EP0552097B1 - Process and apparatus for nickel electroplating - Google Patents

Description

The present invention relates to an improved apparatus and a method of electrolytically coating nickel. It concerns the field of nickel plating by electrolytic coating of metallic or non-metallic parts, using baths nickel plating using nickel sulfamate as input of nickel.

It finds an important application in the Coating Electrolytic Nickel (REDN) inside tubes such as steam generator tubes, cuffs of pressurizer or cover adapters tank of pressurized water nuclear power plants, or any other nuclear or non-nuclear tube.

Another important application concerns nickel plating. elements of electrical connectors and more generally to any nickel plating operation using a nickel sulfamate either by a static process (bath in a tank with fixed electrodes), either by a process dynamic (bath circulation or circulation of parts to nickel).

A third important application concerns the purification of the nickel-plating baths used during the said coatings.

We know that the internal nickel plating of the tube areas U-shaped steam generator, subject to constraints particularly high, can seal micro-cracks or prevent these cracks. As an example of a process known nickel-plating repair, we can see document EP-A-O 167 513.

• d'un récipient contenant le bain de nickelage agité ou non, une anode souvent constituée d'un panier grillagé (par exemple en titane) et rempli de billes de nickel soluble (par exemple celles commercialisées par la Société INCO), et une cathode constituée de la pièce à revêtir de nickel, ou
• des mêmes récipient, bain de nickelage et anode que ci-dessus, mais avec une cathode constituée d'une plaque métallique quelconque (par exemple en acier inoxydable)l'ensemble du dispositif étant, dans ce cas, destiné à préparer le bain de nickelage avant utilisation en le purifiant par élimination, par électrolyse contrôlée, des impuretés métalliques non désirées (par exemple du cobalt dans le cas des installations nucléaires), ou
• d'une anode cylindrique creuse revêtue de nickel soluble et placée au centre du tube à réparer par nickelage constituant la cathode, le bain de nickelage circulant dans un sens entre la cathode et l'anode puis dans le sens opposé à l'intérieur de l'anode.

The devices conventionally used in the field of nickel plating by electrolytic coating consist of:

• of a container containing the nickel bath, stirred or not, an anode often consisting of a mesh basket (for example made of titanium) and filled with soluble nickel beads (for example those sold by the company INCO), and a cathode made the part to be coated with nickel, or
• of the same container, nickel plating bath and anode as above, but with a cathode made up of any metal plate (for example made of stainless steel) the whole device being, in this case, intended to prepare the nickel plating bath before use by purifying it by elimination, by controlled electrolysis, of unwanted metallic impurities (for example cobalt in the case of nuclear installations), or
• a hollow cylindrical anode coated with soluble nickel and placed in the center of the tube to be repaired by nickel-plating constituting the cathode, the nickel-plating bath flowing in a direction between the cathode and the anode and then in the opposite direction inside the 'anode.

However, with the devices described above, during electrolysis, it forms, both at the cathode that at the anode, complex compounds which, from more, can freely recombine with each other.

By complex compounds is meant compounds resulting from the modification of the sulfamate ligand such as by example azodisulfonate.

These complex compounds pose problems when the most common nickel plating operation by the passivation of the nickel anode due in particular to reduction on the cathode of oxidized compounds formed at the anode that unbalance the electrochemical system toward a potential where the anode becomes passive, and / or by an increase electrochemical resistance of the nickel plating cell due in particular to the presence of poorly ionized compounds, this which leads to no longer working under intense conditions or potential desired for nickel plating, to obtain deposits no longer of the required quality and / or rapidly degrade nickel plating baths.

The article "Nickel electroplating cell" page 500, collar. 2 of Chemical Abstracts, vol. 102, n ° 18, May 1985, also makes known a coating device nickel electrolytic according to the preamble of the claim 1. The invention proposes, however, a device in accordance with the characterizing part of the claim 1.

The semi-permeable wall of inert sintered material or polymer prevents the passage of oxidized compounds formed to the anode, from the anode compartment to the cathode compartment.

The invention also aims to provide a method preventing or preventing the degradation of nickel plating baths and use these baths until exhaustion their nickel content, without risking incidents due to the early passivation of the anode in the case where it is made of soluble nickel, i.e. depolarized nickel sulfur, such as for example the products sold by the INCO Company (pellets, beads, etc.).

For this, the invention provides a method of electrolytic coating of a part according to claim 5.

The cathode can consist of the part to coating, this part being in contact with the bath of the cathode compartment.

Furthermore, the method may include a step preliminary to the nickel plating operation in which the cathode consists of a simple electrode allowing electrolysis nickel plating baths, to prevent and prevent their degradation and thus allow their use up to depletion of their nickel content.

To better understand the invention we will describe now in more detail the electroplating device nickel according to the invention.

Figure 1 and Figure 2 show modes individuals implementing the invention, given as non-limiting examples.

Figure 3 shows the evolution of the parameters electrochemical during electrolysis as performed in the prior art.

Figure 4 shows the evolution of the parameters electrochemicals during an electrolysis performed according to the invention.

The schematic representation of Figure 1 includes a container 1 formed of two vertical tanks communicating by a transverse channel, intended to receive the bath 2 to be electrolyzed. A cathode 3 is immersed in one of the vertical tanks and an anode 4 is immersed in the other vertical tank. A semi-permeable wall 5 closes the channel transverse which connects the two vertical tanks and separates thus the anode compartment of the cathode compartment.

FIG. 2 schematically represents a tank 6 intended to receive the bath 7 to be purified. In the bath are immersed a cathode 8 and an anode 9 isolated from the rest of the bath by a semi-permeable wall 10 thus delimiting, around the anode, a compartment inside the nickel plating bath. In such a device the semi-permeable wall can be a frit or a polymer membrane.

The arrangement of Figure 2 can be reversed, that is to say that it is then the cathode which is isolated from the rest of the bath by a semi-permeable wall.

The electrolysis carried out is in itself known both for the connection of the electrodes as for the control of different parameters.

For example, the anode and the cathode could be connected, via a rheostat, to the terminals of a direct current source for supplying voltage U of a few volts at an intensity I of a few amps . A tension measurement device can be mounted between the anode and a reference electrode and will provide the potential (Ea) of the anode relative to the reference electrode.

In the case of coating nickel plating equipment electrolytic of the prior art, the three electrodes: cathode, anode and reference electrode, are placed in the non-compartmentalized tank.

Figure 3 shows that, until time T ₁ , the three parameters I, U, Ea are constant and the electrolysis process takes place normally, beyond T ₁ we have shown the passivation phenomenon of the anode which not only generates an increase in the potential of the anode relative to the reference electrode Ea, but above all which causes a sudden drop in the nickel-plating current I with rapid degradation of the bath by oxidation and formation of a non-homogeneous nickel deposit . This passivation of the anode also produces a deterioration of the bath by acidification with, consequently, the formation of a fragile nickel deposit.

This description based on a potential electrolysis U imposed could also be applied in the case of a electrolysis at imposed intensity I. Instead of falling sudden current I we would note a sharp rise in the tension U, but the consequences on the bath and the quality of the deposit would be the same.

In the case of an apparatus according to the invention, the cathode is placed in one of the two vertical tanks of a device of the kind of that schematically represented in Figure 1, the anode and the reference electrode are placed in the other vertical tank, the semi-permeable wall being placed between the two tanks in the transverse channel.

FIG. 4 shows that, until time T ₁ , the electrolysis evolves in the same way as in the previous case represented in FIG. 3. As in the previous case, the passivation phenomenon of the anode causes a increase in potential Ea.

On the other hand, the parameters of electrolysis in the nickel sulfamate bath continue to be maintained, that is to say that the intensity I and the potential U remain constant.

This description remains valid, that electrolysis either made at an imposed potential U or at an imposed intensity I.

Consequently, neither the quality of the cathode bath nor that of the deposit are not disturbed by the possible passivation of the anode.

The description also makes it possible to understand that it is now possible, thanks to the invention, to use an anode insoluble from the start of electrolysis, which was impossible in the prior art taking into account the degradation quick settings.

To assess the benefits of the invention, two nickel plating operations are carried out, one according to the prior art, the other in separate compartments by a semi-permeable wall, in two nickel plating baths of identical starting composition.

• on prépare 120 cm3 d'une solution de nickelage comprenant :
  • 93 g/l de nickel sous forme de sulfamate et
  • 40 g/l d'acide borique.
• la distance entre les électrodes est de 8 cm,
• les électrodes sont constituées de plaquettes de 1,4 cm x 1,4 cm x 0,1 cm,
• la cathode est en alliage "Inconel 600",
• l'anode est en nickel et recouverte, sur une face, de nickel dépolarisé au soufre,
• avant le nickelage, les électrodes subissent :
• un décapage électrolytique dans l'acide sulfurique à 10 % à 58°C,
  • pendant 60 secondes avec une intensité de 32 A/cm2 pour la cathode,
  • pendant 25 secondes avec une intensité de 32 A/cm2 pour l'anode,
• un rinçage à l'eau,
• une polarisation en milieu acide sulfamique/ sulfamate de nickel à 58°C pendant 30 secondes avec une intensité de 4,8 A/cm2, la cathode étant polarisée cathodiquement,
• les électrodes décrites ci-dessus et une électrode de référence au sulfamate mercureux sont placées dans le bain de sulfamate de nickel,
• au cours de l'opération de nickelage on électrolyse le bain de sulfamate de nickel avec une différence de potentiel U maintenue constante, après une variation linéaire de 0 à U volts en une minute, de manière à avoir en régime stable une densité de courant I comprise entre 20 et 25 A/dm2; la densité de courant et la tension de l'anode (c'est-à-dire le potentiel Ea de l'anode par rapport à l'électrode de référence) sont enregistrées.

In each nickel plating operation:

• 120 cm3 of a nickel-plating solution are prepared comprising:
  • 93 g / l of nickel in the form of sulfamate and
  • 40 g / l boric acid.
• the distance between the electrodes is 8 cm,
• the electrodes consist of plates of 1.4 cm x 1.4 cm x 0.1 cm,
• the cathode is made of an "Inconel 600" alloy,
• the anode is made of nickel and covered, on one side, with sulfur-depolarized nickel,
• before nickel plating, the electrodes undergo:
• electrolytic pickling in 10% sulfuric acid at 58 ° C,
  • for 60 seconds with an intensity of 32 A / cm2 for the cathode,
  • for 25 seconds with an intensity of 32 A / cm2 for the anode,
• rinsing with water,
• polarization in a sulfamic acid / nickel sulfamate medium at 58 ° C. for 30 seconds with an intensity of 4.8 A / cm 2, the cathode being cathodically polarized,
• the electrodes described above and a reference electrode for mercury sulfamate are placed in the nickel sulfamate bath,
• during the nickel-plating operation, the nickel sulfamate bath is electrolyzed with a potential difference U kept constant, after a linear variation from 0 to U volts in one minute, so as to have a steady current density I between 20 and 25 A / dm2; the current density and the voltage of the anode (that is to say the potential Ea of the anode relative to the reference electrode) are recorded.

In the case of a coating nickel plating device electrolytic of the prior art, the three electrodes : cathode, anode and reference electrode for mercury sulfamate, are placed in a non-compartmentalized tank; in in the case of an apparatus according to the invention, the cathode is placed in one of the two vertical tanks of a device of the kind schematically shown in the figure 1, the anode and the reference electrode are placed in the other vertical tank, the semi-permeable wall being a sintered in pyrex n ° 4, 3 mm thick, marketed by SOVIREL company placed between the two tanks in the canal transverse.

Electrolysis results

In both cases, the total duration of the electrolysis was intentionally set at 8:30 a.m.

In the case of the non-compartmentalized tank, the passivation anode intervened after 30 minutes about and was highlighted by the rise of his surface potential with an Ea value of approximately 300 mV up to a value exceeding 1000 mV.

In this first case, for a volume of 60 cm3 of solution in the cathode compartment, or for 5.6 grams of nickel present in the starting solution, 0.86 grams of nickel were deposited on the cathode, i.e. 15% nickel available in the solution, for 8 hours 30 nickel plating; Figure 3 shows the evolution of electrochemical parameters.

In the case of the apparatus according to the invention, passivation, highlighted by the rise in potential of the anode, occurred after 40 minutes of nickel plating. On the other hand, the current density I having remained stable, the nickel plating continued for 8 hours 30 minutes with shutdown voluntary trial; figure 4 represents the evolution electrochemical parameters.

In the latter case, for a volume of 60 cm3 of solution in the cathode compartment, or for 5.6 grams of nickel present in the starting solution, 4.4 grams of nickel were deposited on the cathode, or 78% available nickel in the solution, during the 8 30 hours of nickel plating.

We will now illustrate the interest of the invention when the device according to the invention is used for the purification or regeneration of nickel plating.

I - Après les 8 heures 30 d'électrolyse de l'expérience précédente, le compartiment cathodique a été vidangé et remplacé par du bain neuf et une cathode neuve y a été placée à la place de la cathode d'origine. Dans le compartiment anodique d'origine, on a plongé une cathode neuve à la place de l'anode d'origine. On a donc inversé les deux compartiments. Dès mise en route de l'électrolyse, l'anode placée dans le bain neuf s'est passivée.

II - L'expérience inverse a été réalisée : après 8 heures 30 d'électrolyse, le compartiment anodique a été vidangé et remplacé par du bain neuf avec une cathode neuve à la place de l'anode d'origine, la cathode d'origine ayant été remplacée par une anode neuve qui donc est plongée dans le bain cathodique d'origine déjà utilisé pendant 8 heures 30. Dans ce cas, avec l'électrolyse, le nickelage s'est poursuivi pendant 30 minutes sans passivation, l'arrêt du test ayant été volontaire.

The previous experiment was extended by the following tests:

I - After 8 hours 30 of electrolysis of the previous experiment, the cathode compartment was emptied and replaced by new bath and a new cathode was placed there in place of the original cathode. In the original anode compartment, a new cathode was immersed in place of the original anode. We therefore reversed the two compartments. As soon as the electrolysis was started, the anode placed in the new bath became passivated.

II - The reverse experiment was carried out: after 8 hours 30 minutes of electrolysis, the anode compartment was drained and replaced by a new bath with a new cathode in place of the original anode, the original cathode having been replaced by a new anode which is therefore immersed in the original cathode bath already used for 8 hours 30 minutes. In this case, with electrolysis, nickel plating continued for 30 minutes without passivation, stopping the test having been voluntary.

It can therefore be seen that the initial nickel plating bath has been greatly enriched by complex compounds such as by example azidosulfonate in one of the compartments making impossible any electrolysis, while the bath contained in the other compartment remains capable of ensuring effective nickel plating after 9 hours of using the original bath.

Maintaining the oxidized compound in a compartment specific so as not to pollute the bath allows to perform purification of sulfamate baths by electrolysis (extraction of traces of cobalt for example) without pollution azodisulfonate.

Claims (5)

1. Apparatus for electro-plating an article with nickel using a nickel plating bath having nickel sulfamate as a nickel providing compound, comprising a tank containing the nickel plating bath and a semi-permeable wall (5, 10) which separates a cathode compartment from an anode compartment, in which a cathode (8) and a nickel anode (9) are respectively immersed, characterized in that the wall is of polymere or inert sintered material of such nature that it stops oxyded compounds formed at the anode.
2. Apparatus according to claim 1, characterized in that the tank consists of two vertical vessels communicating via a transverse channel closed by the semi-permeable wall.
3. Apparatus according to claim 1, characterized in that the semi-permeable wall defines a chamber inside the nickel plating bath, around the anode or cathode.
4. A method of electro-plating of an article, comprising passing an electrolysis current through a nickel plating bath which has nickel sulfamate as a nickel providing compound, between a cathode constituted by the article to be coated and an anode of soluble nickel, immersed in the bath and separated by a semi-permeable wall, characterized in that free exchanges between complex compounds formed at the cathode and those formed at the anode are prevented by constituting the wall of inert sintered material or of polymere enabling electrical current to pass.
5. Method according to claim 4, characterized in that, it comprises a preliminary step of circulating an electrical current, during which the cathode consists of a plain electrode.

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