US3929607A

US3929607A - Anodes for electrochemical processes

Info

Publication number: US3929607A
Application number: US445783A
Authority: US
Inventors: Janusz Josef Henryk Krause
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1974-02-25
Filing date: 1974-02-25
Publication date: 1975-12-30
Anticipated expiration: 1992-12-30

Abstract

An anode assembly for an electrolytic cell comprising a foraminate structure of a film-forming metal comprising a plurality of longitudinal members spaced with their longitudinal axes parallel to one another and carrying on at least part of their surface an electrocatalytically active coating, a current lead-in means conductively connected to each longitudinal member, wherein each longitudinal member comprises a channel blade member constituted by a pair of parallel blades having one or more bridge portions connected to the current lead-in means, and wherein the gap between the blades in the vicinity of the bridge portions is greater than the gap between the blades along the length of the member away from the said bridge portions.

Description

O United States Patent [1 1 3,929,607

Krause Dec. 30, 1975 [54] 32825 22 ELECTROCHEMICAL FOREIGN PATENTS OR APPLICATIONS 1,076,973 7/1967 United Kingdom 204/290 F [75] Inventor: Janusz Josei Henryk Krause, 1,431,954 2/1966 France 204/290 F Runcorn, England Primar Examiner-F. C. Edmundson [73] Assi nee: Im erlal Chemical Industries y Q g unlined Londo England Agent, or Fzrm-Cushman, Darby &

[22] Filed: Feb. 25, 1974 211 App]. No.: 445,783 [57] ABSTRACT An anode assembly for an electrolytic cell comprising a foraminate structure of a film-forming metal com- [52] US. Cl. 204/286; 204/288; 204/290 F; prising a plurality of longitudinal members spaced 2 204/219 with their longitudinal axes parallel to one another [51] 3*- C25B 11/02; C25B 11/04 and carrying on at least part of their surface an elec- [58] Field of Search 204/280, 286, 288, 290 R,

trocatalytically active coating, a current lead-in means conductively connected to each longitudinal member, wherein each longitudinal member comprises a chan- [56] References C'ted nel blade member constituted by a pair of parallel UNITED STATES PATENTS blades having one or more bridge portions connected 1,326,134 12 1919 Mershon 204/286 x t th current lead-in means, and wherein the g p 3,308,043 3/1967 Loftfield et a1. 204/219 X tween the blades in the vicinity of the bridge portions 3,409,533 11/1968 Murayama et al.-

20 /2 is greater than the gap between the blades along the Donges et a1 length of the member away from the aid p01- 3,689,384 9/1972 Barbato et al. 204/99 tions 3,838,035 9 1974 Pumphrey 204 250 1 3,839,179 10/1974 Koziol et a1 204/219 11 Claims, 6 Drawing Figures 2 3 i i i 1 I I I 4 5 6 5 4 US. Patent Dec. 30, 1975 Sheet 1 of3 3,929,607

US. Patent Dec. 30, 1975 Sheet 2 of3 3,929,607

I0 3 4 3 IO US. Patlnt Dac. 30, 1975 Sheet 3 of3 3,929,607

ki/oamps Per' Mei-n9 Sguane Co+hade SurPace N I I I 3-0 52 5-4 is is 4'0 4'-2 4'4 voltage DiH-erence between Anode and cathode ANODES FOR ELECTROCHEMICAL PROCESSES This invention relates to anodes for electrochemical processes.

More particularly, it relates to anodes made of a film-forming metal and carrying an electrocatalytically active coating.

Such anodes are advantageously employed in cells for the electrolysis of alkali-metal chloride solutions, the anode being made of a film-forming metal, usually titanium, and carrying a conductive coating which is resistant to electrochemical attack but is active in transferring electrons between the electrolyte and the anode.

The electrocatalytically active material of the conductive coating may suitably consist of one or more of the platinum group metals or their oxides, particularly ruthenium oxide, and in order to anchor this material more securely to the electrode it may be deposited on the anode in admixture with an oxide of a film-forming metal, eg titanium dioxide, to form the coating. Platinum group metals and their conducting compounds, particularly oxides are readily produced by thermal decomposition techniques, as described for example in U.K. Pat. Nos. 1,147,442; 1,195,871; 1,206,863 and 1,244,650.

A typical anode of the type to which this invention relates conveniently comprises a foraminate structure of the film-forming metal carrying on at least part of its surface a conductive coating. The foraminate structure may suitably be built up from a plurality of longitudinally extending members of the coated film-forming metal spaced apart with their longitudinal axes parallel to each other, each one being connected, eg by spot welding, to a conductor member. The conductor member may, for example, be in the form of a bridge plate of an inverted channel shape, which may in turn form part of a conductor assembly in association with a current lead-in rod. The longitudinally extending members comprising the foraminate structure commonly take the form of, for example, flat strips or blades, rods, hemicylindrical channels which are convex upwards or convex downwards, or channels of U-shape or inverted U-shape.

It is desirable to accomodate in the foraminate structure as many longitudinally extending members as possible per unit width thereof, since this results in a reduction in cell voltage with consequent savings in power usage. Moreover, at a given current density, increasing the number of such anode members reduces the current loading per member, which in turn reduces the rate of wear of the coating on the said member with a resultant increase in the life of the coatings. Alternatively, an increased number of such anode members allows the current density to be increased, and hence the cell output, while retaining the same current loading per member as with a reduced number of such members.

In a preferred anode of this type the foraminate structure comprises a plurality of channel blade members each constituted by a pair of parallel blades having one or more bridge portions adapted for attachment to a conductor member and wherein each of the members is of inverted U-shape in the vicinity of the bridge portions when the anode is in use in the cell.

The number of channel blade members that can be accomodated per unit width of foraminate anode struc- 2 ture is however limited in practice by the need to provide a sufficient gap between the blades of each member to allow access of welding head when spot welding the members to a conductor.

We have now modified the shape of each channel blade anode member so as to provide the necessary blade gap at the points of attachment of the member to a conductor member while at the same time increasing the overall effective number of blades per unit width of foraminate anode structure.

According to the present invention we provide an anode assembly for an electrolytic cell comprising a I foraminate structure of a film-forming metal comprising a plurality of longitudinal members spaced with their longitudinal axes parallel to one another and carrying on at least part of their surface an electrocatalytically active coating, a current lead-in means conductively connected to each longitudinal member, wherein each longitudinal member comprises a channel blade member constituted by a pair of parallel blades having one or more bridge portions connected to the current lead-in means, and wherein the gap between the blades in the vicinity of the bridge portions is greater than the gap between the blades along the length of the member away from the said bridge portions.

Each channel blade member is preferably provided with two bridge portions spaced apart either side of and equidistant from the mid-point of the length of the said member. The lengths of said bridge portions are as small as possible (thereby ensuring that the lengths of blades away from the bridge portions are as long as possible) consistent with making a satisfactory electrical connection between the channel blade member and the current lead-in means. Each channel blade member is preferably provided with additional bridge portions at each end of said member for attachment to strengthening support members, for example angle brackets of a film-forming metal. If desired, additional bridge portions may be provided along the length of the channel blade member to increase the rigidity of the member. The lengths of the additional bridge portions are again kept to a minimum, consistent with providing a satisfactory means of attachment or the necessary rigidity, in order to ensure that the length of blade away from the bridge portions is as long as possible. It is not essential that additional bridge portions provided to impart rigidity be as wide as the bridge portions connected to the current lead-in means.

In this specification by a film-forming metal we mean one of the metals titanium, zirconium, niobium, tantalum and tungsten or alloys thereof.

The channel blade member used in the anode according to the invention may be made from a flat rectangular strip of the film-forming metal. A plurality of rectangular slots is punched out along the longitudinal central axis of the strip, the said slots being spaced apart so as to provide solid portions between the slots, said solid portions subsequently constituting the bridge portions of the channel blade member. These solid portions are then pressed out from the strip to be displaced from but parallel to the plane of the strip. The strip is then folded along the lines defined by the longitudinal edges of the slots to give the channel blade member with the appropriate number of bridge portions.

Alternatively, the channel blade member may be made by punching out a plurality of rectangular slots as described above, followed by folding the strip along the lines defined by the longitudinal edges of the slots, and then pressing inwardly those parts of the blades which are intermediate of the bridge portions to provide a reduced inter-blade gap between the said bridge portions.

In yet another method, the channel blade member may be made by introducing a plurality of relief openings along the longitudinal central axis of the strip, followed by cutting slits between the relief openings, and then folding along lines spaced apart from and parallel to the slits to form the blades and the bridge portions and then pressing inwardly those parts of the blades which are intermediate of the bridge portions.

By the term relief opening we meanan opening which assists the strip to open uniformly along each slit when the folding operation is carried out.

The relief opening may be in the form of a slit disposed transversely of the longitudinal slit, but is preferably in the form of a hole of square, rectangular or triangular shape thereby providing an opening for access of the cutting tool used in forming the longitudinal slit. It is especially preferred that length of the transverse slit, the side of the square hole, the transverse dimension of the rectangular hole or the transverse side of the triangular hole, is equal to the distance between the folds on the strip, in which case the relief opening provides a lead for folding.

The anode of the invention preferably has channel blade members which are identical in shape and are spaced so that like parts (eg the bridge portions for attachment to the conductor and the open blade portions) are aligned.

In a preferred anode, the channel blade members are supported from a double-limbed bridge plate of a filmforming metal, especially titanium, mounted across and conductively connected to the bridge portions of the. channel blade members. The said bridge plate is suitably attached to an upright hollow cylindrical tube of a film-forming metal (especially titanium) which is mounted centrally on the conductor bridge plate, the said tube having a copper, steel or aluminium current lead-in rod rigidly inserted therewithin to effect electrical connection with the bridge plate and hence with the channel blade members. The current lead-in rod may conveniently be screwed on to a stud of a film-forming metal, eg titanium, which is itself conductively bonded to the bridge plate.

The electrocatalytically active coating preferably comprises at least one platinum group metal or an oxide thereof and an oxide of a film-forming metal.

By a platinum group metal is meant one of the metals platinum, rhodium, iridium, ruthenium, osmium and palladium.

The coating of the channel blade members is preferably effected for example by a painting and firing technique wherein a coating comprising a platinum group metal oxide and a film-forming metal oxide is deposited on a film-forming metal support by applying a paint composition containing thermally-decomposable compounds of a platinum group metal to a chemicallycleaned surface of the support member, evaporating the paint vehicle and heating the coated support in an oxidising atmosphere to remove the remaining organic constituents of the paint and form the desired oxide coating.

The invention is illustrated, simply by way of example, with reference to the accompanying drawings in which: Y

FIG. 1 is a plan view of a channel blade member FIG. 2 is a perspective view of the channel blade member, and

FIG. 3 is a plan view of three such members forming part of a foraminate anode structure for a mercury cell FIG. 4 is a vertical section through the centre of an anode assembly according to the invention incorporating a plurality of the aforesaid channel blade members FIG. 5 is a vertical section through the centre of the anode assembly at right angles to the section shown in FIG. 4.

FIGS. 1 to 5 are not to scale and like parts are numbered alike.

The channel blade member comprises two bridge portions 1 for spot Welding to a bridge plate 1 1 (shown in FIGS. 4 and 5), two end bridge portions 2 for spot welding to strengthening support members 10 (shown in FIGS. 4 and 5), two additional bridge portions 3 to increase rigidity, and blades 7 (shown in FIG. 2).

The channel blade member is made from a flat rectangular titanium strip (18 gauge; 36 mm long, 19 mm wide) by punching out rectangular slots 4, 5 and 6 along the longitudinal central axis of the strip. The portions of the strip intermediate of the slots 4, 5 and 6, corresponding to the bridge portions 1, 2 are pressed out from the strip so as to be displaced parallel to the plane of the strip, and the strip is folded along the lines defined by the edges of the slots to give the blades 7. In the channel blade anode member thus obtained, the slots 4 and 5 are 50 mm x 2 mm, and the slots 6 are mm x 2 mm. The blades 7 are 6 mm in depth with an interblade gap of 4 mm in the vicinity of the

bridge portions

1, 2 and 3, and an interblade gap of 2 mm in the slotted regions 4, 5 and 6.

In a foraminate anode structure comprising such channel blade members (as in FIG. 3, where only three such members are shown), the members are spot welded at points 8 to a bridge plate 11 and at points 9 to a strengthening support member 10. Up to 88 individual blades 7 may be accommodated in a foraminate anode structure (width 27 cm) as compared with only 54 individual blades of the conventional type having a uniform interblade gap of 4 mm.

Referring to FIGS. 4 and 5, a double-limbed bridge plate 11 of a film-formingmetal, especially titanium, is spot welded at its free ends to the bridge portions 1. The bridge portions 2 are spot welded to the strengthening support member 10 which isan angle bracket of a film-forming metal especially titanium. An upright hollow cylindrical tube 12 of a film-forming metal, especially titanium, is mounted centrally on the bridge plate and conductively bonded thereto, for example by welding. A stud 13 of a film-forming metal, especially titanium, and having a screw thread, is conductively bonded, for example by welding, to the bridge plate .1 l. A current lead-in rod 14, preferably of copper, steel or aluminium, is located axially within the hollow cylinder 12, the said cylinder acting as a sheath to protect the current lead-in rod from electrochemical attack. The current lead-in rod 14 has a screwed recess 15 at its lower end for effecting electrical connection with the stud 13. The current lead-in rod l3.has a screwed recess 16 at its upper end adapted for connection to the current leads (not shown).

The invention is further illustrated by the following Example.

EXAMPLE A titanium anode (A) having a foraminate structure comprising 82 individual blades over a 27 cm width, constructed from 41 channel blade members according to the invention, was compared with a titanium anode (B) having 54 blades (27 cm width) constructed from channel blade members which had a constant blade gap along their length. Both anodes were coated with an electrocatalytically active coating comprising a mixture of ruthenium oxide and titanium dioxide. The electrical activity of the anodes was compared by using each anode in turn to electrolyse sodium chloride brine under standard conditions in a mercury cell and at the same anode to cathode gap (3.00 mm). The relationship between anode current (kiloamps per metre square cathode area) and the voltage difference be tween anode and cathode (volts) is shown in the accompanying FIG. 6. It will be-seen that anode (A) is able to pass a 6% higher current than anode (B) at any given voltage above the reversible potential of 3.l volts, all other conditions being identical. This enables anodes (A) to operate at lower power cost than anode (B).

What we claim is:

1. An anode assembly for an electrolytic cell comprising a foraminate structure of a film-forming metal comprising a current lead-in means including a plate, a plurality of longitudinal members spaced with their longitudinal axes parallel to one another and carrying on at least part of their surface an electrocatalytically active coating, each longitudinal member comprising a channel blade member including a pair of spaced-apart parallel blades and one or more bridge portions, said bridge portions being connected to the plate of the current lead-in means, the gap between the blades in the vicinity of said bridge portions being greater than the gap between the blades along the length of the member away from said bridge portions.

2. An anode assembly as claimed in claim 1 wherein each channel blade member has two bridge portions spaced apart either side of an equidistant from the mid-point of the length of the said member.

3. An anode assembly as claimed in claim 1 wherein each channel blade member has additional bridge portions at each end thereof attached to a strengthening support member.

v the current lead-in means comprises a double-limbed bridge plate of a film-forming metal connected to the longitudinal members, an upright hollow cylindrical tube of a film-forming metal mounted centrally on said bridge plate and conductively bonded thereto, a current lead-in rod adapted to fit said tube, and means for effecting electrical contact between the current lead-in rod and the bridge plate.

8. An anode assembly as claimed in claim 1 wherein the film-forming metal is titanium.

9. An anode assembly as claimed in claim 1 wherein the electrocatalytically active coating comprises at least one platinum group metal or an oxide thereof and an oxide of a film-forming metal.

10. An anode assembly as claimed in claim 9 wherein the electrolytically active coating comprises a mixture of ruthenium oxide and titanium dioxide.

11. An anode assembly for a mercury chlorine cell for the electrolysis of an alkali metal chloride brine comprising: a foraminate structure in the form of a plurality of parallel blades; a conductor comprising a double-limbed bridge plate; an upright cylindrical tube mounted on the bridge plate for carrying a current lead-in rod, said foraminate structure, bridge plate and cylinder being constructed of a film-forming metal, said foraminate structure having an electrocatalytically active coating, each pair of blades being spaced apart and connected to one another by one or more bridge portions which are conductively connected to the bridge plate which is in turn conductively connected to said cylindrical tube for carrying a current lead-in rod mounted on said bridge plate, the gap between the blades where connected by the bridge portions being greater than the gap between the blades at other parts along the length thereof.

Claims

4. An anode assembly as claimed in claim 3 wherein each channel blade member has additional bridge portions along the length thereof to increase the rigidity of the said member.

5. An anode assembly as claimed in claim 1 wherein the bridge portions are relatively short compared with the length of the blades remote from the bridge portions.

6. An anode assembly as claimed in claim 1 wherein the channel blade members are identical in shape and are spaced so that like parts are aligned.

7. An anode assembly as claimed in claim 1 wherein the current lead-in means comprises a double-limbed bridge plate of a film-forming metal connected to the longitudinal members, an upright hollow cylindrical tube of a film-forming metal mounted centrally on said bridge plate and conductively bonded thereto, a current lead-in rod adapted to fit said tube, and means for effecting electrical contact between the current lead-in rod and the bridge plate.