CA1046985A

CA1046985A - Protective anode

Info

Publication number: CA1046985A
Application number: CA197,902A
Authority: CA
Inventors: Luigi Bagnulo
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-04-19
Filing date: 1974-04-18
Publication date: 1979-01-23
Also published as: ATA328674A; JPS5216854B2; US4496444A; AR201314A1; NL188809B; ES425465A1; AT332700B; JPS50116344A; NL188809C; GB1474413A; AU6812074A; BE813932A; BR7402936D0; CH587925A5; NL7405074A

Abstract

ABSTRACT OF THE DISCLOSURE
An anode for the cathodic protection of a metallic structure subject to corrosion includes a strip or band of alumi-nium, zinc, magnesium or alloys thereof. The strip or band is anodic to the metallic structure and has a surface which is adap-ted to face the metallic structure. This surface of the strip or band is provided with a layer of electrically conductive adhesive so as to permit the strip or band to be adhesively secured to the metallic structure and to be in electrical communication the-rewith. In this manner, metallic structure of any arbitrary con-figuration may be cathodically protected under all corrosive con-ditions.

Description

Thc invent:ion re.Late~ ge~eral:L~ I;o the phenome~on o~
corrosion a;nd~ more parti.cu.larl~7 to thc p:rotcction o:~ rnet.lllic s-tructures or surfaces which are subjec-ted to cor:rosi~re conclitions.
Of speci.al interest is -the cathodic pro-tection o~ such metallic s-tructures or surfaces.
It is kno~n that all metallic s-tructures which come into contact with a liquid having the properti.es of an electrolytc are susceptible to the phenomenon o~ spon-taneous corrosion. Such corrosion tends to destroy the metallic structure and, depending - 10 upon the particular eorrosive conditions existing, destruction of the metallic s-truc-ture may occur with1.n a longer or shorter period of time~ :Cn many instances, however9 signi~icant dal~age -to -the metallic s-truc-ture mcay oceur within a short period of -time even though des-truction o~ the me-tallic structures has not yet occurred . Some examples o metallic s~ructures which axe prone -to the phenomenon o~ spontaneous corrosion are as follo~.~rs: racliating panels embedded in ~loor concrete; metallie pipes embedded in or passing through masonry; a~d ~-tanding~ edly rnoun-ted me-talli.c piles. ~ of` these me-tallie structures may come in-to contae-t with water or some other electrolyte. Moreover~ metalli.c structures which axe exposed to the atmosphere are also susceptible to spon- ~ :
. ~ .. , ~ .
taneous eorrosion. .~or instanee7 eaves, gu-tters, motor ve'niele parts, the rolling gates eommonly used ~or loel;ing shops, ete.
are all subject to this phenomenon. .
It is also well kno-~n that corrosion phenomena become in-: tensified with increasing chemico-physical variatio~s along the ~-metallie strueture, whether these chemico-physical variations are ;-~
due to variations in the metallic sur~aee or due to variations in .
the electrolyte wetting the metallio sur~ace or due to variations .
in both thé metallic surface and the electrolyte. ~'he rea~on is that such chemico-physieal variations produce electro-chemical :
systems and electrical ~ields whi.ch enhance the co~rosion and per- ~

:
.

mit its conti~uecl progression.
I-t is ~ur-ther kno~m that the action o~ such elecl;roche-mical sy~tems ancl electrical fields ma~ be nulli~ied by slmply creating elec-trical ~ields which oppose -those due to the chemico-physical variations and buck these fields. One man~er of achiev-ing this is by the use of so-called "sacrifice" anodes which go into solution in -the electrolyte mo~e rea-lily than -the metallic ; surfaces which are to be protected. '~he ~nodes are electrically connected to the me-tallic surface which is -to be pro-tected from corrosion by me~1s of a cable and are then immersed in the elec-trolyte. In this manner9 the anocles se-t up electrical fields op-posing -those due to the chemico-physical variation thereby pro-tecting the metallic structure :Erom corrosionO ~'he protection of metallic surface~ from corrosion by using anodes which are in elec-trical communica-tio~ wi-th -the me-tallic sur~aces and which are immersed in the sa~e elec-trolyte a~ -the metallic surfaccs may be referred to as "cathodic protec-tion" of the metallic surfaces.
However, -there are ma~y instance~ where cathodic protec-tion, when carrie~ out in the con~entional and well-known manners used heretofore9 canno-t be utilized. This would be the case, for example9 wi-th mo-tor vehlcle parts, particularly the lower zones o~ doors and ~enders radia-ting panels and~ in ge~eral, pipes which ~-are embedded in or pass through concrete, masonry or the like, the lower edges of rolling ga-tes generally, eaves, gutters9 etc. ~he fact -that cathodic protec-tio~ cannot be utilised in many instan-ces i8 due to the impossibility of crea-ting -the necessary pro-tec-tive fields under ma~y circumstances, one o~ the reasons ~or this being that the elec-trolyte is often discontinuous so that the elec-trolytic connection between anode and surface to be pro-tected~
~Jhich is essential for the functioning of cathodic protection, is lacking.
I-t is, thexe~ore, a general object of -the invention .

-2-~ ' ' ' ' to eliminate the above-outlined rest:rictions of the applicability or cathodic protection.
Another object of the invention is to provide sacrificial anode for the cathodic protection of structures which permits ca-thodic protection of structures under all conditions of corrosion to be realized.
An additional object of the invention is to provide a sacrificial anode for the cathodic protection of structures which is capable of providing cathodic protection for structures of any arbitrary configuration.
A further object of the invention is to provide sacrifi-cial anode for the cathodic protection of structures which is simple to construct and inexpensive to manufacture~
It is also an object of the invention to provide sacrifi-cial anode for the cathodic protection of structures which is convenient to store and transport.
In accordance with the above objects, the invention pro-vides a sacrificial anode suitable to cathodically protect a metal surface subject to corrosion. The anode has a first surface portion which is to face the metal surface and is provided with a layer of ~
an electrically conductive adhesive which will allow the anode to ;
be secured to the metal surface whereby providing cathodic protec-tion to the metal surface by means of the sacrificial anode under all corrosive conditions.
It will be appreciated that the invention is suitable for effecting cathodic protection of metallic structures of any kind which are susceptible to or subject to corrosion such as, for -instance, the phenomenon of spontaneous corrosion. Moreover, it may be seen that the invention is suitable for effecting cathodic protection or a metallic structure regardless of the ambient si- ~ -tuation or a metallic structure regardless of the ambient situation in which the structure may be found~ In particular, the invention is of great ~dvantage when it is physically impossible to make ' ' .

'"~ ' ' use of the well-known systems of cathodic protection utilised heretofore because of -the discontinuity of the electrolyte which affects the met~llic surface or because the electrolyte has a small thickness along the metallic surface. Under these conditions, the conventional systems of cathodic protection are unable to create protective fields which are of sufficient extent to protect the entire metallic surface~
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following ; description o~ speci~ic embodiments when read in connection with the accompanying drawing.
Fig. 1 is a schematic side view showing one form of an anode according to the invention adhering to a metallic surface;
Fig. 2 is a schematic side view showing another embodi-ment of the invention.
Fig. 3 is a schematic side view showing yet another embo~
diment of the invention.
Referring ~irst to Fig. 1 o~ the drawing, an anode ac-cording to the invention is shown adhering to a surface of a metaI-lic structure 3. In accordance with the invention, the anode on the surface por-tion thereof facing the metallic structure 3, is -provided with a layer of adhesive 2. The adhesive layer 2 secures the anode 1 to the sur~ace of the metallic structure 3.
The anode in accordance with the invention is a sacri-fice anode, that is, an anode having a higher dissolu-tion poten-tial in the electrolyte affecting the metallic structure 3 than the metallic structure 3 itself (or the surface of the metallic structure 3~. ;
In the present instance the metallic structure 3 forms a voltaic couple with the anode 1 going into solution in the electro- ~-lyte acti~g upon the metallic surface. The anode 1 may be compo-. . _ ~

sed o~ aluminum? zinc, m~esiurn, alloys o~ these me-tals ~"ith one anol;her or oth~r alloys con-taining the3e me~-~als. It is o~ par-ticular advantage when specl~ied percentages of other rnetals are aclded to the anode me-tal 1 so as -to improve the anodic properties thereo~. However9 -the anode 1 may comprise any o-ther metals or alloys o~ me-tals, the primary considera-t:ion being that the -~r~
, ~, . o~
anode 1 ~w~ a higher dissolution potential than -that o~ the metal O:e metallic substance to be pro-tected. '~he me-tal or me-tallic subs--tance -to be protected may be any metal or metallic substance which is susceptible -to corrosionj ~ example being iron or iron~
; contalning ma-terials.
; The anode 1 is preferably in the form of a tape, a band or a strip, However, th~ anode 1 may be a component of any sui--table shape or config~lration. In either event, it is advantageous ~or the anode, to have a sma:L1 thickness. ~he dimensions, such a as the Length and width~ of the anode 1 are cho~en so ao to be convenien-t. 'l'he dimensions and con~iguration of -the anode 1 : so should be selected ~e that the anode may be applied directly to all parts of the metallic sur~ace to be pro-tected ~nd so -that the anode may be applied to surfaces of any arbi-trar~ configura--tion. `~
Pre~erably9 the adhesive provided on the anode 1 is wa-terproo~, resistant to -the action of pe-troliferous products or hydrocarbons9 resistant to chemical action, weather-resistant and heat-resistant. It is also of necessity in accorda~ce with the invention that the adhesive ~ electrica:lly conductive. The ; -possession o~ these characteristics by the adhe~i~e makes i-t par-tlcularly feasible to use the anode according to the invention direc-tly on all parts of the metallic surface to be protected.
~...... .... ...... ... ......................................................................... - .
Examples of electrically conductive adhesives are acrylic glues or -~inyl glues which have been sui-tably treated~
~he adhesive forming -the adhesive layer 2 may be sel~-`

- .

, - , ~ . , - .
: . , ~ ~ ,. . ...

~L69~35 adhesive immedia-tely. On the other hand, it is also possible for the adhesive to be present on the surface of the anode 1 in dry form. In the latter event, the adhesive may be activa-ted, that is, made adhesive, by wetting it wi-th a suitable liquid such as, for instance, water, or the adhesive may be activated by heating it or by subjecting it to the action of luminous sources.
If the electrically conductive adhesive is self-adhesive immediately, then it has to be covered with a protective covering, preferably one which has been suitably treated so as to possess low adhesiveness. If the protective covering has been treated so as to be of low adhesiveness, then strong adhesion between the protective covering and the electrically conductive adhesive is prevented and, in this manner, removal of the protective covering from the adhesive is facilitated. Moreover, by providing a protective covering having low adhesiveness, it becomes possible to wind up or roll up the anode while avoiding strong adhesion between the adjacent windings thereof. The protective covering may be of paper, plastic material or some other suitable protective material. An example of a material which has been treated so as to possess low adhesiveness is silicon-treated pape~.
Fig. 2 illustrates the embodiment of the invention where the anode is provided with a protective covering. In Fig.
2I the same reference numerals as in Fig. 1 have been used to designate like components. The protective covering for the adhe-sive layer 2 is designated with the reference numeral 4 in Fig. 2.
In accordance with the invention, it is also possible to treat that s~lrface portion of the anode 1 which is opposite the surace portion thereof provided with the adhesive layer 2 in suitable manner so as to permit the anode to be rolled up or wound up without adhesion of the adjacent windings of the anode to one another.

A further embodiment of the invention is illustrated .
.

in Fig. 3 where a first surface portion of the anode 1, opposite a second surface portion thereof having the adhesive layer 2 thereon, is provided with an insulating material. In the embo-diment shown in the said Fig. 3, a layer 6 of an insulating mate-rial is adhesively secured to the anode by means of a layer 5 of adhesive material. The layer 6 of insulating material may be in the form of a tape, a band or a strip but may also be a component of any suitable shape or configuration. The layer 6 of insulating material may be of any thickness or width and, preferably, has the same dimensions as~ or has larger dimensions than, the surface portion of the anode 1 on which it is provided. The insulating material may be a plastic insulating material or any other conventional material.
Thus, in accordance with the invention, it is necessary that the total surface, i.e. the surface portion of the anode 1 and the similarly dimensioned or larger-dimensioned surface of the insulating material, be provided with adhesive which, at least as far as the surface of the anode 1 is concerned, is absolutely electricall~ conductive.
It will be understood that each of the elements described . - .
above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.
While the invention has been iIlustrated and described -as embodied in a protective anode, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirlt of the present invention.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can be ap-plying current knowledge readily adapt it for various applica-' ~. '~.

i9~3~
-tion~ wi-thout omitti.ng features tha-t 7 frorn the s-t;andpolnt o~ prior art 9 fairt.y con~3ti.-tute essential charac-te~r:i~tics of the generic or specifi.c aspects of thls inventio.:n~ and -there~ore, sllch ad~p--ta-tions should a.~d are in-tended -to be comprehended wi-thin the meaning and range of equi.valence of -the ~o:llowing claims.
Wha-t i.s cla,i.med a~; new and deslred -to be protec-ted by ~e-tters Paten-t is set forth i.n -the appendect claims.

, .

., , ' '~
~' . . , ': ~ ', ~, "
,' ~ , ' ., .
' ' -, .

,. ~. ~......... ..

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A sacrificial anode suitable to cathodically protect a metal surface subject to corrosion, having a first surface por-tion adapted to face said metal surface and provided with a layer of an electrically conductive adhesive, so as to permit said sacrificial anode to be adhesively secured to said metal surface, whereby to allow the cathodic protection of said metal surface by means of said sacrificial anode under all corrosive conditions.

2. An anode as defined in claim 1, having a second surface portion, opposite said first surface portion, provided with an adhesive layer; further comprising an insulating material having dimensions equal to or greater than those of said second surface portion; said adhesive layer adhesively securing said insulating material to said second surface portion.

3. An anode as defined in claim 2, wherein said insu-lating material comprises a plastic.

4. An anode as defined in claim 1, made in one material selected from the group consisting of aluminum, zinc, magnesium, their alloys and combinations of said aluminum, zinc and magnesium with at least one other metal which improves the anodic properties of said substance.

5. An anode as defined in claim 1, said metallic sur-face comprising iron; and wherein said anode is made in one material selected from the group consisting of aluminum, zinc, magnesium, their alloys and combinations of said aluminum, zinc and magnesium with at least one other metal which improves the anodic properties of said substance.

6. An anode as defined in claim 1, having a higher dissolution potential than said metallic surface, whereby to obtain a sacrifice anode.

7. An anode as defined in claim 1, wherein said adhe-sive is resistant to chemical action, resistant to the action of hydrocarbons, weather-resistant and heat-resistant.

8. An anode as defined in claim 1, wherein said adhe-sive comprises a self-adhesive material.

9. An anode as defined in claim 1, wherein said adhe-sive is in dry state and is activable by means of heat, illumina-tion or wetting with a liquid.

10. An anode as defined in claim 9, wherein said li-quid comprises water.

11. An anode as defined in claim 1; and further com-prising a protective covering provided on said adhesive layer, said protective covering being of low adhesiveness so as to faci-litate removal of said protective covering from said adhesive layer and so as to prevent strong adhesion of adjacent windings of said anode upon winding of said anode.

12. An anode as defined in claim 11, wherein said pro-tective covering comprises a material selected from the group con-sisting of paper and plastic.

13. An anode as defined in claim 12, wherein said paper is on a silicon-treated paper.

14. An anode as claimed in claim 1, having a second surface portion, opposite said first surface portion, provided with said adhesive layer; and wherein said second surface portion is treated so as to prevent adhesion of adjacent windings of said anode upon winding of said anode.

15. An anode as defined in claim 1, wherein said anode is configured and dimensioned so as to permit application of said anode to surfaces of arbitrary configuration.

16. An anode as defined in claim 15, wherein said anode is of band-shaped or strip-shaped configuration.

17. An anode as defined in claim 1, wherein said adhesive comprises a material selected from the group consisting of acrylic and vinyl adhesives or period adhesives; said adhesives rendered electrically conductive.