FR2471426A1 - PALLADIUM ELECTRODEPOSITION PROCESS AND ELECTROLYTIC BATH FOR CARRYING OUT SAID METHOD - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A PROCESS FOR ELECTRODEPOSITION OF PALLADIUM AND AN ELECTROLYTIC BATH FOR IMPLEMENTING THIS PROCESS. THE BATH ACCORDING TO THE INVENTION IS A WATER BATH OF 5 TO 50GRAMS PER LITER OF PALLADOSAMINE SALT CHOSEN FROM THE GROUP INCLUDING PALLADOSAMINE CHLORIDE AND PALLADOSAMINE BROMIDE, FROM 100 TO 150GRAMS PER LITER OF SULFAMIC ACID AND 10 PER LITER OF AMMONIUM CHLORIDE. LEDIT BATH HAS A PH INCLUDED BETWEEN 6.5 TO 10.0. THE COATINGS OBTAINED CAN BE USED IN PARTICULAR FOR COATING ELECTRIC CONTACT ELEMENTS.

Description

1.

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  The present invention relates to improvements relating to the palladium electrodeposition process on a metal substrate, and to preferred embodiments of the palladium electrodeposition process on

electrical contact surfaces.

  Electric contract surfaces must have a low and stable electrical resistance. This characteristic is generally obtained by the production of contacts based on materials having these characteristics of low resistance and high stability, or by the manufacture of metal contacts.

  base and plated with a coating of a stable conductive material.

  Gold and other noble metals meet the requirements of

  electrical contact, stability and low resistance. The coats

  gold are generally resistant to oxidation, sulphide

  and other chemical reactions that may reduce their electrical resistance

  cudgel. However, because gold is a valuable and expensive material, it is

  better to find a different coating material.

  Thus, it has been proposed to use palladium deposited by electro-

  deposited on a metal substrate, to obtain the desired characteristics

  Tees. However, it has been found that palladium coatings, produced by various known electrodeposition processes, suffer from a significant number of disadvantages. For many applications, particularly to obtain a coating of electrical contacts, it is essential that the palladium is non-porous. The porosities and cracks in the coating allow foreign matter to penetrate the layer, eventually reaching the support itself. This results in tarnishing and corrosion attacking both the palladium layer and the base metal, which modifies the characteristics of

  electrical conductivity and deteriorates the contact. One of the major disadvantages

  process of the prior art for the plating of palladium

  side in the fact that they were unable to result in a palladium layer

non-porous

  Palladium coatings applied by electroplating on a base substrate as obtained by known methods have not

  satisfied for many other reasons. Some processes of elec-

  trodéposition are slow and lead to uneven coatings constraint and important a large amount of hydrogen in occlusion, which tends to crack

  and peel the surface, especially when the coating is used as a

  electrical tact. Other methods of the prior art are bad because of their poor performance. Some baths are difficult to regenerate when contaminated, others have low deposition and others are too sensitive and require extremely low current density and / or

  very low palladium ion concentration.

  2. Finally, known techniques for effecting palladium electroplating produce noxious fumes, so the treatment is

  must be done under vacuum hoods. Ventilation is not only

  annoying, but increases the cost of the operation. On the other hand, the presence of a large volume of unpleasant and harmful vapor creates a deceptive environment.

  sane and causes health and safety problems.

  A known electrolytic solution, giving off important vapors of amines

  moniac, is described in US Patent No. 3,920,526. The solution described in this patent comprises palladosamine chloride, ammonium chloride and ammonia in aqueous solution. Another electrolytic solution is described

  in U.S. Patent No. 3,925,170; it comprises a compound of palladium

  luble and a soluble electrolyte such as ammonium sulfanate. When these

  The solutions are used for electrodeposition, they release large quantities of gaseous ammonia, so that the solutions become more acidic, which requires continuous monitoring and permanent addition of a base such as ammonium hydroxide. When contaminated, these solutions may

difficult to regenerate.

  The aqueous electrolyte baths of the present invention have the advantage of releasing very little ammonia vapor or other undesirable vapor, and thus do not require any ventilation facility. Coatings

  of palladium electrodeposited from this solution have different properties

  both physical and chemical, which are appreciated in a large number of applications.

  particularly for the coating of electrical contracts. So the

  coatings are not porous, are ductile and well adherent. The strength of

  melting of this electrolytic bath is excellent, and electroplating can be performed for a wide range of current densities and concentrations

  ionic palladium. Finally, these baths, contaminated during a

  regularly, can be regenerated easily and inexpensively.

  Another important advantage of the present invention lies in the fact that these baths do not require additional supply as was the case for known baths. These additives were used in the prior art to control porosity, cracks, tensions, adhesion and other

  characteristics of the coatings. Unfortunately, in addition to the expenses

  the use of these additives, it has been found that they are often

  compatible with palladium, resulting in conductivity or

  an excess as regards one of the characteristics, for example, the

  tility, while decreasing certain other characteristics such as

  ence. All these defects have been removed by the removal of additives that do not

  are more necessary in the context of the present invention.

  This is why the present invention proposes to carry out an electric bath.

3.

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  aqueous trolytic material for rapid and uniform deposition of palladium

  dium having the preferred characteristics of gloss, low electrical resistance, good ductility, low stress, absence of cracks and porosities, low hydrogen occlusion and good adhesion, this solution also releasing very little ammonia gaseous or other inde-

sirables in use.

  Other advantages will appear in the description of examples of

lisation preferred.

  The aqueous electrolytic bath according to the present invention comprises the following compounds with palladosamine chloride (Pd (NH 3) 2 Cl 2), acid

  sulphamic acid (HS03NH2), and ammonium chloride (NH4Cl). Palmar chloride

  ladosamine can also be replaced by good palladosamine bromide

  that this second solution is less advantageous economically.

  The concentrations of the various components contained in the bath

  can be varied between certain limits. The degrees of concentration

  The following are the following: pallarsamine chloride or bromine 5-50 lpg (grams per liter of H20) sulphamic acid 10-150 lpg

ammonium chloride 10-150 gpl.

  On the other hand, the bath preferably has a pH of between 6.5

  and 10.0, and in particular a pH of between 8.0 and 9.0.

  The proportions mentioned above are preferred because if

  the concentration is lowered below 5 grams per liter, the

  quage becomes irregular due to a decrease in palladium ions.

  On the other hand, when the preferred upper limit of 50 grams per liter of palladosamine salt is exceeded, excessive uneconomic deposits are formed. In addition, dark burned deposits will appear and the dispersion power of the solution will be decreased. The electrodeposition process

  as well as the deposited layer itself will be affected if the chloride of am-

  monium or sulphamic acid have concentrations exceeding the limits indicated. According to a still more preferred embodiment, the palladosamine salt will have a concentration of the order of 30 to 40 grams per

  liter. The amount of palladium ions at this concentration ensures a good

  current density and therefore ideal coating characteristics, minimum losses and excellent dispersion power. To obtain optimal plating and ideal coating characteristics, ammonium chloride and sulfamic acid are present in the bath.

  40 to 60 grams per liter. Sulfamic acid and ammonium chloride

  4. monium constitute a new, unique double electrolytic system with high compatibility with palladosamine salts. Although the mechanisms

  chemical and physical processes for electroplating from electrical baths

  aqueous trostatics are not perfectly understood, this electro-

  double lytic, combined with the salt of palladosamine, makes it possible to obtain an

  lytic material with excellent conductivity and dispersal

  able to deposit palladium films quickly and efficiently

  remarkable physical and chemical properties.

  The present aqueous electrolyte solution is obtained as follows:

  1) the palladosamine chloride powder is dissolved in a solution

  aqueous ammonium hydroxide (NH 4 OH: H 2 O in 1: 1 by weight).

  2) aqueous ammonium chloride added to the previous solution.

  3) aqueous sulfamic acid added to the solution obtained after

step 2).

  4) Ammonium hydroxide or sulfamic acid is added in sufficient quantity to bring the pH between 6.5 and 10.0 or preferably

between 8.0 and 9.0.

  The aqueous electrolytic bath can be used in conjunction with conventional systems to obtain a palladium coating on metal-based machined parts. The metal substrate can be made in any

  which conductive material or any metal that does not influence the

  improper electrolytic bath, these metal bases being nickel, copper, cuproberyllium alloys, brass, phosphor-bronze,

  stainless steel, soft iron, silver and the like. In general, before

  In the case of plating, the workpiece must be cleaned and activated by soaking in an acid which removes the oxidized surface, to allow good adhesion of the palladium. Additionally, the surface is pre-plastered with a trace of palladium or other metal to further increase adhesion and remove

  or minimize corrosion due to direct coupling between the

  ladium and the metal base. The base layer is obtained by a metal film

  It is a very thin layer that also protects the metal base from the attacks of the concentrated electrolytic bath, which would lead to contamination of the bath. Such a palladium base layer can easily be obtained by subjecting the

  workpiece machined in a very low concentration bath.

  After cleaning, activation and, if necessary, pre-plating, the machined part is immersed in the present electrolytic bath. The bath can be stirred at a temperature of from 15 to 60 ° C (60 ° -131 ° F) and preferably at a temperature of 18.3 to 40 ° C (65 ° -1050 ° F).

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  in order to obtain the best balance between the characteristics of the coating

  the plating speed and evaporation of the bath.

  A voltage is then applied between a cathode constituted by the machined part immersed in the bath, and an inert anode, for example titanium plated platinum or tantalum or any other suitable material. This potential is applied either continuously or as pulses for a total time sufficient to produce a coating having the desired thickness. In general, these thicknesses range from 25.4 "/ (1 microinch) to 5.08 mm (200 microinches) or more, although thinner coatings can be obtained, but these tend to become porous. also get coatings

  of palladium in successive layers in order to obtain a better

  crystal formation. The treatment time is related to the current density which can be of the order of 1 to 100 amperes per square foot (1 to 100 milliamperes per cm 2). This density will preferably be between 5 and 50 amperes per

  feet to square a frame, 3 to 15 amperes per square foot to place

  Make a cylindrical piece and 5 to 100, 300 or more amps per foot squared to perform selective plating. When the desired thickness is reached, the machined part is removed from the bath and rinsed. During the electrodeposition process, the pH generally increases slightly. As a result, it becomes necessary to add acid to

  maintain the pH at the required value. This represents a particular characteristic

  of the present invention, since the harmful ammonia vapors occurring substantially with all prior art baths are removed. Of course, the concentration of palladium also decreases during the process. It is therefore necessary to add palladosamine salt in

  sufficient to maintain the salt concentration at the required value.

  Electrolytic baths used for the plating of palladium or other metallic coatings tend to become contaminated during their use. The contaminants come from the plated surfaces of the filling equipment, containers and other utensils used. The

  presence of contaminants in the baths, even in quantity. minor, is

  desirable because these agents tend to deposit together with the pallet

  ladium and produce impure coatings. Therefore, it is very important

  carrying simple and economical means to regenerate or purify

  contaminated electrolytic baths.

  In the prior art, it was generally both difficult and

  expensive to proceed with the regeneration of electroplating baths.

  This was partly due to the difficulty of having pure metal components available. These baths had to

  most cases be subjected to a long and complex purification process.

6.

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  In contrast to these techniques of the prior art, the electrolytic bath

  of the present invention can be regenerated in an extremely short way.

  pide and economic. Because the additives usually required in the baths of the prior art are not necessary in this case, the additives are not lost during the regeneration of the bath. It has been found, for example, that the contamination of aqueous electrolytic baths initially prepared according to the principle of the invention and containing salts of palladosamine, sulphamic acid and ammonium chloride as well as

  minor amounts of different contaminants can be regu-

10 as follows:

  1) adjust the pH of the contaminated bath to approximately 3.0 to 5.0 to

  the palladosamine salt and dissolve contaminants that may

  for example, hold copper, zinc and tin and various compounds of these elements. Since the bath is generally at a pH above 6.0 prior to regeneration, it has been found that either sulfamic acid or hydrochloric acid can be used to lower the pH to its desired value. Sulfamic acid is preferred in this application because hydrochloric acid may cause excess chloride in

  the bath that can cause stress in the palladium coating.

  2) The pH adjusted bath is filtered to separate the precipitated salt from the filtrate containing dissolved contaminants. We rinse it

precipitated salt remaining.

  3) the precipitated palladium salt, which is by far the most expensive compound in the bath, can then be redissolved in an alkaline solution such as

  aqueous ammonium hydroxide, a solution containing amide hydroxide

  monium and water in the ratio 1: 1. Sulfamic acid and ammonium chloride can then be added to form a plating bath

electrolytic regenerated.

  The present invention has been described generally, to complete

  different examples will be described below in more detail.

Example 1

  The efficiency of electroplating from an electrolytic bath

  prepared according to the process of the invention has been compared with that of a commercially available palladium bath and that of copper plating.

  from a bath of copper sulphate. Brass panels were raised

  hanged in electrodeposition cells crossed by a current of 1.0 amps, which corresponds to a current density of the order of 15 amperes

per foot squared.

  A bath (bath A) consisting of 18 gpl (grams per liter of H 2 O) of palladium in the form of Pd (NH 3) 2 Cl 2 was used.

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  gpl of ammonium chloride gpl of sulphamic acid pH adjusted to 8.5 using ammonium hydroxide or sulphamic acid

  (temperature maintained around 23 C (74 F).

  The commercial bath used was Palladure 100 (bath B) which is sold by Lea Ronal. Since the efficiency is 100% for copper sulphate under appropriate operating conditions, a standard copper sulphate (bath C) bath was used to confirm the accuracy of the test results. The results are summarized below. Bath A Duration 1 (5 minutes) Duration 2 (4.5 minutes)

  Effective Pd plating 1,9956 g / amp-hr. 1.963 g / amp-hr.

  Pd plating expected 1,990 g / amp-hr. 1,990 g / amp-hro Efficiency 100% 98, 6% Bath B

  Effective Pd plating 1.4316 g / amp-hr. 1.430 g / amp-hr.

  Pd plating expected 1,990 g / amp-hr. 1.990 g / amp-hr.

  Efficiency 71.9% 71.8% Bath C (standard)

  Effective Cu plating 1,1976 g / amp-hr. 1.192 g / amp-hr.

  Cu plating expected 1,186 g / amp-hr. 1.186 g / amp-hr.

  Efficiency 101.0% 100.5% The results of the tests mentioned above prove that one can reach a high efficiency with the bairs according to the invention. This efficiency

  is comparable to that obtained for an ideal copper sulphate bath and

  far from that obtained with the Palladure 100 commercially available.

Example 2

  In this test the pH variation of the prepared baths was evaluated

  according to the process of the invention during an electroplating operation.

  Four 275 ml baths were prepared having the following composition: 18 gpl (grams per liter of H 2 O) of palladium as Pd (NH 3) 2 Cl 2 gpl of ammonium chloride

50 lg of sulfamic acid.

  The starting pH of the baths were adjusted to 7.0, 8.0, 9.0 and 10.0.

  The plating was carried out on brass plates arranged in the

  electroplating units maintained at a temperature of the order of 23 C (74 F.

  The current applied to each of the cells for 5 minutes was an ampere and

  pH was measured after treatment.

  8. The results obtained are shown in Figure 1. Examination of these results shows that when electroplating from a bath with a pH of 7.0 or 8.0, this pH increases somewhat. , which requires ureaddition of acid. For a pH of 9.0 no change is detected. For a pH of 10.0, it decreases somewhat, which requires a minor addition of a base. Coatings obtained by baths with pH greater than 10.0 are

generally unsatisfactory.

Example 3

  The nature of the palladium coatings obtained from baths prepared by the process of the invention was examined as follows. A brass panel was suspended in a container containing 2000 ml containing 1500 ml of bath A corresponding to Example 1. The panel was treated under a

  current of 60 amperes-minutes, after which palladium was added under the

  me Pd (NH3) 2C12 to bring the palladium concentration to 18 grams per liter.

  Sulfamic acid was also added to bring the pH back to 8.5. The electro-

  deposition was carried out for a period of four hours under a current

  an ampere, which corresponds to a current density of around 15 amps.

fathers per foot squared.

  The veneered panel was then removed and examined. In contrary

  predictions based on the results obtained with the help of electronic baths.

  commercial lytic, the edges of the panel showed very little roughness

  or irregularities. The panel was weighed before and after the

  quage, and found that ten grams of palladium were deposited. The panel has slightly curved which implies a slight tension due to the layer of

plating.

  The final pH of the electrolytic bath was 8.9. Given

  the important deposit made, the slight modification of the order of 0, 4 of the pH

  luster a very important feature of the bath according to the invention.

  Then the panel was cut into strips, the slice of these strips was polished and the deposited palladium layer was examined, finding that it was particularly regular. The layer was subjected to a test of

  hardness and it was found that it was sufficient to

  electrical contacts. Microscopic examination revealed

  that the structure was fine and free of inclusions.

  In this particular case, part of the panel was immersed in a 25% nitric acid solution to dissolve the brass. The residual palladium sheet had a thickness of 0.076 to 0.127 mm (0.003-0.005 inches), and was extremely flexible. This sheet was analyzed and found to contain: 9. Copper 0.9% Zinc trace Tin trace Silver 0.03% D Palladium the remainder.

  This analysis shows that the palladium coating obtained is ex-

  extremely pure, which is one of the highly desirable characteristics

  for many applications, including the

clothing of electrical contacts.

  The examples described in detail above illustrate the characteristics of

  of the bath according to the invention. The bath itself does not require any

  ditif to allow to obtain perfect coatings of palladium. This bath poses few problems since it is virtually insensitive to small variations in concentration of palladium, Ph and temperature. It does not release ammonia vapor or other unpleasant or toxic vapors. The bath

  is very conducive to great efficiency and great dispersal power.

  Finally the coatings obtained from this bath are brilliant, well

  adherent, ductile, free from porosity and tension.

  Although the present invention has been described in connection with

  particular examples, it is not limited to these examples and may be subject to different

  various modifications well known to those skilled in the art.

10.

Claims (10)

  An aqueous electrolytic bath for electroplating a non-porous palladium-ductile coating, comprising: from 5 to 50 grams per liter of palladosamine salt selected from the group consisting of palladosamine chloride and palladosamine bromide; from 100 to 150 gr per liter of sulphamic acid, and from 10 to 150 gr per liter of ammonium chloride; said bath having a pH of 6.5 to 0. 2. An electrolytic bath according to claim 1, wherein said palladosamine salt is dosed at 30 to 40 gr per liter, said sulfamic acid at 40 to   gr per liter, and said ammonium chloride at 40 to 60 gr per liter. -   3. Electrolytic bath according to claim 1, whose pH is included between 8.0 and 9.0.   4. Electrolytic bath according to claim 1, containing sufficiently   base or acid to obtain a pH of 8.0 to 9.0.   The electrolytic bath of claim 4, wherein the base is ammonium hydroxide.   6. Process for electroplating a non-porous palladium coating   ductile on a machined part having a conductive surface, comprising   - Pes following: immerse said machined part in an aqueous bath comprising from 5 to 50 gr per liter of palladosamine salt selected from the group consisting of palladosamine chloride and palladosamine bromide, 10 to gr per liter of acid sulfamic acid, and from 10 to 150 gr per liter of chloride   ammonium, said bath having a pH ranging from 6.5 to 10.0; maintain the temperature   this bath between 15 and 55 ° C .; apply a potential between this piece of   born and an inert anode immersed in the bath; and remove the machined part of this bath.   The process according to claim 6, wherein the acid is added   sulfamic bath to maintain its pH to be 8.0 and 9.0.   The method of claim 6, wherein said bath is   maintained in agitation and said potential generates an electrical current density   trolytic content of between 1 and 100 amperes per square foot (1 to fathers per square centimeter).   9. Regeneration process of an electrolytic bath having an excess pH   relative to a pH of 6.0, and containing sulphamic acid, ammonium chloride,   monium, a palladosamine salt belonging to the group comprising palladosamine chloride and palladosamine bromide, and at least a minor amount of acid-soluble contaminating components at pH 3.0 to 5.0, comprising the following steps: adjusting said contaminated bath to a pH between 3.0 and 5.0 with the aid of an acid selected from the group consisting of sulfamic acid and hydrochloric acid to precipitate the palladosamine salt and 11. -1 2471426   to dissolve the contaminating compounds; filter said bath adjusted to separate   salt precipitate; redissolving said precipitated salt in an alkaline medium; and add sulphamic acid and ammonium chloride to form a bath electrolytic regenerated.   The process according to claim 9, wherein the sulfamic acid and   Said alkaline medium is an aqueous solution of ammonium hydroxide.