Technical field
[0001] The present invention relates to anodes of impressed-current cathodic protection
systems comprising a body of current-conducting polymer in the surface of which are
fixed electrochemically active elements, and a method of making such catalytic polymer
anodes.
Background art
[0002] It is known that cathodic protection is effective to prevent corrosion of reinforcing
steel in concrete bridge decks, support structures and parking garages, which are
subject to extensive damage by corrosion of the steel reinforcement due to the presence
of salt and moisture in the normally alkaline concrete environment. Such damage of
reinforced concrete by corrosion results more particularly from the practice of spreading
large amounts of salt on roads in winter, while coastal structures are attacked by
seawater and salt spray.
[0003] Existing cathodic protection techniques for reinforcing steel are nevertheless limited
by the anodes presently available for this purpose, which must have a long life and
a chemically resistant anode structure that is readily adaptable from case to case
according to the size and configuration of the reinforced concrete structure to. be
cathodically protected from corrosion.
[0004] A known type of polymer anode commercially available for use in impressed-current
cathodic protection systems consists of a carbon loaded, current conducting polymer
body with a copper core and operates at a current density limited to a maximum of
about 0.02 A/m
2 to avoid causing damage to the polymer anode surface.
[0005] Another type of anode which is used for cathodic protection of reinforcing steel
consists of carbon fibers which are placed in a groove in the concrete, the groove
then being filled with a grout of electronically conductive carbon-loaded backfill.
Here again, the use of carbon presents serious limitations, since this material is
subject to high operating voltages and therefore a limited lifetime as an anode. This
is a serious limitation since replacement of anodes embedded in concrete is very difficult.
This type of anode also has a high electronic resistivity, so that current can be
carried longitudinally only over very short distances through the carbon fibers.
[0006] Other anodes which are traditionally used for impressed current cathodic protection
are constructed of platinized titanium or platinized tantalum with a more electronically
conductive copper core. Such electrodes are often used for cathodic protection of
underground pipelines, well casings, ship hulls, jetties, drilling rigs, and oil platforms.
These electrodes are expensive and must therefore be used at a higher current density,
up to 1000 A/m
2 in some cases. The expense of such platinized titanium or tantalum electrodes entails
special design problems since a very low current density must be applied to the structure
being cathodically protected. This results in a mismatch of current density between
anode and cathode. Various system designs attempt to accommodate this mismatch, usually
by installation of small anodes at certain locations which are intended to protect
large structures over great distances. Unfortunately, this often leads to unforeseen
current density disparities and inadequate protection of more distant parts of the
structure.
[0007] It is understood that continuous, wire-like flexible anodes for example are more
suitable for cathodic protection of many structures such as underground pipelines
in particular, but until now such anodes were not capable of functioning over extended
periods of time.
[0008] Numerous composite electrodes have moreover been proposed which comprise a polymer
material combined with a dispersed conductive filler, or an electrocatalyst, or both.
The state of the art relating to such composite electrodes may be illustrated for
example by U.S. Patents No. 3,629,007; 3,751,301; 4,118,294; 4,473,450 and European
Patent Application No. 0 067 679.
[0009] European Patent Application No. 0 122 785 for instance proposed and claimed in article
which is suitable for use as an anode in a method for protecting an electrically conductive
substrate from corrosion and which comprises: a first element which provides part
of the electrochemically active surface of the article, and is composed of a conductive
polymer; and a plurality of second elements which provide part of the electrochemically
active surface of the article, are partially embedded in, and project from the surface
of, the first element, and are composed of a material such that, when the article
is used as an anode in a method for protecting an electrically conductive substrate
from corrosion, the electrochemical reactions at the anode take place preferentially
on the second elements rather than the first element. According to the disclosure,
these second elements were carbon fibres or graphite fibres, typically in the form
of multifilament yarn.
[0010] In the unrelated field of anodes for oxygen evolution in an acid electrolyte such
as is used e.g. in metal electrowinning, European Patent Application No. 0 046 727
described and claimed an anode for oxygen evolution in an acid electrolyte, comprising
a base of lead or lead alloy, having catalytic particles comprising at least one catalyst
for oxygen evolution fixed to a support particle consisting of a valve metal. These
particles were partly embedded in the lead or lead alloy base and uniformly distributed
at the surface of the base, so that the particles were firmly anchored and electrically
connected to the base while a substantial non-embedded part of the particles remained
projecting from the surface of the base for contact with the acid electrolyte. Oxygen
could thereby be evolved on the surface of the particles at a reduced potential at
which the underlying lead or lead alloy base essentially served as a current conducting
support for the catalytic particles. Such anodes were useful as replacement of the
conventional lead or lead alloy anodes without catalytic particles.
[0011] An object of the invention is to provide a catalytic polymeric anode with a long
service life which is particularly suitable for the cathodic protection of reinforced
concrete structures, such as bridge decks, parking garages, and coastal structures
exposed to seawater and salt spray, as well as the cathodic protection of underground
pipelines, well casings, ship hulls, jetties, drilling rigs, oil platforms, and the
like.
[0012] According to the invention, there is provided an anode of an impressed-current cathodic
protection system, the anode comprising a body of current conducting polymer in the
surface of which are fixed electrochemically active elements, wherein these active
elements are catalytic particles of valve metal surface-coated with an electrocatalyst.
[0013] The anode according to the invention may comprise any suitable current conducting
polymer body. Carbon loaded polymers are advantageous. The current conducting body
may be made from thermoplastic polymer compounds. The preferred thermoplastic resins
include: polyolefins such as polymers of ethylene and/or propylene; halocarbon polymers
such as polyvinyl chloride, polyvinylidene fluoride and halogen substituted olefinic
polymers; styrenic polymers such as polystyrene, and copolymers of styrene with acrylonitrile,
etc; polyamides such as polycaprolactam; thermoplastic polyesters; and acrylic resins
such as polyacrylates and polymethacrylates. However, higher strength thermoplastics
including polyimides; polyarylene resins, such as polycarbonates, polysulfones and
polyphenylene. oxides and sulfides; and various heterocyclic resins may also be used.
[0014] The invention provides a particularly simple method of manufacturing such a catalytic
polymer anode with an extended service life. According to the method the polymer anode
is made by heating a cable of thermoplastic polymer so as to produce a softened external
layer of the thermoplastic polymer and pressing catalytic valve metal particles onto
said softened external layer of the polymer cable. The catalytic valve metal particles
may advantageously be heated before pressing, the pressing being carried out so that
upon cooling a uniform outer layer of catalytic valve metal particles is anchored
to the surface of the electrode base.
[0015] It has been found that when a carbon loaded polymer forming the anode body is admixed
with up to 50% by weight of conductive fibers such as carbon or metallic fibers the
resulting anode obtained upon extrusion of such material around a metallic core, heating
of the current conducting body and pressing the catalytic valve metal particles has
advantageous properties. Such anodes are found to sustain high electrical currents
while avoiding an excessive voltage drop within the electrode.
[0016] Although the amount of fibers may be as high as 50 weight %, the best results are
obtained when the amount of fibers in the carbon loaded polymer is kept in the range
of 5 to 30% by weight of the polymer. This is based on the finding that the polymer
body made with more than 50% of fibers loses its mechanical properties and when the
amount of fibers is kept below 5% the conductivity of the polymer body is not adequate.
Various conductive fibers may be employed e.g. carbon, glassy carbon, nickel, copper,
aluminium or stainless steel fibers.
[0017] Use of a body of thermoplastic polymer is particularly advantageous in that it allows
a catalytic polymer anode to be produced according to the invention by this extremely
simple and reproducible method, while ensuring an excellent fixation and electrical
connection of said catalytic particles to the surface of the polymer body.
[0018] The anode according to the invention may be produced in a highly simplified manner
in the form of a continuous electrode of any suitable cross-section, for example in
the form of a wire, rod, strip, or sheet.
[0019] This possibility of manufacturing continuous electrodes of any desired cross-section
and length in a simple and reproducible manner is particularly important for the industrial
manufacture of continuous anodes for cathodic protection systems, which generally
entail very high installation costs, and more particularly require anodes which are
readily adaptable to the particular configuration of the structure to be protected
from case to case.
[0020] The body formed of current conducting, carbon-loaded polymer will advantageously
comprise an internal metallic reinforcing core, preferably a copper core, which is
embedded in the carbon loaded polymer body, in order to allow the catalytic polymer
electrode to conduct a sufficiently high electrical current while avoiding an excessive
voltage drop within the electrode.
[0021] The catalytic particles used in the invention advantageously consist of one of the
valve metals titanium, niobium, tantalum, zirconium, or an alloy thereof which exhibits
substantially the same anodic film-forming properties as these valve metals.
[0022] Catalytic particles of titanium sponge which have an irregular size and shape and
are readily deformable may be advantageously pressed into a coherent layer adhering
to the surface of a current conducting polymer body.
[0023] These catalytic valve metal particles are advantageously activated with an electrocatalyst
which provides a reduced oxygen potential and which may comprise at least one precious
metal selected from ruthenium, palladium, iridium, platinum, and rhodium in the metallic
state or, preferably, as an oxide.
[0024] Good results were obtained with a catalytic polymer anode according to the invention
having particles of titanium sponge coated with a ruthenium based catalyst.
[0025] A very small amount of precious metal may be applied to the valve metal particles
and the proportion of precious metal applied may advantageously be at most in the
order of 1 % by weight of the valve metal particles, and advantageously considerably
below 1%. This proportion of precious metal applied may preferably lie in the range
from 0.1% to about 1.0% but may if necessary amount up to about 5%.
[0026] The particle loading of the catalysed valve metal particles may advantageously be
in the range 10 to 100 grams per square meter of the electrode base surface to which
they are applied, but this loading may amount to up to 500 grams per square meter
or more in some cases.
[0027] The catalytic particles employed according to the invention may be prepared in any
suitable manner, for example by a process as described in U.S. Patent No. 4,454,169,
or in U.S. Patent No. 4,425,217.
[0028] The catalytic particles may be simply applied, fixed, and electrically connected
by pressing them onto the surface of a heated thermoplastic polymer body forming the
anode base. These particles may thus be applied by means of rollers, or by drawing
the polymer body through a die. An electronically conductive glue or adhesive may
likewise be used for their electrical connection.
[0029] The impressed-current anodes for cathodic protection systems according to the invention
are used at current densities that do not exceed 500 Alm
2 and are preferably between 10 and 350 A/ m
2. The catalytic polymer anode of the invention is particularly effective in protecting
buried or submerged steel structures such as gas and oil pipelines.
[0030] Test results have shown that the catalytic anode can operate at a much higher current
density and a much lower potential than the conventional polymer anode. Moreover,
it has been established that catalysed valve metal particles such as are applied according
to the invention retain their catalytic activity under extremely harsh anodic corrosion
conditions during operation at a many times higher anode current density.
[0031] The catalytic anode according to the invention may thus be expected to exhibit a
long service life in cathodic protection systems due to the fact that it can operate
at a much lower potential and can thereby protect the current conducting polymer body
from damage by oxidation during operation at a relatively high anode current density.
[0032] The activated polymer anode of the invention may be in the form of cable, sheet,
wire, perforated plate or any other convenient form. However, it has been established
that, for the anode of the invention in which the active catalytic material (e.g.
Ru0
2) is carried on a conductive valve metal carrier and the carrier with the catalyst
thereon is supported on a carbon loaded thermoplastic polymer, the preferred form
is the cable.
[0033] The invention may further be illustrated by the following examples:
Example I
[0034] A catalytic polymer anode was made by applying catalytic titanium particles to an
anode base consisting of a conventional current conducting polymer anode of carbon
loaded polyolefin with a copper core, which is a conventional, wire-shaped polymer
anode (diameter 1 cm) commercially available for impressed-current cathodic protection.
[0035] For this purpose, the polymer anode body was heated to 120°C for 10 minutes and catalytic
titanium particles were then pressed with a roller onto the softened anode surface,
which provided good adherence of the catalytic particles to the anode surface.
[0036] The catalytic particles thus applied consisted of activated titanium sponge with
a particle size in the range from 300 to 840 micrometers. These sponge particles were
activated by impregnation with an activating solution comprising 2.38 g RuCI
3 - aq. (40 wt% Ru), and 3.36 g tetra-ortho- butyl titanate dissolved in 3.2 ml concentrated
HCI and 80 ml butylalcohol, then drying at 100°C in air for 120 minutes, and heat
treating the dried particles in air at 300°C for 30 minutes, at 425°C for 30 minutes,
and finally at 500°C for 10 minutes. This activating treatment qas carried out 2 times
and the catalytic particles thus obtained contained 1% Ru by weight of Ti.
[0037] The total loading of the catalytic particles applied as described corresponded to
100 g/m
2 of the polymer anode surface.
[0038] The catalytic anode thus obtained was tested in a concrete block containing a steel
reinforcement bar, and compared with a conventional polymer anode (without catalyst)
as described above. For this purpose, the catalytic anode and the conventional polymer
anode were symmetrically positioned in the same vertical plane and on opposite sides
of a vertical steel reinforcement bar (at 5 cm from the steel bar), and each anode
was provided with a reference electrode (Ag/AgCI) for measuring its single electrode
potential (S.E.P).
[0039] A block of concrete (9x13x30 cm) containing 8.8 kg/m
3 of NaCI was then cast around the anodes and the steel bar so that they were embedded
while their top ends projected from the concrete block for connection to a D.C. supply
source.
[0040] An impressed current corresponding to an anode current density of 0.11 A/m
2 was passed through the concrete block between the steel bar connected to the negative
terminal of the D.C. source and the anodes connected to the positive terminal, while
the anode potentials were measured over a test period of 1 month.
[0041] The described catalytic anode operated for 30 days at a constant potential of 0.390
V vs. CSE (Copper Sulfate Electrode). On the other hand, the conventional polymer
anode exhibited a potential which rose from about 1 V to about 2 V vs. CSE in the
first 8 days, decreased slightly to 1.8 V after 20 days, then increased slowly once
more to 2.0 V after 30 days.
[0042] The catalytic anode thus operated at a constant potential up to about 1.6 V lower
than the non- catalytic anode, while it may be noted that the anode current density
applied in this test is several times higher than that at which the described conventional
polymer anode can be operated with a satisfactory service life.
[0043] The catalytic anode according to the invention may thus be expected to exhibit a
long service life in cathodic protection systems, due to the fact that it can operate
at a much lower potential, and can thereby protect the current conducting polymer
body from damage by oxidation during operation at a relatively high anode current
density. The catalytic anode according to the invention may be expected to be functional
up to about 500
A/m2.
Example II
[0044] A catalytic polymer anode 150 meters long was made by applying catalytic particles
to an anode base consisting of a carbon loaded polyolefin with a copper core. The
anode base was first prepared by extruding a conductive thermoplastic compound around
a conductive copper core of 1.50 mm diameter wire.
[0045] Catalyst was prepared by activating 500 grams of titanium sponge with a particle
size in the range of 300 to 840 micrometers. After rinsing in acetone and drying at
120°C, the titanium particles were activated by mixing with an activating solution
comprising 17.31 grams RuC1
3 aq. (43 wt.% Ru) in 250 ml acetone, drying for 2 hours, prebaking at 340°C for 30
minutes, and postbak- ing at 400°C for 40 minutes. This activating treatment was carried
out two times and the catalytic particles thus obtained contained 3% Ru by weight
of titanium.
[0046] Catalyst was then continuously applied in a separate step by passing the anode base
through a tube furnace at about 385°C to rapidly heat the polymer surface, passing
through a fixed bed of heated catalyst particles, and passing through a series of
rollers to press the catalyst particles onto the surface of the anode base. The anode
thus prepared was catalyzed with 330 grams of said particles per square meter of anode
surface.
[0047] 110 meters of this anode was then placed in a porous duct for the purpose of protecting
lead- sheathed utility cables. 0.93 amps was applied to the anode resulting in a current
density at the anode surface of 0.35 amps per square meter. Cable to soil potentials
were acceptable for cathodic protection of the cable, ranging from 0.685 to 0.90 volts
vs. a C
US0
4 reference electrode, and contact resistance was measured to be equivalent to, or
slightly lower than, cast iron anodes. Ground anode potentials measured vs. a C
US0
4 reference electrode along the length of the anode at even intervals remained constant,
and were reported as follows:
Example III
[0048] A catalytic polymer anode 100 meters long was made by applying catalytic particles
to an anode base consisting of carbon loaded polyolefin with a copper core. The anode
base was first prepared by extruding a conductive thermoplatic compound around a conductive
copper core of 3.73 mm diameter wire.
[0049] Catalyst particles were prepared and were applied to the anode base as described
in Example II. An anode thus prepared was catalyzed with 300 grams of said particles
per square meter of anode surface.
[0050] A representative sample of this anode 10 centimeters long was operated in 1.0 M H
2S0
4 at 0.327 A, equivalent to a surface current density of 100 amps per square meter.
This anode has operated for over 1,150 hours at a cell voltage of 2.6 to 2.7 volts
without any sign of failure. An anode base of carbon loaded thermoplastic without
catalyst particles failed after only 20 hours of operation, at which time its cell
voltage exceeded 10.0 volts.
Example IV
[0051] A catalytic polymer anode was prepared by applying catalytic particles to an anode
base consisting of a modified carbon loaded polyolefin with a copper core. The anode
base was prepared by extruding a mixture of a conductive thermoplastic compound with
15% by weight of added carbon fibers around a conductive copper core of 3.73 mm diameter
wire. Addition of the carbon fibers had the effect of lowering the volumetric resistivity
of the polymeric phase from 20 ohm-centimeters to 0.20 ohm-centimeters making possible
operation at higher current density.
[0052] Catalytic particles containing 3% Ru by weight of titanium were prepared as described
in Example II, and were then applied to the surface of the anode base by heating the
anode base to 120°C for 10 minutes and rolling the catalytic titanium particles onto
the softened anode surface. The anode thus prepared contained 380 grams of said particles
per square meter of anode surface.
[0053] A representative sample of this anode 2 centimeters long was operated in 1.0 M H
ZS0
4 at 0.655 A, equivalent to a surface current density of 1000 amps per square meter.
This anode operated for over 268 hours at a cell voltage of 3.1 to 3.2 volts without
sign of failure.
[0054] This is a dramatic improvement over the conventional commercially available wire-shaped
polymer anode which cannot be operated at such high current density at all, and which
has a recommended operating current density maximum of only 0.5 amps per square meter.
Technical applicability
[0055] Catalytic polymer anodes of impressed-current cathodic protection systems according
to the invention are especially suitable to prevent corrosion damage of reinforced
concrete structures such as bridge decks, support members and parking garages, or
buried or submerged steel structures such as gas and oil pipelines, offshore production
platforms, fuel storage tanks and well casings.
1. An anode of an impressed-current cathodic protection system, the anode comprising
a body of current conducting polymer in the surface of which are fixed electrochemically
active elements, characterized in that said active elements are catalytic particles
of valve metal surface-coated with an electrocatalyst.
2. The anode of claim 1, wherein said body is formed of a carbon loaded polymer.
3. The anode of claim 1 or 2, wherein said current conducting polymer body contains
dispersed therethrough up to 50% by weight of carbon or metal fibers.
4. The anode of claim 1, 2 or 3 wherein said polymer is a thermoplastic polymer.
5. The anode of claim 4, wherein said thermoplastic polymer is selected from polyolefins,
halocarbon polymers, styrenic polymers, polyamides, thermoplastic polyesters, acrylic
resins and blends of same.
6. The anode of claim 1, 2 or 3 wherein a metallic core is embedded within said current
conducting polymer body.
7. The anode of claim 1 or 2, wherein said valve metal is selected from titanium,
tantalum, niobium, and zirconium.
8. The anode of claim 1 or 7, wherein said electrocatalyst comprises at least one
precious metal selected from ruthenium, palladium, rhodium, iridium and platinum,
in either the metallic state or as an oxide.
9. The anode of claim 8, wherein the catalytic particles comprise said precious metal
in an amount from 0.1% to 5.0% by weight of valve metal.
10. The anode of claim 1, wherein said catalytic valve metal particles are applied
to the surface of said current conducting polymer body in an amount corresponding
to a loading from about 10 to about 500 grams of said catalytic particles per square
meter of said surface.
11. The anode of any of claims 1 to 10, wherein the valve metal is titanium and the
electrocatalyst comprises ruthenium oxide.
12. The anode of any of claims 1 to 11, wherein the polymer body is in the form of
a cable.
13. A method of manufacturing an anode according to claim 12, comprising the steps
of:
(a) heating said cable of a thermoplastic polymer so as to produce a softened external
layer of the thermoplastic polymer; and
(b) pressing said catalytic valve metal particles onto said softened external layer
of thermoplastic polymer, so as to obtain, on cooling, a uniform outer layer of said
catalytic valve metal particles anchored to the surface of said cable of thermoplastic
polymer.
14. The method of claim 13, wherein said catalytic valve metal particles are heated
prior to pressing them onto said softened external layer of thermoplastic polymer.
15. Use of the anode according to any of claims 1 to 12 in an impressed-current anode
of a cathodic protection system for the prevention of corrosion of reinforcing steel
in concrete or buried or submerged steel structures, at an anode current density up
to 500 Alm2.
1. Anode für ein kathodisches Schutzsystem mit aufgezwungenem Strom, wobei die Anode
einen Körper aus stromleitendem Polymer aufweist, in dessen Oberfläche elektrochemisch
aktive Elemente gebunden sind, dadurch gekennzeichnet, daß die aktiven Elemente katalytische
Teilchen aus mit einem Elektrokatalysator oberflächenbeschichtetem Ventilmetall sind.
2. Anode nach Anspruch 1, bei der der Körper aus einem kohlenstoffbelandenen Polymer
gebildet ist.
3. Anode nach Anspruch 1 oder 2, bei der der stromleitende Polymerkörper bis zu 50
Gew.% in ihm dispergierte Kohlenstoff- oder Metallfasern enthält.
4. Anode nach Anspruch 1, 2 oder 3, bei der das Polymer ein thermoplastisches Polymer
ist.
5. Anode nach Anspruch 4, bei der das thermoplastische Polymer aus Polyolefinen, Halogenkohlenwasserstoffpolymeren,
styrolartigen Polymeren, Polyamiden, thermolastischen Polyestern, Acrylharzen und
deren Mischungen ausgewählt ist.
6. Anode nach Anspruche 1, 2 oder 3, bei der ein metallischer Kern innerhalb des stromleitenden
Polymerkörpers eingebettet ist.
7. Anode nach Anspruch 1 oder 2, bei der das Ventilmetall aus Titan, Tantal, Niob
und Zirkonium ausgewählt ist.
8. Anode nach Anspruch 1 oder 7, bei der der Elektrokatalysator mindestens ein Edelmetall
ausgewählt aus Ruthenium, Palladium, Rhodium, Iridium und Platin entweder als Metall
oder als deren Oxid enthält.
9. Anode nach Anspruch 8, bei der die katalytischen Teilchen das Edelmetall in einer
Menge von 0,1 bis 5% bezogen auf das Gewicht des Ventilmetalles enthalten.
10. Anode nach Anspruch 1, bei der die katalytischen Ventilmetallteilchen in einer
Menge auf die Oberfläche des stromleitenden Polymerkörpers aufgebracht sind, die einer
Beladung von etwa 10 bis etwa 500 g der katalytischen Teilchen pro Quadratmeter der
Oberfläche entspricht.
11. Anode nach einem der Ansprüche 1 bis 10, bei der das Ventilmetall Titan ist und
der Elektrokatalysator Rutheniumoxid enthält.
12. Anode nach einem der Ansprüche 1 bis 11, bei der der Polymerkörper in Form eines
Kabels vorliegt.
13. Verfahren zur Herstellung einer Anode nach Anspruch 12, bei dem
(a) das Kabel aus einem thermoplastischen Polymer erwärmt wird, um eine weichgemachte
äußere Schicht des thermoplastischen Polymer herzustellen, und
(b) die katalytischen Ventilmetallteilchen auf die weichgemachte äußere Shicht des
thermoplastischen Polymer aufgedrückt werden, um beim Abkühlen eine einheitliche äußere
Schicht der katalytischen Ventilmetallteilchen zu erhalten, die an der Oberfläche
des Kabels aus thermoplastischem Polymer verankert sind.
14. Verfahren nach Anspruch 14, bei dem die katalytischen Ventilmetallteilchen erwärmt
werden, bevor sie auf die weichgemachte äußere Schicht des thermoplastischen Polymer
aufgedrückt werden.
15. Verwendung der Anode nach einem der Ansprüche 1 bis 12 als Anode mit aufgezwungenem
Strom in einem kathodischen Schutzsystem zur Verhinderung der Korrosion von Armierungsstahl
in Beton oder eingegrabenen oder im Wasser versenkten Stahlstrukturen bei einer Anodenstromdichte
bis zu 500 A/m2.
1. Anode d'un système de protection cathodique à courant imposé, l'anode comprenant
un corps en polymère conducteur de courant dans la surface duquel sont fixés des éléments
électrochi- miquement actifs, caractérisée en ce que les éléments actifs sont des
particules catalytiques de métal redresseur revêtues en surface d'un catalyseur électrochimique.
2. Anode selon la revendication 1, caractérisée en ce que le corps est formé d'un
polymère chargé de carbone.
3. Anode selon la revendication 1 ou 2, caractérisée en ce que le corps en polymère
conducteur de courant contient, dispersés à travers celui-ci, jusqu'à 50% en poids
de carbone ou de fibres métalliques.
4. Anode selon l'une quelconque des revendications précédentes, caractérisée en ce
que le polymère est un polymère thermoplastique.
5. Anode selon la revendication 4, caractérisée en ce que le polymère thermoplastique
est choisi parmi des polyoléfines, des polymères halocar- bonés, des polymères styréniques,
des polyamides, des polyesters thermoplastiques, des résines acryliques et des mélanges
de ceux-ci.
6. Anode selon l'une quelconque des revendications 1 à 3, caractérisée en ce qu'une
âme métalli---que est noyée à l'intérieur du corps en polymère conducteur de courant.
7. Anode selon la revendication 1 ou 2, caractérisée en ce que le métal redresseur
est choisi parmi le titane, le tantale, le niobium et le zirconium.
8. Anode selon la revendication 1 ou 7, caractérisée en ce que le catalyseur électrochimique
est constitué par au moins un métal précieux choisi parmi le ruthénium, le palladium,
le rhodium, l'iridium et le platine, soit à l'état métallique, soit en tant qu'oxyde.
9. Anode selon la revendication 8, caractérisée en ce que les particules catalytiques
contiennent ledit métal précieux à une dose de 0,1 à 5,0% en poids du métal redresseur.
10. Anode selon la revendication 1, caractérisée en ce que les particules catalytiques
de métal redresseur sont appliquées à la surface du corps en polymère conducteur de
courant en une quantité correspondant à une dose d'environ 10 à environ 500 grammes
de particules catalytiques par mètre carré de cette surface.
11. Anode selon t'une quelconque des revendications précédentes, caractérisée ence
que le métal redresseur est le titane et le catalyseur électrochimique se compose
d'oxyde de ruthénium.
12. Anode selon l'une quelconque des revendications précédentes, caractérisée en ce
que le corps en polymère se présente sous la forme d'un câble.
13. Procédé de fabrication d'une anode selon la revendication 12, caractérisé en ce
qu'il consiste à:
a) chauffer le câble formé d'un polymère thermoplastique de façon à produire une couche
externe ramollie du polymère thermoplastique; et
b) presser les particules catalytiques de métal redresseur sur la couche externe ramollie
du polymère thermoplastique de façon à obtenir, après refroidissement, une couche
extérieure uniforme de ces particules catalytiques de métal redresseur ancrées à la
surface du câble en polymère thermoplastique.
14. Procédé selon la revendication 13, caractérisé en ce que les particules catalytiques
de métal redresseur sont chauffées avant de les presser sur la couche externe ramollie
du polymère thermoplastique.
15. Utilisation de l'anode selon l'une quelconque des revendications 1 à 12, en tant
qu'anode à courant imposé d'un système de protection cathodique pour la prévention
de la corrosion d'acier d'armature dans du béton ou dans des constructions ou installations
en acier enterrées ou immergées, avec une densité de courant anodique allant jusqu'à
500 A/m2.