprising at least one superconductive filament (1) of a size between 5 and 500 micron, which is enclosed in a metallic matrix (2) and also comprising at least one highly conductive ohmic element (4),the superconducting filaments being separated from the matrix (2) and from the conductive ohmic element (4) by a protective metallic layer (3), the superconductive filament being formed by a reaction between boron (B) and magnesium (Mg) powders and boron carbide (=B 4 C) powders as a first additive is characterized in that one or more additional powder additives containing carbon are present in the reaction of the powder mixtures including Mg, B and B 4 C. The reaction of the powder mixture to MgB 2 is carried out at temperatures between 500 and 760° C. leading to a maximum of the critical current density, J c , at temperatures at 760° C. and below. |