Anode Assembly For Electrolytic Cells

Abstract

An anode assembly for electrolytic cells comprising: a downwardly-facing, open-ended, horizontally-elongated titanium channel member having a web portion and two depending flange portions integral with the web portion; a titanium tube secured at one end to said web portion in a fluid-tight manner so that said web portion closes said end, said web portion having at least one gas escape opening therethrough located intermediate said tube and each end of said channel an aluminum current lead-in rod at least partially within the tube coaxially therewith having one end friction-welded to said web portion; and a foraminate titanium structure lying in a plane parallel to said web portion and electrically connected to the lower edges of the flange portions, said foraminate structure carrying on at least a part of its surface a coating comprising an operative electrode material.

Description

The present invention relates to an anode assembly for electrolytic cells. More particularly it relates to an anode assembly which is particularly suitable for use in cells where gas is evolved at the anode.

In recent years it has been proposed to employ as anodes, particularly in cells electrolyzing aqueous alkali metal chloride solutions, structures in which a layer of a platinum group metal or metals and/or the oxides thereof constitutes the working anode surface and is carried on a support made of a film-forming metal, usually titanium. The anode conductor leading the current to the anode within the cell may also be constructed of titanium since this metal is resistant to electrochemical attack under the severe anodic conditions ruling in the cell, but in order to reduce capital expenditure and running costs it is desirable to use as far as possible a cheaper and better conducting metal. It has therefore been proposed to use as the current lead-in a composite structure in which a core of copper, steel or aluminum is protected from electrochemical attack by a casing or sheath of titanium. Aluminum is generally the most desirable core metal on the basis of cost/weight for adequate electrical conductivity but such a structure presents the problem of making a mechanically strong and low-resistance electrical connection between the aluminum core and the titanium of the casing or the titanium support member of the anode structure. This is important because the current carried principally by the good-conducting aluminum core must pass in some region across an interface between the aluminum of the core and the titanium of the casing or the anode structure itself in order to reach the working anode surface.

It has been proposed to solve this problem by melting and alloying an aluminum core inside a titanium casing and by soldering an aluminum core into a titanium casing after coating the juxtaposed surfaces of the core and casing with a solderable metal. Melting and alloying is a high temperature process which can cause distortion. Soldering introduces problems of shrinkage between the core and the casing on cooling and is expensive in labor because of the pre-coating operations that are needed.

The present invention overcomes these problems by providing a friction-welded joint between an aluminum current lead-in and a titanium member which supports the anode structure proper. Other advantageous features of the invention will appear hereinafter.

According to the present invention we provide an anode assembly for electrolytic cells which comprises a titanium tube having a flat titanium closure attached in fluid-tight manner across one end, an aluminum current lead-in at least partially within the tube and coaxial therewith having one end friction-welded to the titanium closure, and a foraminate titanium structure carrying on at least a part of its surface a coating comprising an operative electrode material, the said foraminate titanium structure lying in a plane parallel to the said titanium closure and being electrically connected thereto by titanium members which together with the said closure define an inverted channel shape.

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

The operative electrode 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 corrosive media, for instance in chloride electrolytes, the operative electrode 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 which is resistant to electrochemical dissolution in the cell, for instance rhenium, rhenium trioxide, magnetite, titanium nitride, the borides, phosphides or silicides of the platinum group metals, or an oxidic semiconducting compound. The coating comprising an operative electrode material may also 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 electrode material more securely to the supporting titanium structure and to increase its resistance to dissolution in the working cell. A preferred coating comprising an operative electrode material 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.

When an anode assembly according to the invention is installed in a cell, the titanium tube passes through sealing means in the cell casing, for instance the cover of the cell, so that the aluminum current lead-in rod is protected from contact with the cell contents. In general the aluminum current lead-in rod is made of sufficient length to protrude from the titanium tube for easy connection of an electrical bus-bar to the end of the rod outside the cell.

In preferred embodiments of the invention the titanium closure and the titanium members together defining an inverted channel shape are fabricated from one integral piece of titanium metal. Furthermore, the inverted channel shape may extend both laterally and longitudinally well beyond the limits defined by the cross-section of the end of the titanium tube to which the base of the channel forms a closure, and usually will so extend, in order to support a coated foraminate titanium structure of sufficient area to provide the desired working anode area when installed in the cell. Such embodiments are illustrated in the accompanying drawings FIG. 1-7, which are not to scale and in which like parts are numbered alike.

FIG. 1 and FIG. 2 show vertical sections at right angles to each other through the center of an electrode assembly. In these figures the center part of an inverted titanium channel 1 forms a fluid-tight closure across the lower end of titanium tube 2 by virtue of a peripheral weld around the end of the tube indicated as 3. (Other suitable forms, not shown, for the weld 3 are electrical resistance welding and friction welding). An aluminum current lead-in rod 4 has its lower end attached to the center of the channel 1 by a friction weld indicated at 5. The edges of the channel 1 are welded at intervals as indicated at 6 to a horizontally-disposed foraminate titanium structure 7 which carries on at least a part of its surface a coating (not shown) comprising an operative electrode material as defined hereinbefore. The foraminate titanium structure 7 may suitably be a multi-holed titanium sheet, for instance a sheet of expanded titanium metal. Alternatively the foraminate structure may be built up from longitudinally-extended titanium members spaced apart with their long axes parallel to each other, each one being welded to both bottom edges of the inverted channel. These members may be for instance flat strips, rods, hemicylindrical channels which are convex upwards or convex downwards or channels of U-shaped or inverted U-shaped, the closed end of the U being optionally flattened. Yet again, an arrangement approximating to the said built-up structure of longitudinally-extending members spaced apart with their long axes parallel to each other may be produced by pressing from a titanium sheet by means of a slotting and forming tool, whereby a structure with pressed-out louvres is obtained. 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 which alternate with the slots from which the metal forming them has been pressed out. FIG. 3 shows an anode assembly in which the foraminate titanium structure is built up from parallel-spaced titanium strips 8, which each have one long edge welded to both bottom edges of the inverted titanium channel 1 as again indicated at 6. The other parts of FIG. 3 correspond to those of FIG. 2. When the foraminate titanium structure is built up in this manner, at least half of the coating thereon comprising an operative electrode material may suitably be carried on the faces of the strips 8 (the vertical surfaces in the configuration in the drawing), as taught for instance in British Patent Specification No. 1,076,973 for coatings of the platinum group metals on anode surfaces formed from titanium ribs.

If desired, within the scope of the invention the titanium tube which surrounds the aluminum current lead-in may be provided with a flange at its lower end, the fluid-tight joint between the titanium tube and the inverted titanium channel then being made by welding the flange to the channel. Likewise each of the sides of the inverted channel may be terminated by a flange, the foraminate titanium structure carrying the coating comprising an operative electrode material then being welded to these flanges. An anode assembly incorporating these optional features is illustrated in FIG. 4, with the flange 8 and weld 9 replacing the weld 3 of FIG. 1 and the flanges 10 and welds 11 replacing the welds 6 of FIG. 1.

In FIG. 1-4 the aluminum current lead-in rod 4 is shown substantially filling the cross-section of titanium tube 2. In general we prefer this arrangement, in which only sufficient clearance is provided between the rod and the tube for easy assembly of these parts, so as to obtain the lowest electrical resistance in the aluminum rod commensurate with the diameter of the tube employed. It is not, however, essential for the rod to be a close fit within the tube and a wider gap may be provided between these two members if desired.

An anode assembly according to the invention is very suitable for use in a cell wherein gas is evolved at the anode, with the working anode structure of coated foraminate titanium arranged parallel to a substantially horizontal cathode, e.g. a flowing mercury cathode, since gas evolved beneath the current lead-in can pass freely upwards through the foraminate structure into the space beneath the inverted titanium channel. The gas may be allowed to flow out from under the ends of the inverted channel or, if desired, one or more openings to assist the escape of gas may be provided in the top of the channel between the centrally disposed titanium tube and each end of the channel. Suitable arrangements of opening are shown in FIG. 5-7, which are plan views showing only the titanium channel-shaped member 1 and the current lead-in 4 with its surrounding titanium tube 2. In the arrangement of FIG. 5 there is one large opening 12 provided towards each end of the channel. In the arrangement of FIG. 6 there is a plurality of small openings 13 towards each end of the channel and in the arrangement of FIG. 7 the channel is cut away at each end in approximately a V-shape 14 to assist the escape of gas.

Claims

What we claim is:

1. An anode assembly for electrolytic cells which comprises a titanium tube having a flat titanium closure attached in fluid-tight manner across one end, an aluminum current lead-in rod at least partially within the tube and coaxial therewith having one end friction-welded to the titanium closure, and a foraminate titanium structure carrying on at least a part of its surface a coating comprising an operative electrode material, the said foraminate titanium structure lying in a plane parallel to the said titanium closure and being electrically connected thereto by titanium members which together with the said closure define an inverted channel shape.

2. An anode assembly according to claim 1, wherein the said titanium members and the titanium closure which together define an inverted channel shape have been fabricated from one integral piece of titanium metal.

3. An anode assembly according to claim 1, wherein the edges of the titanium channel shape are welded at intervals to the foraminate titanium structure.

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

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 5, wherein the longitudinally-extending titanium members are flat strips which each have one long edge welded to the edges of the titanium channel shape.

7. An anode assembly according to claim 6, wherein at least half the coating comprising an operative electrode material is carried on the faces of the said flat strips.

8. An anode assembly according to claim 1, wherein the foraminate titanium structure is louvred structure formed by pressing a series of of louvre slats from a titanium sheet.

9. An anode assembly according to claim 8, wherein the louvre slats have been turned at right angles to the original plane of the titanium sheet.

10. An anode assembly according to claim 1, wherein the foraminate titanium structure comprises a titanium sheet having a plurality of louvre slats pressed out so as to form a plurality of corresponding slots, the slats having rolled edges so as to form a series of approximately hemicylindrical members which alternate with the slots.

11. An anode assembly according to claim 1, wherein the operative electrode material in selected from the group consisting of platinum group metals and oxides thereof.

12. An anode assembly according to claim 1, wherein the coating comprising an operative electrode material consists of at least one oxide of at least one platinum group metal as the operative electrode material and titanium dioxide.

13. An anode assembly according to claim 12, wherein the said operative electrode material is ruthenium dioxide.

14. An anode assembly for electrolytic cells comprising:

a downwardly-facing, open-ended, horizontally-elongated titanium channel member having a web portion and two depending flange portions integral with the web portion;

a titanium tube secured at one end to said web portion in a fluid-tight manner so that said web portion closes said end, said web portion having at least one gas escape opening therethrough located intermediate said tube and each end of said channel;

an aluminum current lead-in rod at least partially within the tube coaxially therewith having one end friction-welded to said web portion; and

a foraminate titanium structure lying in a plane parallel to said web portion and electrically connected to the lower edges of the flange portions, said foraminate structure carrying on at least a part of its surface a coating comprising an operative electrode material.