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Publication numberUS3671415 A
Publication typeGrant
Publication dateJun 20, 1972
Filing dateAug 21, 1970
Priority dateSep 2, 1969
Also published asDE2043560A1
Publication numberUS 3671415 A, US 3671415A, US-A-3671415, US3671415 A, US3671415A
InventorsKing John Howliston, Smith Frank
Original AssigneeIci Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Continuous lead-in core for an electrode assembly
US 3671415 A
Abstract
An electrode assembly is provided for an electrolytic cell which comprises a substantially horizontally extending foraminate titanium structure carrying on at least a part of its surface a coating comprising an operative anode material, an array of parallel spaced rods approximately covering the area of said foraminate structure, each rod having a titanium casing which is rigidly and conductively connected along its length to the upper surface of said foraminate structure and is also attached to the titanium casing of at least one rectangular bar which passes transversely over said rods by welds which enclose in fluid-tight manner intercommunicating openings through the juxtaposed areas of the casings of said rod and said bar, the casing of each said rectangular bar having an opening in its upper face, and attached in fluid-tight manner to said upper face to enclose said opening an upstanding wall of titanium sheet, the space within said upstanding wall and the titanium casings of said bar and said rods being substantially filled by a continuous core of aluminum or an aluminum alloy, said core being bonded to the surrounding titanium surfaces by an inter diffusion layer of an alloy formed between the core metal and the surrounding titanium metal.
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Description  (OCR text may contain errors)

United States Patent King etal.

[ 1 June 20, 1972 CONTINUOUS LEAD-IN CORE FOR AN ELECTRODE ASSEMBLY [72] Inventors: John I-Iowllston King; Frank Smith, both of Runcorn, England [22] Filed: Aug. 21, I970 [21] Appl.No.: 66,034

[73] Assignee:

[30] Foreign Application Priority Data Sept. 2, 1969 Great Britain .43,329/69 [52] [1.8. CI ..204/284, 204/286, 204/290 F [5 l] Int. Cl .BOlk 3/04, C23b 5/68, C23b 5/74 [58] Field of Search ..204/290 F, 290 R, 284, 286, 204/288, 278, 99, 250

[56} References Cited UNITED STATES PATENTS 3,318,792 5/1967 Cotton et al ..204/290 F X 3,409,533 l l/l968 Murayama et al. ....204/250 X 3,380,908 4/l968 Ono et al. ....204/290 F 3,507,771 4/1970 Donges et al. ....204/290 F 3,562,008 2/l97l Mantinsons 204/290 F 3,297,561 l/l967 Harrison et al. ..204/290 F X FOREIGN PATENTS OR APPLICATIONS 1,045,966 10/ l 966 Great Britain ..204/290 F Primary Examiner-John H. Mack Assistant ExaminerRegan J. Fay Attomey-Cushman, Darby & Cushman ABSTRACT An electrode assembly is provided for an electrolytic cell which comprises a substantially horizontally extending foraminate titanium structure carrying on at least a part of its surface a coating comprising an operative anode material, an array of parallel spaced rods approximately covering the area of said foraminate structure, each rod having a titanium casing which is rigidly and conductively connected along its length to the upper surface of said foraminate structure and is also at tached to the titanium casing of at least one rectangular bar which passes transversely over said rods by welds which enclose in fluid-tight manner intercommunicating openings through the juxtaposed areas of the casings of said rod and said bar, the casing of each said rectangular bar having an opening in its upper face, and attached in fluid-tight manner to said upper face to enclose said opening an upstanding wall of titanium sheet, the space within said upstanding wall and the titanium casings of said bar and said rods being substantially filled by a continuous core of aluminum or an aluminum alloy, said core being bonded to the surrounding titanium surfaces by an inter diffusion layer of an alloy formed between the core metal and the surrounding titanium metal.

7 Claims, 5 Drawing Figures PATENTEDJUMO 1972 saw 2 or 3 CONTINUOUS LEAD-IN CORE FOR AN ELECTRODE ASSEMBLY The present invention relates to an anode assembly for an electrolytic cell. More particularly it relates to an anode assembly that is particularly useful in a mercury-cathode cell for the electrolysis of alkali metal chloride solution.

In recent years it has been proposed to install in cells for the manufacture of chlorine, hypochlorites and chlorates by the electrolysis of alkali metal chloride solutions so-called permanent anodes instead of the conventional graphite anodes which wear away at an appreciable rate in use. The permanent anode comprises a supporting structure made of a film-forming metal, usually titanium, carrying a coating of an operative anode material, i.e. a material which is capable of transferring electrons from the electrolyte to the supporting structure of the anode and which is resistant to electrochemical attack in the cell. The earliest coatings were platinum group metals and/or their oxides. More recently it has been proposed to use a number of other conducting and semiconducting materials which have the necessary catalytic properties and wear resistance to function as anode coatings.

In a mercury-cathode cell where the working anode surface is an approximately horizontal plane parallel to the flowing mercury cathode and where chlorine gas is evolved at the anode arrangements must be made for the gas to escape rapidly upwards as it is formed and there have been several proposals for providing the necessary openings for the escape of gas in coated titanium anode structures. For example it has been proposed to make the horizontally extending titanium support which carries the active coating from a multi-holed titanium sheet of expanded metal or to build it up as a spaced parallel array of titanium rods, narrow strips or other longitudinally extending profiles held together by transverse ribs and to suspend this structure from a central pillar which passes through the cover of the cell and also acts as the current leadin. Anode assemblies of this type cannot, however, provide good current distribution over the whole working area of the anode unless the horizontal member or members that carry the active coating are made undesirably thick and expensive. The present invention provides an anode assembly in which the current distribution is considerably improved, which is resistant to mechanical distortion and which also enables a lowresistance connection to be made to an electrical bus-bar outside the cell.

According to the present invention we provide an anode assembly for an electrolytic cell which comprises a substantially horizontally extending foraminate titanium structure carrying on at least a part of its surface a coating comprising an operative anode material, an array of parallel spaced rods approximately covering the area of said foraminate structure, each rod having a titanium casing which is rigidly and conductively connected along its length to the upper surface of said foraminate structure and is also attached to the titanium casing of at least one rectangular bar which passes transversely over said rods by welds which enclose in fluid-tight manner intercomrnunicating openings through the juxtaposed areas of the casings of said rod and said bar, the casing of each said rectangular bar having an opening in its upper face, and attached in fluid-tight manner to said upper face to enclose said opening an upstanding wall of titanium sheet, the space within said upstanding wall and the titanium casings of said bar and said rods being substantially filled by a continuous core of aluminum or an aluminum alloy, said core being bonded to the surrounding titanium surfaces by an inter diffusion layer of an alloy formed between the core metal and the surrounding titanium metal.

In a preferred embodiment of the invention the opening in the upper face of the casing of each rectangular bar is a rectangular opening and the upstanding titanium wall is also made rectangular and is attached to the upper face of the bar by a continuous weld around the periphery of the said opening so as to provide a large intercomrnunicating area between the core metals of these components.

The substantially horizontally extending foraminate titanium structure which carries the coating comprising an operative anode material may be a multi-holed titanium sheet, e.g. a sheet of expanded titanium metal, or a louvred structure such as may be obtained by pressing out louvres from a titanium sheet by means of a slitting and forming tool. The louvre slats so obtained may suitably be turned at right angles to the original plane of the titanium sheet or they may have each of their edges rolled round to form approximately hemicylindrical members corresponding with the slots from which the metal forming them has been pressed out. A suitable multiholed titanium sheet may also be formed by isostatic pressing of titanium powder, i.e. compacting the powder by hydraulic pressure applied to a flexible mould containing the powder, which is immersed in the hydraulic fluid. The compact is then sintered at about l,050 C. Alternatively the foraminate titanium structure may be built up from longitudinally-extending titanium members spaced apart with their long axes parallel to each other, running transversely beneath the supporting array of aluminum-cored titanium rods and rigidly and conductively connected, e.g. by welding, to the titanium casing of each of the said rods. The longitudinally-extending titanium members which form the foraminate titanium structure may be for instance flat strips, rods, hemicylindrical channels which are convex upwards or convex downwards, or channels of U- shape or inverted U-shape, the closed end of the U being optionally flattened.

In this specification by titanium" we mean titanium metal alone or an alloy based on titanium and having anodic polarization properties comparable to those of titanium as known in the art.

The operative anode material may be any material which is active in transferring electrons from an electrolyte to the underlying titanium structure of the anode assembly and which is resistant to electrochemical attack under the conditions ruling in the cell where the anode is to be used. For use in very corro sive media, for instance in chloride electrolytes, the operative anode material may suitably consist of one or more platinum group metals, i.e. platinum, rhodium, iridium, ruthenium, osmium and palladium, and/or oxides thereof or another metal or a compound which will function as an anode and is resistant to electrochemical dissolution in the cell, for instance rhenium, rhenium trioxide, magnetite, titanium nitride and the borides, phosphides and silicides of the platinum group metals. The coating comprising an operative anode material may also contain oxidic semiconducting compounds or again it may contain electronically non-conducting oxides, particularly oxides of the film-forming metals such as titanium, as is known in the art, to anchor the operative anode material more securely to the supporting titanium structure and to increase its resistance to dissolution in the working cell. A preferred coating for anodes that are to be used in mercury-cathode cells electrolyzing alkali metal chloride solutions consists of at least one oxide of at least one platinum group metal, particularly ruthenium dioxide, as the operative electrode material. and titanium dioxide.

In British Pat. Specification No. 1,045 ,966 there is described a method for the manufacture of aluminum-cored titanium conductors, generally of rod shape suitable for fitting at one end to a graphite anode block or a platinum-coated titanium sheet anode. The current distributing structure of the present anode assembly consisting of a continuous core of aluminum or an aluminum alloy within a titanium casing is suitably manufactured by substantially the same method, of which the essential steps are l) removing any oxide skin from the internal surface of the titanium casing, (2) substantially filling the casing with molten core metal, (3) maintaining the filled casing at a temperature between the melting points of the casing and the core metal for a time sufiicient to form a titanium/core metal interdiffusion alloy zone at the titanium/core metal interface and then (4) allowing the core metal to solidify by cooling, steps 2, 3 and 4 being carried out in an inert atmosphere, e. g. an argon atmosphere.

The oxide skin may be removed from the titanium casing by pickling in a mixture of 20% nitric acid and 4% hydrofluoric acid after degreasing as necessary. It is also preferred to pickle the core metal in 30% caustic soda solution to remove any protective lubricant and oxide before melting. Furthermore, the internal surfaces of the titanium casing, after removal of the oxide skin therefrom, may be coated with a metal chloride/fluoride flux before filling with the core metal to aid alloy bonding of the casing with the core metal.

The time of heating the molten core metal in contact with the titanium casing should not be unnecessarily prolonged so as to avoid creating so much interdiffusion as might weaken the resistance of the titanium casing to corrosive conditions. When the core metal is commercially pure aluminum a suitable time and temperature are 30 minutes at 700 C. The time should be reduced at higher temperatures eg to about 5 minutes at 800 C. Lower temperatures are possible if a lowermelting aluminum alloy is used as the core metal, for instance an alloy of aluminum with one or more of silicon, copper and magnesium, and containing a major proportion of aluminum. At 500 C a suitable time of heating to form the alloy bond is about 6 hours.

Suitable methods of manufacturing the aluminum-cored structure which supports the working anode surface in an anode assembly according to the invention will be further discussed in relation to the accompanying drawings, wherein FIG. I shows in isometric projection one embodiment of such an assembly and also shows a method of connecting an electrical bus-bar thereto,

FIGS. 2-4 illustrate in part sectionalelevation methods of filling the core metal into the titanium casing during the manufacture of such assemblies and FIG. 5 shows in part elevation a suitable method of installing an anode assembly according to the invention in an electrolytic cell.

In FIG. I, each of two current lead-in members 4 consisting of an upstanding rectangular titanium sheet wall surrounding an aluminum core carry the current to a primary current distributor member 3 consisting of a hollow rectangular box of titanium sheet enclosing an aluminum core. The upstanding titanium wall of the current lead-in member 4 is continuously welded around the periphery of a rectangular opening in the upper face of the titanium casing of the primary current distributor member 3 so that the spaces enclosed by the wall of member 4 and the casing of corresponding member 3 are intercommunicating through the said opening. Each primary current distributor member 3 carries current to a parallelspaced array of secondary current distributor members 2, each in the form of a rod consisting of an aluminum core within a titanium tube having a titanium closure at each end. The juxtaposed areas of the titanium tube of each member 2 and the titanium casings of members 3 have intercommunicating openings and these tubes and casings are welded together in fluid-tight manner around the said openings to form passage-ways between the spaces enclosed by each tube and the casings of the members 3.

Referring again to FIG. 1 of the drawing, 1 is a substantially horizontal extending sheet of expanded titanium metal carrying a coating comprising an operative anode material to form a working anode surface. This is supported from above by bonding it to the titanium casings of each of the secondary current distributor members 2 along the length thereof. Because of the good current distribution to the expanded metal sheet 1 and the mechanical strength of the whole structure, the expanded metal sheet may be of quite light gauge and may be bonded to the titanium casings of the secondary current distributors 2 directly, for instance by electrical-resistance welding, or may be connected thereto by electricalresistance welding or argon are spot welding it to a series of titanium studs which have been fixed to the said titanium casings by a capacitor discharge stud-welding process, thus avoiding any significant heating such as might cause distortion or damage.

The expanded metal sheet 1 may be welded in the abovedescribed manner to the secondary current distributor members 2 before or after applying the coating comprising an operative anode material to the sheet. We have found, however, that when the expanded metal sheet is fixed to the current distributor members before applying the active anode coating, steps must be taken to prevent distortion of the sheet during the subsequent coating operation if the coating method involves heating the anode assembly to temperatures such as would cause significant differential expansion between the aluminum-cored supporting network and the sheet, as for instance the conventional method of producing coatings comprising platinum group metals and/or their oxides by applying paint compositions containing compounds of the platinum group metals and then heating at a temperature of about 450 C or higher. Such distortion can be avoided or reduced to an insignificant extent by cutting the expanded metal sheet into sections and welding one section to each of the secondary current distributor members 2. Any minor distortions that do then occur during a subsequent heating step can easily be corrected by simple pressing, whereas we have found that distortion caused in this way in a full-area sheet cannot subsequently be corrected. Likewise when the foraminate titanium structure is built up from longitudinally extending members spaced apart parallel to each other, e.g. titanium strips, distortion in a subsequent hot-coating step can be avoided by cutting each member into short sections. The most suitable procedure is to weld the uncut members to each of the current distributors 2 and then to make narrow expansion gaps in each member by running a saw through them between each pair of neighboring welds before carrying out the hot-coating step.

It will be seen that in the structure described with reference to FIG. 1 of the drawings the titanium casings of current leadin members 4, primary current distributor members 3 and secondary current distributor members 2 form an integral fluid-tight casing with only the upper faces of the lead-in members 4 open and that the spaces enclosed thereby are all intercommunicating one with the next. According to the invention the aluminum core within this integral casing is one continuous core. It is formed by freezing a filling of aluminum from the molten state therein after alloy-bonding to the surrounding casing for the appropriate time in the molten state as described hereinbefore.

In manufacturing the assembly, the aforesaid integral titanium casing of members 2, 3 and 4 may all be welded together, and after cleaning, etching and heating to the required temperature may be filled with the molten core metal through the open tops of the current lead-in members 4 in an argon atmosphere. Perfect filling of the cross-section of each member is not essential so long as continuity is adequately established between the neighboring members. We have found that adequate filling of the intricate array of tubes can be achieved through the open tops of the current lead-in members by rocking the assembly from side to side and end to end as the molten core metal is introduced.

If desired, however, more perfect filling of the remote tubes of current distributors 2 may be ensured by placing a loosely fitting aluminum rod in each of these before closing the titanium end caps, then heating the structure to melt these rods and completing the filling through the top openings of the current lead-in members 4. FIG. 2 of the accompanying drawings illustrates the preferred form of titanium end closure for the titanium tubes of current distributors 2 when this second method of filling is used. In FIG. 2 shown in longitudinal section on a larger scale an end portion 6 of the titanium tube of one current distributor 2 of FIG. 1 with a loosely fitting aluminum rod 7 placed inside. A titanium end closure 8 has then been inserted and sealed in place by welding around the end of the tube as indicated at 9, thus avoiding overheating of the aluminum rod during this welding operation.

When molten aluminum is held in an open-topped titanium casing it has a marked tendency to creep up the titanium walls and can even overflow and run down the outside of the walls unless these are much higher than the general level of the molten aluminum. There is also considerable differential shrinkage of the core from the top when a molten aluminum core is allowed to freeze in an open-topped titanium casing. If, therefore, the integral titanium casing of members 2, 3 and 4 of FIG. 1 is filled with the molten core metal directly through the open tops of the current lead-in member 4 the result after the hot alloy-bonding stage and subsequent cooling will be somewhat as shown in FIG. 3. This figure shows in schematic form a vertical section through part of a primary current distributor 3 with its attached current lead-in member 4. It will be seen that in order to remove the creep and shrinkage defects of the core metal 11 a considerable length of the titanium walls of the current lead-in member 4 would also have to be cut away. This waste can be avoided by clamping around the open top of the titanium walls of the current lead-in member 4 an extension made of a material which is not wetted by the molten core metal, before the core metal is introduced. A suitable arrangement is shown in FIG. 4, wherein a steel box 12 has been employed to clamp an aluminum silicate refractory fiber blanket 13 around the open top of the titanium walls 10. The result after filling with the core metal, hot alloy-bonding of the core to the titanium and subsequent cooling is then as shown in FIG. 4. Only the defect clue to shrinkage in the core remains to be removed, without waste of the titanium retaining walls 10.

An anode assembly according to the invention, for instance the embodiment comprising parts 1-4 of FIG. 1 of the accompanying drawings, is installed in a cell by passing each current lead-in 4 through an opening provided in the cell cover and pulling it up to seat the upper face of the primary current distributor 3 against resilient gasket-means which has been applied around the lead-in 4. This may be done in the manner shown in FIG. 5, wherein parts l-4 refer to the same parts of the anode assembly as in FIG. 1. The assembly is installed in the cell by tapping a threaded spindle 14 into the aluminum core of the lead-in 4, passing the spindle through a conventional bridge-piece l5 resting on the cell cover 16 and tightening downwards on to the bridge piece a nut 17 running on the spindle so as to pull the spindle upwards and compress gasketmeans 18 which has been applied around the lead-in 4 to make a fluid-tight joint.

In FIG. 1 of the accompanying drawings there is also shown a method of attaching a bus-bar outside the cell to the anode assembly. The upper face of each current lead-in 4 is machined to a true plane so that a bus-bar 5, suitably of aluminum, can be secured to it (by bolts not shown) to make good electrical contact with the exposed aluminum core of the lead-in 4. The aforesaid spindle used to pull the anode assembly into place in the cell with the aid of a bridge-piece will then pass down into the aluminum core of the lead-in 4 through the bus-bar 5.

In other embodiments of the invention there may be only one primary current distributor member 3, which will then be placed centrally across the array of secondary current dis tributor members 2. Conversely in a larger assembly there may be more than two primary current distributor members 3 suitably spaced apart. Furthermore the current lead-in 4, which is shown in the drawing as offset towards one end of the corresponding current distributor member 3, may be placed centrally over a central opening in the titanium casing of the member 3.

What we claim is:

1. An anode assembly for an electrolytic cell. which comprises a substantially horizontally extending foraminate titanium structure carrying on at least a part of its lower surface a coating comprising an operative anode material. an array of parallel-spaced titanium tubes approximately covering the area of said foraminate structure, each tube being rigidly and conductively connected along its length to the upper surface of said foraminate structure and is also attached by welds to at least one titanium casing which passes transversely over said tubes, said casing and said tubes havin intercommunicatin uxtaposed openings enclosed by sai titanium casing an tubes in fluid-tight manner, said casing having an opening in its upper face, and attached in fluid-tight manner to said upper face of said titanium casing to enclose said opening an upstanding current lead-in casing of titanium sheet, the communicating spaces within said upstanding current lead-in casing and the titanium casing and said tubes being substantially filled by an integral continuous core of aluminum or aluminum alloy, said core being bonded to the surrounding titanium surfaces by an inter diffusion layer of an alloy fored between the core metal and the surrounding titanium metal.

2. An anode assembly according to claim 1, wherein the opening in the upper face of the casing is a rectangular opening and the upstanding current lead-in casing enclosing said opening is attached to the said upper face by a continuous weld around the periphery of the said opening to form a rectangular enclosure.

3. An anode assembly according to claim 1, wherein the foraminate titanium structure is a sheet of expanded titanium metal.

4. An anode assembly according to claim 3, wherein each of the said tubes is connected to the expanded titanium metal sheet by a series of titanium studs, each of which is welded to the tube and the sheet.

5. An anode assembly according to claim 1, wherein the foraminate titanium structure has been built up from longitudinally extending titanium members spaced apart with their long axes parallel to each other.

6. An anode assembly according to claim 1, wherein the anode material is a material selected from the group consisting of a platinum group metal and an oxide of a platinum group metal.

7. An anode assembly according to claim 1, wherein the coating consists of at least one oxide of at least one platinum group metal and titanium dioxide.

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Classifications
U.S. Classification204/284, 204/290.9, 204/288.2, 204/290.13
International ClassificationC25B9/02, C25B1/00, C25B1/40, C25B11/03, C25B11/00, C25B11/10
Cooperative ClassificationC25B11/03
European ClassificationC25B11/03