US3859197A

US3859197A - Bipolar electrodes

Info

Publication number: US3859197A
Application number: US314728A
Authority: US
Inventors: Pierre Bouy; Daniel Collard
Original assignee: Rhone Progil SA
Current assignee: Rhone Progil SA
Priority date: 1971-12-21
Filing date: 1972-12-13
Publication date: 1975-01-07
Anticipated expiration: 1992-01-07
Also published as: AT320680B; JPS4876785A; NL7217259A; CA990681A; ES409772A1; DE2262141A1; FR2164454B1; CH567578A5; IT974145B; BE793045A; SE388216B; NO138178B; BR7208946D0; FR2164454A1; JPS535630B2; GB1388008A; DE2262141B2; NO138178C

Abstract

Bipolar electrodes are provided having an anodically active part comprising a film-forming metal covered with a conducting layer which is inert to electrolytes, and a cathodically, active part comprising a metal which can be used cathodically, said anodically and cathodically active parts being separated in space and connected together by an electrical connection, characterized in that the two electrolytically active parts are apertured, that the electrical connection between them is made through the contact formed within a plurality of bonded members produced by plating a metal which can be used cathodically with a filmforming metal, and that said bonded members are part of a sealing partition separating the two electrolytically active parts.

Description

United States Patent Bony et al.

[ 1 Jan. 7, 1975 l 1 BIPOLAR ELECTRODES [75] Inventors: Pierre Bony, Enghien-les-Bains;

Daniel Collard, Paris, both of France [30] Foreign Application Priority Data 101020101.102030316076038?;o'o'o'ofe IIIIIIIIIIIIIIIJW IIIIIIIIIIIII'III .T01 31079101010101019101OIQYOK'AYOYOYOYO'OIO'OY 3,770,611 11/1973 Barnabe 204/254 FOREIGN PATENTS OR APPLICATIONS 1,087,529 10/1967 Great Britain 204/266 243,329 12/1946 Switzerland 204/254 Primary Examiner-John H. Mack Assistant ExaminerW. 1 Solomon Attorney, Agent, or FirmLouis F. Reed ABSTRACT Bipolar electrodes are provided having an anodically active part comprising a film-forming metal covered with a conducting layer which is inert to electrolytes, and a cathodically, active part comprising a metal which can be used cathodically, said anodically and cathodically active parts being separated in space and connected together by an electrical connection, characterized in that the two electrolytically active parts are apertured, that the electrical connection between them is made through the contact formed within a plurality of bonded members produced by plating a metal which can be used cathodically with a film-forming metal, and that said bonded members are part of a sealing partition separating the two electrolytically active parts.

9 Claims, 2 Drawing Figures PATENTEB JAN 7 I975 FiG I I I I I I I I I I I I I u u IIIIII'IIIIIIII IIII'II'II'IIIII'IIIIIIII FiGZ BIPOLAR ELECTRODES BACKGROUND OF THE INVENTION The present invention concerns bipolar electrodes in which the anodically and cathodically active parts are separated in space.

It is known that bipolar electrodes have the very substantial advantage of permitting electrolytic cells to be of a very compact construction, and also permitting a simplified supply of easy electrical power owing to the electrical series connection of the elementary electrolytic cells formed by the succession of such electrodes.

Many types of such electrodes have been proposed, but these electrodes are far from being easy to construct and use, particularly due to the difficulty involved in selecting suitable materials; for example, in the electrolysis of alkaline chlorides in which the products obtained are particularly corrosive, precious metals of the platinum group, graphite and some oxides, such as magnetite, have long been considered as the only materials which can be used as anodes. Due to their cost, precious metals of the platinum group can only be used in the form of very thin sheets. Due to the progressive wear to which it is subjected and its weak mechanical qualities, graphite is difficult to be formed in the elaborate and complicated shapes necessary for anodes which would be necessary to achieve better electrolytic yields and to provide a good circulation of the various fluids. These failings make graphite unattractive for use in cells of the filter-press type. Finally, magnetite has even fewer of the general qualities which would make it suitable for such uses.

However, metals having similar particular anodic properties, such'as the film-forming metals, such as titanium, zirconium, niobium, tungsten and tantalum, and their alloys, make it possible, owing to their mechanical properties, to produce complex, rigid anode structures whose dimensions remain stable in the course of use thereof, provided that the anodically active surfaces of such structures are covered with an unattackable conducting layer formed for example by precious metals of the platinum group or their oxides, which may or may not be mixed with other oxides.

However, titanium and other film-forming metals having similar anodic properties are fairly poor conductors. They are also relatively expensive and difficult to weld to other metals which are suitable as conductors, or for forming the cathodically active parts of bipolar electrodes. The result of this is that most of the commonly proposed electrode structures using such metals or alloys are separate anode structures which moreover often require the use oftitanium or such metals or alloys in excessively large amounts, so that the corresponding capital investment is substantial.

The industry is now putting forward mixed metal members comprising a common metal suitable for the cathodic parts; such as mild steel and nickel, plated with titanium or anodically similar metals or alloys, such plating being effected in particular by means of explosion, and other spun or drawn mixed members of various shapes, in which the outer layer is a sheath of titanium or anodically similar metals or alloys, and in which the core comprises another metal, for example, copper or aluminum. In these different members, the bonding between the metals of different natures is such that the electrical contacts made are of very low resistance, and mechanical rigidity of the assembly is insured. However, the possible use thereof in the construction of electrodes must take into account their high cost.

It is an object of the present invention to provide bipolar electrodes which are relatively economical compared to prior art electrodes.

It is also an object of the present invention to provide bipolar electrodes which are free from the disadvantages of prior art electrodes.

Other objects will be apparent to those skilled in the art from the present description, taken in conjunction with the appended drawings, in which:

FIG. 1 is a diagrammatical representation of a a horizontal cross-section of a portion of a bipolar electrode of the invention.

FIG. 2 is a diagrammatical representation of a portion of another bipolar electrode of the invention.

GENERAL DESCRIPTION OF THE INVENTION The present invention provides bipolar metal electrodes for high current density, in the construction of which the above-mentioned combined members are employed in such a way, conjointly with film-forming metals, such as titanium or anodically similar metals or their alloys, and metals which can be used cathodically, such as mild steel and nickel, so that the best possible electrolytic outputs are attained owing to the small voltage drops and the ease of circulation of the fluids and electrolytes.

This result is achieved by virtue of the separation in space of the anodically and cathodically active parts of such electrodes, and, because of their apertured or foraminous nature, the electrical current passing from one to the other by way of the contact formed by the titanium or anodically similar metal or alloy plating on a cathodically suitably metal, such as mild steel or nickel.

It is apparent that the use of apertured or foraminous active electrode parts makes it necessary to prevent the electrodes being attached by the anolyte or the catholyte, and also to prevent mixing of these two liquids, and the current leakage resulting therefrom. Generally, these disadvantages are avoided by positioning a sealing partition between the two anodically and cathodically active parts, the partition partially comprising mixed members produced by plating, through which the current can easily pass. The mixed members are connected by welding to the electrolytically active parts, directly or utilizing intermediary spacer members. The partition must obviously be provided in such a way that it is not attacked by the catholyte and by the anolyte. This can be effected by connecting the mixed members together by means of metal sheets which are joined together and one of which comprises titanium or other film-forming metal or alloy, while the other is a metal which can be used cathodically. It is also possible to use any insulating material which is protected from or made insensitive to corrosion. In most of the latter cases, for example when using a plastics material, the use of sealing gaskets, made particularly of elastomers, is employed. The mixed members can be of any shape whatever, but are preferably elongate and can then be arranged parallel along the height or the width of the electrodes, if the electrodes are rectangular in shape.

Moreover, the anodically and cathodically active parts of the bipolar electrodes can be of various shapes other than flat, the arm of such other shape generally being to increase their active surface areas, with an additional concomitant advantage in the at least partial omission of spacer members for maintaining the spacing between the two active parts of the electrodes. For example, at least one of said parts of the electrodes can be corrugated or formed into fingers. Moreover, it is often advantageous for the two parts to be of shapes such that the projecting portions of one correspond to the recessed portions of the other. Such arrangements are well known and have long been recommended.

The apertured or foraminous parts of the bipolar electrodes according to the present invention comprise for example parallel wires, grids or perforated or expanded apertured 'rnetal sheets. Often the use of expanded sheets having perforations, by judicious utilization of the angle ofinclination of the thin limb portions which form the meshes of the expanded apertured sheets, makes it possible for discharge of the gases to be directed out of the electrolytically active space. Finally, using apertured parts, particularly as regards titanium or similar metals or alloys, causes a reduction which is often excessive in the conductivity of said parts, and in that case it is necessary to add current distribution conductors comprising metals which are good conductors, sheathed with titanium or similar metals or alloys, welded by their sheaths to the apertured parts in question.

The bipolar electrodes of the present invention can be envisaged for use, according to circumstances, with or without diaphragms and for various electrolytic operations. However, they are particularly well suited to the construction of cells for the electrolysis of alkali chloride solutions for producing alkali chloratesor alkaline lyes and chlorine.

SPECIFIC DESCRIPTION OF THE INVENTION In order to disclose more clearly the nature of the present invention, the following examples illustrating the invention are given. It should be understood, however, that this is done solely by way of example and is intended neither to delineate the scope of the invention nor limit the ambit of the appended claims.

EXAMPLE I This example relates to FIG. 1 of the accompanying drawings, which shows a horizontal cross-section of a part of a bipolar electrode in which the cathode and the anode are planar and are apertured or foraminous, being separated by a partition comprising a series of bonded or mixed members 1, only one of which is shown, in the shape of vertical posts of the same height as the bipolar electrode. These bonded or mixed members 1 comprise a sheet of titanium or other filmforming metal, or their alloys, which is desirably about 2 mm. in thickness, plated or bonded by explosion onto mild steel, the total thickness of the members being 12 mm. Continuity of the partition is ensured by the connection to the bonded members, along their edge, of metal sheets which are secured together, one sheet 2 comprising titanium or other film-forming metal and the other sheet 3 comprising mild steel which are respectively welded to the titanium part 4 and the mild steel part 5 of the bonded members 1. Welded to the faces of the titanium parts 4 of the bonded members 1 are titanium plates 6 acting as spacer members, which are themselves welded to an expanded apertured titanium sheet 7 forming the anodically-active part of the electrode. In similar manner, welded to the faces of the mild steel parts 5 of the bonded members are mild steel plates 8 which are themselves welded to a mild steel apertured grid 9 forming the cathodically active part. Deposited electrolytically on the expanded sheet 7 is a platinum and iridium alloy, or other precious metal. This gives a bipolar electrode with an anodic zone 10 and a cathodic zone 11.

The above-described bipolar electrode is suitable for the electrolytic production of chlorine and sodium hydroxide from brine, and its cost price is not excessively high, owing to the restricted weight of the titaniumplated bonded members.

EXAMPLE 2 This embodiment concerns a bipolar electrode in which the cathode and the anode are corrugated and in which the partition comprising the mixed member is similar to that of the above-described embodiment of Example 1. FIG. 2 of the accompanying drawing diagrammatically shows a horizontal section of a part of the electrode. The bonded or mixed members are the vertical posts 12 which are formed by titanium-plated mild steel. The posts 12 are connected by welding by means of two metal sheets which are secured together and which are indicated generally by reference 13. The corrugated anode 14 which comprises an expanded finely-apertured titanium sheet is welded to the posts 12 by means of jointly-drawn copper-titanium members 15. The corrugated cathode 16 formed by a mild steel apertured grid is welded directly to the mild steel face of the posts 12 along the lines 17. By arranging the corrugated surfaces of the electrodes in the manner shown in FIG. 2, it can be seen that the projecting parts of the corrugations of the cathode of one bipolar electrode correspond to the recessed portions of the corrugations of the anode of the bipolar electrode adjacent to the first-mentioned electrode. This arrangement increases the electrolytic surface area relative to the projected surface area of the electrode, and consequently relative to the amount of mixed members used.

In the foregoing examples where a part of element is constructed of titanium, it should be understood that another film-forming metal or alloy thereof may be employed instead of the titanium.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

l. A bipolar electrode having an anodically active part comprising a film-forming metal covered with a conducting layer which is inert to electrolytes, and a cathodically active part comprising a metal which can be used cathodically, said anodically and cathodically active parts being apertured and separated in space, characterized in that the said anodically and cathodically active parts are mechanically and electrically joined by welding to a plurality of bonded members of elongated shape arranged parallel and along the height of the electrode, each of said bonded members comprising a sheet of a film-forming metal bonded to a piece of metal which can be used cathodically, said anodically active part being separated in space from said film-forming metal of said bonded members by means of a film-forming metal intermediary spacer member and said cathodically active part being separated in space from a metal which can be used cathodieally of said bonded members by means of an intermediary spacer member of a metal which can be used cathodically, two adjacent of said bonded members being joined by the agency of two metal sheet secured together, the first of these sheets being made of a filmforming metal welded to the sheet of a film-forming metal of the bonded members and the second of these sheets being made of a metal which can be used cathodically welded to the piece of a metal which can be used cathodically of the bonded members, the whole of the said bonded pieces and the said metal sheets forming a partition providing a hydraulic seal of anolyte and catholyte, said partition serves as an electrical conductor only over a small fraction of its surface.

2. An electrode according to claim 1, characterized wherein the film-forming metal is titanium.

3. An electrode according to claim 1, characterized in that the two apertured electrolytically active parts are rectangular.

4. An electrode according to claim 1, characterized in that the height of the bonded members is substantially equal to that of the electrode.

5. An electrode according to claim 1, characterized in that intermediary spacer members are placed between the anodically active part and said bonded members and comprise a metal core of copper or aluminum, sheathed with a film-forming metal.

6. An electrode according to claim 5, wherein the film-forming metal is titanium.

7. An electrode according to claim 1, characterized in that the two electrolytically active parts are planar.

8. An electrode according to claim 1, characterized in that current distribution conductors formed by metals which are good conductors, sheathed with a filmforming metal are welded by their sheaths to the anodically active apertured parts.

9. An electrode according to claim 8, characterized in that the film-forming metal is titanium.

UNITED STATES PALENT OFFICE ER? FlCATE- OF CORRECTION Patent No. 3, 859,197 Dated! January 975 lnvantofls) Pierre Bouy and Daniel Collard It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below;

Column 2, line l3l l, change "a a. horizontal" to a horizontal Column 2, line 10, ehang eflattached" to attacked Column 2, line 67, change "arm" to aim Signed and sealed this 4th day of March 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C MASON Commissioner of Patents Attestlng Officer and Trademarks WM" Po-1o5o (10m)

Claims

2. An electrode accoRding to claim 1, characterized wherein the film-forming metal is titanium.
3. An electrode according to claim 1, characterized in that the two apertured electrolytically active parts are rectangular.
4. An electrode according to claim 1, characterized in that the height of the bonded members is substantially equal to that of the electrode.
5. An electrode according to claim 1, characterized in that intermediary spacer members are placed between the anodically active part and said bonded members and comprise a metal core of copper or aluminum, sheathed with a film-forming metal.
6. An electrode according to claim 5, wherein the film-forming metal is titanium.
7. An electrode according to claim 1, characterized in that the two electrolytically active parts are planar.
8. An electrode according to claim 1, characterized in that current distribution conductors formed by metals which are good conductors, sheathed with a film-forming metal are welded by their sheaths to the anodically active apertured parts.
9. An electrode according to claim 8, characterized in that the film-forming metal is titanium.