Note: Descriptions are shown in the official language in which they were submitted.
1 3 1 1 ~2
EXPANDED METAL MESH AND COATED ANODE STRUCTURE
BACKGROUND OF THE INVENTION
The most important development in electrolysis
electrodes in recent years has been the advent of
dimensionally stable electrodes following the teachings of
U.S. Patents No. 3,771,385 and 3,632,498. These
dimensionally stable electrodes consist of a base or
substrate of a valve metal, typically titanium, carrying
an electrocatalytic coating such as a mixed oxide of
platinum group metal and a valve metal forming a mixed
crystal or solid solution. Many different coating
formulations have been proposed.
The major use of these dimensionally stable
electrodes has been as anodes in chlor-alkali production
in mercury cells, diaphragm cells and more recently in
membrane cells. Other uses have been as oxygen-evolving
anodes for metal electrowinning processes, Eor
hypochlorite and chlorate production, as metal plating
anodes and so on. Use as an anode in cathodic protection
has also been proposed and as cathodes in certain
processes.
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~ epending on the use, these dimensionally stable
valve metal electrodes have been proposed with various
configurations such as rods, tubes, plates and complex
structures such as an array of rods or blades mounted on a
supporting current conducting assembly as well as a mesh
of expanded valve metal typically having diamond shaped
voids mounted on a supporting current conducting assembly
which provides the necessary rigidity.
~lectrodes in ~he form of platinized valve metal wire
are known for cathodic protection, but in practically
every other application rigidity and dimensional stability
of the electrode are critical factors for successful
operation. For example, many electrolytic cells are
operated with an inter-electrode gap of only a few
millimeters and the flatness and rigidity of the operative
electrode face are extremely important.
For most applications, the dimensionally stable
electrodes operate at relatively high current densities,
typically 3-5 KA/m2 for membrane cells, 1-3 KA/m2 for
diaphragm cells and 6-10 KA/m2 for mercury cells. These
high current densities, combined with the requirements of
planarity/rigidity, necessitate valve metal structures of
substantial current carrying capacity and strength.
Typical known valve metal electrodes of the type with
expanded titanium mesh as operative face use a mesh having
an expansion factor of 1.5 to ~ times providing a void
fraction of about 30 to 70 percent. Such titanium sheets
may be slightly flexible during the manufacturing
processes but the inherent elasticity of the sheet is
restrained, e.g. by welding it to a current conductive
structure, typically having one or more braces e~tending
parallel to the SWD dimension of the diamond-shaped
openings. Such electrode sheets typically have a
current-carrying capacity of 2-10 KA~m2 of the electrode
surface.
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Other electrode configurations are known for special
purposes, e.g., a rigid cylindrical valve metal sheet
mounted in a linear type of anode structure for cathodic
protection ~see U.S. Patent No. 4,S15,886).
Manufacture of the known electrodes usually involves
assembly of the electrode valve metal structure, e.g, by
welding, followed by surface treatment such as
degreasing/etching/sandblasting and application of the
electrocatalytic coating by various methods including
chemi-deposition, electroplating and plasma spraying.
Chemi-deposition may involve the application of a coating
solution to the electrode structure by dipping or
spraying, followed by baking usually in an oxidizing
atmosphere such as air.
SUMMARY OF THE INVENTION
It has now been found that titanium and other valve
metals, e.g., tantalum and zirconium, can be greatly
expanded to a pattern of substantially diamond-shaped
voids having an eYtremely high void fraction. Having been
expanded in this way material cost becomes acceptable and the
expanded metal forms an ideal structure Eor cathodic protec-tion.
Moreover the greatly expanded mesh is flexible and
coilable and uncoilable about an axis along the LWD
dimension. Thus the expanded metal can be supplied in the
form of large rolls which can be easily unrolled onto a
surface to be protected, such as a concrete deck or a
concrete substructure. The pattern of voids in the mesh
is defined by a continuum of valve metal strands
interconnected at nodes and carrying on their surface an
electrocatalytic coating. This multiplicity of strands
provides redundancy for current flow in the event that one
or more strands become broken during shipping or
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1 3 1 1 ~42
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installation. The metal mesh is desirably stretchable
along the SWD dimension of the pattern units whereby a
coiled electrode roll of the mesh can be uncoiled on, and
stretched over, a supporting substrate and into an
5 operative electrode configuration.
The electrode system of the present invention
satisfies all of the requirements for cathodic protection ?
of reinforcing steel in concrete. It consists of the
highly expanded valve metal which is activated by an
10 electrocatalytic coating. Current can be distributed to
the expanded valve metal by a welded contact of the same
valve metal. A multitude of current paths in the expanded
metal structure provide for redundancy of current
distribution and hence the distribution of current to the
15 reinforcing steel is excellent. Installatian is simple
since an electrode of greater than 100 square meters can
be quickly rolled anto the surface of a concrete deck or
easily cut to size and wrapped around a concrete
substructure. However, generally the coated mesh of the
20 present invention may be utilized in any operation wherein
the electrocatalytic coating on a valve metal substrate
will be useful and wherein current density operating
conditions up to 10 amps per square meter of mesh area are
contemplated. Further details of the aspect of cathodic
25 protection in concrete and the installation of coated mesh
for such protection are provided in concurrently filed
Canadian Patent Application Number 508,616, filQd
May 7, 1986.
The electrocatalytic coating used in the present
invention is such that th~ anode operates at a very low
single electrode potential, and may have a life expectancy
of greater than 20 years in a cathodic protection
application. Unlike other anodes used heretofore for the
` 35 cathodic protection of steel in concrete, it i5 completely
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stable dimensionally and produces no carbon dioxide or
chlorine from chloride contaminated concrete. It
furthermore has sufficient surface area such that the acid
generated from the anodic reaction will not be detrimental
to the surrounding concrete.
In a broad aspect, the present invention is directed
to an electrode for electrochemical processes comprising a
valve metal mesh having a pattern of substantially
diamond-shaped voids having LWD and SWD dimensions for
units of the pattern, the pattern of voids being defined
by a continuum of valve metal strands interconnected at
nodes and carrying on their surface an electrochemically
active coating, wherein the mesh of valve metal is a
flexible mesh with strands of thickness less than 0.125 cm
and having a void fraction of at least 80%, said fle.~ible
mesh being coilable and uncoilable about an axis along the
LWD dimension of the pattern units and being stretchable
by up to about 10% along the SWD dimension of the pattern
units and further being bendable in the general plane of
the mesh about a bending radius in the range of from 5 to
25 times the width of the mesh, whereby said electrode can
be uncoiled from a coiled configuration onto a supporting
surface on which the mesh can be stretched to an operative
electrode configuration.
Also the present invention is dlrected to a fast and
economical coating technique for coiled mesh of even
greatly extended length. Such technique can achieve
highly suitable coating results without de]eterious strand
breakage even for the more delicate meshes of greatly
expanded valve metal and which have extremely great void
volume. Compared to prior art techniques for producing
coated valve metal electrodes, considerably greater
electrode areas, for instance about lO0 or even 200 square
meters or even greater electrode surface areas, can be
coated as a continuous expanse. Moreover, this economical
131 1~42
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coating operation can be undertaken and completed with
equipment that typically will be readily av~ilable in
existing facilities having conventional coating apparatus.
In this coating aspect, the present invention thus
pertains to a method of manufacturing an elec-trode for
electrochemical processes, of the type comprising a valve
metal mesh provided with a pattern of substantially
diamond shaped voids having LWD and SWD dimensions for
units of the pattern, the pattern of voids being defined
by a continuum of thin valve metal strands interconnected
at nodes and carrying on their surface an electrocatalytic
coating, with the method comprising: ~a) providing a
flexible, coiled valve metal mesh, the mesh being as
described ~ereinabove and being coiled about an axis along
the direction of the LWD dimension of the pattern, and ~b~
applying an electrocatalytic coating to the surface of the
valve meta]. mesh while same is coiled to provide a
flexible coated mesh electrode in coiled configuration,
the mesh being uncoilable from the coiled configuration
for use as an electrode.
In other important aspects the invention is directed
to greatly expanded valve metal mesh as well as to a
method for preparing such greatly expanded mesh.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 shows a diamond~shaped unit of a greatly
expanded valve metal mesh of the present invention.
FIGURE 2 shows a section of greatly e~panded valve
metal mesh, embodying diamond-shaped structure, and having
a current distributor along the LWD dimension and welded
to mesh nodes.
FIGURE 3 is an enlarged view of a~mesh node,
particularly showing the node double strand thickness.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS
The metals of the valve metal mesh will mostly
be any of titanium, tantalum, zirconium and niobium. The
~ultable ll~etals of the mesh can include alloys of these
metals with other members of the group
and other metals as well as their inter~etallic
mixtures. Of particular interest for its ruggedness,
corrosion resistance and availability is titanium. Where
the mesh will be expanded from a metal sheet, the useful
metal of the sheet will most always be an annealed metal.
As representative of such serviceable annealed metals is
Grade I titanium, an annsaled ti~anium of low
embrittlement. Such feature of low embrittlement is
necessary where the mesh is to be prepared by expansion of
a metal sheet~ since such sheet should have an elongation
of greater than 20 percent. This would be an elongation
as determined at normal temperature, e.g., 20C., and is
the percentage elongation as determined in a two-inch (5
cm.) sheet of greater than 0.025 inch (.0635 cm.)
thickness. Metals for expansion having an elongation of
iess than 20 percent will be too brittle to insure
suitable expansion to useful mesh without deleterious
strand breakage.
Advantageously for enhanced freedom from strand
breakage, the metal used in expansion will have an
elongation of at least about 29 percent and will virtually
always have an elongation of not greater than about 40
percent. Thus metals such as aluminum are neither
contemplated, nor are they useful, for the mesh in the
present invention, aluminum being particularly unsuitable
because of its lack of corrosion resistance. Also with
regard to the useful metals, annealiny may be critical as
for example with the metal tantalum where an annealed
sheet can be expected to have an elongation on the order
1 3 1 1 ~ ~ 2
of 37 to 40 percent, which metal in unannealed form may be
completely useless for preparing the metal mesh by having
an elongation on the order of only 3 to 5 percent.
Moreover, alloying may add to -the embrittlement of an
elemental metal and thus suitable alloys may have to be
carefull~ selected. For example, a titanium-palladium
alloy, commercially available as Grade 7 alloy and
containing on the order of 0.2 weight percent palladium,
will have an elongation at normal temperature of above
about 20 percent and is expensive but could be
serviceable, particularly in annealed form. Moreover,
where alloys are contemplated, the expected corrosion
resistance of a particular alloy that might be selected
may also be a consideration. For example, in Grade I
titanium, such is usually available containing 0.2 weight
percent iron. However, for superior corrosion resistance,
Grade I titanium is also available containing less than
about 0.05 weight percent iron. Generally, this metal of
lower iron content will be preferable for many
applications owing to its enhanced corrosion resistance.
The metal mesh may then be prepared directly from the
selected metal. For best ruggedness in extended metal
mesh life, it is preferred that the mesh be expanded from
a sheet or coil of the valve metal. It is however
contemplated that alternative meshes to expanded metal
meshes may be serviceable. For such alternatives, thin
metal ribbons can be corrugated and individual cells, such
as honeycomb shaped cells can be resistance welded
together from the ribbons. Slitters or corrugating
apparatus could be useful in preparing the metal ribbons
and automatic resistance welding could be utilized to
prepare the large void fraction mesh. By the preferred
expansion technique, a mesh of interconnected metal
strands can directly result. Typically where care has
been chosen in selecting a metal of appropriate
~ ~ T 1 ~2
elongation, a highly serviceable mesh will be prepared
usin~ such expansion techni~ue with no broken strands
being present. Moreover with the highly serviceable
annealed valve metals having desirable ruggedness coupled
with the requisite elongation characteristic, some
stretching of the expanded mesh can be accommodated during
installation of the mesh. This can be of particular
assistance where uneven substrate surface or shape will be
most readily protected by applying a mesh with such
stretching ability. Generally a stretching ability of up
to about 10 percent can be accommodated from a roll of
Grade I titanium mesh having characteristics such as
discussed hereinbelow in the example. Moreover the mesh
obtained can be expected to be bendable in the general
plane of the mesh about a bending radius in the range of
from 5 to 25 times the width of the mesh.
Where the mesh is expanded from the metal sheet, the
interconnected metal strands will have a thickness
dimension corresponding to the thickness of the initial
planar sheet or coil. Usually this thickness will be
within the range of from about 0.05 centimeter to about
0.125 centimeter. Use of a sheet having a thickness of
less than about 0.05 centimeter, in an expansion
operation, can not only lead to a deleterious number of
broken strands, but also can produce a too flexible
material that is difficult to handle. For economy, sheets
of greater than about 0.125 centimeter are avoided. As a
result of the expansion operation, the strands will
interconnect at nodes providing a double strand thickness
of the nodes. Thus the node thickness will be within the~
range of from about 0.1 centimeter to about 0.25
centimeter. Moreover, after expansion the nodes for the
special mesh will be completely, to virtuall~ completely,
non-ahgulated. By that it is meant that the plane of the
nodes through their thickness will be completel~, to
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virtually completely, vertical in reference to the
horizontal plane of an uncoiled roll of the mesh.
In considering the preferred valve metal titanium,
the weight of the mesh will usually be within the range of
from about 0.05 kilogram per square meter to about 0.5
kilogram per square meter of the mesh. Although this
range is based upon the exemplary metal titanium, such can
nevertheless serve as a useful range for the valve metals
generally. Titanium is the valve metal of lowest specific
gravity. On this basis, -the range can be calculated for a
differing valve metal based upon its specific gravity
relationship with titanium. Referring again to titanium,
a weight of less than about 0.05 kilogram per square meter
of mesh will be insufficient for proper current
distribution in enhanced cathodic protection. On the
other hand, a weight of greater than about 0.5 kilogram
per square meter will most always be uneconomical for the
intended service of the mesh.
The mesh can then be produced by expanding a sheet or
coil of metal of appropriate thickness by an expansion
factor of at least 10 times, and preferably at least 15
times. Useful mesh can also be prepared where a metal
sheet has been expanded by a factor up to 3~ times its
original area. Even for an annealed valve metal of
elongation greater than 20 percent, an expansion factor of
greater than 30:1 may lead to the prep.aration of a mesh
exhibiting strand breakage. On the ot~ler hand, an
expansion factor of less -than about 10:l. may leave
additional metal without augmenting cathodic protection.
Further in this regard, the resulting expanded mesh should
have an at least 80 percent void raction for efficiency
and economy of cathodic protection. Most preferably, the
expanded metal mesh will have a void fraction of at least
about 90 percent, and may be as great as 92 to 96 percent
or more, while still supplying sufficient metal and
1 3 1 1 ~42
economical current distribution. With such void fraction,
the metal strands can be connected at a multiplicity of
nodes providing a redundancy of current-carrying paths
through the mesh which insures effective current
distribution throughout the mesh even in the event of
possible breakage of a number of individual strands, e.g.,
any breakage which might occur during installation or
use. Within the expansion factor range as discussed
hereinbefore, such suitable redundancy for the metal
strands will be provided in a networ~ of strands most
always interconnected by from about 500 to about 2000
nodes per sqllare meter of the mesh. Greater than about
2000 nodes per square meter oE the mesh is uneconomical.
On the other hand, less than about 500 of the
interconnecting nodes per square meter of the mesh may
provide for insufficient redundancy in the mesh.
Within the above-discussed weight range for the mesh,
and referring to a sheet thickness of between about
0.05-0.125 centimeter, it can be expected that strands
within such thickness range will have width dimensions of
from about 0.05 centimeter to about 0.20 centimeter. For
the special application to catho~ic protection in
concrete, it is expected that the total surface area of
interconnected metal, i.e., including the total surface
area of strands plus nodes, will provide between about 10
percent up to about 50 percent of the area covered by the
metal mesh. Since this surface area is the total area, as
for example contributed by all four faces of a strand of
square cross-section, it will be appreciated that even at
a 90 percent void fraction such mesh can have a much
greater than 10 percent mesh surface area. This area will
usually be referred to herein as the "surface area of the
metal" or the "metal surface area". If the total surface
area of the metal is less than about 10 percent, the
resulting mesh can be sufficiently fragile to lead to~
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deleterious strand breakage. On the o-ther hand, greater
than about 50 percent surface area of metal will supply
additional metal without a commensurate enhancement in
protection.
After expansion the resulting mesh can be readily
rolled into coiled configuration, such as for storage or
transport or further operation. With the representative
valve metal titanium, rolls having a hollow inner diameter
of greater than 20 centimeters and an outer diameter of up
to 150 centimeters, preferably 100 centimeters, can be
prepared. These rolls can be suitably coiled from the
mesh when such is prepared in lengths within the range of
from about 40 to about 200, and preferably up to 100,
meters. For the metal titanium, such rolls will have
weight on the order of about 10-50 kilograms, but usually
below 30 kilograms to be serviceable for handling,
especially following coating, and particularly handling in
the field during installation for cathodic protection.
In such greatly expanded valve metal mesh it is most
typical that the gap patterns in the mesh will be formed
as diamond-shaped apertures. Such "diamond-pattern" will
feature apertures having a long way of design (LWD) from
about 4, and preferably from about 6, centimeters up to
about 9 centimeters, although a longer LWD is
contemplated, and a short way of design ~SWD) of from
about 2, and preferably from about 2.5, up to about 4
centimeters. In the preferred application of cathodic
protection in concrete, diamond dimensions having an LWD
exceeding about 9 centimeters may lead to undue strand
. ,~.~,
breakage and undesirable voltage loss. An 5WD of less
than about 2 centimeters, or an ~WD of less than about
centimeters, in the preferred application, can be
uneconomical in supplying an unneeded amount of metal for
desirable cathodic protection.
Referring now more particularly to Fig. l an
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individual diamond shape, from a sheet containing many
such shapes is shown generally at 2. The shape is formed
from strands 3 joining at connections (nodes~ 4. As shown
in the Figure, the strands 3 and connections 4 form a
diamond aperture having a long way of design in a
horizontal direction. The short way of design is in the
opposite, vertical direction. When referring to the
surface area of the interconnected metal strands 3, e.g.,
where such surface area will supply not less than about lO
percent of the overall measured area of the expanded metal
as discussed hereinabove, such surface area is the total
area around a strand 3 and the connections 4. For
example, in a strand 3 of square cross-section, the
surface area of the strand 3 will be four times the
depicted, one-side-only, area as seen in the Figure. Thus
in Fig. 1, although the strands 3 and their connections ~
appear thin, they may readily contribute 20 to 30 percent
surface area to the overall measured area of the expanded
metal. In Fig. 1, the "area of the mesh", e.g., the
s~uare meters of the mesh, as such terms are used herein,
is the area encompassed within an imaginary line drawn
around the periphery of the mesh.
In Fig. 1, the area within the diamond, i.e., within
the strands 3 and connections 'L, may be referred to herein
as the "diamond aperture ". It is the area having the LWD
and SWD dimensions. For convenience, it may also be
referred to herein as the "void", or referred to herein as
the "void fraction", when based upon such area plus the
area of the metal around the void. As noted in Fig. 1 and
as discussed hereinbefore, the metal mesh as used herein
has extremely great void fraction. Although the shape
depicted in the figure is diamond-shaped, it is to be
understood that many other shapes can be serviceable to
achieve the extremely great void fraction, e.g.,
scallop-shaped or hexagonal.
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Referring now to Fig. 2, several individual diamonds
21 are formed of individual strands 22 and their
interconnections 25 thereby providing diamond-shaped
apertures. A row of the diamonds 21 is bonded to a metal
strip 23 at the intersections 25 of strands 22 with the
metal strip 23 running along the LWD of the diamond
pattern. The assembly is brought together by spotwelds
24, with each individual strand connection (node) 25
located under the strip 23 being welded by a spotweld 24.
Generally the welding employed will be electrical
resistance welding and this will most always simply be
spot welding, for economy, although other, similar welding
technique, e.g., roller welding, is contemplated. This
provides a firm interconnection for good
electroconductivity between the s-trip 23 and the strands
22. As can be appreciated by reference particularly to
Fig. 2, the strands 22 and connections 25 can form a
substantially planar configuration. As such term is used
herein it is meant that particularly larger dimensional
sheets of the mesh may be generally in coiled or rolled
condition, as for storage or handling, but are capable of
being unrolled into a "substantially planar" condition or
configuration, i.e., substantially flat form, for use.
Moreover, the connections 25 will have double strand
thickness, whereby even when rolled flat, the
substantially planar or flat configuration may
nevertheless have ridged connections.
Referring then to the enlarged view in FIG. 3, it can
be seen that the nodes have double strand thickness (2T~.
Thus, the individual strands have a lateral depth or
thickness (T) not to exceed about 0.125 centimeter, as
discussed hereinabove, and a facing width (W) which rnay be
up to about 0.20 centimeter.
The expanded metal mesh can be usefully coated. It
is to be understood that the mesh may also be coated
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- 15 -
before it is in mesh form, or combinations might be
useful. Whether coa-ted before or after being in mesh
form, the substrate can be particularly useful for bearing
a cataly-tic active material, thereby forming a catalytic
structure. As an aspect of this use, the mesh substrate
can have a catalyst coating, resulting in an anode
structure.
The metal, including coiled metal mesh, before
electrocatalytic coating operation, may proceed through
one or more of various pretreatment procedures. Such
procedures may be simplistic, for example a simple rinse
operation. Not infrequently the mesh may have, e.g., as
by being imparted from the expansion operation, oils or
other surface contamination. Therefore, a suitable
pretreatment technique will often include a solvent
degreasing operation. This can most always be
accomplished with typical halocarbon solvent such as the
chlorinated and/or fluorinated solvents as represented by
chlorotrifluoromethane, methylene chloride and
perchloroethylene. Other pretreatments for the coiled
metal mesh may include the further typical techniques such
as pickling and etching, as well as dry honing, i.e., sand
blasting. In dry honing, a gritty and very finely
divided, hard particulate can be blasted at the coiled
mesh at high velocity. In a representative etching
operation most usually an aqueous solution of inorganic
acid will be used to contact the metal mesh as by spray or
dip contact. Generally a strong inorganic acid aqueous
solution, e.g., hydrochloric acid at a strength of up to
about 30 percent concentration or more, can be utili~ed.
It is also contemplated that combination pretreatment
techniques may be employed. Such combination operations
can include not only those where two different steps for a
single operation are useful, e.g., a combination o~ spray
and dip technique for degreasing, but also a combination
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such as a washing or rinsing action combined with mild
abrasive treatment. Where several pretreatment operations
are employed, for example degreasing and e-tching,
intermediate steps between each operation may be used,
such as drying and/or rinsing steps and the like.
It will be most suitable to pretreat the valve metal
mesh from typical expansion operation by ~irst degreasing,
as in a commercial degreaser containing a boiling
halocarbon solvent, e.g., perchloroethylene and then
follow the degreasing by etching. This etching may
include contact with an aqueous, concentrated hydrochloric
acid solution, as by dip coating contact for a time up to
about 20 minutes. A contact time of greater than about 20
minutes can lead to deleterious loss of metal in the
etching operation. Usually the coiled metal mesh will be
dipped into the etching solution for a time of at least
about 5 minutes to pro~ide sufficient metal surface
roughness for enhanced coating adhesion and distribution.
The useful concentrated hydrochloric acid solutions can
contain acid in an amount within the range from about S to
about 30 percent.
The liquid coating composition used will be such an
electrochemically active coating as can be useful when
applied as a lightweight coating. This lightweight
coating, or "low loading" coating will often be at a
coating weight of less than about 0.5 gram of platinum
group metal per square meter of the metal mesh substrate.
On the other hand some coatings will be useul when
present in an amount of as little as about 0.05 gram of
platinum metal per square meter of a metal mesh
substrate. As representativs of the electrochemically
active coatings are those provided from platinum or other
platinum group metals or they can be represented by activ~
oxide coatings such as platinum group metal oxides,
magnetite, ferrite, cobalt spinel or rnixsd metal oxide
.,,.,. ~.
1 31 1 4~2
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coatings. Such coatings have typically be~n developed for
use as anode coatings in the industrial electrochemical
industry. Suitable coatings of this type have been
generally described in one or more of the l).S. Patents
3,265,526, 3,632,498, 3,711,385 and 4,52~,084. The mixed
metal oxide coatings can often include at least one oxide
of a valve metal with an oxide of a platinum group metal
including platinum, palladium, rhodium, iridium and
ruthenium or mixtures of themselves and with other
metals. It is preferred for economy that the low load
electrocatalytic coatings be such as have been disclosed
in the U.S. Patent No. 4,528,084.
It is contemplated that coatings will be applied to
the coiled metal mesh by any of those means which are
useful for applying a liquid coating composition to a
metal substrate. Such methods include dip spin and dip
drain techniques. Moreover spray applicatian and
combination techniques, e.g., dip drain with spray
application can be utilized. With the above-mentioned
coating compositions for providing an electrochemically
active coating, a modified dip drain operation of the
coiled metal mesh will be most serviceable. In this
operation, the coil will be dipped into a bath of coating
composition in a manner whereby the axis through the
hollow center of the coil is at least substantially
parallel to the surface of the liquid coating
composition. The coil can be partly immersed or
completely submersed in the coating composition. During
contact it is then preferred to rotate the coil around its
central axis to provide for thorough and even distribution
of the liquid coating composition on the metal substrate.
ParticularIy where large rolls of coiled~metal are coated,
this technique is preferable as only partial immersion of
the coil in the coating solution is needed, with the
subsequent rolling operation providing for thorough
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wetting out of the coating composition on the mesh
substrate. To enhance such coating operation, the coil
may be immersed and rotated, withdrawn from the coating
composition bath, and then reimmersed and rotated, or
counterrotated, with such operation being repeated to
thoroughly coat the coiled mesh. In alternative
processing, the hollow center of the coil can be vertical
and the coil hung in this manner is then either partially
or completely dipped, i.e., up to total coil immersion, in
the coating composition. Following any o~ the foregoiny
coating procedures, upon removal from the liquid coating
composition, the wet coil may simply dip drain or be
subjected to other post coating technique such as forced
air drying.
Typical curins conditions for the electrocatalytic
coating can include cure temperatures of from about
300C. up to about 600C. Curing times may vary from
only a few minutes for each coating layer up to an hour or
more, e.g., a longer cure time after several coating
layers have been applied. The curing operation can be any
of those that may be used for curing a coating on a metal
substrate. Thus, oven curing, including conveyor ovens
may be utilized. Moreover, infrared cure techniques can
bs useful. Preferably for most economical curing, oven
curing is used and the cure temperature used will be
within the range of from about 450C. to about 550C.
At such temperatures, curing times of only a few minutes,
e.g., from about 3 to 10 minutes, will most always be used
for each applied coating layer.
It has been found that the coils of gr~atly expanded
mesh, although being lightweight, are nevertheless
difficult to handle since sharp mesh edges can make manual
handling hazardous. The coating is thus particularly
suitable for reducing injury in the manual handling
operations associated with the colled mesh. For
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facilitating the manual handling ease of the mesh, as when
a coil is placed into or removed from storage or when
proceeding to subsequent operation, such as assembling
with other elements, the coating assists in this ease
of handling such. And such is
especially desirable as in the case of providing the
electrochemically lightweight active coating as this will
not thereafter interfere with subsequent electrical
resistance welding. Thus, the above-described coating
operation can be utilized following coiled mesh production
whereby the resulting coated article can not only proceed
to subsequent processing operation, but will also lend
itself to ready manual handling in such operation.
In utilizing the coiled mesh it will often be
desirable to affix additional metal members to the mesh,
such as after coating. For example, metal current
distributor members can be metallurgically bonded to the
coated coil. Attachment of additional metal members can
occur following the coating operation. Although various
metallurgical bonding techniques for assembling the coated
roll with additional metal elements are contemplated, it
has been found that electrical resistance welding can be
efficiently employed. Thus, where the additional metal
elements include current distribution members, these can
be utilized as strips applied to the unrolled mesh and the
strips can be spot welded across the mesh at the nodes.
Furthermore, in such an assembly the current distributor
members can have the low loading of electrocatalytic
coating. Electrical resistance welding can be
successfully employed to prepare these coated metal
assemblies even where the metals for welding in
face-to-face contact will each be coated faces. Such
current distributor member can then connect outside of the
concrete environment to a current conductor, which current
conductor being e~ternal to the concrete need not be so
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131 1~2
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coated. For example in the case of a concrete bridge
deck, the current distribution member may be a bar
extending throu~h a hole to the underside of the deck
surface where a current conductor is located. In this way
all mechanical current connections are made external to
the finished concrete structure, and are thereby readily
available for access and service if necessary.
Connections to the current distribution bar external to
the concrete may be of conventional mechanical means such
as a bolted spade-lug connector.
Application of the coated mesh for corrosion
protection such as to a concrete deck or substructure can
be simplistic. A roll of the greatly expanded valve metal
mesh with a suitable electrochemically active coating,
sometimes referred to hereinafter simply as the "anode",
can be unrolled onto the surface of such deck or
substructure. Thereafter, means of fixing ~esh to
substructure can be any of those useful for binding a
metal mesh to concrete that will not deleteriously disrupt
the anodic nature of the mesh. Usually, non-conductive
retaining members will be useful. Such retaining members
for economy are advantageously plastic and in a form such
as pegs or studs. For example, plastics such as polyvinyl
halides or polyolefins can be useful. These plastic
retaining members can be inserted into holes drilled into
the concrete. Such retainers may have an enlarged head
engaging a strand of thP mesh under the head to hold the
anode in place, or the retainers may be partially slotted
to grip a strand of the mesh located directly over the
hole drilled into the concrete~
Usually when the anode is in place and while held in
close contact with the concrete substructure by means of
the retainers, an ionically conductive overlay will be
employed to completely cover the anode structure. Such
overlay may further enhance firm contact between the anode
- ~31 1~2
and the concrete substructure. Serviceable ionically
conductive overlays include portland cement and
polymer-modified concrete.
In typical operation, the anode can he overlaid with
from about 2 to about 6 centimeters of a portland cement
or a latex modified concrete. In the case where a thin
overlay is particularly desirable, the anode ma~ be
generally covered by from about 0.5 to about 2 centimeters
of polymer modified concrete. The expanded valve metal
mesh substrate of the anode provides the additional
advantage of acting as a metal reinforcing means, thereby
improving the mechanical properties and useful li~e of the
overlay. It is contemplated that the metal mesh anode
structure will be used with any such materials and in any
such techniques as are well known in the ar~ of repairing
underlying concrete structures such as brid~e decks and
support columns and the like.
The following examples show ways in which the
invention has been practiced, but should not be construed
as limiting the invention.
EXAMPLE 1
An imperforate sheet of Grade I -titanium 100
centimeter (cm) wide x 300 cm long x 0.889 millimeter (mm)
thick (T), and having an elongation at 68C. of 24
percent for a 2-inch (5 cm.) sheet greater than 0.025 inch
(0.0635 cm.) thick, was expanded to a diamond pattern.
The dies doing the piercing o~ the sheet also acted as
forming dies to expand the punched slits into the
diamond-shaped openings. The process employed a punch
with a full indexing to one side to complete the design.
Each diamond measured 7.62 cm LWD x 3.38 cm SWD.
~` 35 Expansion factor was l9 to 1, e.g., a test sheet 16~ cm.
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131 14~2
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long was expanded during the patterning to approximately
30.5 m, providing a void fraction of 95 percent. The
final strand dimension was 0.889 mm (T) x 0.914 mm (W).
Expansion was at a rate of 220 strokes per minute with no
broken strands. The finished expanded titanium had a
weight of 0.20 kilogram (Kg) per square meter (m2~ of
the resulting mesh and an actual metal surace area
~strands plus nodes) of 0.23 m2 per square meter of the
resulting mesh. The 30.5 m long mesh was conveniently
stored and handled in rolled configuration.
A current distribution bar was spot welded to one end
of a piece of the expanded titanium, taken from the
unrolled mesh, which measured 30 cm x 38 cm. The
structure was next vapor de~reased in perchloroethylene
vapor and etched in a 20 weight percent ~Cl solution for 5
minutes. It was thereafter water rinsed and steam dried.
It was then coated with mixed oxides of tit~nium and
ruthenium in which the ruthenium content was 0~35 gram per
square meter. Anodes prepared in this manner were
subjected to accelerated life testing at high current
density in 1.0 M H2SO4. An anode at 300,000 (3 x
10 ) milliamps (mA) per square meter failed after 7.5
hours, and an anode at 100,000 (1 x 105) mA per square
meter failed after 82 hours under these conditions. Usin~
known relationships between current density and anode
lifetime, these results extrapolate to an expected life of
over 200 years at a practical current density of 100 mA
per square meter of the metal surface area of the expanded
-~ titanium.
An anode prepared as described above is then placed
on top o~ a chloride contaminated concrete block and
overlaid with 50 mm thickness of portland cement. A
second identical anode is also placed on top of a chloride
contaminated concrete block and overlaid with a 38 rnm
thickness of latex modified concrete. Both structures are
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131 14~2
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judged by visual inspec-tion to have desirable interbonding
of the cement to concrete for the one block and of the
modified concrete to concrete for the second ~lock. From
the hereinabove described accelerated life tests,
lifetimes of anodes in these blocks are therefore expected
to be very long.
EXAMPLE 2
An imperforate coil of Grade I titanium 114
centimeters (cm) wide x 1.69 meters (m) long x 0.635
millimeter (mm) thick, and having an elongation at 68C.
of 24 percent (for a 2-inch (S cm.) sheet greater than
0.02S inch (0.0635 cm.) thick), was expanded to a diamond
pattern in the manner described in Example 1. Each unit
diamond of-:the pattern measured 7.62 cm LWD x 3.38 cm
SWD. Expansion factor was 27 to 1, e.g., the test sheet
1.69 m long was expanded during the patterning to
approximate-y 45.7 m, providing a void fraction o 96
percent. The final strand dimension was 0.635 mm x 0.736
mm. Expansion was at a rate of 2Z0 strokes per minute
with no broken strands. The finished expanded titanium
had a weight of 0.12 kilogram (Kg) per square meter (m2)
of the resulting mesh and an actual metal ~urface area
(strands plus nodes) of O.:L6 m2 per square ~eter of the
resulting mesh.
The expanded metal coming through the ~xpansion
apparatus was easily coiled into a roll. The resulting
roll had an approximately 30 cm diameter interior hollow
~`~ zone and an overall outside diameter of about 40 cm. The
weight of the rol,l was approximately 11.8 kilos. Titanium
metal tie wires were used to prevent the roll from
uncoiling in further operation. A support rod was passed
through the central hollow zone of the roll and the rbd
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extended beyond -the roll at each end whereby lines
attached to each end from overhead were used with lifting
apparatus. By means of this support rod assembly the roll
was then lowered into a degreasing machine containing
boiling perchloroethylene solvent. The roll was retained
in the overhead vapor zone ~or about 20 minutes.
Thereafter, again by use of the support rod assembly, the
degreased coil was immersed for lO minutes in an aqueous
solution of 20 weight percent hydrochloric acid, which
solution was maintained at 95C. Following this etching
operation the coil was removed from the etching solution,
water rinsed for about 15 minutes followed by steam drying
for about 20 minutes.
Again by way of the support rod assembly, the coil
was then dipped into a bath of coating solution for
providing an electrochemically active coating on the
coil. Coating solutions such as the one of this bath fall
under the U.S. Patent No. 3,632,498, example l. Since
this depth of coating solution was less than the diameter
of the coil, the coil was slowly rotated to expose the
entire coil to the coating solution. Furthermore, the
coil was lifted from -the solution, rotated slightly around
the support rod, redipped into the coating solution and
rerolled through the solution. Upon final removal from
the coating solution, the coil was agitated by a liyht
manual shaking and then was retained over the tank of
coating solution for approximately 30 minutes to permit
solution that has been temporarily retained in corners of
the diamond-shaped units to drain, as well as to permit
the coil to dry.
Th~ dried coil was maintained on its support rod
apparatus and by means of this support was then introduced
to a conveyor oven. The coil proceeded through the oven
in a time of 4 minutes whereby the wire mesh facing the
hollow c^ntral zone of the coll attained a temperatuFe of
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approximately 500C. Upon removal from the oven, the
coil was reconveyed for a second 4 minute pass through the
oven. After the second pass, th~ coil is permitted to
cool. It was then subsequently uncoiled and found to
contain no broken strands or adjacent strands stuck
together by such coating and curing operation, and thus
was easil~ and completely uncoiled.
In analysis of coils coated in this manner, wherein
the coils have been uncoiled and test pieces cut out for
analysis, the coatin~ has been found to provide mixed
oxides of titanium and ruthenium in which the ruthenium
content is 0.35 gram per square meter. Furthermore, such
coating has been found to be sufficiently distributed
throughout the mesh that all randomly selected areas for
analysis demonstrate desirable coating content. Anodes
prepared from such randomly selected samples and subjected
to accelerated life testing have all demonstrated enhanced
performance sufficient for these mesh anodes to serve in
cathodic protection, such as protection of steel
r~inforced concrete. The coating and curing process using
the mesh in coiled form, is thus judged to be highly
desirable for supplying coated mesh which will be
serviceable as such anodes.
As illustrative of exemplary meshes which can be or
have been useful, there are presented the following:
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Mesh S~ecifications
Type 1 Mesh
Composition Titanium Grade 1
Width of Roll 45 inches (112.5 cm)
Length 250 to 500 ft. (75 to 150 m)
Weight 26 lbs./1000 ft.2 (11.7 kg/lOOm2)
Diamond Dimension 3" LWD x 1 1/3" SWD
(7.6 cm LWD x 3.3cm SWD)
Resistance Lengthwise
(45 inch/112.5 cm wide) .0~6 ohm/ft. (0.086 ohm~m~
Resistance Widthwise with
Current Distributor .007 ohm/ft. (0.02 ohm/m~
Bending Radius 3/32 inches (0.24 cm)
Bending Radius in Mesh Plane 50 ft. (15 m)
Type 2 Mesh
Composition Titanium Grade 1
Width of Roll 4 ft. (122 cm)
Length 250 to 500 ft. (75 to 150 m)
Weight 45 lbs./1000 ft,2 (20.2 kg/100 m2)
Diamond Dimension 3" LWD x 1 1/3" SWD
(7.6 cm LWD x 3.3 cm SWD)
ResistancQ Lengthwise
(4 ft., 122 cm wide) .014 ohm/ft.
Resistance Widthwise with
Current Distributor .005 ohm~ft. (0.016 ohm/m~
Bending Radius 3/32 inches ~0.24 cm)
Bending Radius in Mesh Plane 50 ft. (15 m)
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When the coated metal mesh is used for cathodic
protection, such as for retarding corrosion in steel
reinforced concrete, the mesh will be connected to a
current distribution member. Such a member will most
always be a valve metal and preferably is the same metal
alloy or intermetallic mixture as the metal most
predominantly found in the expanded valve metal mesh.
This current distribution member must be firmly affixed to
the metal mesh. One preferred manner of firmly fixing the
member to the mesh is by welding, e.g., electrical
resistance welding such as spot welding. Moreover, the
welding can proceed through the coating. Thus, a coated
current distributor strip can be laid on a coated mesh,
with coated faces in contact, and yet the welding can
readily proceed. The strip can be spot welded to the mesh
at every node and thereby provide uniform distribution of
current thereto. Such a current distributor strip member
positioned along a piece of mesh about every 30 meters
will usually be sufficient to serve as a current
distributor for such piece.
