Note: Descriptions are shown in the official language in which they were submitted.
1 X157827
COMBINATION INNER PLATE AND OUTER ENVELOPE ELECTRODE
Background of the Invention
In cells such as chlorate cells for the production
of chlorate by the electrolysis of brine, it has been
known to use coated titanium anodes. The anodes can
comprise a plurality of spaced-apart members and the
members can be positioned side-by-side in parallel rows.
The anode members can be connected together and such
connections can be by members taking different forms such
as ribs and base plates. These connecting members, which
may be positioned in a manner transverse to parallel rows
of anodes may serve as current distributors for
impressing an electrical current onto the anode members.
It has been known that the titanium anodes may
carry a coating, such as an electrocatalytic coating of a
platinum group metal oxide, with the anodes being in the
form of plates. For example, British Patent No.
1,076,973, published July 26, 1967, discloses titanium
plate anodes, which plate anodes are in parallel rows,
side-by-side and spaced apart one from the other. The
plate anodes can have an electrocatalytic coating and, as
shown in the patent, a transverse rib member serving as a
current distributor or busbar.
i a~
X157827
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U.S. Patent No. 4,022,679 discloses titanium
described in the form of bands or strips which are coated
and serve as anodes. The bands or strips run parallel to
one another and are spaced apart from each other.
Current is distributed to these parallel rows of titanium
strips by a transverse bar of uncoated titanium which is
welded to the strips.
For distributing current to the electrodes, the
distributor may be in the form of a sheet or a plate,
sometimes referred to as the base plate of the cell.
U.S. Patent 4,078,986 shows a titanium sheet serving as a
base plate of a cell. To the base plate, there are
welded parallel rows of support ribs and from these ribs
there extend anodes in sheet form. These anodes may be
fabricated of titanium and provided with an
electrocatalytically active coating. The sheet anodes
are welded to the ribs.
In these various constructions when it is time to
recoat the anodes, it has been conventional to remove the
plate anodes from the cell, including cutting the plate
anodes from a base plate. The anodes can then have the
old coating removed by vigorous processing which may
include abrasive blasting of the anode surfaces.
Thereafter, a fresh coating is applied to the anode
plates and then they are reinstalled in the cell, e.g.,
by welding again to the base plate.
It would be highly desirable to have a more
expedient manner of refurbishing used electrodes. It
would also be most desirable if such innovation could
improve turn around time to reduce plant outages.
Summary of the Invention
An innovation is now disclosed which greatly reduces
turn around time in the refurbishing of electrodes in use
in commercial operation. Not only is turn around time
reduced, but also conventional processing steps, e.g.,
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cutting and removal of old anodes, are eliminated. Thus,
overall plant operating efficiencies and economies are
enhanced.
In one aspect, the invention is directed to an
electrode comprising an at least substantially flat inner
plate member having front and back major faces and an
edge, and an outer envelope member tightly encasing the
inner plate member on at least the front and back major
faces thereof. The outer envelope member is in
sufficient contact with the inner plate member,such as by
welding, to pass electrical current between the plate
member and the envelope member, and a coating is present
on the outer surface of the envelope member.
In another aspect, the invention is directed to the
method of refurbishing a plate electrode having front and
back major faces and an edge, with the refurbishing
retaining the electrode in secured engagement to a
current distributor, which method comprises covering the
plate electrode with an outer envelope member, tightly
engaging the outer envelope member with the plate
electrode and establishing electrical connection between
such outer envelope member and the plate electrode.
In yet another aspect, the invention is directed to
an electrode cover comprising at least one generally
elongated, hollow envelope member having inner and outer
major faces, each envelope member having a hollow
interior with the inner major face being present in such
interior, the hollow interior being adapted for encasing
an electrode which is in plate form, with there being a
coating on such outer major face.
In a still further aspect, the invention is directed
to a U-shaped electrode cover having a base member of
short width dimension at the base of the U, with a side
member having a long length dimension at each side of the
base member for providing the U-shaped electrode cover,
such cover having inner and outer major faces, with the
outer face of at least one side member being adapted for
21 5 78 2 7 '
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facing engagement with a plate member, such side member
having at least one side extension section providing a
side member larger than the plate member.
Brief Description of the Drawings
Fig. 1 is a perspective view, showing an electrode
of the invention having an outer envelope encasing an
inner electrode plate, the view being in partial cut-
away.
Fig. lA is a section end view, for two electrodes as
shown in Fig. 1, mounted in a base.
Fig. 2 is a perspective view, in partial cut-away,
of a variation of an electrode of the invention.
Fig. 2A is a section end view, for two electrodes as
shown in Fig. 2, mounted in a base.
Fig. 3 is a perspective view of yet another
electrode variation of the invention.
Fig. 4 is a perspective view of two electrodes,
spaced apart, each in partial cut-away.
Fig. 4A is a section end view for the electrodes of
Fig. 4 mounted in a base.
Fig. S is a perspective view of a top corner section
of an electrode, showing a plate-and-envelope variation
in partial cut-away.
Description of the Preferred Embodiments
Electrodes which have been utilized commercially,
typically as anodes, can be in plate form and usually
will be referred to herein for convenience as being in
"plate" form. However, it is to be understood that these
electrodes can be appropriately considered to be in such
form as bands, strips, sheets or blades. Moreover, it is
further contemplated that with such plate form
electrodes, the sheets may be perforated, e.g., as in the
form of a mesh. The plate electrodes are at least
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substantially flat, that is, the working surface of the
area is usually virtually completely flat, while a minor
portion of the electrode, such as where the electrode
might be attached to a current distributor, could be
5 flanged or bent. In addition to being flat, the plate
electrode is also non-circular, e.g., it will be
rectangular rather than elliptical, in its general shape.
The electrode as most often contemplated will be non-
perforate and inflexible, i.e., solid and rigid, and have
front and back major faces as well as an edge. when it
is rectangular, the edge of the plate electrode will more
particularly take the form of two sets of opposed
parallel edges. If it is elongated and narrow, e.g., in
the form of a strip or a blade, but in rectangular shape,
it will have a parallel set of short edges and a parallel
set of long edges. Usually one short edge will be
affixed to a current distributor.
For the electrodes of the present invention, the
inner plate member is as discussed above. Around it will
be an outer envelope member. This may be referred to
herein for convenience simply as the "envelope", or the
"jacket" or the "cover" member. This cover member may be
made at least substantially from plates, as will be
discussed further hereinbelow, and the plates may be of
the bands, strips, or sheets and the like as discussed
hereinabove. The plates as most often contemplated will
be non-perforated and inflexible, i.e., solid and rigid.
These plates can have front and back major faces and an
edge. Generally these plates will cover at least the
front and back major faces of the plate electrode (Fig.
3) and welding may cover the edge (Fig. 5), as will be
discussed hereinbelow. It is further also contemplated
that the plates can be sheets which may be perforate,
e.g., mesh. Both the inner plate member and the envelope
member generally will be a metal member. Where the
electrode is to be utilized in an electrolysis such as of
brine, the metal for the inner plate member and outer
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envelope member is advantageously of a valve metal, e.g.,
titanium, tantalum, niobium, zirconium, hafnium,
molybdenum, tungsten, or aluminum as well as alloys and
intermetallic mixtures thereof. In such brine
electrolysis, for both the inner plate and outer
envelope, titanium is the preferred metal owing to its
economical availability and desirable electrical and
chemical properties.
The invention electrode may be useful in an
electrolytic process as anode or cathode or both.
However, for convenience, the electrode may often be
referred to herein simply as the "anode". Representative
electrolytic processes include the electrowinning of
metals, electrodeposition of metals, electrolytic
treatment of waste streams for removal of impurities, or
for disinfection or the like, electrolysis of typically
aqueous solutions of salts, such as electrolysis of
brine, for the production of chlorine or chlorate.
Referring then to the drawings, and more
particularly to Fig. 1, an invention electrode 1 has an
inner plate 2 and an outer envelope 3. The inner plate 2
is provided by a used electrode in plate form. At the
top portion of the inner plate 2 the outer envelope 3 has
a cover section 4 which bridges over the top of the inner
plate 2, thus covering the top of the inner plate 2. In
the figure, a portion of the top section 4 and outer
envelope 3 is shown in a partial cut-away view, exposing
a top corner of the inner plate 2 for clarity. At the
bottom of the electrode 1, the outer envelope 3 has
flanges 5,5' which flare outwardly from the inner plate
2. Thus the outer envelope member is the outer envelope
3 including the cover section 4 and flanges 5,5'. Also
at the bottom of the electrode, the outer envelope 3
stops short of the full extension of the inner plate 2
thereby exposing an extension portion 6 of the inner
plate 2. At the bottom of the electrode 1, the outer
envelope 3 has a partial cut-away view exposing the
21 578 2 7
extension portion 6 for clarity. Except for the
extension portion 6, the outer envelope 3 completely
covers the inner plate 2.
Referring then to Fig. lA, the inner plate 2 is
covered with an outer envelope 3. At the base of the
electrode, the inner plate 2 has an extension portion 6
which projects into, and is securely adhered to a base
plate 7. The base plate 7 can serve as a current
distributor. The lower end of the outer envelope 3
terminates in flanges 5,5'. These flanges 5,5' abut face
to face to the base plate 7 and are secured thereto such
as by welding 8 along their side edges to provide
desirable electrical contact between the base plate 7 and
the outer envelope 3. The welding 8 at the sides of the
flanges 5,5' can also secure adjacent flanges 5,5' one to
the other. Additional welding (not shown) can also be
carried out completely across the front and back of the
flanges 5,5', and therefore around the entire bottom
perimeter of the outer envelope 3. By all of this
welding, the envelope 3 is secured to the base plate 7.
This perimeter welding can also seal completely the
juncture of the envelope 3 with the base plate 7. The
welding provides an electrical connection between the
base plate 7 and the outer envelope 3.
Referring to Fig. 2, the electrode 1 has an inner
plate 2 and an outer envelope 3. At the top portion of
the inner plate 2 the outer envelope 3 has a cover
section 4 (the inner plate 2 is shown at a cut-away
portion, including a portion of this cover section 4),
which bridges over the top of the inner plate 2, thus
covering the top of the inner plate 2. At the bottom of
the electrode, the outer envelope 3 stops short of the
full extension of the inner plate 2. As shown partly in
a cut-away section of the outer envelope 3, the inner
plate 2 has an extension portion 6 projecting beyond the
outer envelope 3. Except for the extension portion 6,
the outer envelope 3 covers the inner plate 2.
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Referring then to Fig. 2A, the inner plate 2 is
covered with an outer envelope 3. At the base of the
electrode, the inner plate 2 has an extension portion 6
which projects into, and is securely adhered, such as by
welding, to a base plate 7. The base plate 7 can serve
as a current distributor. At the lower end of the outer
envelope 3, the envelope 3 terminates in edges which abut
the base plate 7. The outer envelope 3 can be secured to
the base plate 7 such as by welding 8 around the entire
bottom perimeter of the outer envelope 3 where it adjoins
the base plate 7. The entire perimeter welding 8
provides desirable electrical contact between the base
plate 7 and the outer envelope 3. The inner plate 2 is
then completely sealed by the outer envelope 3 and
welding 8.
Referring then to Fig. 3, the electrode 1 has an
inner plate 2 and an outer envelope 3. This envelope 3
has an elongated (long length dimension) element on each
side of the plate 2. At the top portion of the inner
plate 2 the outer envelope 3 has a cover section 4 which
bridges between the two elongated elements (each of which
are substantially plate shaped), and the cover section 4
also bridges over the top of the inner plate 2, thus
covering the top of the inner plate 2. However, long
parallel edges 9 of the inner plate 2 (which edges 9
define the thickness dimension of the inner plate 2) are
left exposed by the version of the envelope 3 shown in
Fig. 3. These edges 9 can be sealed, such as by welding
(not shown). Along the outer face of one of the
elongated elements of the envelope 3 there is placed a
separator 16. This can serve to maintain a separation
between the electrode 1 and adjacent assembly. The
separator 16 can be secured to the envelope 3, such as by
adhesive, and may be made from a material resistant to
the environment of the electrode, which material may
suitably be polytetrafluoroethylene.
z1~'~82'~
9
At the bottom of the electrode 1, each of the
elongated elements terminates in a flange 5,5', or foot.
Each of the flanges 5,5' flare outwardly from the inner
plate 2. Moreover at the bottom of the electrode 1, the
outer envelope 3 stops short of the full extension of the
inner plate 2 thereby exposing an extension portion 6 of
the outer envelope 3. The outer envelope 3 is in secure,
electrically conductive contact with a base plate (note
shown) such as in the manner shown and described
hereinabove in connection with Figs. 1 and lA. Where
welding is used along the outer edges 9, this welding
(not shown) plus the outer envelope 3, can assist in
completely sealing the inner plate 2. In such instances,
it is the envelope 3 plus welding that completely covers
the inner plate 2.
Referring next to Fig. 4, two electrodes 1,1' each
have an inner plate 2. This plate 2 is essentially
encased in envelope sections 11. At the top portion of
the inner plate 2 each envelope section 11 has a top
extension section 12 which extends past the top end of
the inner plate 2 (which is shown in partial cut-away of
the envelope sections 11). Also, the envelope sections
11 have side extension sections 13 which extend past the
side edge of the inner plate 2. Where the extension
sections 12,13 of adjacent envelope sections 11 come
together, they pinch together leaving only a seam and can
be secured together, e.g., in sealing engagement, such as
by welding (not shown) along the seam. At the bottom,
between the two electrodes, a facing pair of long length
dimension envelope sections 11 interconnect at a base 18
(at the side edges of the base 18). This base 18 has a
short width dimension between the adjacent inner plates
2. The short width dimension base 18 with the long
envelope sections 11 form a U-shaped cover member
segment. The inner envelope sections 11 provide
elongated side members at each side of the base 18.
These envelope sections 11, on their outer faces, are in
21 57827
facing engagement with inner plates 2. These envelope
sections 11, on their inner faces, can be coated. These
sections plus the base (and which may include the
extension sections 12, 13) can form a seamless, one-piece
5 U-shaped cover member.
At the bottom of each electrode, the outer envelope
sections 11 stop short of the full extension of the inner
plate 2 thereby exposing an extension portion 6 of the
inner plate 2 (as shown in partial cut-away of the
10 envelope sections 11). An adjacent pair of the outer
envelope sections 11, including the extension sections
12, 13, when sealed together as by welding, can
completely cover the inner plate 2 of each electrode,
except for the exposed extension portion 6. Also secured
at the side extension sections 13 can be support pins 14.
These pins 14 support electrically non-conductive, e.g.,
polytetrafluoroethylene, separator strips 15 which can
serve to maintain the electrode separate from an adjacent
electrode. The separator strips 15 can be formed with
bent edges and apertures which fit around the support
pins 14, whereby the separator strips can be snapped into
place over the support pins 14. The separator strips 15
may also be adhesively held in place, thereby obviating
the support pins 14.
Referring then to Fig. 4A, each inner plate 2 is
covered with a pair of outer envelope sections 11. At
the bottom of the envelope sections 11, the base 18 outer
surface is in contact with a base plate 7. At the base
of each electrode, the inner plate 2 has an extension
portion 6 which projects into, and is securely adhered
to, such as by welding, a base plate 7. The bottom of
the envelope sections 11 can be welded to the base plate
7 at the front and back of the extension portion 6, i.e.,
across the width of the plate 2, in the manner as shown
in Fig. 2A. The base plate 7 can serve as a current
distributor.
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11
Referring then to Fig. 5, an electrode 1 has an
inner plate 2. This plate 2 is snugly sandwiched between
envelope sections 11. At the top portion of the inner
plate 2 each envelope section 11 has a top extension
section 12 which extends past the top end of the inner
plate 2. Also the envelope sections 11 have side
extensions sections 13 which extend past the side edge of
the inner plate 2. These side extension sections 13 can
extend past the side edge of the plate 2 at both the
front and back of the plate 2. Where the extension
sections 12, 13 of the adjacent envelope sections 11 face
one another, they can be secured together in sealing
engagement by welding 17 across the entire width of the
edges of the inner plate 2. This welding 17 can be along
the long parallel side edges, both front and back,
between the side extension sections 13, as well as along
the top short edge between the top extension sections 12.
The bottom short edge of the inner plate 2 can be affixed
to the base plate 7 (Fig. 4A). For this construction,
the cover member is thus provided not only from the
envelope sections 11, but also by the welding 17 at three
sides of the inner plate 2.
To refurbish old electrodes, even those containing
residual surface coating, the electrodes as inner plates
2 can be retained in a base plate 7 and need not have old
coating removed. For purposes of this exemplification,
and referring more particularly to Figs. 4 and 5, U-
shaped cover member segments of a base 18 and side
envelope sections 11 can be fitted between adjacent inner
plates 2. In this fitted engagement, the outer face of
the base 18 can be fitted in firm contact against the
base plate 7. Also, outer faces of envelope sections 11
can fit firmly against adjacent faces of inner plates 2.
All such firm engagement enhances electrical connections
between the envelope sections 11 and the inner plates 2.
Welding 17 can then be provided along the exposed edges
of the inner plates 2, with preferably the plate
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12
extension sections 12, 13 providing some to all of the
weld metal. Thus, in addition to any of the above
discussed mechanical engagement that occurs by the
fitting of the U-shaped cover member segments between
adjacent inner plates 2, there is additionally good
metallurgical connection between the inner plates 2 and
the U-shaped cover member segments which can be provided
by the welding 17. This metallurgical and mechanical
engagement provides for a desirable electrical connection
between the outer envelope sections 11 and the inner
plates 2.
Referring again to Fig. 1, and as mentioned
hereinabove, both the inner plate member 2 and the outer
envelope 3 are generally metal members, typically valve
metal members with titanium being preferred. Titanium is
also the preferred metal where the outer envelope is in
envelope sections 11 as shown in Fig. 4. The outer
surface of the outer envelope 3, or envelope sections 11,
will advantageously be electrocatalytically coated, with
a coating as will be discussed further hereinbelow in
greater detail. As noted in the Figs. 1 and lA, the
outer envelopes 3 can be individual hollow envelope
members of inverted U-shapes. They will have a hollow
interior having an inner face for contacting an inner
plate 2. Such hollow envelopes are placed over the inner
plates 2 and welded together between adjacent plates as
well as to the inner plate 2 after placement, e.g., the
welding 8 of Figure lA and 2A. It is also contemplated
that the outer envelopes 3, as well as the envelope
sections 11 of Fig. 4, can be preformed. That is, prior
to placement over the inner plates 2, these envelopes 3
can be secured together as by welding or in seamless
connection to form large, one-piece structures of, e.g.,
many envelopes 3 welded together. Such large structures
may then be slipped over many inner plates 2, such as
rows of inner plates 2. Such large preformed structures
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13
will also be serviceable where the outer envelope 3 is in
the form as shown in Fig. 3.
As noted in Fig. 4, the outer envelopes can be in
sections, including extension sections 12, 13 as shown in
Fig. 5. Advantageously, these sections will be
preassembled or formed into one piece. For example, a
base 18 can have a side envelope 11 welded at each side
edge to form a U-shaped envelope cover member . The
extension sections 12,13 can be welded to the side
envelope 11. The resulting member, with weld seams, is
then slipped between adjacent plates 2. Such a member
may also be formed as a seamless, one-piece segment of
the overall envelope that likewise can be slipped between
adjacent plates 2. Other configurations for structuring
envelope sections are also contemplated, such as having
sections where the weld joints are down the broad face of
the inner plate 2 rather than at the short sides thereof.
Also, other connections for the inner plates 2 with a
base plate 7 rather than an extension portion 6
projecting into the base plate 7, are contemplated. For
example, the inner plates 2 may be flanged and secured to
current lead-in members, such as shown in U.S. Patent
4,078,986.
Wherever welding is utilized, the type of welding is
preferably gas tungsten arc welding or tungsten and inert
gas welding, but other welding techniques such as
electron beam may be utilized. The deposited metal
remaining after the welding will most always be left as
is, but can also be subject to further operation, e.g.,
machined, polished or trimmed.
In a cell such as for the electrolysis of brine to
produce chlorate, the inner plates 2 at their edge will
typically have a width (thickness) on the order of 0.1
inch. For such inner plates 2, it is contemplated that
the outer envelope 3, at each side of the inner plate 2
will have a thickness dimension on the order of from
about 0.02 inch to about 0.04 inch. Although the outer
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14
envelopes 3 and envelope sections 11 have been shown in
the figures to be solid, it is also contemplated that the
envelope 3 and sections 11 may be in mesh form. The
securing, as by welding, of the mesh form cover can
provide for desirable electrical connection without the
need for providing a sealing of the inner plate 2.
Although discussions have been made hereinbefore
typically pertaining to a base plate 7, it is to be
understood that other structure, e.g., bar shape, is
contemplated for the base. In general it is contemplated
that any base structure which can be utilized for plate
anodes, will be serviceable as the base structure in the
present invention. Usually such base structure will be
metallic and made from an electrically conductive metal
such as titanium or steel. In Fig. 4 the support pins 14
are typically metallic and are made of a metal similar to
the plate 2, e.g., titanium. Affixed to these pins 14,
such as by being snapped in place, are the separator
strips 15. These are electrically non-conductive
separator strips typically made from a polymeric material
such as polytetrafluoroethylene.
Since the inner plates 2 can be old electrodes,
which may contain at least some residual coating, it is
preferred for enhanced current distribution that the
cover structure be as shown in Fig. 5. Welded regions
can provide good current distribution, which in part will
be due to the welded areas providing firm contact to the
inner plates 2, even through an old,. residual coating.
In the structure of Fig 5, the welding 17 provides
current distribution to three edges of the inner plate 2
(the fourth edge of the inner plate 2 being secured to a
base plate 7). Moreover, the welding 17 in Fig. 5 is
between the extension sections 12, 13, which provides for
comparative ease of welding, when compared with the
welding between flanges 5, 5' adjacent a base plate 7
(Fig. lA). Wherever applied, the welding can provide a
desirable seal, e.g., between envelope sections 11, for
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reducing to eliminating crevice corrosion. With the
structure of Fig. 5, because of the extension sections
12, 13 of the envelope sections 11, a welding arc can be
struck to an edge of the inner plate 2. This can be
5 utilized to affect pooling of the metal of the extension
sections 12 at the top edge of the inner plate 2. In
this manner, the metal of the weld 17 is contributed in
whole or in part from such extension sections 12. A
similar result can be achieved for the weld 17 along the
10 front and back edges of the inner plate 2 for the side
extension sections 13. Using this technique, no
additional metal need be contributed for the welding.
As representative of the electrochemically active
coatings that may be applied to the outer surface of the
15 outer envelope 3 or envelope sections 11 are those
provided from platinum or other platinum group metals or
they can be represented by active oxide coatings such as
platinum group metal oxides, magnetite, ferrite, cobalt
spinel or mixed metal oxide coatings. Such coatings have
typically been developed for use as anode coatings in the
industrial electrochemical industry. They may be water
based or solvent based, e.g., using alcohol solvent.
Suitable coatings of this type have been generally
described in one or more of the U.S. Patent Nos.
3,265,526, 3,632,498, 3,711,385, and 4,528,084. The
mixed metal oxide coatings can often include a platinum
group metal including platinum, palladium, rhodium,
iridium and ruthenium or mixtures of these as well as
mixtures with other metals. Further coatings can
comprise tin oxide, manganese dioxide, lead dioxide "
cobalt oxide, ferric oxide, platinate coatings such as
MXPt304 where M is an alkali metal and X is typically
targeted at approximately 0.5, nickel-nickel oxide and
nickel plus lanthanide oxides.
