US3761385A

US3761385A - Electrode structure

Info

Publication number: US3761385A
Application number: US00158414A
Authority: US
Inventors: W Ruthel; Long J De
Original assignee: Hooker Chemical Corp
Current assignee: Oxytech Systems Inc
Priority date: 1971-06-30
Filing date: 1971-06-30
Publication date: 1973-09-25
Anticipated expiration: 1990-09-25
Also published as: IT956912B; GB1366429A; BE785407A; FR2143784B1; FR2143784A1; JPS5210424B1; US3761384A; DE2231196A1; CA974933A; NL7208707A

Abstract

AN ELECTRODE, SUITABLE FOR USE IN AN ANODE ASSEMBLY OF A CELL FOR THE ELECTROLYSIS OF ALKALI METAL HALIDE SOLUTIONS WHICH COMPRISES A MULTI-LAYERED, PLATE-LIKE STRUCTURE, SUBSTANTIALLY RECTANGULAR IN SHAPE. THIS STRUCTURE IS FORMED OF AN INNER PLATE OF AN ELECTRICALLY CONDUCTIVE MATERIAL, SUCH AS ALUMINUM, COPPER, OR IRON. THIS INNER PLATE IS ENCAPSULATED WITHIN TWO OUTER PLATES OF A VALVE METAL, SUCH AS TITANIUM, TANTALUM, OR NIOBIUM. THE TWO OUTER PLATES ARE IDSCONTINUOUSLY BONDED TO THE INNER PLATE BY EFFECTING A FUSION OF THAT PORTION OF THE INNER PLATE AT THE BOND THE THE OUTER PLATE, WITH NO SUBSTANTIAL FUSING OF THE OUTER PLATE. THE EXTERIOR OF THESE OUTER PLATES IS COVERED WITH AN ELECTRICALLY ACTIVE COATING OF A NOBLE METAL, NOBLE METAL ALLOY, NOBLE METAL OXIDE, OR MIXTURES THEREOF.

Description

Sept. 25, 1973 w. w. RUTHEL. ETAL ELECTRODE STRUCTURE Filed June 5o, 1971 3 I B h I H v .Wxlxubx xxxxxxxxxxxxxxxx Al lll n :0. HHK HHI||HI|HH\\& 9 9 m 9 r\\ xxxxxxxxxxxxvxxxxxxxxxvccm f) Il a )(H HHHV HH() (W .H 4 ,n N l 5 3 l 'United States Patent O U.S. Cl. 204-290 F 7 Claims ABSTRACT F THE DISCLOSURE An electrode, suitable for use in an anode assembly of a' cell for the electrolysis of alkali metal halide solutions which comprises a multi-layered, plate-like structure, substantially rectangular in shape. This structure is formed of an inner plate of an electrically conductive material, such as aluminum, copper, or iron. This inner plate is encapsulated within two outer plates of a valve metal, such as titanium, tantalum, or niobium. The two outer plates are discontinuously bonded to the inner plate by effecting a fusion of that portion of the inner plate at the bond to the outer plate, with no substantial fusing of the outer plate. The exterior of these outer plates is covered with an electrically active coating of a noble metal, noble metal alloy, noble metal oxide, or mixtures thereof.

This invention relates to an improved electrode structure, and more particularly it`relates to an improved metallic or dimensionally stable electrode which is suitable for use in an anode assembly of a cell for the electrolysis of alkali metal halide solutions.

In recent years, considerable development work has been done on metallic or dimensionally stable electrodes, particularly for use as anodes in electrolytic cells for the production of chlorine, hypochlorites or chlorates by the electrolysis of alkali metal chloride solutions, for use as anodes for the cathodic protection of iron and steel structures immersed in sea water, or for anodes for the electrodialysis of brackish water, and the like. Although many electrodes of this type have been proposed, one of the most promising has been an electrode having a base of a socalled valve metal, such as titanium, and an electrically active coating of a noble metal, noble metal alloy or noble metal oxide, such as platinum, ruthenium oxide or the like.

Although from the standpoint of their electrical characteristics and chemical resistance to the conditions encountered in many of these applications, electrodes of this type have been generally satisfactory, their adaptai tion for these uses has not been without some problems. Inasmuch as the electrical conductivity of the Valve metals, such as titanium, is relatively low, as compared to materials such as copper or aluminum, the size of these electrodes has been somewhat limited, so as to maintain the electrical operating cost at an -acceptable level. Although attempts have been made to overcome this problem by providing the titanium electrodes with a core of a more conductive material, such as copper, diiculties have been encountered in the fabrication of electrodes of this type.

It is, therefore, an object of the present invention to provide an improved electrode of the metallic or dimensionally stable type which is suitable for use in an anode assembly of a cell for the electrolysis of alkali metal halide solutions.

Anotherobject of the present invention is to provide anpimprovevd metallic electrode of the above type which maybe fabricated' in a wide variety of sizes without sacricing electrical operating eciencies.

A further object of the present invention is to provide an improved method for fabricating metallic or dimensionally stable electrodes.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

In the drawings which are attached hereto and form a part hereof,

FIG. l is a sectional view of an electrode of the present invention;

FIG. 2 is a plan view of the conductive metal inner core of the present electrodes;

FIG. 3 is a plan view of the electrode of the present invention with the top outer plate removed;

FIG. 4 is a plan view of the assembled electrode of the present invention.

Pursuant to the above objects, the present invention includes an electrode, suitable for use in an anode assembly of a cell for the electrolysis of alkali metal halide solutions which comprises a multi-layered structure, substantially rectangular in shape, having (l) An inner plate of an electric-ally conductive metal, said plate having two sets of substantially oppositely disposed sides, one side of one of said sets having at least one slot running from the side, in the direction toward the oppositely disposed side and terminating short thereof,

(2) Two outer plates of a valve metal selected from titanium, t-antalum and niobium, which plates are disposed on either side of said inner plate, said outer plates being of a size such that they overlap said inner plate around its entire periphery, said outer plates being bonded to each other around the periphery of said inner plate so as to encapsulate said inner plate, said outer plates further being discontinuously bonded to said inner plate between the slots in said inner plate and between said slots and the outer edges of said inner plate, said bond being formed by fusion of the portion of the inner plate at the bond to said outer plates with substantially no fusion of the outer plates and (3) An electrically active coating on the exterior of said outer plates, said coating being formed of a noble metal, noble metal alloy, noble metal oxide or mixtures thereof, wherein said noble metals are selected from platinum, palladium, ruthenium, rhodium and iridium. It has been found, that the electrodes of the present invention have excellent operating characteristics and may be fabricated in a wide variety of sizes without any substantial adverse elfect on these characteristics.

More specifically, the electrodes of the present invention may be utilized in any suitable assembly, such as an anode assembly of a cell for the electrolysis of alkali metal halide solutions. One particularly suitable anode assembly of this type is described in a copending application filed of even date herewith, and identified as Ser. No. 158,238. These electrodes may, however, be used with various other assemblies, which provide suitable mounting means, electrical connections, and the like, depending upon the nature of the environment in which the electrode is to be used. Although, as has been indicated, these electrodes are particularly adapted for use in the electrolysis of alkali metal halide solutions, they may also be used, with appropriate assemblies, in other areas, such as for the electrodialysis of brackish water, the cathodic protection of iron and steel structures immersed in sea water, and the like.

The present electrodes are multi-layered, plate-like structures which, desirably, are substantially rectangular in shape. Although these electrodes may be fabricated in various other shapes, the substantially rectangular shape has been found to be particularly adaptable for most uses. In general, the overall size of these electrodes will be dictated by the particular environment in which they are used. It has been found, however, that where solid titanium electrodes have generally been restricted to sizes not substantially in excess of about 1 foot by 2 feet, because of the high operating costs encountered, due to the relatively high resistance of the titanium where larger sizes are used, the size of the electrodes of the present invention need not be so limited. Thus, with these electrodes, sizes as large as 3 feet by 3 feet, 3 feet by 4 feet, 5 feet by 5 feet, or even larger, are feasible and practical without sacrificing the electrical operating eiiiciencies. It is, therefore, possible when using the electrodes of the present invention, to optimize the size and shape of the cell design so as to obtain the maximum production from the cell per square foot of floor space which it occupys. Additionally, the overall capital investment for cells utilizing these electrodes is also appreciably less than for cells utilizing solid titanium electrodes.

The present electrode structures are formed of an inner plate of an electrically conductive material, i.e., a material having an electrical conductivity which is greater than that of the valve metals, such as titanium. Desirably, the inner plate is formed of aluminum, copper, iron, or alloys of these metals, although other metals may be used as well. In many instances, aluminum has been found to be particularly preferred as the electrical conductive material, both from the standpoint of cost and physical properties, although copper or iron or their alloys, may also be satisfactorily used.

This inner plate is formed so as to have two sets of substantially oppositely disposed sides. In general, the overall dimensions of this inner plate will be dictated by the desired final dimensions of the finished electrodes. Similarly, the thickness of this inner plate will be dictated by not only the desired dimensions of the final finished electrode and the particular assembly in which it is to be used, but also by the strength i.e., rigidity, and the electrical conductivity that is desired. Typically, where the finished anode is to be used in an anode assembly of a cell for the electrolysis of alkali metal halide solutions, thicknesses of this inner plate of from about 1/8" to Mi" have been used. These values are merely exemplary, however, as plate thicknesses both less than and greater than this range may also be used, depending upon the requirements in each particular application.

This inner plate is formed so that one side of one of the two sets of sides has at least one slot which runs from the side, in a direction toward the oppositely disposed side, but terminates short of the oppositely disposed side. Desirably, this inner plate is provided with a plurality of these slots, the particular number being determined, primarily, by the overall size of the plate. In general, it has been found to be desirable that a sufficient number of these slots be provided such that the distance between the slots is not substantially greater than about 24 inches. Typically, from about 3 to 5 of these slots will be used. Although these slots are desirably substantially parallel to each other and to one set of oppositely disposed sides and substantially perpendicular to the other set of sides, the slots may also be formed so as to be non-parallel. Similarly, the length and width of these slots may vary considerably, with slot lengths which are not substantially in excess of about four-fifths of the distance between the two sides and slot Widths of from about 1A; to 2 inches, being typical. As with the thickness of this inner plate, however, these values are merely exemplary of those which may be used.

This inner plate of the electrically conductive material, such as aluminum, is disposed between two outer plates of a valve metal which is selected from titanium, tantalum and niobium. Of these, in many instances, the preferred metal has been found to be titanium and for this reason, hereinafter specific reference will be made to titanium. This is not to be taken as a limitation on the valve metals which may be used, however, since in many instances satisfactory results may also be obtained when using tantalum or niobium.

The two outer plates of titanium are of substantially the same shape as the inner plate of aluminum and are of a size such that when they are disposed on either side of the inner aluminum plate, they overlap the inner plate around its entire periphery. Although the amount of this overlap should be sufficient to permit the outer plates t0 be bonded to each other around the periphery of the inner plate, other than being sufficient to provide for this, the specific amount of the overlap has not been found to be critical. By bonding the two outer plates to each other around the entire periphery of the inner plate, the inner aluminum plate is encapsulated within these outer titanium plates, thereby protecting it from chemical attack by the solutions in which the electrodes are used. This bonding of the two outer plates to each other may be effected in any convenient manner, which will provide for this encapsulation, such as by resistance welding or the like.

The two outer plates of titanium are discontinuously bonded to the inner plate of aluminum. By discontinuously bonded, it is meant that the plates are not bonded to each other over their entire innerface. This bonding of the outer plates to the inner plate is made between the slots in the inner plate and between the slots and the outer edges of the inner plate. The bond is formed by fusion of that portion of the inner plate at the bond to the outer plates, with substantially no fusion of the outer plates. This bonding may be effected by spot-welding techniques, or, in a preferred embodiment, by means of a roller seam resistance weld. In either instance, the spot weld or the seam weld are disposed so as to be between the slots of the inner `aluminum plate and between the edge of the inner plate and the slot closest to the edge, as has been indicated above. Desrably, those bonds do not extend beyond the slots in the aluminum inner plate, which slots terminate short of the one side of the plate, as has been indicated above.

In forming these bonds between the aluminum inner plate and the titanium outer plates, the welding temperatures used are controlled so as to obtain the fusion of the inner plate at the bond, without effecting any substantial fusion of the titanium outer plates. It has been found that where the welding temperatures used are too low, there will be insuicient melting or fusion of the aluminum plate to effect an adequate bond. Conversely, where the temperatures are too high, there may be fusion of the titanium outer plate with the resulting puncture or rupture of the plate, thus permiting corrosion of the aluminum inner plate by the solutions in which the electrodes are used. The bonding will, thus, be effected by the development of sutiicient heat to locally melt the aluminum at the point of the application of the heat, with substantially no melting or fusion of the titanium, so that upon the subsequent resolidiication or recrystallization of the aluminum an intimate bond is formed with the titanium.

The electrode structure, having the titanium outer plates bonded to the aluminum inner plate in the manner described above, has, as the linal layer, an electrically active coating on the exterior of the titanium outer plates. This electrically active coating is formed of a noble metal, noble metal alloy, noble metal oxide, or mixtures thereof. The noble metals in these compositions are selected from platinum, palladium, ruthenium, rhodium and iridium. Particularly, preferred coatings of this type are the noble metal oxide coatings, such as those containing ruthenium oxide. These electrically active coatings may be applied to the exterior of the titanium outer plates in any convenient manner. Typical of the application techniques which may be used, as are known to those in the art, are electrolytic applications, including both electroplating and electrophoretic deposition, vapor phase depositions, electroless plating, as well as various cladding techniques, and the like. Typically, the electrically active coating will be of a thickness of from about 4 to 60 microinches, although in many instances both greater and lesser thicknesses may be used.,In general, however, because of the cost of such coating materials, it is preferred to utilize as thin a coating as possible, consistent with aV reasonable economic life. Y

Referring now to the drawing, as is shown in FIG. 1, which is a sectional view of the electrode of the present invention, this electrode is formed of an inner core or plate 1, two

outer plates

3 and 4 and an outer layer 5 on the outside of the

outer plates

3 and 4. The inner plate 1 is of an electrically conductive material such as aluminum, copper, iron, and alloys thereof, with aluminum being preferred. The

outer plates

3 and 4 are formed of a valve metal, with titanium being preferred. The outer coating 5 on the

plates

3 and 4 is of an electrically active material such as a noble metal, noble metal alloy, noble metal oxide and mixtures of these, which coatings containing ruthenium oxide being preferred. The

plates

3 and 4 are bonded to each other preferably by welding, as is shown at 7.

Referring now to FIGS. 2 and 3, the aluminum inner plate 1 is substantially rectangular in shape and has two sets of substantially oppositely disposed

sides

9 and 11 and 13 and 15. Side 11 has a plurality of slots 17 formed therein, which slots run from side 11 toward the oppositely disposed side 9, but terminate short of this side. Although these slots are desirably substantially parallel to each other and to sides 13 and 1S and substantially perpendicular to sides 11 and 9, they may be positioned in a non-parallel relationship, e.g., in a fan-like shape.

As is shown in FIG. 3, the aluminum inner plate 1 is placed on a titanium outer plate 3, which latter plate is of substantially the same shape as plate 1. The size of plate 3, however, is such that it overlaps plate 1 around its entire periphery. As is shown in FIG. 4, the second titanium outer sheet 4 is placed on top of the assembly shown in FIG. 3 and the entire assembly is bonded together. The titanium

outer sheets

3 and 4 are discontinuously bonded to the aluminum inner sheet 1 by means of seam welds 19. These welds 19 are made between the slots 17 of the aluminum inner plate 1 and also between the

outer edges

15 and 13 of sheet 1 and the slots closest to these edges. Additionaly, the titanium

outer sheets

3 and 4 are bonded to each other by means of the Weld 7 which is around the entire periphery of the electrode. The exterior surfaces of the titanium outer plates are then coated with the electrically active coating material 5, as shown in FIG. 1. It is to be appreciated that although, in IFIG. 4, the titanium

outer sheets

3 and 4 are shown as being bonded to the aluminum inner sheet 1 by means of the seam welds 19, these seam welds may be replaced by a series of spot welds, positioned in the same relative areas, if desired.

In fabricating the electrodes of the present invention, a plate or sheet of aluminum or other electrically conductive material is formed into the desired substantially rectangular shape and slotted in the manner shown in FIG. 2. Thereafter, the slotted aluminum plate is placed between two outer plates of titanium or a similar valve metal, which outer plates are of a size such that they overlap the inner aluminum plate around its entire periphery. The outer titanium plates are then bonded to the inner aluminum plate by resistance welding the titanium-aluminum-titanium sandwich to form a seam weld between the slots in the aluminum plate and between the edge of the aluminum plate and the slots closest to the edge. As has been indicated, this welding is carried out at temperatures such that there is a melting or fusion of the aluminum, without substantial melting or fusion of the titanium. In this manner, there is one bond between the aluminum and titanium in each section or finger of the aluminum plate and it is through these bonds that the electrical conductivity between the aluminum and titanium is effected.

Thereafter, the two outer titanium plates or sheets are bonded to each other around the entire periphery, preferably by resistance welding, so as to encapsulate the alumi- A num inner plate within a titanium envelope, thus forming a leakproof, modular unit in which the aluminum is protected from vthe corrosive action of the solutions in which the electrodes are used. This sealed unit is then coated on its exterior surfaces With an electrically active coating, the preferred coating being a mixture of noble metal oxides, which includes ruthenium oxide. In a preferred embodiment, this electrically active coating of noble metal oxides is deposited on the exterior of the titanium outer plates by means of electrophoretic deposition from a dispersion of the noble metal oxides in a solvent. Other coating techniques, as are known to those in the art, may also be used, depending upon the particular electrically active coating which is desired.

The electrodes of the present invention, fabricated in the manner as has been set forth hereinabove, have been found to have excellent electrical characteristics, exhibiting an appreciably lower voltage drop in use than do coated, solid titanium electrodes of the same size. Moreover, by bonding the inner and outer plates of this electrode to each other in the manner which has been described, there has been found to be relatively little physical distortion of the electrode during fabrication. Itis, therefore, feasible to fabricate these electrodes in relatively larger sizes than has been heretofore possible with solid titanium electrodes, while still maintaining the necessary physical tolerances and the overall electrode assembly and without sacrificing the electrical characteristics, e.g., without encountering unacceptable voltage drops.

While there have been described various embodiments of the invention, the compositions and methods described are not intended to be understood as limiting the scope of the invention as it is realized that changes therewithin are possible and it is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may `be utilized.

What is claimed is:

1. An electrode, suitable for use in an anode assembly of a cell for the electrolysis of alkali metal halide solutions, which comprises a multi-layered structure having (l) an inner plate of an electrically conductive metal,

said inner plate having two sets of substantially oppositely disposed sides, one side of one of said sets having a plurality of slots running from the side, in the direction toward the oppositely disposed side and terminating short thereof,

(2) two outer plates of a valve metal selected from titanium, tantalum and niobium, which plates are disposed on either face of said inner plate, said outer plates being of the size such that they overlap said inner plate around its entire periphery, said outer plates being `bonded to each other around the periphery of said inner plate so as to encapsulate said inner plate, said outer plates further being discontinuously bonded to said inner plate by a plurality of bonds disposed only between the slots in said inner plate and between said slots and the outer edges of said inner plate, the width of said bonds being less than the width of the spaces between said slots and the width of the spaces between said slots and the outer edges of said inner plate and the length of said bonds being such that the bonds do not extend beyond said slots, said bonds further being formed by fusion of the portion of the inner plate at the bond to said outer plates with substantially no fusion of the outer plates and (3) an electrically active coating on the exterior of said outer plates, said coating being formed on a noble metal, noble metal alloy, noble metal oxide or mixtures thereof, wherein said noble metals are selected from platinum, palladium, ruthenium, rhodiumY and iridium.

2. The electrode as claimed in claim 1 wherein the inner and outer plates are substantially rectangular in shape.

Y 3. The electrodes as claimed in claim 2 wherein the slots are substantially parallel to each other and to oneset of sides of said plates.

4. The electrode as claimed in claim 3 wherein the discontinuous bond between the inner plate and the outer plates is a resistance welded seam.

5. The electrode as claimed in claim 3 wherein the discontinuous bond between the inner plate and outer plates is a series of spot welds.

6. The electrode as claimed in claim 4 wherein the inner plate is selected from aluminum, copper, iron and alloys thereof.

7. The electrode as claimed in claim 6 wherein the inner plate is aluminum, the outer plates are titanium, and the electrically active coating is a noble metal oxide'coating containing ruthenium oxide.

A References Cited UNITED STATES PATENTS.

3,380,908 Ono et al. 204-290 F OTHER REFERENCES n Der-Pub. 689,485, March 1969, Tr, T 860.019.

U.S. Cl. X.R.