As is well-known, superconducting ceramics may be used for many applications. For all superconductor applications, however, electrical interconnections must somehow be made between the current carrying superconductor and other electrical components. For example, the source of energy and the load carried by the electrical energy must be operatively connected to the superconductor. Ideally, these interconnections have low resistance to electric current flow, to complement the energy transmission savings provided by the superconductor. Not just any electrically conducting element, however, is suitable for use as an electrical interconnector between the superconductor and either a source of electricity or a load. Besides having low electrical resistivity, the interface established between the interconnecting element and the superconductor should also have a low electrical contact resistance. This is because current can more easily bypass cracks in the superconductor structure by shunting through the interconnecting element when the interface between the superconductor and the interconnecting element has low electrical resistance. The element should also preferably be chemically non-reactive with the ceramic superconductor, to prevent undesired doping of the superconductor by the interconnecting element during the sintering process.
Moreover, the interconnecting element should also protectively coat the surface of the ceramic superconductor, to prevent diffusion of water or carbon dioxide into the ceramic superconductor. As is well known, when water or carbon dioxide diffuses into and thereby contaminates a ceramic superconductor, the superconducting properties of the contaminated ceramic are adversely affected. The protective coating provided by the interconnecting element, however, should allow certain other elements, such as oxygen, to diffuse through the coating and into the ceramic superconductor structure. Such oxygen diffusion is necessary in order to properly oxygenate the superconductor. As is well known in the art, oxygenation of the superconductor results in a more efficient superconducting transmission medium.
Silver is an element which is useful as a protective coating for a ceramic superconductor, because silver satisfies the criteria discussed above. To deposit a layer of silver onto a ceramic superconductor, a number of deposition methods can be used. One method which is relatively simple and inexpensive to use is electrophoresis. Electrophoresis has several advantages over other coating methods. First, a silver coating having a thickness of about three to thirty (3-30) microns can be relatively quickly deposited onto a substrate using electrophoresis. A silver coating three to thirty (3-30) microns thick provides adequate protection for the superconductor substrate. Also, a silver coating which is electrophoretically deposited onto a substrate can be heated to sinter the silver into a dense coating relatively quickly, as compared to the ordinarily longer heating times required to sinter silver when binder materials are used to adhere the silver to the substrate.
As is well-known, however, electrophoresis is ordinarily accomplished by placing the object to be coated into a waterbased solution in which the coating material is suspended and in which the coating material develops an electrical charge. An electrode is also positioned in the solution and a voltage is applied to the electrode to electrophoretically deposit the coating material onto the object to be coated. Unfortunately, as mentioned above, contact between a ceramic superconductor and water should be avoided, in order to prevent damage to the ceramic. Accordingly, existing electrophoresis methods which use a water-based solution are unsuitable for depositing silver onto a ceramic superconductor.
In light of the above discussion, it is an object of the present invention to provide a process for substantially completely and uniformly coating a superconductor ceramic with a material having relatively low electrical resistance. In addition, it is an object of the present invention to provide a process for coating a superconductor ceramic with a material which substantially prevents diffusion of water and carbon dioxide through the material into the superconductor ceramic. Moreover, it is an object of the present invention to provide a process for coating a superconductor ceramic with a material which permits the diffusion of oxygen through the material and into the superconductor ceramic, and which does not require the use of water during the process. Additionally, it is an object of the present invention to provide a process for coating a superconductor ceramic with a material which is relatively chemically inert vis-a-vis the superconductor ceramic material. Also, it is an object of the present invention to provide a process for coating a superconductor ceramic which does not chemically deteriorate the superconductor ceramic material. Finally, it is an object of the present invention to provide a process for coating a superconductor ceramic with a material that is relatively easy and cost effective to use.