US3437579A

US3437579A - Anode assembly

Info

Publication number: US3437579A
Application number: US537745A
Authority: US
Inventors: Frank Smith
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1965-04-20
Filing date: 1966-03-28
Publication date: 1969-04-08
Anticipated expiration: 1986-04-08
Also published as: NL6605125A; ES325731A1; BE679483A; AT263816B; CH454099A; GB1069605A; DE1571741A1

Description

United States Patent 3,437,579 ANODE ASSEMBLY Frank Smith, Widnes, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed Mar. 28, 1966, Ser. No. 537,745 Claims priority, application Great Britain, Apr. 20, 1965, 16,539/ 65 Int. Cl. B01k 3/04; C01b 11/26 US. Cl. 204-288 8 Claims The present invention relates to an improved anode assembly for use in electrolytic cells having horizontal cathodes, especially cells of the mercury cathode type for the production of chlorine and caustic alkali from alkali metal chloride solutions.

In electrolytic cells with horizontal cathodes the anodes are usually suspended above he cathode surface by conducting rods, which pass through the cell cover and serve also as conductors carrying the current to the anodes and as a means of adjusting from outside the cell the position of the anodes relative to the cathode. In cells of this type used for the electrolysis of alkali metal chloride solutions the anode is usually a graphite plate and for many years the conducting rod which terminates in a bore in the anode plate and supports the anode has also been of graphite. It has more recently been proposed to replace the graphite rod by a metal, which has a higher electrical conductivity than graphite, the metal within the bore in the graphite anode plate being protected by impregnating the plate around the bore so as to render it imprevious to the corrosive electrolyte and gas in the cell; for instance the graphite may be impregnated with a wax as taught in our co-pending British application No. 17,659/63.

The present invention provides an improved anode assembly in which a metal of high electrical conductivity is used to carry the current into the cell but which avoids the operation of impregnating the anode plate to protect the metal conductor each time a worn anode is replaced.

According to the present invention we provide an anode assembly which comprises a horizontally-extending graphite anode plate, a graphite conductor member impregnated throughout with a wax or resin and terminating in a bore in the upper surface of the said plate making intimate electrical connection with the walls of said bore, a cylindrical metal conductor terminating in a bore in the upper surface of the graphite conductor member and extending upwardly out of said bore, the walls of the bore in the graphite conductor member being coated with a solderable metal and the metal conductor being fixed thereto by means of a fusible metal or metal alloy solder, and a sleeve of titanium having a cylindrical section closely surrounding the said upwardly extending portion of the metal conductor and having an outwardly and down- Wardly directed flanged portion at its lower end, which flanged portion is sealed to the upper rim of the graphite conductor member by an interposed layer of sealing material and a bonding agent.

In this specification the term titanium includes not only titanium itself but also alloys based on titanium and having anodic polarisation properties comparable with those of titanium. Examples of the latter are titaniumzirconium alloys containing up to 14% of zirconium, alloys of titanium with up to of a platinum metal such as platinum, rhodium or iridium and alloys of titanium with niobium or tantalum containing up to of the alloying constituent.

By a wax we mean a hydrocarbon or a chlorinated hydrocarbon which is solid at the working temperature of the cell but which has a melting point at some higher temperature. The wax may for instance be a fully chloriice nated hydrocarbon which is therefore completely resistant to further chlorination if exposed to chlorination conditions in a cell or it may be an unchlorinated or partially chlorinated hydrocarbon of which the products of chlorination remain solid at the working temperature of the cell and thereby maintain the impermeability of the im pregnated graphite conductor member to the cell electrolyte and products of electrolysis. The preferred wax is hexachlorobenzene. Other suitable waxes include solid aliphatic hydrocarbons, both natural and synthetic, solid aromatic hydrocarbons and higher chlorinated naphthalenes.

The graphite conductor member may be impregnated with the wax before or after soldering the metal conductor into the bore in the graphite. If ordinary eutectic tin/lead solder (melting point 183 C.) is used it is preferable to carry out the impregnation after the solder ing operation so as to avoid melting the wax during soldering. If the wax impregnation is carried out first, we prefer to use a low-melting solder such as a bismuth/lead alloy containing 55.5% bismuth and 44.5% lead by weight, which melts at 124 C.

A suitable resin for impregnating the graphite conductor member is a polyester resin, which may be introduced cold in the liquid state and afterwards cured by heating the impregnated graphite.

The metal conductor may suitably be a copper or mild steel rod and it may be provided with a section of enlarged diameter at the end which is to enter the graphite conductor so as to increase the area of the joint between these two members. The metal conductor may also be a composite structure of two metals; for instance a copper rod or tube may be fixed at one end into a bore in a mild steel block of larger diameter, for example by a screwed and soldered joint, and the mild steel block is then soldered into a bore in the graphite conductor.

In a preferred methods of making the anode assembly, a cylindrical graphite conductor member, suitable 3 to 4 in. diameter and about 1.5 in. long, is impregnated with hexachlorobenzene by placing the graphite in a heated chamber so that it attains a temperature of about 250 C., i.e. slightly higher than the melting point of the wax, evacuating the chamber, running into the chamber molten hexachlorobenzene also at about 250 C. so that the graphite is immersed in the molten wax, allowing the graphite to soak in the wax for one hour, cooling the chamber and its contents to room temperature, removing the graphite from the wax and cleaning ofif excess wax from its surface. A bore is then machined in the centre of one end of the graphite cylinder to produce a hollow cylinder with walls and closed end about 0.375 in. thick. The inner walls of the cylinder are coated with a solderable metal, suitably copper, for instance by electrodeposition, metal spraying or electroless plating. A mild steel disc of thickness equal to the depth of the bore in the graphite is machined to fit into the graphite cylinder with a clearance of about 0.020 in. to take the solder, a bore is made in the centre of one face of the mild steel disc and 'a copper rod is fixed into this bore by means of a screwed and soldered joint, using ordinary eutectic tin/ lead solder. The mild steel disc is then fixed in the bore in the graphite conductor member by soldering, using a low-melting-point solder, after first tinning the surfaces of the copper-plated graphite and the mild steel with the chosen solder. A thin-walled titanium tube which is a close fit on the copper rod is welded at one end to a titanium flange having a turned-over edge to fit around the upper rim of the graphite cylinder. The titanium tube is then pushed over the copper rod and the titanium flange is sealed to the upper rim of the graphite cylinder, using an interposed layer of sealing material after coating the titanium and the graphite with a bonding agent, and making the joint under pressure. Suitable sealing materials are uncured soft rubber, liquid uncured depolymerised rubber and liquid uncured ebonite. These may be bonded under pressure to the titanium and the graphite after coating these members with a conventional rubber-bonding agent and are then preferably cured in situ by heating the assembly for 6 hours at 70 C. The anode assembly is completed by force-fitting the closed end of the graphite cylinder into a bore about 0.75 in. deep in a graphite anode plate which is machined out to give an interference fit of ODDS-0.009 in.

Within the scope of the invention the sealed joint between the titanium flange and the graphite conductor member may be reinforced if desired by adding an adjustable titanium clip to encircle the turned-over edge of the flange and tightening the clip so as to maintain the joint under pressure around the upper rim of the graphite.

The graphite conductor members of the assembly are most conveniently obtained by cutting short cylindrical lengths from a graphite rod. Such graphite rods have been extruded in the longitudinal direction ready for the graphitising process and we have found that they can contain a few large pores running in the direction of extrusion and that these pores may not be adequately sealed by the subsequent wax impregnation. We prefer therefore, within the scope of the invention, to place a resilient sealing membrane between the metal conductor and the graphite anode plate in order to close any such pores in the graphite conductor member. For this purpose a sealing membrane, such as a layer of uncured soft rubber, may be placed in the bottom of the bore in the graphite cylinder before soldering in the metal conductor. Alternatively a sealing membrane may be placed over the bottom of the bore in the graphite anode plate. With this latter arrangement it is also advantageous to increase locally the sealing pressure applied to the membrane by the force exerted during the fitting of the anode plate. This may be done for example by using a concentrically-corrugated sealing membrane having alternate thick and thin sections, by machining concentric grooves in the outer surface of the base of the graphite conductor member or in the base of the bore in the anode plate or by inserting a pressure ring, suitably of titanium, of slightly smaller diameter than the bore in the anode plate, beneath the sealing membrane.

With an anode assembly according to the invention an anode plate that has become worn in use may be removed from the graphite conductor member and the anodesupporting assembly may be re-used without disturbing the metal to graphite joint or the titanium to graphite seal by simply force-fitting a new anode plate to it after machining a bore in the new plate and machining the graphite conductor member to a suitable interference fit.

The invention is further illustrated in the accompanying diagrammatic drawings, which show preferred embodiments of the anode assembly and are not to scale.

In FIG. 1 of the drawings, 1 is a graphite conductor member in the form of a hollow cylinder which is impregnated throughout with hexachlorobenzene and has been electrolytically-coated with copper on its inner vertical walls. 2 is a mild steel cylindrical core which has been soldered to the graphite conductor with a lowmelting solder after inserting soft uncured rubber sealing membrane 3 in the bore in the graphite conductor. 4 is a copper rod which has been screwed and'soldered into the steel core 2 as indicated at 5. 6 is a thin-walled titanium tube closely fitting around copper rod 4 and carrying at its lower end a welded-on horizontal flange 7 having a turned-down edge as shown to fit around the rim of graphite conductor 1. (The flange 7 may alternatively slope downwards from the centre outwards, i.e. in a conical fashion, again having a turned-down edge to fit around the rim of graphite conductor 1.) 8 is a layer of sealing material which has been placed around the upper 4.- rim of the graphite conductor 1 and has been bonded under pressure to the graphite and to the inner surface of the titanium flange 7 so as to make a sealed joint between these two members. 9 is a graphite anode plate which has been bored out to make an interference fit with the lower end of graphite conductor 1, and these two members have been force-fitted together as shown.

When an anode assembly of this type is installed in an electrolytic cell, the upper end of titanium tube 6 is passed through sealing means provided in the cell cover so that the titanium tube protects the copper rod 4 from contact with electrolyte and gas within the cell and the electric supply for the anode can be connected outside the cell to the upper end of copper rod 4 which projects beyond the end of titanium tube 6.

FIG. 2 shows the same arrangement as FIG. 1 with the same numbering of parts except that soft rubber sealing membrane 3 has been omitted and, instead, sealing membrane 10 has been inserted in the bore in anode plate 9 with beneath it a titanium pressure ring 11 of slightly smaller diameter than this bore before anode plate 9 and graphite conductor 1 have been force-fitted together. Also, in accordance with an aforementioned optional feature of the invention, an adjustable titanium clip 12 has been fitted encircling the turned-over edge of titanium flange 7, which clip has been tightened to maintain the sealed joint between the flange and the graphite conductor 1 under pressure.

What I claim is:

1. An anode assembly which comprises a horizontallyextending graphite anode plate, a graphite conductor member impregnated throughout with a wax or resin and terminating in a bore in the upper surface of the said plate making intimate electrical connection with the walls of said bore, a cylindrical metal conductor terminating in a bore in the upper surface of the graphite conductor member and extending upwardly out of said bore, the walls of the bore in the graphite conductor member being coated with a solderable metal and the metal conductor being fixed thereto by means of a fusible metal or metal alloy solder, and a sleeve of titanium having a cylindrical section closely surrounding the said upwardly extending portion of the metal conductor and having an outwardly and downwardly directed flanged portion at its lower end, which flanged portion is sealed to the upper rim of the graphite conductor member by an interposed layer of sealing material and a bonding agent.

2. An anode assembly according to claim 1, wherein the metal conductor is a composite structure consisting of a steel lower portion which is inserted in the bore in the graphite conductor member and a copper stern terminating in a bore in the steel.

3. An anode assembly according to claim 1 wherein the graphite conductor member is impregnated with hexachlorobenzene.

4. An anode assembly according to claim 1, wherein the graphite conductor member is impregnated with a polyester resin.

5. An anode assembly according to claim 1, wherein the titanium flanged portion is sealed to the graphite conductor member by a layer of rubber which has been cured by heating after being bonded in the soft uncured state to the titanium and the graphite by a rubber-bonding agent.

6. An anode assembly according to claim 1, wherein the seal between the titanium flanged portion and the graphite conductor member is maintained under pressure by a titanium clip encircling the downwardly directed portion of the flange.

7. An anode assembly according to claim 1, wherein there is a resilient sealing membrane between the entire lower end surface of the metal conductor and the graphite conductor member.

8. An anode assembly according to claim 1, wherein there is a resilient sealing membrane between the entire References Cited UNITED STATES PATENTS Gleave 204-294 Burns 204-294 XR Carlin 204-294 XR Hass et a1 204-286 6 3,140,991 7/1964 Gardiner 204-219 3,260,662 7/1966 Henegar 204-279 3,345,283 10/1967 Shibata et al. 204-288 XR JOHN H. MACK, Primary Examiner. D. R. JORDAN, Assistant Examiner.

US. Cl. X.R.