A METHOD OF FABRICATING A BATH OF ELECTROLYTE FOR PLATING
A PLATINUM-BASED METALLIC UNDERLAYER ON A METALLIC
SUBSTRATE
The invention relates to a method of fabricating a
5 bath of electrolyte for plating a platinum-based metallic
underlayer on a metallic substrate.
Such metallic underlayers are used in particular for
coating a substrate made of a metal part that needs to
withstand high levels of mechanical and thermal stress in
10 operation, and in particular a substrate made of
superalloy. Such a thermomechanical part may in
particular constitute a part for an aviation or
terrestrial turbine engine. By way of example, said part
may constitute a blade or a vane of the turbine in the
15 turbine engine, and in particular in a high pressure
turbine of an airplane turboprop or turbojet.
The search for increased efficiency from turbine
engines, in particular in the field of aviation, and also
for reducing fuel consumption and polluting emissions of
20 gas and unburnt fuel have led to fuel combustion being
performed closer to stoichiometric conditions. That
situation is accompanied by an increase in the
temperature of the gas leaving the combustion chamber and
going to the turbine.
2 5 At present, the limiting temperature for usc: of
superalloys is about 110O0~,wh ile the temperature of the
gas at the outlet from the combustion chamber or at the
inlet of the turbine may be as high as 1600°C.
Consequently, it has been necessary to adapt the
30 materials of the turbine to this increase in -temperature,
by improving techniques for cooling turbine blades and
vanes (hollow blades and vanes) and/or by improving the
properties of those materials for withstanding high
temperatures. This second technique, used in combination
35 with superalloys based on nickel and/or cobalt, has led
to several solutions, including solutions involving
depositing a thermally insulating coating on the
superalloy substrate, which coating is known as a
"thermal barrier" and is made up of a plurality of
layers
The use of thermal barriers in aeroengines has
5 become widespread over the last thirty years, and it
enables the temperature of the gas at the inlet to the
turbines to be increased, the stream of cooling air to be
reduced, and thus the efficiency of engines to be
improved.
10 Specifically, the insulating coating serves to
establish a temperature gradient through the coating on a
cooled part under steady operating conditions that has a
total amplitude that may exceed 100"~fo r a coating
having a thickness of about 150 micrometers (pm) to
15 200 pm and that presents conductivity of 1.1 watts per
meter per kelvin ( W m - K . The operating temperature of
the underlying metal forming the substrate for the
coating is thus decreased by the same gradient, thereby
giving rise to considerable savings in the volume of
20 cooling air that is needed and to considerable increases
both in the lifetime of the part and also in the specific
consumption of the turbine engine.
It is known to have recourse to using a thermal
barrier comprising a layer of ceramic based on zirconia
25 stabilized with yttrium oxide, i.e. yttrium-stabjiized
zirconia having a molar content of yttrium oxide lying in
the range 4% to 12% (and in particular in the range 6% to
8 % ) , and that presents a coefficient of expansion that is
different from that of the superalloy constituting the
30 substrate, with thermal conductivity that is quite low.
Among the coatings used, mention may be made of the
fairly widespread use of a layer of ceramic based on
zirconia that is partially stabilized with yttrium oxide,
e.g. zr0.92y0.0S301.96~
3 5 In order to anchor this ceramic layer, a metal
underlayer having a coefficient of expansion that ideally
is close to that of the substrate is generally interposed
between the substrate of the part and the ceramic layer.
-In this way, the metal underlayer ser-ves firstly to
reduce the stress due to the difference between the
coefficients of thermal expansion of the ceramic layer
5 and of the substrate-forming superalloy.
The underlayer also provides adhesion between the
substrate of the part and the ceramic layer, it being
understood that adhesion between the underlayer and the
substrate of the part takes place by interdiffusion, and
10 adhesion between the underlayer and the ceramic layer
takes place by mechanical anchoring and by the propensity
of the underlayer to develop a thin oxide layer at high
temperature at the ceramic/underlayer interface, which
oxide layer provides chemical contact with the ceramic.
15 In addition, the metallic underlayer provides the
superalloy of the part with protection against corrosion
and oxidation phenomena (the ceramic layer is permeable
to oxygen).
Specifically, it is known to use an underlayer
20 constituted by nickel aluminide including a metal
selected from platinum, chromium, palladium, ruthenium,
iridium, osmium, rhodium, or a mixture of those metals,
and/or a reactive element selected from zirconium (Zr),
cerium (Ce) , lanthanum (La), titanium (Ti), tantalum
25 (Ta), hafniun~ (Hf), silicon (Si), and yttrium (Y) .
By way of example, a coating of the (Ni,Pt)Al type
is used in which platinum is inser-ted in the nickel
lattice of P-NiA1 metallic compounds.
When preparing thermal barriers, platinum performs
30 two functions: it acts as a diffusion barrier to prevent
interdiffusion of aluminum from the layer to the
substrate. Furthermore, platinum aluminide increases the
resistance to corrosion at high temperature and the
adhesion of protective layers. However, platinum
35 aluminide coatings degrade quickly at 1100°C: there exist
phase transformations associated with interdiffusion of
the elements of the coating and of the substrate.
Under such circumstances, the metallic underlayer
may be constituted by a platinum-modified nickel
aluminide NiPtAl using a method that comprises the
following steps: preparing the surface of the part by
5 chemical cleaning and sand-blasting; electrolytically
plating a coating of platinum (Pt) on the part;
optionally heat-treating the result in order to cause Pt
to diffuse into the part; using chemical vapor deposition
(CVD) or physical vapor deposition (PVD) to deposit
10 aluminum (Al); optionally heat-treating the result to
cause Pt and A1 to diffuse into the part; preparing the
surface of the metallic underlayer as formed in -this way;
and using electron beam physical vapor deposition
(EB-PVD) to deposit a ceramic coating.
15 Platinum is thus deposited electrolytically before
the thermochemical treatment of vapor phase
aluminization.
It should be recalled that electroplating serves to
reduce onto a conductive part (the cathode) a metallic
20 complex initially present in the solu-tion by causing an
electric current to flow from an anode (an electrode
where an oxidation reaction takes place) to a cathode
onto which deposition (plating) takes place (and at which
other reduction reactions may take place simultaneously).
2 5 Solutioris of various compositions are comniercially
available for platinum plating. The pH of such solutions
may be basic, acidic, or neutral.
The compounds obtained at the end of platinum
extraction are ammonium hexachloroplatinate (IV):
30 (NH,) 2PtC1, or potassium hexachloroplatinate (IV) : K,PtCl,.
The main compounds of platinum presen-t in platinum
plating baths are derived from transforming those
compounds.
Ignoring degree of oxidation 0 which corresponds to
35 the metal, there are two other degrees of oxidation: -1-11
and +IV, which correspond to complex species. Depending
on the nature of the ligands in solution suitable for
forming complexes with the metallic cations in solution,
the stability and the rea~tivity of the complex will
vary.
Numerous formulations of electrolyte baths for
5 platinum plating have already been proposed, and they
comprise various chemical species in aqueous solution,
imparting its properties on the bath.
Nevertheless, numerous drawbacks persist. In
particular, the baths of electrolyte that have been
10 proposed are of significant cost, in particular because
of the cost of the chemicals used to regenerate them.
Furthermore, the possibility of regeneration is limited
and leads to the bath having a lifetime that is short,
since it presents technical characteristics that are not
15 stable and that degrade with aging of the bath.
An object of the present invention is to provide an
electrolyte bath for plating platinum on a metal
substrate, which electrolyte bath presents improved
technical performance, in particular plating parameters
20 and conditions that are identical or practically
identical regardless of the shape of the part, a
deposition rate that is identical or practically
identical regardless of the applied current density,
deposition quality that complies with specifications, and
25 an improved lifetime.
To this end, according to the present invention, the
method of fabricating a bath of electrolyte is
characterized in that it comprises the following steps:
a) providing a first system having ligands and amine
30 functional groups, said first system being constituted by
an aqueous solution of an amino ligand comprising at
least one compound X-(NH,),, where X belongs to the group
constituted by (CH,, CH,-CM,, CH,- (CH,),), or NH, or an
xp-(NH,)+, salt where -x is an acid radical belonging to the
35 group constituted by (PO,,-, HPO,,-, H,PO,-, HPO,,- and H,PO,-,
SO,,-, HS04-, HS04-, and H,SO,, CH,COO-, CH,COOH, and
CH,COO-), or H,SO,, or CH,COOH, and where -n, -m, and -p are
non-zero integers; -
b) providing a second system forming a buffer
system;
5 C) providing a third system providing a metallic
salt, and constituted by an aqueous solution of platinum;
d) providing a fourth system suitable for imparting
the property of conduction to the medium; and
el mixing together the four systems so as to obtain
10 the said electrolyte bath.
In this way, it can be understood that preference is
given to using a complex that results from bonding
between an amino ligand and a platinum-based metallic
salt. In particular, a ligand is chosen without a carbon
15 chain and with only one arnine function: NH, (ammonia) or
an xNHqt salt or an ammonium X-NH,) where X is selected
either as an inert molecule that is not involved in the
main reaction, or else as a molecule that interacts in
the formulation reaction.
2 0 Preferably, the metallic salt of the third system is
selected from salts of platinum of degree of oxidation
IV.
This solution also presents the additional advantage
of making it possible to use salts of platinum of degree
25 of oxidation IV, which are much more stable than salts of
platinum of degree of oxidation 11.
Overall, by means of the solution of the present
invention, it is possible to provide an electrolyte bath
that presents improved lifetime, with plating properties
30 that remain satisfactory and stable over time.
Also according to the invention, the first system,
the second system, and the fourth system are grouped
together in a single solution forming a first solution B.
Advantageously, the first solution B includes an
35 xp-(NH,)', salt, where x=HPOq2- and p=2, and/or x=H2P0,- and
p=l.
Preferably, the first system forms a solution A
constituted by-an aqueous solution of platinum, inchding
sodium hydroxide (NaOH) and at least one salt of platinum
of degree of oxidation IV.
5 Under such circumstances, and preferably, the molar
ratio of the quantity of sodium hydroxide (NaOH) to the
quantity of salt of platinum of degree of oxidation IV is
2.
Also according to the invention, during step c), the
10 third system forms a second solution A constituted by an
aqueous solution of platinum comprising sodium hydroxide
(NaOH) and at least one salt of platinum of degree of
oxidation IV, and during step e), the following substeps
are performed:
15 el) covering the first solution B and raising its
temperature to at least 50°C for at least lh30; and
e2) mixing the second solution A with the first
solution B to form an electrolyte bath including a
platinum amino complex.
2 0 In a preferred in~plementation, after step e), a step
f) is performed during which said bath of electrolyte is
heaked to a temperature lying in the range 80°C to 97'C
for at least two hours; and
then a step g) is performed during which a deposit
25 of platinum is electroplated on a metallic subsl.t:ate
using said bath of electrolyte.
Furthermore, in the invention, during substep e2),
the second solution A is added into the first solution B.
Under such circumstances, and advantageously, prior
30 to substep e2), the first solution B is raised to a
temperature of 60°C.
Preferably, said salt of pla-tinum of degree of
oxidation IV is defined by Y,PtM, with Y=NH,+, Ht, or K',
and M=Cl- or OH-.
35 Advantageously, in the second solution A, said salt
of platinum of degree of oxidation IV is diarnrnonium
hexachloroplatinate of formula (NH,) ,PtCl,.
Advantageously, in the first system, said xp-(NH,)',
amine compounci comprises diammonium hydrogen phosphate
(NH,) ,HPO, and/or ammonium dihydrogen phosphate NH,H,PO,.
In a preferred formulation, the first system
5 includes diammonium hydrogen phosphate (NH,) ,HPO, and
ammonium dihydrogen phosphate NH,H,PO, with a molar ratio
of 2 between the quantity of ammonium dihydrogen
phosphate NH,H,PO, and the quantity of diamrnonium hydrogen
phosphate (NH,) ,HPO,.
10 One or another or several of the following
provisions is/are also preferably adopted:
the first solution B provided in step a) is
obtained with water presenting a temperature of about
30°C;
15 the second solution A provided in step c) is
obtained with water presenting a temperature of about
45°C;
during step b), the temperature of the first
solution B is raised to at least 50'~ for at least 3h30;
20 and
during step d), said bath of electrolyte is raised
to a temperature of at least 80°C for at least three
hours (e.g. 85°C for 3 h).
The present invention also provides a method of
25 fabricating a platinum-based metal underlayer from the
bath of electrolyte obtained by the above-described
fabrication method, characterized in that it comprises
the following steps:
f) providing a metallic substrate, in particular a
30 substrate made of superalloy;
g) heating said bath of electrolyte; and
h) electroplating a deposit of platinum on said
metallic substrate using said ba-th of electrolyte.
The present invention also provides a set of
35 solutions for fabricating a bath of electrolyte for
making a platinum-based metallic underlayer on a metallic
substrate, the set being characterized in that it
comprises:
a first solution B constituted by an aqueous
solution of an amino ligand comprising at least one
5 compound X-(NH,),, where X belongs to the group
constituted by (CN,, CH3-CH,, CH3- (CH,),) , or NH, or an
xP-(NH,)+, salt where - x is an acid radical belonging to the
group constituted by (PO,,-, HPOg2-, H,PO,-, HPO,,- and H,P04-,
SO,,-, HS0,-, HS0,-, and H,SO,, CH,COO-, CH,COOH, and
10 CH,COO-), or H,SO,, or CH,COOH, and where - n, -m, and -p are
non-zero integers; and
- a second solution A constituted by an aqueous
solution of platinum, including sodium hydroxide (NaOH)
and at least one salt of platinum of degree of oxidation
15 IV.
Preferably, in the second solution A, said salt of
platinum of degree of oxidation IV is defined by Y,PtM,
with Y=NH,+, H+, or K+, and M=Cl- or OH-.
Advantageously, said salt of platinum of degree of
20 oxidation IV is diammonium hexachloroplatinate of formula
(NH,) ,PtCl,.
Preferably, the molar ratio of the quantity of
sodium hydroxide (NaOH) to the quantity of salt of
platinum of degree of oxidation IV is 2.
25 In a preferred implementation, in the first solution
B, said xP- (NH,) +, amine compound comprises diammonium
hydrogen phosphate (NH,),HPO, and/or ammonium dihydrogen
phosphate NH,H,PO,.
In a preferred variant, the first solution B
30 includes diammonium hydrogen phosphate (NH,) ,HP04 and
ammonium dihydrogen phosphate NH,H,P04 with a molar ratio
of 2 between the quantity of ammonium dihydrogen
phosphate NH,H,PO, and the quanti-ty of diammonium hydrogen
phosphate (NH,) ,HPO,.
35 Finally, the invention also provides the bath of
electrolyte that results from the fabrication method of
the invention. Such a ba-th of electrolyte for making a
platinum-based metallic underlayer on a superalloy
- substrate is characterized in thakit includes an amino
complex of platinum with the wavelength of a Pt-NH, or
Pt-NH, bond and a buffer solution.
5 Other advantages and characteristics of the
invention appear on reading the following description
made by way of example and with reference to the
accompanying drawings, in which:
Figures 1A to 11, 2A and 2B are various plots
10 showing the characteristics and the behavior of various,
electrolytic baths fabricated using the fabrication
method of the invention.
An electrolytic bath makes it possible to deposit
(i.e. electroplate) platinum using a technique that is
15 particularly ecological and economic (performed in a
short length of time, and performed under atmospheric
pressure, thereby avoiding evacuation equipment) compared
with techniques of chemical vapor deposition (CVD) or
thermal sputtering.
2 0 In addition, this plating method is compatible for
use with parts having holes: the shape of the lines of
current prevent any significant deposition taking place
inside the holes, and in particular inside cooling holes
of small size, which holes are thus not obstructed.
2 5 It should also be observed that using such method
avoids having recourse to dangerous chemicals and to
producing toxic waste.
Example 1
30 In this example, the bath is formulated from four
ingredients organized as two distinct solutions A and B
that are heated and stirred separately in order to cause
the ingredients to react within each of the solutions,
prior to mixing together the two solutions A and B.
35 Thereafter, the mixture of the two solutions A and B
is heated and stirred. Once the time for heating the AtB
mixture has elapsed, the platinum electroplating bath is
ready for use in performing electroplating.
In particular, solution A includes, amongst other
ingredients, the platinum salt(s) and solution B is the
5 solution that contains, amongst other ingredients, the
ligands (it should be recalled that a ligand is an ionic
or molecular chemical entity carrying chemical functions
that enable it to bond with one or more metallic
entities, generally a cation, with the association of a
10 metallic entity and one or more ligands forming a
structure that is soluble in solution and known as a
complex).
To fabricate one liter of electrolytic bath with
8 grams (g) of platinum per liter, the procedure is as
15 follows:
Preparing solution B: in 300 milliliters (mL) of
distilled water (<500 ohms ( a ) ) at 3O0C, place 44.0 g of
diammonium hydrogen phosphate having the chemical formula
(NH,) ,HPO, (i.e. 0.33 moles) and 75.0 g of ammonium
20 dihydrogen phosphate of chemical formula NM,H,PO, (i.e.
0.65 moles). The molar ratio between the quantity -d of
ammonium dihydrogen phosphate and the quantity of
diammonium hydrogen phosphate is 2. Once the salts have
dissolved, cover the solution and raise to 50°C during
25 4 hours (h) 30 minutes (min) .
Preparing solution A: in 300 mL of distilled water
at 45"C, place 5 g of sodium hydroxide of chemical NaOH
(i.e. 0.080 moles) and 18.3 g of the platinum salts
diammonium hexachloroplatinate of formula (NH,),PtCl,
30 (i.e. 0.040 moles). The molar ratio between the quantity
of sodium hydroxide and the quantity of diammonium
hexachloroplatinate salt is 2. Allow the platinum salts
to dissolve within solution A.
Once solution B is ready and hot, prepare solution
35 A and add it to solution B, after raising it to 60°C.
To finish, raise the A+B mixture (of pH previously
adjusted to 6.3 by adding a basic solution such as, for
example, sodium hydroxide, potassium hydroxide, sodium
triphosphate) to 8 5 " f~o r 3 h. All of the solutions
should be covered during the heatlng steps.
More generally, with this solution B including
5 diammonium hydrogen phosphate of chemical formula
(NH4),HP04 and ammonium dihydrogen phosphate of chemical
formula NH4H,P04, the pfI of the mixture of the solutions
A+B should be set to lie in the range 6 to 10, and
preferably in the range 6 to 7.
10 In the context of this formulation, and in order to
identify the best operating conditions for performing
platinum electroplating, an experimental design with nine
baths was performed using different temperatures and
times for heating solution B and then the A+B mixture, as
15 specified in Table 1 below, with test 2 corresponding to
the above-specified procedure:
Table 1
ppp
9 95C 8 h 85°C 1 h
2 0 For each formulated bath, test pieces were plated
with platinum at different currents. Each test piece was
weighed before and after plating.
On the basis of the increase in weight, it was thus
possible to determine:
deposition rate (in grams per hour per square
decimeter (g/h/dm2)) at each current;
the plateau of the bath;
the current at the beginning of the plateau;
the mean deposition rate of the plateau;
the standard deviation of the plateau; and
the ratio between the minimum and maximum rates
obtained over the plateau.
The three tables 2-1 to 2-3 below give the results
10 obtained with the three baths that were found to give the
best results at the end of the experiment.
Table 2-1
15 Table 2-2
I
Table 2-3
I I
I I bath after I plateau I of plateau I standard I ratio of 1
Plateau characteristics
Furthermore, the bath of test 2 provides the
following advantages:
5 This is the bath for which the greatest degree of
Color of Mean rate
Test 2
Test 4
Test 7
repeatability was observed, and which, compared with a
reference bath, the mean deposition rate was large for a
new bath (Figure lA), and remained sufficiently high
during operation (Figure 1A). The bath of test 2 is
10 repeatable since the curve for mean rate and for
dispersion of fabrications 1 and 2 are superposable,
which clearly demonstrates the extreme degree of
Start of
reproducibility of the fabrication. In contrast, it can
be seen that the fabrication curves 1 and 2 for the bath
15 of test 7 and even more for the bath of test 4 can be
distinguished, so the bath of test 4 is the least
electrolysis
Clear
Cloudy
Cloudy
repeatable, which is why bath 4 is not preferred.
Furtherrr~ore, the bath of test 2 presents gor~d
dispersion of the plateau (Figure lB), it being recalled
20 that the presence of a "plateau" corresponds to obtaining
a deposition rate that is identical regardless of the
applied current and regardless of the shape of the part
being treated. On each fabrication, two plateaus were
4A
4A
4A
implemented. One plateau was studying the gain in weight
25 as a function of the applied current density. In inhouse
fabrications, the dispersion decreases wi-th
increasing amount of electrolysis performed in the bath.
This is not true of the reference bath where the bath
(g/h/dm2)
2.0232
1.8264
1.7736
deviation
0.27
0.34
0.25
plateau
0.65
0.79
0.61
becomes increasingly dispersed with increasing number of
ele~~rolysepse rformed.
Likewise, it can be seen that the bath of test 2
presents little loss of platinum over time (Figure IC)
5 and that the mean effectiveness (Figure 2A) and the
deposition rate (Figure 2B) of the bath are practically
identical after three successive regenerations.
Concerning losses of platinum, we found numerous loses of
platinum with the reference bath, mainly in the form of a
10 solid precipitate of platinum on the bottom of the
vessel. Furthermore, with the reference bath, the
greater the number of electrolyses performed using the
bath, the greater its tendency to form precipitates on
the bottom of the vessel. In contrast, for baths of the
15 invention, it is observed that platinum losses are
smaller, and above all constant over time (constant with
increasing number of electrolyses). Furthermore, the
bath of test 2 is the bath that presented the smallest
loses of platinum and thus the bath of test 2 is the most
20 profitable from an economic point of view.
Overall, and as can be seen from the curves of
Figures 1D to 1F and 1G to 11, the baths of tests 4 and 7
give results that are very similar to those of test 2.
Furthermore, as can be seen from Figures 2A and 2B,
25 the electrolyte bath of test 2 gives results thal are
stable over time in terms of deposition rate, with this
continuing after the bath has been regenerated several
times: the deposition rate is practically unchanged
between the first and third regenerations.
30 In order to regenerate a bath, platinum salts are
added to the bath so as to raise its platinum content.
Once the platinum salts have been added, the bath is left
while being stirred at 65°C for 12 h to 24 h so that the
salts become fully dissolved in the bath.
35
Example 2
The fabrication of the bath of electrolyte is
analogous to that of the procedure of Example 1, apart
-from the following points.
Solution B comprises 43.5 g of ammonium hydrogen
sulfate of chemical formula NH,HSO, and 76 g of diammonium
5 sulfate of chemical formula (NH,),SO,, and water. It was
raised to 50°c for 4h30.
The pH of the mixture of solutions A+B was set in
the range 1 to 5.
10 Example 3
The fabrication of the bath of electrolyte is
analogous to that of the recipe of Example 1, apart from
the following points.
Solution B comprises 102.4 g of ammonium acetate of
15 chemical formula CH,COONH, and 39.6 g of acetic acid of
chemical formula CH,COOH.
The solution was raised to 50°C for 4h30.
The pH of the mixture of the solutions A+B was set
to lie in the range 1 to 5.
2 0 In the invention, the ligand is preferably selected
from aliphatic polyamines having 3 to 20 carbon atoms in
a straight or branched carbon chain.
Advantageously, the ligand is selected from primary
polyamines such as diaminopropanes such as
25 1,3-diaminopropane and 1,2-diaminopropane,
diethylenetriamine, 1,4-diaminobutane, 1,6-diaminohexane;
secondary polyamines such as N,N' dimethyl-1,3-propanediamine;
and tertiary polyamines such as N, N, N', N'
tetramethylethylenediamine. It is preferred to select
30 diaminopropanes for the ligands.
CLAIMS
1. A fabrication method for fabricating a bath of
electrolyte for plating a platinum-based metal underlayer
on a metal substrate, the method comprising the following
5 steps:
a) providing a first system having ligands and amine
functional groups, said first system being constituted by
an aqueous solution of an amino ligand comprising at
least one compound X-(NH,),, where X belongs to the group
10 constituted by (CH,, CH3-CH,, CH3-(CH,),), or NH, or an
xP-(NH,)+,salt where -x is an acid radical belonging to the
group constituteci by (POQ3-,H P0,2-, H,PO,-, HPO,'- and H,PO,-,
SO,,-, HSO,-, HS0,-, and H,SO,, CH,COO-, CH,COOH, and
CH3COO-), or H,SO,, or CH,COOH, and where -n, m-, and -p are
15 non-zero integers;
b) providing a second system forming a buffer
system;
C) providing a third system providing a metallic
salt, and constituted by an aqueous solution of platinum;
2 0 d) providing a fourth system suitable for imparting
the property of conduction to the medium; and
e) mixing together the four systems so as to obtain
the said electrolyte bath;
the method being characterized in that the first
25 system, the second system, and the fourth systerrl are
grouped together in a single solution forming a first
solution 8, in that during step c), the third system
forms a second solution A constituted by an aqueous
solution of platinum comprising sodium hydroxide (NaOH)
30 and at least one salt of platinum of degree of oxidation
IV, and in that during step e), the following substeps
are performed:
el) covering the first solution B and raising its
temperature to at least 50°C for at least lh30; and
3 5 e2) adding the second solution A to the first
solution B and mixing the second solution A with the
first solution B to form an electrolyte bath including a
platinum amino complex.
2. A method according to claim 1, characterized in that
5 the first solution B includes an xp-(NH,)+, salt, where
x=HPO,,- and p=2, and/or x=H,PO,- and p=l.
3. A method according to claim 1, characterized in that
the third system forms a second solution A constituted by
10 an aqueous solution of platinum, including sodium
hydroxide (NaOH) and at least one salt of platinum of
degree of oxidation IV.
4. A fabrication method according to claim 2,
15 characterized in that after step e), a step f) is
performed during which said bath of electrolyte is heated
to a temperature lying in the range 80°C to 97°C for at
least two hours; and
then a step g) is performed during which a deposit
20 of platinum is electroplated on a metallic substrate
using said bath of electrolyte.
5. A method according to the preceding claim,
characterized in that prior to substep e2), the first
25 solution B is raised to a temperature of 60°C.
6. A method according to claim 3, characterized in that
said salt of platinum of degree of oxidation IV is
defined by Y,PtM, with Y=NH,+, Hi, or K+, and M=Cl- or OH-.
3 0
7. A method according to the preceding claim,
characterized in that in the second solution A, said salt
of platinum of degree of oxidation IV is diammonium
hexachloroplatinate of formula (NH,) ,PtC16.
3 5
8. A method according to claim 4, characterized in that
the molar ratio of the quantity of sodium hydroxide
(NaOH) to the quantity of salt of platinum of degree of
oxidation IV is 2.-
9. A method according to any preceding clalm,
5 characterized in that the flrst system, said xp-(NH,)+,
amine compound comprises diammonium hydrogen phosphate
(NH,) ,HPO, and/or ammonlum dlhydrogen phosphate NH,H,PO,.
10. A method according to the preceding claim,
10 characterized in that the first system includes
diammonium hydrogen phosphate (NH,),HPO, and ammonium
dihydrogen phosphate NH,H,PO, with a molar ratio of 2
between the quantity of ammonium dihydrogen phosphate
NH,H,PO, and the quantity of diarnmonium hydrogen phosphate
15 (NH,) ,HPO, .