US3313721A

US3313721A - Dish-shaped anode

Info

Publication number: US3313721A
Application number: US784273A
Authority: US
Inventors: Rodney B Teel
Original assignee: ENGLEHARD IND Inc
Current assignee: ENGLEHARD IND Inc; ENGLEHARD INDUSTRIES Inc; BASF Catalysts LLC
Priority date: 1958-12-31
Filing date: 1958-12-31
Publication date: 1967-04-11
Anticipated expiration: 1984-04-11
Also published as: DK132338B; DE1229816B; FR1240939A; BE584834A; GB944715A; NL246885A

Description

April 11, 1967 R. B. TEEL 3,313,721

DI SH- SHAPED ANODE Filed Dec. 31, 1958 3 Sheets-Sheet l PLAT! NUM I v -PLATINUM u TITANIUM F I 3 A PLATINUM I \T/TANIUM FIG.3B

RODNEY B TEEL INVENTOR.

ATTORNEY April 11, 1967 R. B. TEEL 3,313,721

DI SH- SHAPED ANODE Filed Dec. 31, 1958 3 Sheets-Sheet 2 PLATINUM 6 12 4 -ANODE TITANIUM ANODE TITANIUM 20B H6 6 //PLATINUM RODNEY B. TE'EL INVENTOR.

l-QM ATTORNEY Filed Dec.

3 Sheets-Sheet 5 RODNEY BTEEL INVENTOR.

EDZCQ E maozq QON 00w 3223.2.

ATTORNEY United States Patent OfiFice 3,313,721 Patented Apr. ll, 1967 3,313,721 RISE-SHAPED Al IUDE Rodney i3. Teel, Wilmington, N.C., assignor, by mesne assignments, to Englehard Industries, Inc, Newark, NJ., a corporation of Delaware Filed fies. 31, 1958, Ser. No. 784,273 1 Claim. (Ci. 2tl il96) The present invention relates to anodes which are used in cathodic protection systems for the control of corrosion and, more particularly, to insoluble anodes used in impressed current cathodic protection systems for the control of metallic corrosion in sea water.

It is well known that when structures made from the common engineering metals, e.g., steel, are in contact with substances which can conduct electricity by means of the ionic mechanism, i.e., electrolytes, corrosion is an important factor which must be considered from the engineering standpoint. Among the many types of protective systems which are used industrially to control and minimize corrosion is the so-called impressed current cathodic protection system. Basically, this system comprises passing a direct current through an electrical circuit wherein the metal to be protected is the cathode and an external, preferably insoluble, electrode is the anode. Both the anode and the cathode are in contact with the electrolyte which is the corroding medium.

In setting up the impressed current type of cathodic protection system, many conditions must be taken into consideration. Of great importance is the fact that the current density of the impressed current at the surface of the metal to be protected must be of such magnitude that corrosion will be suppressed. Coupling this fact with the economic desirability of producing an anode which has the smallest possible surface area commensurate with adequate protection, it is obvious that an anode material should be capable of handling large anode current densities. In order to eliminate frequent re placement of the anode, the anode should be made of a material which is practically non-consumable. Fur ther, in order to permit the anode to be used in practice, it must be durable and resistant to mechanical impact. Another desideratum of the anode is that it be relatively inexpensive in order that a large investment need not be made in a permanent cathodic protection system. Although many attempts were made to overcome the foregoing dificulties and other disadvantages, none, as far as I am aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that by means of a novel composite structure an electrode can be produced which is especially suitable for use in impressed current cathodic protection systems for control of corrosion.

It is an object of the present invention to provide an inexpensive non-consumable electrode adapted to be subjected to current densities up to at least about 550 amperes per square foot (a.s.f.) when in contact with aqueous halide-containing corroding media.

Another object of the invention is to provide an economical novel composite anode having improved resistance to mechanical damage which is adapted to be used at current densities up to about 550 a.s.f.

Another object of the invention is to provide a novel composite anode which is not detrimentally affected by discontinuities and/ or imperfections resulting from cracks, porosity, etc., in or to the anodic surface, for example, by accidental damage occurring in manufacture or use.

A further object of the invention is to provide an improved method of cathodically protecting a metal structure from the adverse action of corrosion.

A still further object of the invention is to provide a metallic anode which does not require external insulation at the lead-in portions.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a view in part section of the novel electrode of the present invention;

FIG. 2 depicts an alternative electrode in accordance with the present invention;

FIG. 3 is a part sectional view of a strip electrode in accordance with the present invention;

FIG. 3A is a part sectional view of an alternative strip or sheet electrode in accordance with the present invention;

FIG. 3B is a sectional view of a still further modification of an electrode in accordance with the present invention;

FIG. 4 shows in section a still further electrode in accordance with the present invention;

FIG. 5 illustrates schematically the system used in accordance with the present invention for cathodically protecting metal immersed in sea water;

FIG. 6 shows an electrode arrangement contemplated in accordance with the present invention for cathodically protecting pipe lines which are buried in soil; and

FIG. 7 illustrates a ship hull and shows an advantageous positioning of anodes in accordance with the present invention.

Generally speaking, the present invention contemplates a composite electrode structure adapted to be used in impressed current corrosion protection systems and particularly adapted to be subjected to current densities up to at least about 550 a.s.f. comprising a current-discharging surface made of metal selected from the group consisting of platinum, rhodium and alloys with other platinum group metals containing at least about of platinum and/or rhodium, superimposed on and intimately bonded in metal-to-metal electrical contact to a base of titanium metal. The platinum group alloys can contain up to about 10% of other elements which do not detrimentally aiiect the corrosion resistance thereof. The electrode can also have an inner core of metal having good electrical conductivity. Metals suitable for the inner core include copper, silver--and aluminum. It is to be observed, however, that when such an inner core is used it must be completely enclosed in or completely sheathed by titanium metal so that it will not readily be exposed to a corroding medium through inadvertence or accident. The present invention also contemplates the method of cathodically protecting metal structures through the use of the electrode of the present invention. In general, the improved method in accordance with the present invention comprises applying an electrical potential diiierence between an electrode as described above and a metallic structure to be protected when both are in contact with the electrolyte so as to oppose galvanic currents and thereby suppress corrosion. The metal to be protected is made cathodic with respect to the anode.

Advantageous results are obtained when substantially pure platinum is superimposed on or bonded to titanium to provide the anode of the present invention. The platinum can be plated, clad, sprayed, spot welded, vacuum deposited, resistance welded or attached in any manner whatsoever to the titanium so long as it is in metalto-metal electrical contact with the titanium underbase. Particularly advantageous methods of applying the platinum metal are vacuum sublimation and cathodic sputterplatinized platinum surface which can accommodate a higher current. In place of platinum, platinum metal alloys such as platinum-palladium alloys containing up to about 50% palladium, platinum-rhodium alloys containing up to about 10% rhodium, platinum-ruthenium alloys containing up to about 5% ruthenium and platinum-iridium alloys containing up to about iridium can be used to advantage. Commercially available rhodium can also be used with advantage and can be applied satisfactorily to the titanium base by standard electroplating techniques.

In general, it is most advantageous to use pure or commercially pure titanium as the base for the platinum metal. Alloys of titanium containing at least about 90% titanium generally are satisfactory although they usually have a higher electrical resistivity than pure titanium.

In carrying the invention into practice, anodes can take the form as shown in the drawing. Referring now thereto, FIGURE 1 illustrates a rod-like bi-rnetal electrode of the present invention having a base 11 made of titanium and having a continuous platinum-metal sheath 12 superimposed thereon in metal-to-metal electrical contact with said titanium. The novel bi-metal electrode contemplated in accordance with the present invention can also have other configurations. For example, a bimetal electrode, made from a titanium lead wire extending to a bi-rnetal platinum-titanium electrode or any platinum surface at which current discharge will occur, is also contemplated in accordance with the present invention. The advantage of the titanium lead is that it will conduct electricity from the current source to the point of desired discharge and will not suffer corrosion because of the formation of a high resistance surface film where its surface contacts the electrolyte. The point of junction or contact between the titanium lead and the platinum-titanium electrode or any platinum surface at which current discharge will occur has all the desirable qualities of the novel bi-metal electrode of the present invention.

While reference has been made to the use of a continuous platinum surface or coating on a titanium base, the platinum surface need not necessarily be continuous. As shown in FIG. 2, platinum metal 12 can be dispersed on the surface of a titanium rod. Of course, forms of electrodes other than rods may be used. FIG. 3 illustrates a strip of titanium having a sheath 12 of platinum metal. FIG. 3A shows an anode having only one side which is coated with platinum. The anode shown in section in FIG. 3B is most advantageous, since it provides an extensive current distribution shield made of titanium 11 with a current discharging button of platinum 12 substantially centrally located thereon. It is to be observed that the anode as shown in FIG. 3B is circular when viewed in plan. The dished shape of titanium 11 in this embodiment of the anode, is particularly advantageous for use in conjunction with ship hulls in sea water. The electrode can also be in the form of a button, a wire, a small plate or foil or in any form whatsoever so long as the platinum metal is in metal-to-metal electrical contact with the titanium metal and suitably disposed to discharge current. An alternative, highly advantageous form of the electrode of the present invention is shown in FIG. 4, wherein titanium metal 11 has an inner core of metal 13 which has good electrical conductivity. The titanium 11 is externally sheathed by platinum 12. Metal 13 may be copper, silver, aluminum, etc., and must be in electrical contact with and completely sheathed by a substantially thick layer of titanium. Advantageously, the titanium layer should be at least about 10 mils thick in order to minimize any danger of accidentally exposing the underlying core.

In practice, the novel anode of the present invention is used in impressed current corrosion protection systems as shown in FIGS. 5 and 6. In FIG. 5 an aqueous electrolyte 14 such as sea water is shown for convenience in container 15. Metal to be protected 16, for example, steel, is at least partly immersed in electrolyte 14. An electrical circuit is provided so that unidirectional current is passed from battery 17 or other source of electromotive force through conductor It; and rheostat 19 (or other control means) into anode 2i and cathodically protected metal 16. Anode 29 has a platinum layer 12 superimposed on and bonded in metal-to-metal electrical contact with a titanium base ill. The electrical circuit is completed through electrolyte 14. A reference electrode 21 and means 22 for measuring potential difference can be provided in the manner shown in order to indicate the extent of (or need for) cathodic protection. FIG. 6 illustrates the application of the present invention in the cathodic protection of metallic structures which are buried beneath the ground. For example, a metallic pipe line 23, set below ground level 24 in soil 25 which normally contains electrically conductive water, is usually covered by a non-metallic covering 2-1. In accordance with the present invention pipe line 23 may be cathodically protected in an impressed current system through the use of platinum-coated titanium anodes 20a or 2017. The platinum-titanium electrode can be in the form of a Wire as illustrated at Zha Where an advantage would be gained in being able to spiral it around a non-metallic coated metal pipe which is to receive cathodic protection after it has been buried in the soil. Alternatively, the electrode can be in the form of a pipe or rod such as illustrated at 2% which is driven or buried in the soil as part of a ground bed system. Anode 2% can be either totally covered by the soil or partially exposed above the soil. It is preferred to completely cover the anode in the soil.

The anode of the present invention is most advantageously used in controlling corrosion on steel ship hulls. As shown in FIG. 7, anodes 280 or 20d may be mounted either directly on hull 27 or on the keel 28 of a ship. Such anodes are electrically insulated from the hull 27 at the point of placement. Appropriate electrical connections are made from a DC. source to the anode and to the hull 27 so that said hull is cathodically charged. The anodes must be mounted below waterline 29 and advantageously are positioned about two-thirds the distance from how 3% to stern area 21. Under any conditions the anodes 280 and/or 20d must be completely immersed in the water no matter what the condition of loading of the ship.

The present invention makes it possible to retain the electrical advantages of platinum through the use of a substantially cheaper bi-metal electrode construction including a platinum element. The bi-metal electrode comprises a platinum outer layer, coating or surface, which need not be complete and an inner supporting member made of titanium. The bi-metal anode permits electrical discharge from the platinum surface or surfaces thereof but not from any surface portions comprising titanium.

In many instances the high current capacity of the novel platinum-titanium anode will reduce the cost of a cathodic protection installation because of the smaller number of anodes that would be required to produce the necessary current. From a practical standpoint, the minimum thickness of the platinum layer in the novel electrode should be about five millionths of an inch. The upper limit of platinum thickness is determined by economics. While it is usually desirable that the entire surface of the intended anode area be covered with platinum, this is not an essential requirement for the novel anode of the present invention.

While the particular structure of the anode must be designed with specific reference to the structure to be protected, basically the novel electrode comprises a structural mass of titanium upon which. is deposited a surface of platinum which can be continuous or discontinuous and of any size, shape or thickness so long as electrical conductance is achieved between the titanium underlayer and the platinum and the platinum is disposed to discharge the current to the electrolyte. Practical considerations dictate the specific structure of the electrode. For example, an anode for the protection of ship hulls should be rugged in order to minimize the adverse effects of in in ances where adverse mechan- .1 action is datively s1 ht such as in the cathodic the purpose of giving those skilled in the art at understanding of the i vention, the following illustrative examples are given:

Example I A -inch length of titanium wire, 0.065 inch in diameter, or" the grade sold under the designation T175A which contains nominally 0.1% iron, 0.02% nitrogen, a nia num of 0.04% carbon and a maximum of 0.08% en, with the balance being essentially titanium, was tip,-.-d with a globule or" platinum. The platinum globule had a diameter about 0.12 inch. The untipped end of the titanium wire was coa.e with a plastic tape so that only two inc s including the globular tip was exposed. The tipped wire so constructed was introduced as an anode into an electrical circuit which included flowing sea water as the eiectrolyste, a bare steel sheet as the cathode and a variable source of direct current and was used to cathodically protect the steel sheet for two periods of two weeks. During the first two week period, the anode was subjected to a current density, with respect to titanium, of 3.5 a.s.f. and, with respect to platinum, of 34 est. During the second two week period, the anode was subjected to a current density of 7.1 a.s.f., with respect to titanium and, with respec to platinum, of 69 a.s.f. During each period, satisfactory operation of the anode was observed and cathodic protection of the bare steel sheet was achieved.

Example 11 A steel ship hull is protected from corrosion due to contact with water and, in particular, sea water, by attaching thereto externally an anode having a base of titanium and a current discharging surface of platinum. The anode is electrically insulated from the hull and is connected in an electrical circuit including a source of direct current and the hull as a cathode. Two forms of anodes are advantageous. A strip-like anode is advantageously mounted on the keel of the hull whereas a circular anode having a centrally located discharging surface is advantageously mounted on the hull. It is to be noted that the novel anode is not operative until it is included in an electrical circuit including the hull as a cathode and an electrical power means operative to provide a potential diderence between the anode and the hull. Such electrical power means include batteries and rectified alternatin current circuits.

It is to be observed that the electrode of the present invention can be employed in impressed current cathodic protection systems for the prevention of corrosion not only of ship hulls but also drilling platforms, floating docks, seaplane hulls, underground pipe lines, tank cars, tank trucks, tanks, chemical processing apparatus, bulk liquid compartments, among others. The novel anode of the present invention can also be employed as in inert anode in metal electroplating operations, anodizing operations and in other electrochemical processes where control 6 of the current discharging areas of a gross structure is desired. 7

Although the present invention has been described in con unction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claim.

I claim:

A substantially circular dish-shaped bi-laye'r anode especially well suited for use in impressed current cathodic protection systems for control of corrosion and capable of being subjected to current densities of up to about 550 amperes per square foot, which comprises a substantially circular dish-shaped non-porous mass of titanium metal, and affixed thereto and bonded in metal-to-metal electrical contact with the dish-shaped titanium metal mass a substantially centrally located electrical current discharging buttom of metal selected from the group consisting of platinum, rhodium, platinum group metal alloys containing at least about 50 percent platinum, platinum group metal alloys containing at least about 50 percent rhodium, and platinum group metal alloys containing at least about 50 percent platinum plus rhodium, the anode being free of layer of metal intermediate the platinum group metal of the current discharging button and the titanium metal mass, and also free of material unclergoin substantial consumption when in contact with sea water and during electrical current discharge through the anode.

References Cited by the Examiner UNITED STATES PATENTS 84,671 12/1868 Baker et a1. 204-197 388,592 8/1888 Siebel 204-196 571,380 11/1896 Lisk 204-197 989,596 4/1911 Geppert 204-147 1,415,186 5/1922 Meadows et al 204-147 1,477,099 12/1923 Baum 204-290 2,491,225 12/1949 Stearns 204-147 2,631,115 3/1953 Fox 204-290 2,719,797 10/1955 Rosenblatt 04-290 2,762,771 9/1956 Preiser 204197 2,772,231 11/1956 Waite et a1 204-197 2,776,940 1/1957 Oliver 204-196 2,795,541 6/1957 Muller 204-290 2,826,543 3/1958 Sabins 204-197 2,863,819 12/1958 Preiser 204-196 2,865,832 12/1958 Pitzer 204-290 2,908,623 10/1959 Doring 204-196 3,108,939 10/1963 Sabins 204-290 FOREIGN PATENTS 780,479 2/1935 France. 904,490 2/ 1954 Germany.

3,388 9/1903 Great Britain. 614,799 12/1948 Great Britain. 23 6,579 6/ 1945 Switzerland.

JOHN H. MACK, Primary Examiner. JOSEPH REBOLD, JOHN R. SPECK, Examiners. T. SMEGAL, T. TUNG, Assistant Examiners,