Abstract:
An essentially planar electrowinning anode made of infiltrated sintered metal, e.g. lead infiltrated sintered titanium having longitudinally extending bars of lead metallurgically bonded to and shielded by the infiltrated metal. Advantageously the anode is made up of at least two strips of lead infiltrated, sintered titanium with a lead bar bridging the junction of the strips.

Description:
The present invention is concerned with an essentially planar anode and, more particularly, is concerned with an essentially planar anode made of sintered anodically passivatable metal infiltrated with a metal capable of anodically forming an electroconductive oxide. 
     HISTORY OF THE PRIOR ART AND PROBLEM 
     Composite anodes of the kind in question, particularly anodes made of sintered titanium infiltrated with lead or lead alloys are disclosed in U.S. patent application Ser. No. 850,290 filed Nov. 10, 1977 in the names of Turillon, Nordblom and Hull, the disclosures of which application are incorporated herein by reference. Similar disclosures also incorporated herein by reference, somewhat abbreviated, are found in corresponding U.K. Pat. No. 2,009,491A of June 13, 1979. These prior art disclosures related to electrode structures, particularly anodes, which are made by grinding titanium sponge to powder, forming this powder to a compact having about 20% to about 50% porosity and sintering the compact under a protective atmosphere to provide a mechanically strong, porous matrix. This matrix is then infiltrated with molten lead or lead alloy under a protective atmosphere until at least the exterior portion of the pores of the matrix are filled with infiltrated metal. The infiltrated metal is then anodically oxidized to an electroconductive oxide, eg., lead dioxide insoluble in the electrolyte in which the anode is used. While the physical and mechanical characteristics of lead-infiltrated sintered titanium are excellent, particularly when the sintered titanium, prior to infiltration, is about 50% to about 80% of theoretical titanium density, the product is somewhat limited in electrical conductivity. In additiion infiltrated sintered metal may be practically limited in dimension by the method of manufacture. For example, using roll compaction, porous, sintered titanium of essentially uniform quality can be made in strips up to about 40cm wide. Much beyond this width, it becomes difficult to maintain uniform porosity across the strip. Thus the infiltrated product produced from too wide strip will vary in amount of contained infiltrated metal across the width of the strip. 
     Commercial anodes such as used in the electrowinning of zinc are usually at least about 55 cm wide and up to 100 cm or more long. With conventional zinc electrowinning anode materials such as argentiferous lead, the material can be readily cast to anode size as a slab perhaps 0.8 cm thick or thicker. In order to use the composite infiltrated, sintered metal as full scale zinc electrowinning anodes it is necessary for the available strips to be joined. Further, if infiltrated sintered metal is available in the required widths for full scale anode, it is still useful to provide internal, longitudinally extending conductors in infiltrated sintered metal anodes adapted to carry currents sufficient to provide anode current densities of about 3 to about 10 amps/dm 2 . 
     THE INVENTION 
     According to the invention, full scale anodes, particularly electrowinning anodes for zinc and other metals comprise a plurality of strips of infiltrated sintered metal in an essentially co-planar parallel array. Each of said strips are metallurgically bonded to at least one bar of metal extending the length of said strips. The metal of said bar is one which is capable of anodically forming a protective oxide coating in the electrolyte in which said anode is used and which has an electrical conductivity superior to the infiltrated sintered metal. The bars have a total cross-sectional area adequate for efficient passage of electric current the length of said anode: each one of said bars is laterally sheathed in the infiltrated, sintered metal of adjacent strips and the bars provide means for contact with means for feeding electric current to the anode. Even more broadly, the anodes of the present invention include structures having surfaces of infiltrated sintered metal with current carrying metal bars contained therein. The full scale electrowinning anodes are usually made from infiltrated, sintered metal (ISM) by forming on one face, near a side edge, of a flat ISM strip a depression or groove extending a length of the strip equal to the length of the full scale electrowinning anode; overlapping the depression with a flat portion adjacent an edge of another strip of ISM of equal length; metallurgically bonding metal of both strips at the site of the depression or groove to metal which is anodically oxidizable to form a protective oxide coating in the electrolyte in which the anode is used, and; repeating the process stepwise with additional strips until a width sufficient for a full scale anode is achieved. This process provides an essentially planar anode structure comprising a plurality of ISM strips, each pair of stirps joined by an ISM metal connector, the connector and the strip sheathing the sides at least one rod-like, longitudinally extending, mass of metal adhered to the infiltrated surface of both overlapping parts, said rod-like mass of metal comprising a conducting member in said anode and providing means for making electrical contact with said anode. 
    
    
     OBJECTS OF THE INVENTION AND BRIEF DESCRIPTION OF THE DRAWINGS 
     It is an object of the present invention to provide a process for joining strip-form, infiltrated sintered metal. 
     Another object of the present invention is to provide a novelly joined full scale electrowinning anode made of infiltrated sintered metal. 
     Other objects and advantages will become apparent from the following description taken in conjunction with the drawing in which: 
     FIG. 1 is a perspective view of an anode of the present invention; 
     FIG. 2 is a cross-sectional view of the anode of FIG. 1 at section II--II; 
     FIG. 3 is a cross-sectional view of a different anode of the present invention; 
     FIG. 4 is another cross-sectional view of a still different anode of the present invention; and 
     FIG. 5 is a still further cross-sectional view of another anode of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Anodes of the present invention are depicted in the drawing. Referring thereto and, particularly to FIG. 1, a rectangular anode of the invention comprises a plurality of strips 11 of infiltrated sintered metal (ISM) in parallel, co-planar array. Usually the sintered matrix of the ISM is titanium, eg., ground, compressed and sintered titanium sponge. However, the sintered matrix can be made of niobium or tantalum or, for that matter, any metal which will passivate under anodic conditions in the electrolyte in which the anode is being used. The infiltrating metal of the ISM is advantageously lead or an alloy rich in lead such as lead-tin alloys containing up to about 10% by weight of tin, leadantimony alloys containing up to about 15% by weight of antimony and the like. In place of lead, metals such as tin or manganese which form an electrolyte-insoluble, electroconductive oxide under anodic conditions can also be used as infiltrants providing, of course, that the infiltrating metal completely blocks the pores on the surfaces of the electrode exposed to electrowinning electrolyte. Each of strips 11 about 0.8 to about 3 mm thick is formed with depression or groove 12 extending the length of strip 11. Flat portion 13 of strip 11 is placed in overlapping relationship with depression 12 of the adjacent strip 11 and held in place, for example, by spot welding. The cavity formed by the overlap extending the length of strips 11 is then filled with a metal 14 compatible with the filling metal of the ISM. In the usual case where the ISM is lead-infiltrated sintered titanium metal, the compatible metal is lead or an alloy rich in lead, i.e., containing greater than about 90% lead. The stiffening members in the anode as depicted in FIG. 1 formed from compatible metal 14 are bonded to each of the adjacent strips 11, serve to unitize these strips and also serve as a means of connection of hanger 15 and current conductors 16. Current conductors 16 comprising tinned copper roads having hangar member 15 on one end thereof are advantageously fixed to strips 11 by being embedded in compatible metal 14 eg. lead, during emplacement of compatible metal 14 in the cavity formed by overlap of strips 11. Metal 14, in the completed anode 11 comprises electric current carrying rods which are metallurgically bonded to and sheathed by ISM except at the exposed ends of the rods. 
     The cross-sections of FIGS. 3, 4 and 5 of the drawing depict alternative embodiments of the anode of the present invention. In FIG. 3 there are depicted connector members 17 having double depressions therein designed to bridge and hold together flat strips 18 using two closely spaced masses of compatible metal 14. FIG. 4 shows a similar alternative wherein connector members 17 have a wider inner flange 19 but connect flat strips 18 in essentially the same manner as do bridging members 17. The embodiment of FIG. 5 is essentially the same as that of FIGS. 1 and 2 except that masses of metal 14 are on both sides of the plane of the anode in the embodiment of FIG. 5 whereas in the embodiment of FIG. 1 masses of metal 14 are on one side of the plane of the anode. 
     Those skilled in the art will appreciate that, in addition to the structures depicted in the drawing, other equivalent structures including combinations of the embodiments of FIGS. 1 to 5 can be employed as anodes of the present invention. Specifically included are structures having laterally extending stiffening corugations or members in addition to the longitudinally extending stiffening numbers made of compatible metal 14. 
     The anode structure of the present invention is particularly useful in the electrowinning of zinc, copper and like metals electrowon from sulfate electrolytes. It is believed, based upon laboratory scale tests, that the anode structure of the present invention will significantly outlast presently used argentiferous lead anode structures in the electrowinning of zinc. 
     Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.