Composite conductor having heat resistance and oxidation resistance and method of manufacturing the same

Abstract: In accordance with a first aspect, provided is a composite conductor comprising a core part (1) which is made of copper or a copper alloy, a conductive ceramics layer (2) which is provided around the core part (1), and a nickel layer (3) which is provided in the exterior of the conductive ceramics layer (2). In accordance with a second aspect, provided is a method of manufacturing a composite conductor comprising the steps of coating the periphery of a core material which is made of copper or a copper alloy with a mixture of conductive ceramics and a binder, covering the coated wire with a nickel tape under an atmosphere of an inert gas or a reducing gas, welding the seam of the tape, clading the wire by a clading die, and drawing the same. The composite conductor has a high conductive property, and its conductivity is not reduced even if the same is used under a high temperature. Further, this composite conductor can be manufactured at a low cost.

Description: Field of the Invention The present invention relates to an electric conductor, which can be used under a high temperature and/or in an oxidizing atmosphere. Description of the Background Art An electric conductor is generally made of aluminum, an aluminum alloy, copper or a copper alloy. However, aluminum has a low melting point of 660°C and exhibits no strength under a high temperature. An aluminum alloy also has similar problems. On the other hand, copper has a melting point of 1063°C and is superior to aluminum in strength against a high temperature, while the same is easily oxidized under a high temperature. A copper alloy also has a similar problem. Thus, a heat-resistant conductor is formed by a nickel-plated copper wire which is made of copper having a nickel-plated surface. However, although such a nickel-plated copper wire causes no problem when the same is used at about 400°C, its conductive property is reduced under a higher temperature due to diffusion and alloying of copper and nickel. When the wire is used at 600°C for 2000 hours, for example, its conductivity is reduced by about 20 %. While platinum and gold have no such problem, it is inadvisable to put these materials into practice since the same are extremely high-priced. EP-A-0 170 440 and EP-A-0 179 527 disclose both temperature resistant composite conductors. However, the problem is that diffusion between the components of the composite material could arise and deteriorate the conductivity of the conductor. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the prior art and provide a highly conductive conductor, whose conductivity is not reduced under a high temperature, at a low cost. A composite conductor according to the present invention is defined in claim 1. Preferred embodiments are defined in subclaims 2-7. In order to prevent the nickel layer from oxidation under a high temperature, an oxidation inhibiting ceramics layer may be further provided in the exterior of the nickel layer. The inventive composite conductor can be manufactured by the method defined in claim 8. When a ceramics layer is further provided around the nickel layer in order to prevent the same from oxidation, this layer can be formed around the drawn wire. In the composite conductor according to the present invention, the core part is made of copper or a copper alloy. Copper or a copper alloy, having the highest conductivity next to silver, is remarkably low-priced as compared with silver, and industrially available. Thus, the inventive composite conductor comprising a core part of copper or a copper alloy can be manufactured at a low cost, and is industrially available. It is possible to improve strength under a high temperature without much reducing conductivity, by employing a copper alloy containing 0.1 % of silver. According to the present invention, the conductive intermediate layer is made of titanium boride or carbon. According to the present invention, the conductive intermediate layer which is provided between the core part and the nickel layer is adapted to prevent interdiffusion from the core part and the nickel layer under a high temperature. According to the present invention, therefore, the conductivity is not reduced even if the conductor is used for a long time in a high-temperature oxidizing atmosphere. The conductive intermediate layer is preferably not more than 0.05 µm in thickness. Further, particles forming the intermediate layer are preferably not more than 5 µm in mean particle diameter. In an oxidizing atmosphere of at least 500°C, oxidation of nickel may not be negligible and hence it is preferable to provide an oxidation inhibiting ceramics layer in this case, in order to prevent the nickel layer from oxidation. For the purpose of preventing oxidation, the ceramics layer is preferably at least 0.3 µm in thickness. In order to particularly provide sufficient insulability, it is preferable to employ insulating ceramics to coat the oxidation inhibiting ceramics layer in a thickness of at least 1 µm. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing a composite conductor according to an embodiment of the present invention. Referring to Fig. 1, a conductive intermediate layer 2 is provided around a core part 1 of copper or a copper alloy, and a nickel layer 3 is provided around this conductive intermediate layer; and Fig. 2 is a sectional view showing a composite conductor according to another embodiment of the present invention. Referring to Fig. 2, an oxidation inhibiting ceramics layer 4 is further provided around a nickel layer 3. DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention are now described. Example 1 A continuously supplied copper wire of 2.8 mm in wire diameter was degreased and washed. Then, 10 percent by weight of phenol resin, serving as a binder, was added to and sufficiently mixed with titanium boride powder of 0.3 µm in mean particle diameter. This mixture was continuously extruded and bonded to the periphery of the copper wire which was degreased and washed. Thus, a titanium boride coating layer of 1 µm in thickness was formed. Then, an inert gas or a reducing gas was sprayed onto this wire, which in turn was covered with a nickel tape of 0.3 mm in thickness. After the seam of this tape was welded, the wire was clad and drawn by squeezing into a wire of 1.0 mm in diameter. The as-obtained wire exhibited conductivity of 83 % IACS. This wire exhibited conductivity of 82 % IACS after the same was maintained at a temperature of 500°C for 2000 hours. The nickel layer of this wire was partially oxidized. Example 2 The surface of the nickel layer provided on the wire which was prepared in Example 1 was further coated with an SiO 2 ceramics layer of 3 µm in thickness. This wire exhibited conductivity of 83 %. Further, the wire exhibited the same conductivity of 83 % IACS, after the same was maintained under environment of 500°C for 2000 hours. No oxidation was recognized in this wire. Comparative Example For the purpose of comparison, a nickel-plated copper wire of 1.0 mm in wire diameter, being coated with a nickel plating layer of 10 µm in thickness, was subjected to measurement of conductivity, which was 92 % IACS. The conductivity was reduced to 65 % IACS after the nickel-plated copper wire was maintained under environment of 500°C for 2000 hours. The nickel plating layer provided on the surface of this wire was oxidized. As hereinabove described, the composite conductor according to the present invention has an excellent conductive property and can be manufactured at a low cost, since its core part is made of copper or a copper alloy. Further, the conductive intermediate layer is provided between the nickel layer and the core part, whereby it is possible to prevent interdiffusion under a high temperature as well as to minimize reduction of conductivity. In addition, the conductive intermediate layer can contribute to the conductive property, to attain high conductivity. Thus, the composite conductor according to the present invention is useful as a conductor for a heat-resistant insulated wire.

Claims: A composite heat resistant and oxidation resistant electrical wire, comprising: an electrically conducting core consisting of copper or a copper alloy; an electrically conducting intermediate layer circumferentially surrounding said core, said intermediate layer being made of an electrically conducting material selected from the group consisting of titanium boride and carbon; and a nickel layer circumferentially surrounding said electrically conducting intermediate layer. The composite electrical wire according to claim 1, further comprising an oxidation inhibiting ceramics layer provided on the exterior of said nickel layer. The composite electrical wire according to claim 1 or 2, wherein said copper alloy contains at least 0.1 % by weight of silver. The composite electrical wire according to any of claims 1 to 3, wherein said electrically conducting intermediate layer has a thickness of at least 0.05 µm. The composite electrical wire according to any of claims 1 to 4, wherein particles forming said electrically conducting intermediate layer and said oxidation inhibiting ceramics layer are at the most 5 µm in mean particle diameter. The composite electrical wire according to any of claims 2 to 5, wherein said oxidation inhibiting ceramics layer is at least 0.3 µm in thickness. The composite electrical wire according to any of claims 2 to 6, wherein said oxidation inhibiting ceramics layer is at least 1 µm in thickness. A method of manufacturing a composite heat resistant and oxidation resistant electrical wire, comprising the steps of: preparing a core consisting of copper or a copper alloy; coating said core by extruding a mixture of a binder and powder of a conductive material selected from the group consisting of titanium boride and carbon to form an electrically conductive intermediate layer around said core; covering the obtained wire having said electrically conductive intermediate layer with a nickel tape under an inert gas or reducing gas atmosphere, continuously welding the seam of said tape and cladding said wire by a cladding die; and drawing the clad wire into a prescribed wire diameter. The method of manufacturing a composite wire according to claim 8, further comprising the step of forming a ceramics layer around said drawn wire. The method of manufacturing a composite wire according to claim 8 or 9, wherein said binder consists of a phenol resin.

Inventors: INAZAWA SHINJI, SAWADA KAZUO, YAMADA KOUICHI, INAZAWA, SHINJI, SAWADA, KAZUO, YAMADA, KOUICHI, Inazawa, Shinji, c/o Itami Works, Sawada, Kazuo, c/o Itami Works, Yamada, Kouichi, c/o Itami Works
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LIMITED
Application year: 1992
Main classification: H01B3
IPC codes: H01B7, H01B13, H01B1, H01B5, H01B3