EP2839059B1 - Method of forming an electrolytic bath for making a platinum-based metallic underlayer on a metallic substrate - Google Patents

Description

The invention relates to a method of manufacturing an electrolytic bath for producing a platinum-based metal underlayer on a metal substrate.

Such metal sub-layers belong in particular to a coating on a substrate consisting of a metal part called to withstand high mechanical and thermal stresses in operation, in particular a superalloy substrate. Such a thermomechanical part constitutes in particular an aeronautical or terrestrial turbine engine part. Said part may for example be a blade or a turbomachine turbine distributor and in particular in a high-pressure turbojet or turboprop turboprop turbine.

The search for increasing the efficiency of turbomachines, in particular in the aeronautical field, and the reduction in fuel consumption and pollutant emissions of gases and unburnt have led to approaching the fuel combustion stoichiometry. This situation is accompanied by an increase in the temperature of the gases leaving the combustion chamber towards the turbine.

Today, the limit temperature of use of the superalloys is of the order of 1100 ° C, the temperature of the gases at the outlet of the combustion chamber or turbine inlet up to 1600 ° C.

As a result, the turbine materials had to be adapted to this temperature rise, by perfecting the cooling techniques of the turbine blades (hollow blades) and / or by improving the high temperature resistance properties of these materials. This second route, in combination with the use of superalloys based on nickel and / or cobalt, has led to several solutions among which the deposition of a thermal insulating coating, called a thermal barrier, composed of several layers, on the substrate in superalloy.

The use of thermal barriers in aircraft engines has become widespread over the last thirty years and makes it possible to increase the inlet temperature of the gases in the turbines, to reduce the cooling air flow and thus improve the efficiency of the engines.

Indeed, this insulating coating makes it possible to create on a cooled part, in steady state of operation, a thermal gradient across the coating, whose total amplitude can exceed 100 ° C for a coating of about 150 to 200 microns thick. having a conductivity of 1.1 Wm ^-1 .K ^-1 . The operating temperature of the underlying metal forming the substrate for the coating is reduced by the same gradient, which results in significant gains in the necessary cooling air volume, the service life of the part and the specific consumption of the material. turbine engine.

It is known to use the use of a thermal barrier comprising a yttria-stabilized zirconia-based ceramic layer, namely a yttria-containing zirconia comprising a molar content of yttrium oxide between 4 and 12% (especially between 6 and 8%), which has a coefficient of expansion different from the superalloy constituting the substrate and a relatively low thermal conductivity.

Among the coatings used, there will be mentioned the rather general use of a zirconia-based ceramic layer partially stabilized with yttrium oxide, for example Zr _0.92 Y _0.08 O _1.96 .

In order to ensure the anchoring of this ceramic layer, a metal underlayer, with a coefficient of expansion ideally close to the substrate, is generally interposed between the substrate of the part and the ceramic layer. In this way, the metal sub-layer firstly makes it possible to reduce the stresses due to the difference between the thermal expansion coefficients of the ceramic layer and the superalloy forming the substrate.

This underlayer also provides adhesion between the substrate of the part and the ceramic layer, knowing that the adhesion between the underlayer and the substrate of the part is by inter-diffusion, and that the adhesion between the underlayer and the ceramic layer is made by mechanical anchoring and by the propensity of the underlayer to be developed at high temperature, at the ceramic / underlayer interface, a thin oxide layer which ensures the chemical contact with ceramics.

In addition, this metal sub-layer ensures the protection of the superalloy of the part against corrosion and oxidation phenomena (the ceramic layer is permeable to oxygen).

In particular, it is known to use a sublayer consisting of a nickel aluminide comprising a metal selected from platinum, chromium, palladium, ruthenium, iridium, osmium, rhodium, or mixture of these metals and / or a reactive element selected from zirconium (Zr), cerium (Ce), lanthanum (La), titanium (Ti), tantalum (Ta), hafnium (Hf), silicon (Si) and yttrium (Y).

For example, a (Ni, Pt) Al type coating is used in which the platinum is inserted into the nickel network of the β-NiAl intermetallic compounds.

When developing thermal barriers, platinum has a dual role: it is a diffusion barrier to prevent the diffusion of aluminum from the layer to the substrate. In addition, platinum aluminide increases the corrosion resistance at high temperature and the adhesion of protective layers. In fact, platinum aluminide coatings rapidly degrade at 1100 ° C: there are phase transformations related to the inter-diffusion of the elements of the coating and the substrates.

In this case, this metal sub-layer may consist of a NiPtAl platinum-modified nickel aluminide, according to a process comprising the following steps: the preparation of the surface of the part by chemical etching and sanding; depositing on the part, by electrolysis, a platinum coating (Pt); the possible heat treatment of the assembly to diffuse Pt in the room; aluminum deposition (Al) by chemical vapor deposition (CVD) or physical vapor deposition (PVD); the possible heat treatment of the assembly to diffuse Pt and Al in the room; the preparation of the surface of the formed metallic underlayer; and electron beam evaporation (EB-PVD) deposition of a ceramic coating.

Thus, the platinum is deposited electrolytically before the thermochemical treatment of aluminization in the vapor phase.

As a reminder, electroplating reduces a complexed metal entity initially present in the solution by passing an electric current over a conductive part (the cathode). between an anode (electrode seat of an oxidation reaction) and a cathode on which deposition takes place (and on which other reduction reactions can take place simultaneously).

There are commercially available casting solutions of different compositions. The pH of these solutions can be basic, acidic or neutral.

The compounds obtained after the extraction of platinum are ammonium hexachloroplatinate (IV): (NH ₄ ) 2 PtCl ₆ or potassium hexachloroplatinate (IV): K ₂ PtCl ₆ . The main platinum compounds present in the casting baths are derived from the transformation of these compounds.

Apart from the degree of oxidation 0 corresponding to the metal, there are two other oxidation states: + II and + IV, corresponding to complex species. Depending on the nature of the ligands in solution capable of forming complexes with the metal cations in solution, the stability and reactivity of the complex will be different.

Many electroplating baths for depositing platinum have been proposed to date and include a number of chemical species in aqueous solution, giving the bath its properties. We can also, for example, quote documents GB 2 351 089 , EP 0 465 073 and US 4,427,502 which disclose electrolytic baths comprising platinum compounds.

However, many disadvantages persist. In particular, the electrolytic baths proposed have a significant cost, particularly because of the cost of the products used to regenerate them. In addition, this possibility of regeneration is limited and leads to a short life of the bath because it has unstable technical characteristics and which degrade with the aging of the bath.

The present invention aims to provide an electrolytic bath for the deposition of platinum on a metal substrate, which electrolytic bath has an improvement in technical performance, including identical or almost identical parameters and deposition conditions regardless of the geometry of the piece, an identical or almost identical deposition rate regardless of the current density applied, a deposition quality in accordance with the specifications, and an improved service life.

1. a) on fournit un premier système comportant des ligands et des groupements fonctionnels amines, ledit premier système étant constitué d'une solution aqueuse avec ligand aminé comprenant au moins un composé X-(NH₂)_n, avec X appartenant au groupe constitué de (CH₃, CH₃-CH₂, CH₃-(CH₂)_m), ou NH₃ ou un sel x^p-(NH₄)⁺p avec x un radical acide appartenant au groupe constitué de (PO₄ ^3-, HPO₄ ^2-, H₂PO₄ ^-, HPO₄ ^2- et H₂PO₄ ^-, SO₄ ^2-, HSO₄ ^- et CH₃COO^-), n, m et p étant des entiers non nuls,
2. b) on fournit un deuxième système formant un système tampon,
3. c) on fournit un troisième système fournissant un sel métallique, et constitué d'une solution aqueuse avec platine,
4. d) on fournit un quatrième système permettant d'apporter la propriété conductrice au milieu,
5. e) On mélange les quatre systèmes, ce par quoi on obtient le dit bain électrolytique.

For this purpose, according to the present invention, the method of manufacturing an electrolytic bath is characterized in that it comprises the following steps:

1. a) providing a first system comprising ligands and amine functional groups, said first system consisting of an aqueous solution with an amino ligand comprising at least one X- (NH ₂ ) _n compound, with X belonging to the group consisting of CH ₃ , CH ₃ -CH ₂ , CH ₃ - (CH ₂ ) _m ), or NH ₃ or a salt x ^p- (NH ₄ ) ⁺ p with x an acid radical belonging to the group consisting of (PO ₄ ^3- , HPO ₄ ^2- , H ₂ PO ₄ ^- , HPO ₄ ^2- and H ₂ PO ₄ ^- , SO ₄ ^2- , HSO ₄ ^- and CH ₃ COO ^- ), n, m and p being non-zero integers,
2. b) providing a second system forming a buffer system,
3. c) providing a third system providing a metal salt, and consisting of an aqueous solution with platinum,
4. d) providing a fourth system for bringing the conductive property to the medium,
5. e) The four systems are mixed, whereby the so-called electrolytic bath is obtained.

In this way, it is understood that the use of a complex resulting from the bond between an amino ligand and a platinum metal salt is preferred. In particular, we chose a ligand without carbon chain and a single amine function: NH ₃ (ammonia) or a salt xNH ₄ ⁺ or an X-NH ₂ ammonium) or X is chosen either as inert molecule, spectator of the main reaction is as an interacting molecule in formulation reactions.

The metal salt of the third system is chosen from platinum salts of oxidation state IV.

This solution also has the additional advantage of allowing, in addition, to use platinum salts of oxidation degree IV, much more stable than platinum salts of oxidation state II.

Overall, thanks to the solution according to the present invention, it is possible to provide an electrolytic bath having an improved lifetime for satisfactory and stable residence properties over time.

Also, according to the invention, the first system, the second system and the fourth system are grouped into a single solution forming a first solution B.

Advantageously, the first solution B comprises a salt x ^p- (NH ₄ ) ⁺ _p with x = HPO ₄ and p = 2 and / or x = H ₂ PO ₄ and p = 1.

Preferably, the third system forms a second solution A consisting of an aqueous solution with platinum, comprising sodium hydroxide (NaOH) and at least one platinum salt of degree of oxidation IV.

In this case, preferably, the molar ratio between the amount of sodium hydroxide NaOH and the amount of platinum salt of oxidation degree IV is 2.

• e1) on couvre la première solution B et on porte sa température à 50°C minimum pendant au moins 1H30,
• e2) on mélange la deuxième solution A avec la première solution B pour former un bain électrolytique qui comporte un complexe de platine aminé,

Also, according to the invention, during step c), the third system forms a second solution A consisting of an aqueous solution with platinum, comprising sodium hydroxide (NaOH) and at least one platinum salt with a degree of oxidation IV, and during step e), the following sub-steps are carried out:

• e1) the first solution B is covered and its temperature is raised to at least 50 ° C for at least 1H30,
• e2) mixing the second solution A with the first solution B to form an electrolytic bath which comprises a platinum amine complex,

According to a preferred embodiment, after step e), a step f) is carried out during which said electrolytic bath is heated at a temperature of between 80 ° C. and 97 ° C. for at least two hours.
then a step g) is carried out during which electroplating of a platinum deposit on a metal substrate is carried out with said electrolytic bath.

Furthermore, according to the invention, during the sub-step e2), the second solution A is added to the first solution B.

In this case, advantageously, prior to substep e2), the first solution B is brought to a temperature of 60 ° C.

Preferably, said platinum salt of oxidation state IV is defined by Y ₂ PtM ₆ with Y = NH ₄ ⁺ , H ⁺ or K ⁺ , and M = Cl ^- or OH ^- .

Advantageously, in the second solution A, said oxidation state platinum salt IV is diammonium hexachloroplatinate of formula (NH ₄ ) ₂ PtCl ₆ .

Advantageously, in the first system, said amine compound x ^p - (NH ₄ ) ⁺ p comprises diammonium hydrogen phosphate (NH ₄ ) ₂ HPO ₄ and / or ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ .

According to a preferred formulation, the first system comprises diammonium hydrogenophosphate (NH ₄ ) ₂ HPO ₄ and ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ with a molar ratio of 2 between the amount of ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ and the amount of diammonium hydrogen phosphate (NH ₄ ) ₂ HPO ₄ .

• la première solution B fournie à l'étape a) est obtenue avec de l'eau présentant une température de l'ordre de 30°C,
• la deuxième solution A fournie à l'étape c) est obtenue avec de l'eau présentant une température de l'ordre de 45°C,
• lors de l'étape b), on porte la température de la première solution B à 50°C minimum pendant au moins 3H30,
• lors de l'étape d), on chauffe ledit bain électrolytique à une température d'au moins 80°C pendant au moins trois heures (par exemple à 85°C pendant 3 heures).

One or more of the following provisions is / are preferably also adopted:

• the first solution B supplied in step a) is obtained with water having a temperature of the order of 30 ° C,
• the second solution A supplied in stage c) is obtained with water having a temperature of the order of 45.degree.
• during step b), the temperature of the first solution B is brought to 50 ° C minimum for at least 3H30,
• during step d), said electrolytic bath is heated to a temperature of at least 80 ° C for at least three hours (for example at 85 ° C for 3 hours).

• f) On fournit un substrat métallique, notamment un substrat en superalliage,
• g) on chauffe le dit bain électrolytique, et
• h) On réalise l'électrodéposition d'un dépôt de platine sur ledit substrat métallique avec ledit bain électrolytique.

The present invention also relates to a process for manufacturing a platinum-based metal underlayer from the electrolytic bath obtained according to the manufacturing method which has just been described, characterized in that it comprises the following steps :

• f) providing a metal substrate, especially a superalloy substrate,
• g) the said electrolytic bath is heated, and
• h) Electroplating a platinum deposit on said metal substrate with said electrolytic bath.

• une première solution B constituée d'une solution aqueuse avec ligand aminé, comprenant au moins un composé X-(NH₂)_n, avec X appartenant au groupe constitué de (CH₃, CH₃-CH₂, CH₃-(CH₂)_m), ou NH₃ ou un sel x^p- (NH₄)⁺p présentant une seule ou plusieurs fonctions amine et avec x un radical acide appartenant au groupe constitué de (PO₄ ^3-, HPO₄ ^2-, H₂PO₄ ^-, HPO₄ ^2- et H₂PO₄ ^-, SO₄ ^2-, HSO4^- et CH₃COO^-, n, m et p étant des entiers non nuls, et
• une deuxième solution A constituée d'une solution aqueuse avec platine, comprenant de la soude (NaOH) et au moins un sel de platine de degré d'oxydation IV.

The present invention also relates to a set of solutions for the manufacture of an electrolytic bath for the production of a platinum metal underlayer on a metal substrate, characterized in that it comprises:

• a first solution B consisting of an aqueous solution with an amino ligand, comprising at least one compound X- (NH ₂ ) _n , with X belonging to the group consisting of (CH ₃ , CH ₃ -CH ₂ , CH ₃ - (CH ₂ ) _m ), or NH ₃ or a salt x ^p- (NH ₄ ) ⁺ p having one or more amine functions and with x an acid radical belonging to the group consisting of (PO ₄ ^3- , HPO ₄ ^2- , H ₂ PO ₄ ^- , HPO ₄ ^2- and H ₂ PO ₄ ^- , SO ₄ ^2- , HSO ₄ ^- and CH ₃ COO ^- , n, m and p being non-zero integers, and
• a second solution A consisting of an aqueous solution with platinum, comprising sodium hydroxide (NaOH) and at least one platinum salt of oxidation degree IV.

Preferably, in the second solution A, said platinum salt of degree of oxidation IV is defined by Y ₂ PtM ₆ with Y = NH ₄ ⁺ , H ⁺ or K ⁺ , and M = Cl ^- or OH.

Advantageously, said platinum salt of oxidation state IV is diammonium hexachloroplatinate of formula (NH ₄ ) ₂ PtCl ₆ .

Preferably, the molar ratio between the amount of sodium hydroxide NaOH and the amount of platinum salt of oxidation degree IV is 2.

According to a preferred embodiment, in the first solution B, said amine compound x ^p- (NH ₄ ) ⁺ _p comprises diammonium hydrogen phosphate (NH ₄ ) ₂ HPO ₄ and / or ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ .

In a preferred variant, the first solution B comprises diammonium hydrogen phosphate (NH ₄ ) ₂ HPO ₄ and ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ with a molar ratio of 2 between the amount of ammonium dihydrogenophosphate NH ₄ H ₂ PO ₄ and the amount of diammonium hydrogen phosphate (NH ₄ ) ₂ HPO ₄ .

Finally, the invention also relates to the electrolytic bath resulting from the manufacturing method according to the invention. Such an electrolytic bath for producing a platinum-based metal underlayer on a superalloying substrate is characterized in that it comprises a platinum amine complex of the wavelength of a Pt-NH bond. ₃ or Pt-NH ₂ and a buffer solution

• les figures 1A à 1I, 2A et 2B représentent différentes courbes montrant les caractéristiques et le comportement de différents bains électrolytiques fabriqués selon la méthode de fabrication de l'invention.

Other advantages and characteristics of the invention will become apparent on reading the following description given by way of example and with reference to the appended drawings in which:

• the FIGS. 1A to 1I, 2A and 2B represent different curves showing the characteristics and behavior of different electrolytic baths manufactured according to the manufacturing method of the invention.

An electrolytic bath makes it possible to deposit the platinum in a way which is particularly ecological and economical (short time of realization, realization under atmospheric pressure avoiding the equipment of putting under vacuum) compared to techniques of deposition in vapor phase or thermal projection.

In addition, the implementation of this deposition method is compatible with pierced parts: the geometry of the current lines preventing significant deposition in the holes, in particular small cooling holes which are thus not obstructed.

It should also be noted that the use of such a method avoids the use of dangerous chemicals and the production of toxic waste.

EXAMPLE 1

In this example, the bath formulation is made from four ingredients distributed between two separate solutions, A and B, heated and stirred separately to react the ingredients together in each solution, before mixing together the two solutions A and B.

The mixture between the two solutions A and B is then itself heated and stirred. Once the heating time of the mixture A + B is respected, the platinum plating bath is ready for use for carrying out the electroplating.

In particular, solution A comprises, inter alia, the platinum salt (s), and solution B is the solution comprising, inter alia, ligands (it is recalled that a ligand is a chemical entity, ionic or molecular, bearing chemical functions allowing it to bind to one or more metallic entities, usually a cation, the association of a metallic entity with one or more ligands forming a soluble edifice in solution called complex).

• préparation de la solution B : dans 300 ml d'eau distillée (< 500Ω) à 30°C, mettre 44,0 g de diammonium hydrogénophosphate de formule chimique (NH₄)₂HPO₄ (soit 0.33 mole) et 75,0 g d'ammonium dihydrogénophosphate de formule chimique NH₄H₂PO₄ (soit 0.65 mole). Le ratio molaire entre la quantité d ammonium dihydrogénophosphate et la quantité de diammonium hydrogénophosphate est de 2. Une fois les sels dissous, couvrir la solution et la porter à 50°C pendant 4H 30.
• Préparation de la solution A : dans 300 ml d'eau distillée à 45°C, mettre 5g de soude de formule chimique NaOH (soit 0,080 mole) et 18,3 g de sel de platine hexachloroplatinate de diammonium de formule (NH₄)₂PtCl₆ (soit 0,040 mole). Le ratio molaire entre la quantité de soude et de sel d'hexachloroplatinate de diammonium est de 2. Laisser dissoudre les sels de platine au sein de la solution A ;
• Une fois la solution B prête et chaude, la solution A est préparée et est ajoutée dans la solution B préalablement portée à 60°C.
• Pour finir, le mélange A+B (dont le pH est au préalable ajusté à 6.3 par ajout d'une solution basique telle que, par exemple, de la soude, de la potasse, du triphosphate de sodium) est portée à 85°C pendant 3 heures. Toutes les solutions sont couvertes pendant les étapes de chauffe.

To manufacture a liter of electrolytic bath at 8 g / liter of platinum, the procedure is as follows:

• preparation of solution B: in 300 ml of distilled water (<500 Ω) at 30 ° C., put 44.0 g of diammonium hydrogen phosphate of chemical formula (NH ₄ ) ₂ HPO ₄ (ie 0.33 mole) and 75.0 g ammonium dihydrogenphosphate of chemical formula NH ₄ H ₂ PO ₄ (ie 0.65 mol). The molar ratio between the amount of ammonium dihydrogen phosphate and the amount of diammonium hydrogen phosphate is 2. Once the salts have dissolved, cover the solution and bring it to 50 ° C. for 4 hours 30 minutes.
• Preparation of solution A: in 300 ml of distilled water at 45 ° C., put 5 g of sodium hydroxide of the chemical formula NaOH (ie 0.080 mole) and 18.3 g of diammonium hexachloroplatinate platinum salt of formula (NH ₄ ) ₂ PtCl ₆ (ie 0.040 mol). The molar ratio between the amount of sodium hydroxide and diammonium hexachloroplatinate salt is 2. Let the platinum salts dissolve in solution A;
• Once solution B is ready and hot, solution A is prepared and is added to solution B previously heated to 60 ° C.
• Finally, the mixture A + B (whose pH is previously adjusted to 6.3 by addition of a basic solution such as, for example, sodium hydroxide, potassium hydroxide, sodium triphosphate) is brought to 85 ° C. during 3 hours. All solutions are covered during the heating stages.

More generally, with this solution B comprising diammonium hydrogen phosphate of chemical formula (NH ₄ ) ₂ HPO ₄ and ammonium dihydrogenphosphate of chemical formula NH ₄ H ₂ PO ₄ , the pH of the mixture of solutions A + B is set between 6 and 10 and preferably between 6 and 7.

As part of this formulation, and in order to identify the best operating conditions for the realization of the platinum plating, an experiment plan with 9 baths was conducted, where the heating temperatures and the heating times of the solution B then of the mixture A + B are different and mentioned in table 1 which follows, test 2 corresponding to the above detailed recipe: Table 1 Test no. T ° heating B (° C) Heating time B (h) T ° heater AB (° C) Heating time AB (h) 1 50 ° C 1:30 50 ° C 1 hour 2 50 ° C 4:30 85 ° C 3h 3 50 ° C 8h 95 ° C 8h 4 85 ° C 1:30 85 ° C 8h 5 85 ° C 4:30 95 ° C 1 hour 6 85 ° C 8h 50 ° C 3h 7 95 ° C 1:30 95 ° C 3h 8 95 ° C 4:30 50 ° C 8h 9 95 ° C 8h 85 ° C 1 hour

For each bath formulated, pions are coated with platinum at different intensities. Each pawn is weighed before and after deposit.

• La vitesse de dépôt (g/h/dm²) pour chaque intensité
• Le plateau du bain
• L'intensité de début de plateau
• La vitesse moyenne du plateau
• L'écart-type du plateau
• L'écart entre la vitesse minimale et maximale obtenue sur le plateau.

Thanks to the mass gain, we can thus determine:

• The deposition rate (g / h / dm ² ) for each intensity
• The bath tray
• Intensity of plateau start
• The average speed of the plateau
• The standard deviation of the plateau
• The difference between the minimum and maximum speed obtained on the board.

The three tables 2-1 to 2-3 below present the results obtained with the 3 baths giving the best results at the end of the experimental plan. Table 2-1 Experience settings T ° heating B (° C) Heating time B (h) T ° heater AB (° C) AB heating time (h) Bath color after heating Trial 2 50 ° C 4:30 85 ° C 3h limpid Trial 4 85 ° C 1:30 85 ° C 8h limpid Trial 7 95 ° C 1:30 95 ° C 3h limpid Deposit rate (g / h / dm ² ) 8A 1A 4A 16A 24A 8A Trial 2 2.4455 .8164 1.9618 2.2618 2.2564 1.6127 Trial 4 2.0782 .1727 1.4982 2.0236 2.2891 1.4945 Trial 7 2.0509 0.6782 1.5600 2.1164 1.9073 1.5109 Tray characteristics Bath color after electrolysis Start of the plateau Average speed of the plateau (g / h / dm ² ) Standard deviation plateau Distance Vmin / Vmax of the plateau Trial 2 limpid 4A 2.0232 0.27 0.65 Trial 4 Trouble 4A 1.8264 0.34 0.79 Trial 7 Trouble 4A 1.7736 0.25 0.61

In addition, the bath of test 2 offers the following advantages:

It is a bath whose great repeatability has been observed, and which compared to a reference bath, the average deposition rate is important for a new bath ( Figure 1.A ), and remains sufficiently important during operation ( Figure 1.A ). The bath of the test 2 is indeed repeatable because the curves of the average speed and the dispersion of the fabrications 1 and 2 are superimposable, which shows the extreme reproducibility of the manufacture. On the other hand, one can distinguish the curves of the manufacture 1 and 2 for the Bath of the test 7 and even more for the bath of the test 4, which, him, is less repeatable, why the bath 4 is not not privileged.

In addition, the bath of test 2 shows a good dispersion of the plateau ( Figure 1.B ), being reminded that the presence of a "plateau" corresponds to obtaining an identical deposition rate regardless of the current density applied and regardless of the geometry of the treated part. Indeed, each production, two trays were made. A plateau is the study of the mass gain as a function of the current density applied. In domestic manufacture, the dispersion decreases at the most electrolysis is carried out in the bath. This is not the case in the reference bath where the more electrolysis is carried out the more the bath disperses.

Also, it is noted that the bath of test 2 shows little loss of platinum over time ( Figure 1 C) and that the average efficiency ( Figure 2A ) and speed ( Figure 2B ) of the bath is almost identical after three successive regenerations. Concerning the platinum losses, we encounter with the reference bath many platinum losses, mainly in the form of a platinum solid precipitate at the bottom of the tank. In addition, for the reference bath, the more the bath undergoes electrolysis and the more it tends to form precipitates at the bottom of the tank. On the other hand, it is observed for the baths according to the invention that the platinum losses are lower and above all constant in time (constant with the electrolyses). In addition, the bath of test 2 is the one with less platinum losses, so the bath of test 2 is more economical from the economic point of view.

Overall, as can be seen from the curves of Fig 1.D to 1.F and 1.G to 1.I , the baths of tests 4 and 7 offer results quite similar to those of test 2.

Moreover, as Figures 2.A and 2.B the electrolytic bath of test 2 gives stable results over time, in terms of deposition rate, after several regenerations of the bath: the deposition rate is almost unchanged between the first and the third regeneration.

To regenerate a bath, we add platinum salts in the bath to enhance its platinum content. Once the salts have been added, the bath is left stirring at 65 ° C. for 12 to 24 hours so that all the salts are dissolved in the bath.

EXAMPLE 2

The manufacture of the electrolytic bath is similar to that of the recipe of Example 1, except for the following points.

Solution B comprises ammonium hydrogen sulphate of chemical formula (NH ₄ ) ₂ SO ₄ in an amount of 43.5 g and diammonium sulphate of chemical formula NH ₄ S O ₄ in an amount of 76 g and water . The whole is brought to 50 ° C during 4:30.

The pH of the mixture of solutions A + B is set between 1 and 5.

EXAMPLE 3

The manufacture of the electrolytic bath is similar to that of the recipe of Example 1, except for the following points.

Solution B contains ammonium acetate of chemical formula CH ₃ COONH ₄ in an amount of 102.4 g and acetic acid of chemical formula CH ₃ COOH in an amount of 39.6 g.

The whole is brought to 50 ° C during 4:30.

The pH of the mixture of solutions A + B is set between 1 and 5.

According to the invention, preferably, the ligand is chosen from aliphatic polyamines of 3 to 20 carbon atoms with a linear or branched carbon chain.

Advantageously, the ligand is chosen from primary polyamines such as diaminopropanes such as 1,3-diaminopropane and 1,2-diaminopropane, diethylenetriamine, 1,4-diaminobutane and 1,6-diaminohexane; secondary polyamines such as N, N 'dimethyl-1,3-propanediamine; and tertiary polyamines such as N, N, N ', N' tetramethylethylenediamine. The ligands preferentially chosen are diaminopropanes.

Claims (9)

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 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-(NH₂)_n, where X belongs to the group constituted by (CH₃, CH₃-CH₂, CH₃-(CH₂)_m), or NH₃ or an x^p-(NH₄)⁺ _p salt where x is an acid radical belonging to the group constituted by (PO₄ ^3-, HPO₄ ^2-, H₂PO₄ ^-, HPO₄ ^2- and H₂PO₄ ^-, SO₄ ^2-, HSO₄ ^-, and CH₃COO^-) and where n, m, and p are 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;

   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 system, the second system, and the fourth system are grouped together in a single solution forming a first solution B, in that during step c), the 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 in that during step e), the following substeps are performed:

   e1) covering the first solution B and raising its temperature to at least 50°C for at least 1h30; and

   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 the first solution B includes an x^p-(NH₄)⁺ _p salt, where x=HPO₄ ^2- and p=2, and/or x=H₂PO₄ ^- and p=1.
3. A fabrication method according to claim 2, 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 of platinum is electroplated on a metallic substrate using said bath of electrolyte.
4. A method according to the preceding claim, characterized in that prior to substep e2), the first solution B is raised to a temperature of 60°C.
5. A method according to claim 1, characterized in that said salt of platinum of degree of oxidation IV is defined by Y₂PtM₆ with Y=NH₄ ⁺, H⁺, or K⁺, and M=Cl^- or OH^-.
6. 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 (NH₄)₂PtCl₆.
7. 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.
8. A method according to any preceding claim, characterized in that the first system, said x^p-(NH₄)⁺ _p amine compound comprises diammonium hydrogen phosphate (NH₄)₂HPO₄ and/or ammonium dihydrogen phosphate NH₄H₂PO₄.
9. A method according to the preceding claim, characterized in that the first system includes diammonium hydrogen phosphate (NH₄)₂HPO₄ and ammonium dihydrogen phosphate NH₄H₂PO₄ with a molar ratio of 2 between the quantity of ammonium dihydrogen phosphate NH₄H₂PO₄ and the quantity of diammonium hydrogen phosphate (NH₄)₂HPO₄.

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