US3443055A - Laminated metal electrodes and method for producing the same - Google Patents

Description

May 6, 1969 GWYNN ET AL LAMINATED METAL ELECTRODES AND METHOD FOR PRODUCING THE SAME Filed Jan. 14, 1966 M rrryl INVENTORS Ross M. 6wY/v/v M v ATTORNEY United States Patent 3,443,055 LAMINATED METAL ELECTRODES AND METHOD FOR PRQDUCING THE SAME Ross M. Gwynn, 916 Dornajo Way 95825, and Tim Therny, 7025 Uranus Parkway 95823, both of Sacramento, Calif.

Filed Jan. 14, 1966, Ser. No. 520,596 Int. Cl. B23k 11/06 U.S. Cl. 219-83 20 Claims ABSTRACT OF THE DISCLOSURE A superior electrode, uniquely durable in chlorinating, hypochlorinating and related electrolytic processes comprising a laminated body of platinum metal foil bonded to a compatible metal substrate which is highly resistant to electrolytic oxidation, the bonding being effected by applying along a line of contact between a small diameter cylindrical member of hard conductive metal, rotatable in a massive electric conductor, in engagement with said foil, and a second massive electric conductor in engagement with said substrate, a pressure of about 10 to 300 pounds per linear inch, and an electric current below 12 volts at an amperage to provide at least 3 kva. per linear inch of said line of contact, while advancing said small diameter cylindrical member in a direction perpendicular to said line of contact at a rate to provide a bonding heat sufficient to soften, without melting, the substrate surface.

The platinum metal can be platinum, rhodium, iridium or ruthenium or alloys thereof; the substrate metal can be tantalum, titanium, niobium or alloys thereof; and the bonding is preferably efi'ected at a pressure of 50 to 150 pounds per linear inch, using direct current of 0.1 to 5 volts at an amperage to provide 7 to 100- kva. per linear inch.

In electrolytic processes generally, and particularly in the electrolysis of chlorides and the production of hypochlorites or percompounds, intense corrosion can be encountered at the anode unless suitably resistant materials are employed in such anodes. Even with a normally resistant metal such as tantalum or titanium the action of chlorine being liberated at the anode so alters or oxidizes the metal surface as to rapidly reduce its electric conductivity or increase its overvoltage, thus impairing its usefulness as an anode.

Materials which are found most advantageous from the standpoint of both chemical resistance and electric conductivity comprise the metals of the platinum group, including in particular ruthenium, rhodium, iridium, and platinum, and mixtuers and alloys thereof. Unfortunately the scarcity and cost of such metals prevents their use as anodes for most electrolytic processes except as such metals are applied in thin layers or foils to less expensive supporting materials.

Various methods have been used in the past in attempts to suitably coat a substrate, such as tantalum, niobium, titanium, and alloys thereof, with metals of the platinum group, but with varying degrees of success and practicability. United States Patent No. 2,719,797, for example, discloses chemical decomposition or electrolysis to form thin deposits of platinum metals, in conjunction with heating to effect a bond with the substrate. These methods, however, tend to produce uneven or incomplete coatings of the platinum metal, and there is a substantial tendency for the heat treatment to modify the platinum metal composition and its electric conductivity, thereby reducing its effectiveness as an anode surface material.

It is pointed out in said United States Patent No. 2,719,797 that attempts to cover the tantalum strip with a platinum metal foil to hold the metals together, as by Patented May 6, 1969 sweating, rolling or hammering, have proved to be unsatisfactory because the platinum metal foil is held to the tantalum only by mechanical contacts which is not sufficient to permit its use as an anode.

It is now discovered in accordance with the present invention that the type of intimate bond of platinum metals with titanium or other substrate indicated to be desirable but difficulty obtainable in United States Patent No. 2,719,797 can be achieved in a practical and economical way by bonding platinum metal foil to tantalum, titanium, niobium or other suitable substrate material under the influence of pressure and locally generated thermoelectric heat. The substrate surface preferably is prepared for bonding as for example by being roughened slightly to exhibit a matte appearance. A clean matte surface, free of oxide, organic residues, and excess adsorbed gases improves bonding and minimizes the chance of blister formation. Bonding can be further enhanced if desired, by applying to the cleaned matte surface, suitably by electrolitic disposition, a very thin coating of' palladium, silver, or other soft chlor-resisting solder-type metal which will aid in alloy formation at the interface between the substrate and foil.

In carrying out the new method a cleaned or prepared plate of tantalum, titanium, or niobium or other substrate material is disposed in bearing engagement with a massive electric conductor with a sheet of platinum metal foil, suitably of a thickness within the range of about 0.0003 to 0.002. inch, overlying the opposed face of said plate. A second somewhat smaller massive conductor grooved to rotatably receive a hard, small-diameter, cylindrical conducting element is then brought into bearing engagement with the foil-substrate assemblage and pressure is applied to provide a pressure of 10' to 300 pounds and suitably 50 to 150 pounds per linear inch of contact between said cylindrical element and supported foilsubstrate assemblage. While maintaining this pressure and slowly advancing said line of contact in a direction perpendicular to the axis of said element a low voltage, high amperage current is applied across said massive conductors to create a very high electrothermal intensity along said line of contact to bond the foil and substrate. The voltage should preferably be below 12 volts and suitably within the range of about 0.1 to 5 volts, and the amperage sufficiently high to provide a current in excess of 3, and preferably within the range of about 7 to kva. (kilovoltamperes) per linear inch along said line of contact. Either direct or alternating current can be used for the bonding, but direct current is preferred.

In order to avoid mechanical damage to the delicate foil, the cylindrical element, which may be tungsten, tungsten carbide, alloys of tungsten carbide with small amounts, i.e., less than 25%, of an alloying metal selected from the group consisting of cobalt, tantalum and titanium and mixtures thereof, or even stainless steel, is rotated in a manner to provide rolling engagement with the foil and sliding engagement with the grooved conductor, with the speed of rotation being geared to the rate of forward motion desired for said line of contact. To effect the desired bonding between the platinum metal foil and the substrate it is necessary to momentarily generate along said line of contact a glowing temperature sufiicient to soften but not melt the substrate surface. The heat build-up is a function of the time of contact at a particular bonding site and if the forward feed of the line of contact is permitted to stop while the high kva. current is being applied, the resulting local overheating can melt or break through the thin platinum foil. It should be noted in this connection that the high temperature generated along said line of contact is rapidly dissipated with normal movement of said line of contact due to the conductivity and high heat capacity of the lower massive conductor.

The rotation of the cylindrical element is adjusted to advance the line of contact which a speed, generally 6 to 36 inches per minute to provide effective bonding without danger of burn-through. Optimum speed with an apparatus of particular electrical output will vary depending upon the length of the line of contact between the cylindrical element and the assemblage being bonded. By way of illustration an apparatus with an electrical capacity of 58 kva. can bond approximately 16 square inches per minute. This would mean if there is a one inch line of contact between the cylindrical element and the assemblage being bonded this line of contact should be advanced at the rate of about 16 inches per minute, whereas with a line of contact /2 inch in length the speed of movement should be about 32 inches per minute.

The operator is assisted in selecting the proper forward speed for the particular heating potential being applied by the characteristic glowing or bright red color in the area of said line of contact. The optimum temperature generated in the vicinity of the line of contact should be in the softening range for the substrate metal and suitably within about 100 to 500 degrees C. below the melting point for the substrate metal. Under a given set of conditions, however, it is desirable that pressure, electrical potential, and rate of movement of the line of contact be maintained substantially constant for each pass over the foil-substrate assemblage, and for the several passes which may be necessary to fully cover the area of said assemblage.

The resulting bonded assemblage appears to be fundamentally different from similar type assemblages prepared by methods heretofore available. At most of the interface between the platinum metal foil and the substrate there is an alloy zone that forms a strong mechanical bond between the two. This, alloy zone, however, extends only part way through the thickness of the foil and does not modify the chemical nature of the outer surface of the foil. On the other hand, the high intensity heat and pressure may anneal the outer surface of the foil and give the bonded assemblage a uniquely activated and continuous platinum metal surface.

In order to better visualize the mechanics of carrying out the present method, attention is directed to the accompanying drawing in which a number of adaptations of the method have been schematically illustrated, with essential parts of the apparatus identified by suitable reference characters in each of the views, and in which:

FIG. 1 is a side view of one type of apparatus setup taken in a direction axially of the cylindrical element.

FIG. 2 is a view substantially on the line 22 of FIG, 1.

FIG. 3 is a fragmentary view similar to FIG. 2 showing a modification.

FIG. 4 is a side view of another type of apparatus setup taken axially of the cylindrical element.

FIG. 5 is a view taken in the direction of the arrows 55 as seen in FIG. 4.

FIG. 6 is an enlarged fragmentary sectional view of an edge portion of a platinum metal-substrate assemblage.

FIGS. 7 to 9 are views similar to FIG. 6 showing various ways of covering edge and reverse side surface of the substrate.

In FIGS. 1 to 3 of the drawing the apparatus schematically illustrated is adapted for either power driven or manual operation. A massive electric conductor is employed in the form of a heavy bed 10 of copper or suitably a somewhat harder copper alloy such as coppersilver or copper-beryllium alloy. A 2% beryllium-copper alloy is especially hard and durable. Secured to the bed 10 is at least one and preferably a plurality of electrical leads 11 appropriate for applying the low voltage, high imperage current above mentioned to the bed 10.

A workpiece 12 in the form of a plate of tantalum,

titanium, niobium or an alloy thereof, is placed on the conductor bed 10 and a coextensive or slightly larger sheet of platinum metal foil 13 is laid over the plate 12. The size and thickness of the plate 12 can be varied within wide limits in preparing electrodes for different intended uses. By way of illustration, electrodes for use in cells to chlorinate swimming pools, or sterilize domestic drinking water may use a plate 12 measuring only about 2 inches by 6 inches and about thick, whereas for electrodes intended to treat sewage or to be used industrially the surface area may be several square feet with appropriately greater thickness to provide the strength and stiffness desired.

At 14 is diagrammatically shown a movable, massive conductor suitably fashioned from copper or copper alloy, as in the case of the bed 10, which is provided with an arcuate groove 15 to receive an elongated hard cylindrical conducting element 16 which is long enough to extend beyond the edge of the bed 10, as seen in FIG. 2. The cylindrical element 16 which, as previously mentioned, may be fashioned from various materials, such as tungsten, tungsten carbide or stainless steel is suitably of a diameter within the range of about inch to /4 inch, it being understood in this connection that the smaller the diameter of the element 16 the narrower will be the effective line or zone of contact as the element 16 is pressed downwardly against the superimposed foil 13 and plate 12. The movable massive conductor 14 is provided with at least one, and preferably with a plurality of electrical leads 17. In fact, in order to accommodate the required low voltage, high amperage current and still provide mobility in the conductor 14, it is preferable to employ a plurality of small flexible leads 17 since a single lead would generally be so large as to interfere with movement of the conductor 14.

With a downward force W to compress the foil 13 and plate 12 between the element 16 and bed 10, the element 16 is rotated in the direction of the arrow 18 at a speed to provide the desired advancing of the element 16 in the direction of the arrow 19 so that under the influence of the low voltage, high amperage current applied to the leads 11, 17, the foil 13 and plate 12 are bonded together beneath the advancing line of contact with the element 16.

Factors to be considered in determining the proper downward force W, current applied to the leads 11, 17 and speed of movement in the direction of the arrow 19 have been previously described and need not be repeated here. It is to be noted, however, that the application of the force W in the control of movement in the conductor 14 and rotation of the element 16 can be effected either mechanically or manually depending upon the size and number of plates 12 to be surfaced with platinum metal foil 13. For purposes of illustration FIGS. 1 and 2 of the drawing may be considered as representing a manually operated assemblage in which an operator would hold the conductor 14 in one hand, applying the downward force W thereto, and with the other hand would rotate the element 16 by means of an offset crank 16(0) at one end thereof. When operated in this manner the speed of movement in the direction of the arrow 19 is controlled by the rate of rotation of the element 16 by the hand crank 16(a).

In FIG. 3 of the drawing there is shown a slight modification of the structure of FIGS. 1 and 2 wherein the cylindrical element 16 has a central portion of slightly enlarged diameter, as indicated at 16(b), which becomes the effective length of the element 16 for contacting the superimposed foil 13 and plate 12. With this adaptation the groove 15 in the conductor 14 has an offset 15(a) to closely accommodate the large diameter portion 16(b) of the element 16, so that there is electrical contact between the element 16 and the conductor 14 throughout the entire length of the groove 15, 15(a).

The modified construction of FIG. 3 can be advantageously used with both manually operated and power driven apparatus, and permits the apparatus to bond foil 13 to plates 1-2 of varying width by merely passing the assemblage through the apparatus a number of times to progressively bond the foil 13 to the plate 12 along overlapping paths which are substantially the width of the axial length of the enlargement 1 6(b). By way of illustration, in a manually operated assemblage a rotating element 16 might be employed having an enlargement 16(1)) having an axial length of one-half inch or slightly less, in which event four to five passes over a plate 12 which is 2" wide, would permit bonding of the foil 13 across the entire width of the plate. In this instance a factor controlling the optimum axial length of the enlargement 16( b) could be the downward force W which could be effectively applied in manual operation. On the other hand, with a mechanically driven apparatus handling large electrodes for industrial purposes, where the width of the plate 12 might be one to two feet or more, a primary factor in determining optimum length of the enlargement 16(b) could be the practical limitation on the supply of low voltage, high amperage current to the leads 11, 17. In other words, it would be a matter of economics whether the handling of wide plates 12 by several passes through the apparatus with a power source of moderate size might be more practical than a single pass operation which might require much larger transformers to provide adequate low voltage, high amperage current.

In FIGS. 4 and 5 there is diagrammatically shown a type of apparatus which is better suited to the quantity of mechanical bonding of foil 13 to plates 12. In this type of apparatus the bed is replaced by a massive conductor 20 in the form of a relatively large-diameter, rotatable cylinder fashioned from copper or copper alloy, as described in connection with the bed 10*. In this type of apparatus the upper mlassive conductor 14 with the groove 15 to receive the rotatable cylindrical element 16 is supported in a manner to align the force W to the axis of the element 16 and the axis of the cylindrical conductor 20 in a common plane. The diameter of the cylindrical conductor 20 should be ten to twenty times the diameter of the element 16 so that when a plate 12 and foil 13 are passed between the element 16 and cylindrical conductor 20 there is a substantially greater line or zone of contact with the plates 12 than with the foil 13. Furthermore, the large mass of the cylindrical conductor 20 permits rapid flow of heat from the zone of contact with the plate 12.

The cylindrical conductor 20 and the upper massive conductor 14 are provided with suitable leads 11, 17 respectively, for applying low voltage, high amperage current thereto, as above described, and there is diagrammatically illustrated at 21 in FIG. 5 a drive and gear mechanism whereby the cylindrical conductor 20 is rotated in the direction of the arrow 22, and the element 16 is rotated in the direction of the arrow 23 at identical surface speeds while being electrically insulated one from the other. A support 24 is preferably employed to facilitate proper aligning of the plate 12 and superimposed foil 13 as they are fed between the cylindrical conductor 20 and element 16, and a second support 2-5 is also preferably employed to receive bonded articles as they are delivered in the direction of the arrow 26.

The downward force W can be applied by any suitable mechanical linkage, hydraulic ram, or the like, appropriate for the size or width of plate 12 to be handled. In this connection it will be noted that the width of the cylindrical conductor 20 and length of the element 16 can be substantially varied depending upon the width of plates 12 to be handled. Furthermore, it is to be understood that the modification shown in FIG. 3 wherein the element 16 has a short axial portion of enlarged diameter, which becomes the effective bonding portion thereof, can also be employed in the apparatus diagrammatically shown in FIGS. 4 and 5.

With the relatively smaller mass of the upper conductor 14 and the concentration of heat in the vicinity of the cylindrical element 16, it is sometimes desirable to provide passages 30- in the conductor 14 for circulation of a cooling fluid. Such means for cooling the conductor 14 would be of special value in an apparatus set-up intended for extended periods of continuous operation.

The conductor 14 may also be subject to wear or scaling within the groove 15, 15a, particularly when the conductor is made of copper. This can be minimized by switching to the use of harder alloys of copper as above mentioned, or by using other conductive materials such as tantalum, rhodium, gold or their alloys in at least the portions forming inner surfaces of the groove 15, 15a.

The enlarged showing in FIG. 6 illustrates an edge portion of a plate 12 bonded to foil 13' with the zone of weld or bond indicated at 27. In many instances 'where a platinum metal is bonded to a plate of titanium, niobium or tantalum, the edge 12(a) and reverse side 12(b) of the plate may simply be left uncoated, thereby providing in effect an electrode having one operating surface. Alternatively, the edge 12(0) and reverse side 12(b) can be coated with a protective film 28 of epoxy resin, glassy ceramic, or other non-metallic material. For other electrode uses it may be preferable to fold the foil '13 around the plate edge 12(a) and under the reverse side 12(1)), as seen at 13(a) in FIG. 8, in which event the portion 13(a) can be bonded to the reverse side 12(b) of the plate using apparatus of the type above described but with the portion 13(a) engaged by the element 16 or enlargement 16(b) thereof. Here again a coating 28-(11) of epoxy resin, glassy ceramic or the like, can be applied, if desired, to portions of the plates 12 which are not coated with platinum metal.

In some types of electrolytic processes it is desired that both surfaces of an electrode be active surfaces. In such event a second platinum metal foil 13' can be applied to the reverse side 12( b) of the previously bonded assemblage using the apparatus above described with the foil 13' in contact with the element 16 or enlargement 16(b) thereof. It should be noted in this connection that in a second pass of the assemblage through the apparatus heat is conducted sufficiently rapidly away from the bonding site by the bed 10 or cylindrical conductor 20 so that little or no change is effected in the previously bonded platinum metal layer. In other words, the bonding heat is effectively concentrated at a limited zone in which the element 16, or enlargement 16(b) thereof, is in engagement with superimposed foil and the plate 12. A double face assemblage, such as shown in FIG. 9, can have the edge portions sealed in various ways. Overlapping edges ofthe foils 13, 13' can be brought together and welded as seen at 29 or alternatively a film 28(1)) of epoxy resin, glassy ceramic, or other protective nonmetallic material can be applied.

While in the foregoing description reference has been made to the bonding of platinum metal to plates or substrates of tantalum, titanium, niobium and their alloys, (a typical alloy being -85% titanium and 20-15% molybdenum), it should be noted that the method is also effective in bonding platinum metals to other substrates including aluminum, nickel, and certain stainless steels. These other metals, which might be classed as compatible metals, apparently enter into suflicient alloy formation 'with the platinum metal to securely bond the continuous platinum metal foil to the substrate when assembled under the conditions which characterize the present invention. Thus, in its broad concept the inven tion is concerned with the bonding of platinum metal foil to any compatible metal substrate. There is special advantage, however, when producting electrodes for use in electrolysis involving chlorine production or formation of hypochlorite or percompounds to employ as substrate a metal such as tantalum, titanium, or niobium, or their alloys, which are sufiiciently resistant to corrosive attack so that local damage to a platinum metal coating will not lead to progressive destruction of the electrode.

Laminated electrodes prepared in accordance with the present invention have been found superior to previously available electrodes in various chlorinating and hypochlorinating treatments of water, including in particular sterilization of drinking water, purification of swimming pool water and treatment of sewage. Such electrodes are also superior in chlorite production, and in various fuel cells, electrodialyses, and electro-organic reactions.

Various changes and modification in the method for preparing laminated metal articles and the laminated articles thus produced, as herein disclosed, may occur to those skilled in the art, and to the extent that such changes and modifications are embraced by the appended claims, it is to be understood that they constitute part of the present invention.

We claim:

1. The method of making electrodes that comprises bonding a platinum metal foil to a compatible metal substrate which is highly resistant to electrolytic oxidation by applying along a line of contact between a small diameter cylindrical member of hard conductive metal, rotatable in a massive electric conductor, in engagement with said foil, and a second massive electric conductor in engagement with said substrate, a pressure of about 10 to 300 pounds per linear inch, and an electric current below 12 volts at an amperage to provide at least 3 kva. per linear inch of said line of contact, while advancing said small diameter cylindrical member in a direction perpendicular to said line of contact at a rate to provide a bonding heat sufiicient to soften, without melting, the substrate surface.

2. The method as defined in claim 1, wherein the pressure applied is within the range of 50 to 150 lbs. per linear inch.

3. The method as defined in claim 1, wherein the voltage applied is within the range of 0.1 to 5 volts.

4. The method as defined in claim 1, wherein the applied electric current provides 7 to 100 kva. per linear inch, and said line of contact is advanced at a rate to provide a temperature at the substrate surface which is 100 to 500 C. below the melting point of the substrate.

-5. The method as defined in claim 1, wherein the pressure applied is 50 to 150 lbs. per linear inch, the electric current is direct current of 0. 1 to 5 volts and an amperage to provide 7 to 10 kva. per linear linch.

6. The method as defined in claim 1, wherein the second massive conductor is a fiat bed adapted to engage a large surface of the reverse side of said substrate.

'7. The method as defined in claim 1, wherein the second massive conductor is a cylindrical rotatable body having its axis parallel to the axis of said small diameter cylindrical member, and having a diameter 10 to 20 times the diameter of said cylindrical conductor.

8. The method as defined in claim 1, wherein said massive conductors are formed of a conductive metal selected from the group consisting of copper and highly conductive harder alloys of copper.

9. The method as defined in claim '1, wherein said small diameter cylindrical member is formed of a hard conductive metal selected from the group consisting of tungsten, tungsten carbide, alloys of tungsten carbide, and stainless steel.

10. The method as defined in claim 1, wherein said small diameter cylindrical member has a portion of slight- 1y enlarged diameter for engagement with said foil, the length of said large diameter portion being substantially less than the length thereof which is in rotatable engagement with the associated massive conductor.

11. The method as defined in claim 1, wherein the platinum metal in said foil is selected from the group consisting of platinum, rhodium, iridium, and ruthenium and alloys thereof.

12. The method as defined in claim 1, wherein the substrate metal highly resistive to electrolytic oxidation is selected from the group consisting of tantalum, titanium, niobium and alloys thereof.

13. An electrode particularly adapted for anode use comprising a laminated body of a platinum metal foil bonded to a compatible metal substrate which is highly resistant to electrolytic oxidation prepared by the method defined in claim 1, the platinum metal of said foil being selected from the group consisting of platinum, rhodium, iridium and ruthenium and alloys thereof, the metal substrate being selected from the group consisting of tantalum, titanium, niobium and alloys thereof, and said laminated body being characterized by a bonding alloy zone at most of the interface between said foil and substrate, and a smooth continuous outer surface on said foil which is unaltered by said alloy zone.

14. An electrode as defined in claim 20, wherein the substrate is a fiat plate with a platinum metal foil bonded to at least one fiat surface thereof.

15. An electrode as defined in claim 20, wherein the substrate is a flat plate with a platinum metal foil bonded to at least one flat surface thereof, and surfaces thereof not coated with foil are covered with a non-metallic protective film.

16. An electrode as defined in claim 15, wherein said non-metallic protection film is an epoxy resin.

17. An electrode as defined in claim 15, wherein said non-metallic protective film is a glassy ceramic.

18. An electrode as defined in claim 20, wherein the substrate is a fiat plate with a platinum metal foil bonded to opposed fiat surfaces thereof.

19. An electrode as defined in claim 20, wherein the substrate is a flat plate with a platinum metal foil bonded to opposed fiat surfaces thereof, and the edges are sealed with overlapping platinum metal foil.

20. An electrode comprising a laminated body of a platinum metal foil bonded to a compatible metal substrate which is highly resistant to electrolytic oxidation prepared by the method defined in claim 1, said laminated body being characterized by a bonding alloy zone at most of the interface between said foil and substrate, and a smooth continuous outer surface on said foil which is unaltered by said alloy zone.

References Cited UNITED STATES PATENTS 5/1919 Palmer 219-82 Eldred 29-l94 OTHER REFERENCES RICHARD M. WOOD, Primary Examiner.

B. A. STEIN, Assistant Examiner.

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