Note: Descriptions are shown in the official language in which they were submitted.
Electroformed copper foils are the backbone of modern elec-
tronic devices. As integrated circuits have found their way into ever
increasing numbers of products. the quantity of foil required has in-
creased correspondingly yet the rate at which these foils could be pro-
duced has been limited because even the best dimensionally stable anodes
available were not capable Or withstanding the conditions
required for optimum foil production.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided
an anode for oxygen evolution consisting essentially of a substrate of
a film forming metal having thereon a multilayer coating comprising an
interior layer and an exterior layer, as follows. The interior layer
consists essentially of substantially pore free platinum applied electro-
lytically to a thickness of at least about 150 microinches, e.g.~ about
150 to 400 microinches, then densified by heat treating in an oxygen
containing atmosphere at from 600C to 775C so as to close the pores
in the platinum layer. The exterior layer consists essentially of
iridium oxide, and optionally not more than about 3% rhodium oxide,
said exterior layer having been applied by thermal decomposition of
one or more thermally decomposable iridium and, optionally. rhodium
compounds in an oxygen containing atmosphere at a temperature of not
more than about 600C, e.g., at a temperature of from 400C to 550C,
or from about 450C to about 500C.
Other aspects of the invention are described in the
following detailed description.
DETAILED DESCRIPTION OF THE INVENTION AND
PREFERRED EMBODIMENTS THEREOF
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The anodes of the present invention are particularly
suitable for producing high purity, pore-free copper foils at high
speed and low cost under severe conditions because these
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anodes withstand high acid concentrations, current
densities and temperatures which would rapidly destroy
the anodes known to the prior art. In particular, the
anodes of the present invention are formed by a three
step process which is extremely sensitive in its details
but, when carried out properly, produces extremely robust
and durable anodes.
In the first step of the process, platinum is
electrodeposited on a valve metal substrate which has
been thoroughly descaled, degreased and cleaned. It is
critical that the platinum be applied to a thickness of
from at least about 150 microinches up to about 400
microinches, preferably the thickness will be at least
about 225 microinches, more preferably at least about 250
microinches.
The second step of the process involves a thermal
treatment referred to as "densification" which is essen-
tial for obtaining the anodes of the present invention.
In the "densification" step, the platinum coated anode is
heated in air and maintained at a temperature between 600
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.and 775C for about ~ to 2 hours or until the stress is
relieved in the electrodeposited coating and pores
resulting from the electrodeposition process have closed.
The final step in the process is applying a
5 catalytic oxide outer coating consisting essentially of
at least about 97% IrO2 and up to about 3~ Rh2O3 by
applying thermally decomposable iridium and rhodium
compounds to the "densified" platinum coated substrate,
then decomposing the compounds by heating in air to form
the oxides. It has been found that it is essential to
effect the decomposition at temperatures of no more than
about 600C as the products formed are much less durable
when higher temperatures (for example, around 690~C) are
used. The amount of the thermally decomposable compounds
applied should be sufficient to provide a loading of at
least about 15 m /g of iridium (calculated based on the
weight of the metal), preferably 20 m /g, more preferably
25 2 ~
The substrates to which the coating is applied may
be any of the well known film forming metals which, if
uncoated, will rapidly passivate by formation of an
adherent protective oxide film in the electrolyte for
which the anode is intended. Typical substrates are
formed from titanium, tantalum, vanadium~ tungsten,
aluminum, zirconium, niobium and molybdenum in the form
of tubes, rods, sheets, meshes, expanded metals or other
specialized shapes for specific applications. For
formation of electrolytic copper foil, it is particularly
preferred to use anodes in the shape of cylinders or as a
; 30 portion of a cylinder which conform to the shape of the
mandrel or drum so that the electrolytically formed foil
will be of uniform thickness and may easily be removed
from the cathode drum. In many cases, the core of the
anode will be copper or another highly conductive metal
such as aluminum or highly conductive ferrous alloys clad
with a film forming metal outer layer such as titanium.
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Prior to application of the electrolytic layer, the
substrate is cleaned and descaled such as by blasting
with aluminum oxide particles in an air jet, then
chemically cleaned and degreased. Normally, the anode is
coated immediately subsequent to degreasing but the
anodes may be stored for for a few days between
degreasing and coating without ill effect.
The electrolytic coating of platinum may be applied
by immersing the substrate in an aqueous, platinum,
electroplating bath opposite a conventional dimensionally
stable counterelectrode and passing a current of from
about 7 to about 70 amps per s~uare foot through the
substrate until at least 150, preferably 225, more
preferably 250 microinches of platinum have been applied.
Any conventional platinum electroplating bath may be
used. Typically, such baths are in aqueous dispersons,
solutions or admixtures containing compounds of platinum
such as ammine, nitrito or hydroxy complexes, as well as
various known additives for brightening, improving the
ductility of the deposited film and isolating impurities
as well as improving the conductivity of the bath.
Typical pla-tinum compounds include H2PtCl6, KzPt(OH2~,
H2Pt(NO2)2SO4 and diammine dinitroplatinum (II)~ Useful
formulations for platinum electroplating baths are
disclosed in F. Lowenheim, Modern Electroplating, 3rd Ed.
1974, pp. 355-357 and
F. Lowenheim, Electroplating, McGraw Hill 1978~ pp.
298-299. Prepared concentrates for preparing and
replenishing platinum electroplating baths are
commercially available. To achieve a high quality
platinum layer, the temperature of the bath should
preferably be maintained at from about 150 to about 200F
(65 to 93C).
After the platinum coat has reached the desired
thickness, the anode may be removed from the bath and
subjected to a thermal treatment termed "densification"
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to stress relieve the coating and close pores therein.
If the "densification" step is omitted, or not performed
properly, the anodes formed are less durable as they
passivate prematurely. Thermal densification can be
accomplished by heating the platinum coated anode in air,
nitrogen, helium, vacuum or any convenient atmosphere to
a temperature of between about 550C and 850C for from
about 15 minutes to several hours depending on the nature
of the as deposited platinum film. It may be determined
that the thermal densification step is complete by
visually observing the coating and noting when pore
closure occurs and the coating becomes much more highly
reflective.
After thermal densification is complete, the anode
may be cooled then coated with an iridium oxide outer
layer by thermal decomposition of iridium containing
compounds in an oxygen containing atmosphere. Iridium
compounds that may be used include hexachlororidic acid
(NH4)2IrCl6 and IrC14, as well as iridium resinates and
other halogen containing compounds. Typically, these
compounds are dispersed in any convenient carrier such as
isobutanol, and other aliphatic alcohols, then applied to
the substrate by any convenient method such as dipping,
brushing on or spraying. In most cases an amount of
iridium bearing carrier is applied which is sufficient to
deposit a loading of from about 0.5 to about 3.0 grams
per square meter, preferably 1 to 2 grams per square
meter, of iridium (calculated as metal) on the substrate,
which is then fired in air at from about 400C to no more
than about 550C, preferably 450C to about 500C, to
drive off the carrier and convert the iridium compounds
-to the oxides. This procedure is repeated until the
total amount of iridium applied is at least about 15,
preferably at least about 20, more preferably at least
about 25 grams per square meter (calculated as metal).
The temperature of the thermal decomposition step is
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extremely critical. As will be demonstrated in the
following Examples, when a decomposition temperature in
excess of about 600C is used for decomposition of the
iridium compounds, the resulting anode is much less
durable, but when the iridium compound is decoMposed at
temperatures of 600C or below, preferably from about
400C to about 550C, more preferably from 450C to
500C, the resulting anode is surprisingly durable and
long lived even when evolving oxygen in baths at
temperatures in excess of about 65C which will normally
ruin the prior art anodes in short order.
In many cases, it will be advantageous to include up
to about 3~ Rh2O3 in the iridium oxide film to promote
adhesion. This may be accomplished by incorporation of
any convenient, conventional rhodium compound into the
iridium bearing coating composition. Rhodium resinates
are particularly convenient.
Copper foils may be electroformed using the anodes
of the present invention by immersing the anode in a bath
at a p~ of from 0.2 to 3 containing suitable copper
species such as copper sulfate, copper chloride and other
soluble copper compounds opposite a cathode such as
stainless steel or other corrosion resistant alloys and
passing a current of from about 400 to about 2,000 amps
~ 25 per square foot of anode (4,300 to 21,000 A/m2) through
;~ the bath and evolving oxygen at the anode. It is
considered particularly surprising that the anodes of the
present invention exhibit high durability even when use~
at bath temperatures in excess of 65C up to about 90C.
It is also considered surprising that anodes of the
present invention remain suitable for use at a sulfuric
acid concentration from about 100 to about 250
grams/liter even when operating at current densities from
about 500 up to about 3,000 amps per square foot (5,400
to 32,000 A/m2). Under these conditions, prior art
anodes rapidly become useless and even anodes similar to
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.the present invention, but not prepared strictly in
accordance therewith, fail rapidly. It is extremely
desirable for copper foil producers to be able to use
these severe conditions as under these conditions more
efficient, rapid and economical production of foil can be
achieved. Thus, the anodes of the present invention
satisfy a long felt but unsatisfied need for anodes which
were capable of being used under conditions which are
suitable for high speed, energy efficient production of
high purity, pore free films of electrolytic copper foil.
They are also e~treMely suitable for those applications
in which a porous foil is desired as well as for other
applications involving oxygen evolution such as
electrogalvanizing, electrowinning and electrosynthesis.
Example l
This Example illustrates the production of an anode
in accordance with the present invention. A substrate of
titanium of dimensions 4" by 8" by 0.062" was descaled,
cleaned and degreased, then electrolytically coated with
platinum to a thickness of 250 microinches. The platinum
coating was then densified by heating in air at 690C for
3/4 hour. After cooling, a coating consisting of about
98% IrO2 and 2% Rh2O3 was applied by painting the
substrate with a solution of hexachloroiridic acid and a
rhodium resinate dispersed in butanol, then firing in air
at 450C and repeating this procedùre 15 times until the
coating weight reached 15 grams of iridium ~as metal~ per
square meter. When it was used in electroformir.g of copper
foils at a p~ of about 0, a current density of about 1860
ASF (20,000 A/m~), and a temperature of about 60C, the
anode was still operating at this writing after 4,000
hours at an essentially constant overvoltage of 2.83
volts.
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Exam~ple ?
The procedure of Example 1 was repeated except that
the iridium oxide (thi.rd step) was formed at 690C. When
used under conditions similar to those in Example 1 (pH
0, current density 1860, and temperature of 60C) the
anode failed after 620 hours.
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