Note: Descriptions are shown in the official language in which they were submitted.
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ELECTRODE FOR THE ELECTROPLATING OR ELECTRODEPOSITION OF A
METAL
FIELD OF THE INVENTION
The invention relates to the field of electrodes for the electroplating or
electrodeposition
of a metal comprising at least one topcoating layer and at least one
electrochemically
active coating layer and to the method for producing the same.
BACKGROUND OF THE INVENTION
In electroplating and, more generally, in electrodeposition processes, a thin
metal
coating is formed starting from cations of the metal dissolved in an
electrolytic bath and
deposited over a designated cathodic surface via an electrolytic reaction. The
reaction
is carried out within an electrolytic cell containing at least an anode-
cathode pair
immersed in the electrolytic bath. The cells are often equipped with
dimensionally stable
anodes, such as activated titanium anodes, and the electrolyte typically
contains a
certain amount of added organic elements. These additives, which usually
comprise
brighteners, levelers, surfactants and suppressors, are used for example to
promote a
uniform deposition of the metal and to control its physical-mechanical
properties, such
as its tensile strength and elongation. However, during operation, these
organic
constituents degrade over time, mainly through oxidation occurring at the
anode. The
resulting additive consumption affects the quality of the metal
plating/deposition and
also strongly impacts on the overall costs of the process.
Furthermore, the process conditions for electroplating and electrodeposition
of metals
may be very harsh on the cell components, especially on the activated anodes.
The
corrosive electrolytes, and in certain applications the high current
densities, affect the
electrode lifetime and performance by degrading the active coating layer and
further
aggravate the amount of additive that is consumed.
Electrodes for the electroplating or electrodeposition of a metal comprising
at least one
topcoating layer based on tantalum oxides over an activated electrode, i.e. an
electrode
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provided with at least an electrochemically active coating layer, are known to
the
applicant to partially address the aforementioned issues.
In US6527939 and US2004031692 there is taught the use of a valve metal or tin
topcoating layer on an activated electrode to protect the underlying
electrocatalytic
coating layer in applications involving oxygen evolution, and to prevent
organic
elements or other oxidizable species in the electrolyte from oxidation. The
valve metal
topcoating layer is taught to be formed from a valve metal alkoxide in an
alcohol
solvent, with or without the presence of an acid, or using salts of the
dissolved metals.
However, the preparation methods described in the art for valve metal topcoats
in
general, and in particular the preparation methods of Ta- or Sn-based topcoats
taught in
the prior art examples, were not found to work as well for other valve metal
topcoating
compositions, in particular for Nb-based compositions.
Additionally, Sn-based topcoatings are generally not desirable in applications
such as
copper foil, where even a small tin contamination of the electrolyte may
negatively affect
the quality of the deposited copper.
It would be therefore desirable to provide an alternative or improved
electrode for
electroplating/electrodeposition processes showcasing extended service life
and limited
additive consumption.
It would be also desirable to provide an alternative and improved method for
producing
an electrode comprising a Nb-based topcoating layer for electroplating and
electrodeposition processes.
SUMMARY OF THE INVENTION
The present invention relates to an improved activated electrode for
electroplating and
electrodeposition processes, and the method for producing the same. The
electrode is
operated in electrolyte environments containing organic additives, where it
may reduce
the amount of organic constituent lost via oxidation.
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The activated electrode is provided with at least one topcoating layer
containing niobium
oxide that may induce an improved barrier effect to additive consumption,
wherein the
Nb-based topcoating layer is obtainable by thermal decomposition of acid
precursors,
namely aqueous niobium oxalate in acetic acid.
Other benefits and advantages of the invention will become apparent to those
skilled in
the art based on the following detailed specification.
DETAILED DESCRIPTION OF THE INVENTION
Under one aspect, the invention relates to an electrode suitable for the
electroplating or
electrodeposition of a metal from an electrolyte solution in an electrolytic
cell comprising
a conductive substrate, at least one topcoating layer of a first composition
and at least
one electrochemically active coating layer of a second composition different
from the
first one, the electrochemically active coating layer being positioned between
the
conductive substrate and the topcoating layer, the first composition
containing 90-100%
niobium or oxides thereof, expressed in weight percentage referred to the
metal.
Contrary to the electrodes obtained via the preparation methods disclosed in
the art, the
inventor has surprisingly observed that the Nb-based topcoating layer obtained
via
thermal decomposition of a precursor solution comprising an aqueous solution
of
niobium oxalate in acetic acid provides an advantageous impact on additive
consumption, thereby improving the quality of the deposited/plated metal.
Additionally,
the Nb-based topcoating obtainable via the aforementioned process may extend
the
service life of the electrode by minimizing the exposure to the electrolyte of
any platinum
group metal or oxide thereof that may be present in the electrochemically
active coating.
The foregoing can be achieved without an adverse effect on the cell electrode
potential.
Thus, the electrode according to the invention may represents a viable and
advantageous alternative with respect to electrodes provided with Ta- and Sn-
based
topcoats described in the art.
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By Nb-based topcoating layer it is meant a topcoating layer containing 90-100%
niobium or oxides thereof, expressed in weight percentage referred to the
metal.
Additionally, the electrode provided with the Nb-based topcoating according to
the
invention may also represent an improved alternative with respect to the
electrodes
provided with Nb-based topcoating layers obtained by the preparation methods
described in the art. Such methods teach, for example, the use of alkoxydes or
chlorides of the valve metal as precursors, dissolved in an alcohol solvent,
with or
without the presence of an acid. While these known methods yield suitable
results when
the valve metal is tantalum, they are less satisfactory when the valve metal
is niobium.
In general, niobium chlorides hydrolyse in the presence of moisture, even when
water is
present just in traces. As a result, the chloride precipitates as niobium
oxide thereby
hindering the coating application and causing stability issues of the coating
solution.
The inventor found, as expected, that the tendency of these niobium precursors
to
hydrolyse adversely affects the performance of the resulting topcoating.
Indeed, the Nb-
based topcoating layers obtained starting from NbCI5 in hydrochloric acid or
in alcoholic
solutions (such as butanol, isopropanol and ethanol), were found not to
deliver a
suitable and reproducible electrode.
In particular, the high evaporation rates of the alcohols strongly affect the
stability of the
resulting solution, as can be observed in particular for ethanol and
isopropanol.
Additionally, since the topcoating layers are thermally treated at
temperatures well
above 100 C, it is generally desirable to waive the use of inflammable
solutions, such
as alcohols, in the electrode preparation process.
The Nb-based topcoating layers obtained starting from Nb alkoxides yielded to
extremely porous electrodes with a very poor barrier effect towards additive
consumption.
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Among all the solutions listed above, only NbCI5 in butanol was found to
produce a
working electrode, however the latter underperformed in terms of additive
consumption
and lifetime with respect to both the Nb-based topcoats according to the
present
invention and the Ta-based topcoats known in the art.
5
The above may explain why, to the inventor's knowledge, electrodes for the
electroplating or electrodeposition of metals provided with a Nb-based
topcoating are
not commercially available and are not usually employed in the envisaged
applications.
In general, the electrode according to the invention is particularly useful as
a
dimensionally stable anode, in particular when used in the electrodeposition
of copper
foil from a sulfate electrolyte, for example in the production of printed
circuit boards.
The electrode according to the invention may also be advantageously used for
electrochemical processes where it is desirable to reduce the oxidation of
oxidizable
species in solutions, for instance to inhibit the production of chlorine
and/or hypochlorite,
in systems with low levels of chloride.
The electrode according to the invention may be used, for instance, in an
undivided
electrolytic cell where the opposite electrodes are separated by a physical
gap
containing the electrolyte. The cell may include a bag of insulating material,
such as a
plastic material like polypropylene, surrounding the anode.
In the electroplating and electrodeposition of metals of interest, the
electrolyte will
typically be a water-based solution where the metal to be plated/deposited is
dissolved.
The electrolyte will typically contain additives such as brighteners,
levelers, surfactants
and suppressors. The additives may include disulfide compounds such as
bis(sodiumsulfopropyl)disulfide (SPS), polyethylene glycols or amines.
The conductive substrate of the electrode may be a valve metal, for example
titanium,
tantalum, zirconium, niobium, and tungsten. Alternatively, tin or nickel may
be used. The
suitable metals of the conductive substrate can include, besides the
aforementioned
elemental metals themselves, their alloys and intermetallic mixtures. A
preferred
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material for the conductive substrate is titanium because of its sturdiness,
corrosion-
resistance properties and general availability.
The conductive substrate may be in any form suitable to perform its purpose;
in
particular, it may be in form of a plate, mesh, sheet, blade, tube or wire.
As customary in the field, before application of any of the coating layer over
the
substrate, the latter is preventively cleaned and optionally treated for
enhanced
adhesion by any conventional technique known in the art, such as intergranular
etching,
__ blasting or plasma spraying, followed by surface treatment to clean the
substrate and
remove any residues attached thereto.
The substrate surface may be optionally subject to other preparation steps,
such as
pretreatment before application of the coating layers. For example, the
surface may be
subjected to a hydriding or nitriding, or it may be provided with an oxide
layer by heating
the substrate in air or by anodic oxidation.
The electrode according to the invention is activated with an
electrochemically active
coating comprising at least one electrochemically active coating layer having
a
composition different than the composition of the topcoating layers.
The electrochemically active coating is placed between the topcoating and the
conductive substrate. The topcoating likely hinders the larger additive
molecules in the
electrolyte from reaching the electrochemically active coating and oxidizing
thereon,
while still ensuring adequate access of other components of the electrolyte to
the
underlying electrochemically active coating.
The electrochemically active coating layer composition may be a mixture of
valve
metals, such as magnesium, thorium, cadmium, tungsten, tin, iron, silver,
silicon,
tantalum, titanium, aluminium, zirconium and niobium, and platinum group
metals, such
as iridium, osmium, palladium, platinum, rhodium, ruthenium.
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A mixture of iridium and tantalum has been found to work very well in the
execution of
the invention; preferably said mixture contains 50-80% iridium and 20-50%
tantalum
expressed in weight percentage referred to the elements.
The electrochemically active coating layer may be applied directly on the
conductive
substrate or over an optional underlayer, which may promote adhesion of the
electrochemically active coating layer to the electrode substrate and/or
prevent
pass ivation of the conductive substrate.
It is understood that the underlayer will have a composition different from
the
composition of the electrochemically active coating.
The underlayer may comprise a mixture of valve metal oxides, such as a mixture
of
tantalum and titanium oxides. The latter has been found to work well in the
execution of
the invention. In particular, a composition of 10-40% Ta and 60-90% Ti has
been
observed to provide very good adhesion of the electrochemically active coating
layer to
the electrode substrate and to prevent passivation.
Each electrochemically active coating layer, and each optional underlayer, may
be
formed according to the methods known in the art.
Preferably, the electrochemically active coating is formed by thermal
decomposition of
precursors. Preferably, the precursors are decomposed at a temperature of 400-
600 C.
Optionally, the thermally decomposed coating may be further baked at a
temperature of
430 - 600 C after the application of the last layer.
The Nb-based topcoat according to the invention is applied in at least one
layer over the
electrochemically active coating; each topcoating layer is dried according to
standard
procedures known in the art and is then thermally decomposed.
The skilled person will apply as many topcoating layers as required to achieve
the
desired loading. The inventor has found that in general, a total amount of Nb
in the
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topcoating between 2-18 g/m2 gives good results. In order to reduce the number
of
cycles, a reduced loading of 2-12 g/m2, preferably 7-10 g/m2, may be used.
A higher loading, for instance between 12-18 g/m2 may provide further improved
additive consumption.
Such loadings may be achieved in a number of layers, i.e. preparation cycles,
that will
depend on the pick up of each topcoating layer. A number of 3-20 cycles, and a
pick-up
of 0.5-2 gNb/m2 per layer, has been found to work well in the execution of the
invention.
It is to be understood that any of the coating layers utilized in the
electrode according to
the invention may be applied by any of those means known in the art to be
suitable for
the application of a liquid composition to an electrode substrate, such as
application by
brush or roller coater, dip spin and dip drain methods, spraying, electro-
spraying or any
combination of the afore mentioned techniques.
In general, the capacity of an electrode to minimize additive consumption
depends,
among other parameters, on the thickness of the topcoating, which in turn, for
a given
metal pick-up per layer, may be linked to the number of preparation cycles.
The inventor
observed that the Nb-based topcoating of the electrode according to the
invention may
reach the same thickness of Ta-based topcoats with half the number of
topcoating
layers, when using the same pick-up per layer.. While topcoating thickness is
not the
only parameter affecting the capacity of the coating to prevent additive
consumption, it
is noted that it contributes to such effect by introducing a physical
separation between
the electrode active layer and the organic constituents in the electrolyte.
The inventor observed that the barrier effect of the Nb-based topcoat
according to the
invention, per g/m2 of total metal loading of the topcoat, is improved of more
than 51%
with respect to the barrier effect of the same electrode without topcoat.
The improvement in barrier effect was measured via cyclic voltammogram,
determining
the effect of the topcoating on the oxidation of ferrous ions in an
electrolytic cell
according to the procedure set out in COMPARISON TEST 3.
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In general, the characteristic cyclic voltammogram peak of the
electrochemically and
chemically reversible reaction Fe(II)-> Fe(III) + e- changes according to the
type of
topcoating applied, as a function of its thickness and porosity.
At fixed experimental conditions (such as temperature, redox reaction, scan
rate, redox
probe of the referenced experiment), the peak height of the cyclic
voltammogram of the
electrode will result proportional to the number of iron (II) ions able to
penetrate the
"barrier" provided by the topcoating and to get oxidized at the active layer
of the
electrode.
The higher the peak height, the lower the barrier effect of the topcoating to
iron (II) ions
consumption, and therefore the lower the barrier effect of the topcoating to
brightener
consumption, though the latter will also be partly affected by other
parameters, such as
the specific brightener molecules used.
The inventors have quantitatively calculated the improvement in barrier effect
provided
by the topcoating by dividing the peak height of the cyclic voltammogram of
the
electrode without the topcoating by the peak height of the cyclic voltammogram
of the
same electrode with the topcoating. The result is then adjusted to the total
metal load in
g/m2 present in the topcoating.
Under one embodiment, the topcoating layer of the electrode according to the
invention
contains substantially 100% Nb or oxides thereof.
With the expression "substantially 100% Nb or oxides thereof" it is meant a
topcoating
layer consisting of niobium, save for possible traces of the elements that
diffuse from
the coating underneath or traces of impurities in the precursor solution.
The topcoating of the electrode according to the present embodiment is such as
may be
obtained via thermal decomposition of the niobium precursor solution according
to the
invention, i.e. an aqueous solution of niobium oxalate in acetic acid, where
the acetic
acid may be diluted in deionised water.
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The electrode according to this embodiment has been found to exhibit an
improved
barrier effect to additive consumption with respect to electrodes provided
with Ta-based
topcoating with same number of layers and same loading.
5 Additionally, the electrode according to this embodiment has been found
to exhibit a
strongly improved barrier effect with respect to electrodes provided with Nb-
based
topcoating layers prepared according to the methods described in the art.
In particular, in connection with the present embodiment, the inventors
observed that
10 the barrier effect of the Nb topcoating, per gNb/m2, is improved above
85%, and even
above 100%, with respect to the barrier effect of the electrochemically active
coating
alone, as measured according to the procedure set out in COMPARISON TEST 3.
Under an alternative embodiment, the Nb-based topcoating layer is provided
with at
least one doping agent suitable to be incorporated as doping agent precursors
into the
precursor solution of the first composition, such as antimony, indium,
molybdenum,
tungsten, bismuth or tantalum. Such doping agents may typically be present in
an
amount from about 0.01`)/0 to about 10%, by weight in the topcoating layer,
preferably in
an amount from about 0.01% to about 5%. The doping agent may be in the form of
the
metal or its oxides, including suboxides.
The present invention also relates to an electrode suitable for the
electroplating or
electrodepositing of a metal from an electrolyte solution in an electrolytic
cell comprising
a conductive substrate, a topcoating comprising at least one topcoating layer
of a first
composition containing 90-100% niobium or oxides thereof and at least one
electrochemically active coating layer of a second composition different from
the first
one, wherein the adjusted barrier effect of the topcoating is 51-200% the
barrier effect of
the underlying electrochemically active coating, as measured by means of
cyclic
voltammetry in the presence of the redox probe Fe(II)IFe(III). The measurement
of the
.. adjusted barrier effect shall be carried out as described in COMPARISON
TEST 3, by
dividing the peak height of the cyclic voltammogram of the electrode without
topcoating
with the peak height of the electrode with the Nb-based topcoating, and
adjusted for the
total metal loading of the topcoating (in g/m2).
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The Nb-based topcoating according to the present embodiment can be obtained
via
thermal decomposition of a precursor solution comprising a Nb precursor
solution of
aqueous niobium oxalate in acetic acid. Said precursor solution corresponds to
the
precursor solution described in the present document, alone or in connection
with all
preferred or alternative embodiments concerning the invention.
Nb-based topcoatings prepared with the Nb precursors solutions described in
the art
exhibit, at best, an adjusted barrier effect which does not reach an
improvement of 51`)/0
with respect of the uncoated electrode.
According to a preferred embodiment of the above electrode, the first
composition of the
electrode above contains substantially 100% Nb or oxides thereof and the
improvement
in barrier effect of the electrode with said topcoating is 85-200% times the
barrier effect
of the electrode without topcoating, and may reach 100-200%, measured per
total
gNb/m2.
Under a further aspect, the invention relates to a method for manufacturing
the
electrode hereinbefore described. The method comprises coating a conductive
substrate with an electrochemically active coating comprising at least one
layer, and
subsequently forming a topcoating over the electrochemically active coating.
The
topcoating comprises at least one topcoating layer containing 90-100% niobium
or
oxides thereof. Each topcoating layer is formed by performing the following
sequential
steps:
(i) applying over the activated conductive substrate a precursor solution
comprising
a Nb precursor solution;
(ii) drying the precursor solution at a temperature of 50-100 C for 5-20
minutes,
preferably at a temperature of 50-70 C for 7-15 minutes;
(iii) thermally decomposing the dried precursor solution at a temperature
of 320-
600 C for 5-20 minutes.
Preferably, the above thermal decomposition step is carried out at 350-550 C
for 5-20
minutes, even more preferably at a temperature of 470-550 C for 7-15 minutes.
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Steps (i)-(iii) may be repeated as many times as necessary to achieve the
desired metal
loading, in cyclic fashion.
The skilled person understands that after each cycle, at the end of the
thermal
decomposition step (iii) of the precursor solution, the electrode will be
allowed to cool
until reaching room temperature before proceeding with the subsequent cycle.
A number of cycles between 3-20 has been found to yield a topcoating thickness
that
provides a suitable barrier effect. In some embodiments, a number of cycles
between 4-
16 has been found to work without detriment to the increase in overpotential,
thus
maintaining a relatively low number of thermal cycles with consequent cost
savings.
The above mentioned Nb precursor solution is obtained by mixing an aqueous
solution
of niobium oxalate in diluted acetic acid.
The concentration of Nb in the Nb precursor solution may be chosen between 20-
50 g/I.
This range has been observed to ensure a particularly compact topcoating layer
structure, which is beneficial for reducing additive consumption.
By diluted acetic acid it is meant CH3000H diluted in water, preferably
deionised water,
preferably at a concentration of 5-20%, even more preferably at a
concentration of 7-
13% to provide particularly good wettability.
According to the claimed method, the formation of at least one topcoating
layer occurs
over an activated substrate, i.e. a substrate provided with at least one
electrochemically
active coating layer. The latter may be formed directly over the clean or
pretreated
substrate, or above at least one optional underlayer coated over the
substrate.
The electrochemically active coating layer, the optional underlayer and the
electrode
substrate may be according to any of the embodiments hereinbefore described.
According to one embodiment, the precursor solution consists of a Nb precursor
solution. The resulting electrode will be therefore provided with a topcoating
containing
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substantially 100% Nb or oxides thereof, save for traces of the elements of
the
electrochemically active coating that may partly diffuse into the topcoating,
or traces of
other metals in the Nb precursor solution.
According to an alternative embodiment, the precursor solution contains a Nb
precursor
solution and a doping agent precursor solution, where the doping agent is
chosen from
the group consisting of antimony, indium, molybdenum, tungsten, bismuth,
tantalum and
the weight ratio of Nb versus the doping agent in said precursor solution is
90-
99,999:10-0,001; preferably 95-99,999:5-0,001.
Under a different aspect, the present invention relates to an unseparated
electrolytic cell
for the electroplating or electrodepositing of a metal from an electrolyte
solution
comprising at least one anode and at least one cathode partly or completely
immersed
in the electrolyte solution. The electrolyte solution contains the metal to be
deposited/plated in solution and at least one organic substituent.
The anode used in the cell is the electrode herein before described.
The cell may be used in printed circuit board applications.
For example, the cell according to the invention may be used in the
electrodeposition of
copper foil from an aqueous electrolyte containing copper sulfate.
The organic substituent may be an organic additive.
Under a different aspect, the present invention relates to a process for the
electroplating
or electrodeposition of a metal from an electrolyte solution, wherein the
process is
carried out in any electrolytic cell as hereinbefore described and at least
one anode in
said cell is operated so that the consumption of the organic substituent
present in the
electrolyte is reduced without detriment to the anode potential in the cell.
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The following examples are included to demonstrate particular ways of reducing
the
invention to practice, whose practicability has been largely verified in the
claimed range
of values.
It should be appreciated by those of skill in the art that the equipment,
compositions and
techniques disclosed in the following represent equipment, compositions and
techniques discovered by the inventor to function well in the practice of the
invention;
however, those of skill in the art should, in light of the present disclosure,
appreciate
that many changes can be made in the specific embodiments which are disclosed
and
still obtain a like or similar result without departing from the scope of the
invention.
EXPERIMENT PREPARATION
In all the electrode samples used in the following EXAMPLES, COUNTEREXAMPLES
.. and COMPARISON TESTS, the electrode substrate was manufactured starting
from a
titanium grade 1 mesh of 100 mm x 100 mm x 1 mm size, degreased with acetone
in an
ultrasonic bath for 10 minutes. The mesh was then subjected to steel grit
sandblasting,
and was subsequently etched in HCI 20% weight at boiling point.
EXAMPLE 1
A clean electrode substrate sample was coated with an electrochemically active
coating
solution containing a mixture based on oxides of iridium and tantalum at a
65:35 weight
ratio.
The electrochemically active coating precursor solution was applied in 10
layers, with a
total loading of 15 g/m2 of iridium.
Each electrochemically active coating layer was applied by brush and dried at
a
temperature of 50 C for 10 minutes. Each electrochemically active coating
layer was
then thermally decomposed at a temperature of 510 C for 15 minutes and finally
was
allowed to cool down to room temperature before proceeding with the next
layer.
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The activated electrode was then coated with a topcoating solution of Nb
precurors.
The Nb precursor solution consisted of an aqueous solution of niobium oxalate
at 45 g/I
in 13% aqueous CH3000H.
5
The topcoating was applied in 9 layers, with a total loading of Nb of 9 g/m2.
Each topcoating layer was applied by brush and dried at a temperature of 55 C
for 10
minutes. Each topcoating layer was then thermally decomposed at a temperature
of
10 500 C for 10 minutes and allowed to cool down to room temperature before
proceeding
with the next layer.
The electrode thus obtained was labelled Si.
15 COUNTEREXAMPLE 1
A sample electrode was prepared according to the procedure outlined in Example
1,
except that the Nb precursor solution consisted of NbCI5 dissolved in butanol,
the
concentration of niobium in the Nb precursor solution being 45 g/I.
The electrode thus obtained was labelled CS1.
COUNTEREXAMPLE 2
A clean electrode substrate sample was coated with the electrochemically
active
coating described in Example 1, according to the procedure described therein.
The activated electrode was then coated with a topcoating solution of Ta
precursor.
The Ta precursor solution consisted of an aqueous solution of TaCI5 at 45
gTa/I in
butanol.
The topcoating solution was applied in 9 layers, with a total loading of Ta of
9 g/m2.
Each topcoating layer was applied by brush and dried at a temperature of 55 C
for 10
minutes. Each topcoating layer was then thermally decomposed at a temperature
of
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500 C for 10 minutes and allowed to cool down to room temperature before
proceeding
with the next layer.
The electrode thus obtained was labelled CS2.
COUNTEREXAMPLE 3
A clean electrode substrate sample was coated with an electrochemically active
coating
as described in Example 1.
The activated electrode was then coated with a topcoating solution of Ta
precursor as
described in COUNTEREXAMPLE 2 with the exception that the topcoating solution
was
applied in 18 layers, with a total loading of Ta of 18 g/m2.
The electrode thus obtained was labelled CS3.
Samples 51, CS1, 0S3 showed an average topcoating thickness of 4 micrometers,
as
measured with SEM cross section imaging. Sample 0S2 showed an average
thickness
of 2 micrometers.
COMPARISON TEST 1
All samples were measured for brightener consumption by running a dummy copper
plating in Haring cell for 190 minutes at 25 ASF (Ampere per Square Foot).
For the anode, samples 51, CS1, CS2, CS3 were alternatively used inside a
polypropylene bag.
The cathode was a brass plate.
The electrolyte contained water, sulphuric acid, formaldehyde, organic salt
and copper
sulphate. The organic salt, i.e. the brightener, was 3,3'-
dithiobis[propansulfonate] of
disodium.
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The brightener consumption was measured by cyclic voltammetry stripping by
determining the charge required to consume 1 I of brightener. The results are
reported
in Ah/1 in Table 1.
COMPARISON TEST 2
All samples underwent a lifetime test in a beaker in H2504 150 g/I at 1 kA/m2,
and were
monitored every 1000 hours.
The deactivation times of each sample, corresponding to the time (in hours)
required to
measure a sudden increase of cell voltage above 6V, are listed in TABLE 1.
COMPARISON TEST 3
The barrier effect of samples 51, C51, C52, C53 was measured by means of
cyclic
voltammetry in the presence of the redox probe Fe(11)1Fe(111).
A solution of 50 ml of Fe(II) was prepared with 20 g/I of Fe(II) from ferrous
sulphate in
H2504 150 g/I.
The experiment was carried out in a three-electrode cell at room temperature
(25 C) at
a scan rate of 20 mV/s.
The counterelectrode was a dimensionally stable titanium anode of 3 cm2 active
area
and coated with the 65% iridium and 35% tantalum electrochemically active
coating
prepared as described in Example 1 and with no topcoating.
The reference electrode was a saturated calomel electrode.
For each tested sample 51, C51, C52, C53, a baseline electrode referenced as
BL was
prepared according to the procedure set out in EXAMPLE 1, with the exception
that no
topcoating layer was applied over the electrochemically active coating.
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Samples 51, C51, 052, 053, and the baseline BL were cut to a 10 mm x 30 mm
size
and covered with Teflon tape so as to leave an active area of 10 x 10 mm2.
The experiment consisted of five tests, where the working electrode was
alternatively
selected from samples 51, C51, 052, 0S3 and the baseline BL.
The peak height of the cyclic voltammogram was measured for all samples and
BL.
The improvement in the topcoating barrier effect (TO BE) of each sample 51,
C51,
052, 053, was calculated as the ratio between the peak height of the
corresponding
baseline BL electrode and the peak height measured for the sample, i.e.:
TO BE (sample) = peak height (BL)/ peak height (sample).
The improvement in the topcoating barrier effect of each sample was then
adjusted for
the total metal loading of the topcoating, as obtained by dividing the TO BE
(sample) by
the amount of metal in the topcoating, measured in g/m2, and expressing the
number in
percentage (per g/m2).
The results of the measurements are listed in TABLE 1.
Sample Brightener Deactivation TO BE Adjusted
consumption time TO BE
(Ah/l) (h) (per g/m2)
51 26700 3761 9.47 105.2%
CS1 14100 3420 4.50 50.0%
0S2 24190 3548 7.52 83.6%
0S3 26000 3003 8.20 45.6%
TABLE 1
The previous description shall not be intended as limiting the invention,
which may be
used according to different embodiments without departing from the scopes
thereof, and
whose extent is solely defined by the appended claims.
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Throughout the description and claims of the present application, the term
"comprise"
and variations thereof such as "comprising" and "comprises" are not intended
to
exclude the presence of other elements, components or additional process
steps.
The discussion of documents, acts, materials, devices, articles and the like
is included
in this specification solely for the purpose of providing a context for the
present
invention. It is not suggested or represented that any or all of these matters
formed part
of the prior art base or were common general knowledge in the field relevant
to the
present invention before the priority date of each claim of this application.
