Electrode and method
United States Patent 1 Grunig l l ELECTRODE AND METHOD [75} lm cntor: James K. Grunig. Tucson. Ariz.  
 [73} Assignee: The Anaconda Company. New  
 \ ork, NY  
  OTHER PUBLlCATlONS Defensive Publication 689.485. March 1969, 8M]  
  45] Apr. 1,1975  
 Primary liruminer-F. C. Edmundson Attorney, Agent. or Firm-Pennie &amp; Edmonds [57 l ABSTRACT An electrode for use in electrometallurgical applications is in the form of a composite sheet comprising a copper inner layer. a refractory metal outer layer on each side of said copper layer. said outer layers being substantially coextensive and extending beyond the edges of said copper layer, in at least that portion of the electrode subject to anodic attack, to form a channel defined by the edges of said copper layer and the portions of outer layers extending beyond the edges of the copper layen and a refractory valve metal in said channel and the method of making such electrode. said refractory valve metal having a lower melting point than said refractory metal outer layers.  
 5 Claims 5 Drawing Figures ELECTRODE AND METHOD BACKGROUND OF THE INVENTION At present. there are a variety of electrodes used in electrometallurgieal applications. In order to extend electrode life. there are now under development composite sheet materials for supporting electrically active materials used as anodes. for example, in electrowinning procedures. Typically. such sheet materials consist of a sheet of copper covered by sheets of a refractory metal for example. a valve metal such as tantalum or columhium. A valve metal is a metal which forms an electrically nonconducting film on its surface when oxidized. The principal refractory valve metals are titanium. zirconium. hafnium, columbium. tantalum. molybdenum, and tungsten.  
  These composite sheets are ordinarily from about 0.05 to 0.09 inch thick and are produced by layering together thicker sheets of the metals rolling the combined sheets to the desired thickness. and shearing the thus formed composite sheet to size. After shearing the composite sheet has an exposed surface of copper all about the edges thereof which would he attacked electrochemically upon use if not protected. As a consequence. a variety of methods have been tried. none entirely satisfactory, in an effort to protect the copper edge from attack. One method has been to coat the exposed copper edge with a non-conductive material, but this has not proven satisfactory since such coatings have been subject to chemical attack and are rapidly removed from the electrode during use leaving the copper exposed.  
 SUMMARY OF THE INVENTION The present invention provides a composite sheet electrode which is rapidly and easily fabricated and which protects the copper edges against electromechanical and chemical attack.  
  Briefly stated, the present invention comprises an electrode for use in electromctallurgical applications comprising a composite sheet comprising a copper inner layer. a refractory metal. which may with advantage be a valve metal. outer layer on each side of said copper layer. said outer layers being substantially coextensive and extending beyond the edges of said copper layer. in at least that portion of the electrode subject to anodic attack. to form a channel defined by the edges ofsaid copper layer and the portions of outer layers extending beyond the edges of the copper layer. and a refractory valve metal in said channel. said refractory valve metal having a lower melting point than said refractory metal outer layers. The invention also comprises the method of making such electrode comprising forming a composite sheet of desired thickness comprising a copper inner layer and a refractory metal outer layer on each side of said copper layer and having an exposed edge of copper. removing a portion of the copper edge to form a channel between the new copper edge and the portions of said outer layers extending beyond said new copper edge. and sealing said channel with a refractory valve metal of lower melting point than the refractory metal forming the outer layers.  
 DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of a composite material electrode after shearing having an exposed copper surface;  
  FIG. 2 is a transverse cross-sectional view of the electrode taken along line 2-2 of FIG. 1;  
  FIG. 3 is a view similar to FIG. 2 showing a portion of the copper edge layer removed leaving a channel about the edge of the electrode;  
  FIG. 4 is an enlarged fragmentary view of one portion of the electrode of FIG. 3 showing an electrically and chemically impermeable material in said channel; and  
  FIG. 5 is a view similar to FIG. 4 showing the impermeable material filling the channel.  
 DETAILED DESCRIPTION Referring to the drawings, there is shown an electrode I0 comprising an inner copper layer 11 and outer refractory metal layers 12 and [3. The shape of the electrode can be varied widely and does not form any part of the instant invention. As discussed above. the composite electrode is formed by placing sheets of a refractory metal about a central copper layer and rolling the combined sheets to the desired thickness. The combined sheets are then sheared to the proper size and shape desired for the final electrode. as depicted in FIG. I, leaving an exposed copper edge I4.  
  In carrying out this invention, it is necessary that the copper edge 14 shown in FIGS. 1 and 2 be preferentially removed as by chemical or electromechanical etching or mechanical milling. The chemical etching can be-accomplished using any of the conventional materials. such as acids, which will attack copper but not the refractory material. In like manner. the electromechanical etching can be accomplished using currents and solutions known to preferentially remove the copper without attacking the refractory metal. Mechanical milling can be accomplished by use of an abrasive wheel whose diameter or thickness is such that it will fit between the refractory metal layers 12 and 13 to selectively abrade and remove only the copper. It is preferred to remove the copper to a depth about equal to the thickness of the copper layer. FIG. 3 illustrates the electrode after the copper removal and shows channel 15 formed by the new copper edge 16 and the portions of the outer layers 12 and 13 which extend beyond the copper edge 16. The channel need only be formed along that portion of the electrode that is to be subjected to anodic attack.  
  After the preferential removal of copper has been accomplished. a refractory valve metal of lower melting point than the refractory metal of the outer layers 12 and I3 is placed in the channel 15. As best shown in FIG. 4, a strand or wire 17 of impermeable material is placed in the channel 15. The use ofa wire is preferred. although other forms of the material can also be used. The dimensions of the wire are such that when treated as hereinafter discussed, it will be sufficient to seal the channel IS and completely cover the exposed new edge 16 of the copper. The low melting valve metal is heated so as to melt the same and form the seal 18 as depicted in FIG. 5. Conventional arc welding techniques under an inert atmosphere, such as argon. with either consumable or non-consumable electrodes. are used to melt the material. The temperature used is that suffcient to melt the material 17, but not sufficient to advcrsely affect the refractory metal outer layers 12 and 13. By heating under argon, it is possible also to avoid the formation of any brittle alloys of the impermeable material. The result is a strong seal 18 which completely covers the copper. However, other known heating methods, such as ion bombardment, ultrasonic energy heating, and laser heating, may be used to melt the wire.  
  As to materials, the refractory metal outer layer is preferably either columbium or tantalum, although any of the other usual refractory metals used in making composite electrodes can be utilized. Copper is the preferred core or inner layer. With respect to the refractory valve metal used in forming the seal, it is preferred to use a refractory valve metal which has a melting point substantially below the melting point of the material of the refractory metal outer layers. A preferred material for use to create a seal in accordance with this invention is titanium, which melts some 800C. below columbium and some l328C. below tantalum, both of which may be used as a material of the outer layer.  
 Other metals which are electrically or chemically impermeable when subjectcd to anodic attack can also be used. Other combinations of refractory valve metals include columbium to seal tantalum, columbium to seal tungsten, and tantalum to seal tungsten. ln each of these latter combinations the material of the seal has a melting point substantially below the melting point of the material of the outer layers.  
  Because the melting point of the refractory valve metals are generally above copper a means of melting the valve metal must be used which is a sufficiently intense source of heat to melt the lower melting valve metal completely while melting only an inconsequential amount of copper.  
  The thickness of the inner copper layer and the refractory outer layers can vary widely, but it is preferred to have a composite in which the inner copper layer is from about 0.05 to 0.08 inch thick, and the outer refractory metal layers from about 0.00l to 0.005 inch thick.  
 While the invention has been described in connection with a preferred embodimebt, it is not intended to limit the invention to the particular form set forth, but, on the contrary, it is intended to cover such alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.  
 What is claimed is;  
  I. An electrode for use in electrometallurgical applications comprising a copper layer, a pair of refractory metal layers, said refractory metal layers being formed of like material and disposed in juxtaposed relation on opposite sides of said copper layer, said refractory metal layers forming outer layers of said electrode, said outer layers being coextensive one with the other and at least with said copper layer in those portions of said electrode not subject to anodic attack and extending beyond said copper layer in those portions of said electrode subject to anodic attack to define a channel outlined by an edge of said copper layer and extending portions of said outer layers, and means in said channel for sealing said copper layer in said portions of said electrode, said sealing means formed by a refractory valve metal having a melting point between that of the material of said copper layer and outer layers and sub stantially below that of the outer layers.  
 2. The electrode of claim I wherein the refractory metal outer layer is selected from tantalum and columbium and the refractory valve metal is titanium.  
  3. The electrode of claim 1 wherein said copper layer has a thickness of about 0.05 to 0.08 inch and said outer layers each have a thickness of about 0.00] to 0.005 inch.  
  4. The electrode of claim 1 wherein the channel depth is substantially equal to the thickness of said copper layer.  
  5. The electrode of claim 4 wherein said refractory metal outer layer is columbium having a thickness of about 0.001 to 0.005 inch, said copper layer has a thickness of about 0.05 to 0.08 inch, and the refractory valve metal is titanium.