GB2090867A

GB2090867A - Electrodeposition of white palladium

Info

Publication number: GB2090867A
Application number: GB8137925A
Authority: GB
Original assignee: Hooker Chemicals and Plastics Corp
Current assignee: Occidental Chemical Corp
Priority date: 1980-12-17
Filing date: 1981-12-16
Publication date: 1982-07-21
Also published as: HK67286A; CH647010A5; ES8304221A1; JPS57123993A; SE8106693L; ES508036A0; GB2090867B; AT375965B; AU7753281A; ATA527381A; IT8149860A0; DE3147251A1; BR8108191A; AU530024B2; FR2496128A1

Abstract

Electroplating baths for obtaining white deposits of palladium metal comprise: (a) a source of palladium (e.g. palladium diaminodinitrite), (b) an ammonium conductivity, salt, (c) an organic brightener, and (d) ammonium hydroxide in an amount sufficient to adjust the pH to about 8 to 10, the source of palladium metal being present in an amount sufficient to deposit palladium but less than that which will cause darkening of the deposit. n

Description

SPECIFICATION Bath and method for the electrodeposition of white palladium The present invention relates to an electroplating bath for the deposition of white palladium metal on various surfaces. More particularly, the invention is concerned with baths for producing thin deposits of white palladium metal.

As is known in the art, the use of conventional palladium baths produces deposits which are grey in colour. There are rhodium baths, on the other hand, known to produce white deposits which are very useful in the decorative art industries. In view of the relatively high cost of rhodium as compared to palladium, it would be desirable to be able to obtain a white finish from palladium baths as a substitute for the rhodium finishes now being employed. Previous attempts to produce a white palladium metal deposit were unsuccessful because the deposit was not white enough for the intended purposes, e.g., as a substitute for the conventional white rhodium deposits. It would also be useful for commercial purposes to be able to obtain readily thin, white deposits of palladium metal.

U.S. Patent 330,149 which issued to Pilet et al. in 1885, does mention the production of a "white palladium deposit". The electroplating bath of Pilet et al. contained palladium chloride, ammonium phosphate, sodium phosphate or arnmonia, and, optionally, benzoic acid. The operating pH of the bath is not disclosed, although it is stated that ammonia is "boiled" off and "the liquid which was alkaline, becomes slightly acid". As indicated, the use of benzoic acid is disclosed to be optional, but the patentees disclose that it bleaches the deposit and makes the deposit more striking on iron and steel.

Electroplating baths designed to improve the brightness of palladium or palladium alloy deposits on metal substrates are also known in the art. See, for example, U.S. Patent 4,098,656 which issued to Deuber in 1 978. In this patent the improved brightness is achieved by utilizing in the bath both Class I and Class II organic brighteners and an adjusted pH range of from 4.5 to 12.

In accordance with the present invention it has now been discovered than thin, white palladium metal deposits can be obtained by utilizing an electroplating bath formed form a bath soluble source of palladium and a bath soluble ammonium salt as the conductivity material. The bath must also contain ammonium hydroxide, and a particular type of organic brightener. These components as well as an adjusted pH of at least about 8 are essential in order to obtain the desired whitenes of the palladium metal deposit.

In general, the electroplating baths of this invention comprise the following components: (a) A bath soluble source of palladium metal (b) A bath soluble conducting salt (c) An organic brightener (d) Ammonium hydroxide and optionally, a buffer.

The use of the brightener in these baths not only tends to increase the.whiteness of the palladium metal deposit but permits thicker metal deposits without loss of the desired degree of whiteness, in contrast to baths which do not contain the brightener.

The source of the palladium metal in the electroplating bath of this invention may be a paIladiuni amine complex, such as the nitrate, nitrite, chloride, sulphate and sulphite complexes. Typical of such complexes which may be used are palladium diaminodinitrite and palladosamine chloride, with palladium diaminodinitrite being preferred.

The palladium content of the plating bath will be at least sufficient to deposit palladium on the substrate when the bath is electrolyzed but less than that which will cause darkening of the deposit.

Typically, the palladium concentration will be about 0.1 to 20 grams/litre, with concentrations of about 1 to 6 grams/litre being preferred.

The conductivity salt may be any bath soluble ammonium salt, such as ammonium sulphate, ammonium chloride or dibasic ammonium phosphate. Mixtures of such ammonium-containing inorganic salts may also be utilized. The amount of ammonium conductivity salt in the plating bath will be at least that which will provide sufficient conductivity to the bath to effect the palladium electrodeposition, up to the maximum solubility of the salt in the bath. Typically, the ammonia conductivity salt will be present in an amount of about 30 to 120 grams/litre, with amounts of about 50 to 100 grams/litre being preferred.

The buffering agent is preferably ammonium biborate, since it also enhances the whiteness of the deposit. It will be understood, however, that other buffers such as sodium tetraborate, can also be used effectively in these particular baths. Buffers other than the borates may also be employed, provided that they maintain the pH within the desired range of 8 to 10. The amount of the buffering agent or agents used may vary from about 0 to 50 g/l, and preferably about 10 to 30 g/l.

Another essential material employed in formulating the electroplating bath of this invention is ammonium hydroxide. This compound is used in an amount sufficient to raise the pH of the bath to the desired range of 8 to 10, with a pH range of 9 to 9.5 being preferred. In general, the ammonium hydroxide is employed in amounts ranging from about 10 to 50 ml per litre of the plating bath.

The organic brighteners required in the bath are the Class I and Class Il nickel brighteners. Organic brighteners which can be employed for the present purposes are described in Modern Electroplatinez, 2nd Ed., F. A. Lowenheim (Ed.) pages 272 et seq. (1963) and Metal Finishing Guidebook and Directory, 42 Ed., pages 358 et seq. (1073). Such brighteners are disclosed in column 1, line 2 to column 2, line 8, of U.S. Patent No. 4,098,656; the disclosure of which is incorporated herein by reference.Specific organic brighteners which have been found to be especially useful for the purpose are enumerated below: CLASS I NICKEL BRIGHTENERS Saccharin Sodium Benzene Sulphonate Benzene Sulphonamide Phenol Sulphonic Acid Methylene bis (naphthalene) Sulphonic Acid CLASS II NICKEL BRIGHTENERS 2-Butyne-1,4-diol Benzaldehyde-o-sodium Sulphonate 2-Butene-1,4-diol Allyl sulphonate The concentration of the individual brighteners may ra, ige from about 1 to 5 g/l, and preferably about 1 to 3 g/l. Some compounds may fall within the description of both Class I and II, but that will not affect their utility in the present baths. As distinct from the requirement of U.S.Patent No. 4,098,656 that at least one brightener from each class of nickel brighteners must be used in the present invention only one organic brightener from either class has to be employed in order to obtain the desired results.

As discussed above, the electroplating bath of the invention must be operated at a pH of at least 8, and preferably art a pH of about 9 to 9.5.

The temperature of the plating bath may be maintained between room temperature and 1 600F (71 OC). In order to avoid the emission of excess ammonia from the solution, the plating temperature preferably will be below about 1 300F (540 C). Current densities from about 0.1 to 50 ASF (i.e., about 0.01 to 5.4 A/dm2) are suitable for most purposes. For rack plating, a current density of from 2 to 20 (0.22 to 2.2 ASD), and preferably about 10 ASF (1.1 ASD), may be employed.

A further feature of the present invention is to produce thin deposits of palladium so as to further ensure the production of a white deposit. Thus, the deposit thicknesses may vary from about 0.01 to 1.0 micron, and preferably from 0.03 to 0.4 micron.

The "whiteness" characteristic of the present invention is quantified in terms of white light reflectivity measured by spectrophotometric methods such as utilizing a Perkin-Elmer 559 spectrophotometer and plating the deposits to be studied over 1 inch by 1 inch (2.5 x 2.5 cm) panels preplated with 0.5 mils of copper and 0.5 mils of nickel, referred to hereinafter as the nickel plated panels, to eliminate any surface imperfections. The white light reflectivity of these panels is scanned in the transmittance mode from 400 to 700 nanometers against a magnesium oxide reference plate. The sample deposit scan is then compared to a similar scan of a rhodium deposit.

The preferred electroplating baths having a pH of at least 8, according to the present invention are as follows: Component Concentration Pd(NH3)2(NO2)2* 1 to 6 g/l (as Pd) Conductivity salt 50 to 100 g/l Organic Brightener (Class 1 1 to 3 g/l or Class II) Ammonium Hydroxide 10 to 50 ml/l Buffer O to 50 g/I * Palladium diaminodinitrite The invention can be put into practice in various ways and a number of specific embodiments will be described to illustrate the invention with reference to the accompanying Examples, wherein the temperatures are given in degrees centigrade, and to the accompanying drawing which is a graph which illustrates the improved whiteness of the deposits of the present invention as compared to the prior art.

The graph plots % reflectivity as the ordinate against the wave length in nm of the reflected light; line A is for a rhodium plating; line B for Example 1; line C for Example 2; line D for Example 3; line E for Example 3 of Deuber U.S. Patent 4098656 and line F for Pilet U.S. Patent 330,149.

EXAMPLE 1 A palladium electrolytic solution was prepared by dissolving the following ingredients in water: Component Concentration Palladium Diaminodinitrite 2 g/l (as Pd) Dibasic Ammonium Phosphate 96 g/l Ammonium Biborate 25 g/l Ammonium Hydroxide 24 ml/l Benzaldehyde-o-sodium 2 g/l Sulphonate The amount of ammonium hydroxide used in the above formulation raised the pH to about 9.

Plating was performed at a temperature of 220C, a current density of 10 ASF (1.1 ASD) for 30 seconds.

on a nickel plated panel to produce a white palladium deposit having a thickness of 0.25 to 0.35 microns. The ammonium biborate acted as a buffer to maintain the pH at the desired level and to enhance the desired whiteness of the resulting palladium metal deposit.

EXAMPLE 2 A plating bath similar to that of Example 1, with the use of a different brightener, was formulated as follows: Component Concentration Palladium Diaminodinitrite 2 g/l (as Pd) Dibasic Ammonium Phosphate 96 g/l Ammonium Hydroxide 24 ml/l Ammonium Biborate 25 g/l 2-Butyne-1,4-diol 2 g/l The adjusted pH was 9 and the plating process was operated under the same conditions as in Example I to produce a white palladium deposit having a thickness of 0.25-0.35 microns. The reflectivity of the palladium metal deposit on the nickel plated panel is given below in Table 1.

EXAMPLE 3 A plating bath, similar to that of Example 1, with the exception that a Class I nickel brightening agent was utilized, was formulated as follows: Component - Concentration Palladium Diaminodinitrite 1 g/l (as Pd) Dibasic Ammonium Phosphate 50 g/l Ammonium Biborate 25 g/l Ammonium Hydroxide 24 ml/l Saccharin (Class I brightener) 2 g/l The aqueous solution contained sufficient ammonium hydroxide to raise the pH to 9. The plating operations were carried out under the same conditions as Examples 1 and 2 to produce a white palladium deposit having a thickness of 0.25-0.35 microns.

In the following Table 1 the white light reflectivity of the palladium deposits on the nickel plated panels of Examples 1 through 3 was compared with a standard rhodium deposit (made as described below) on a nickel plated panel as well as deposits made in accordance with Example 3 of the Deuber U.S. Patent No. 4,098,656 and the Pilet U.S. Patent No. 330,149 (page 1, lines 77-102 and page 2, lines 1-8). The Deuber and Pilet deposits had a thickness of 0.25-0.35 microns. The Perkin-Elmer spectrophotometer and the test procedure described above were employed.

TABLE I % Reflectivity Deposit 400nm 500nm 600nm 700nm Rhodium 80.5 85.0 88.5 90.5 Deuber 60.0 71.5 78.0 80.5 Pilet 51.5 60.0 66.5 72.0 Example 1 67.0 78.0 83.0 85.0 Example 2 66.0 75.5 80.5 83.0 Example 3 67.0 77.0 81.5 83.5 The foregoing data reveal that the electroplating baths of this invention produce a palladium metal deposit having a significantly improved reflectivity to white light when compared to both Deuber and Pilet. The visual difference in whiteness is so significant that for commercial applications it can be the difference between acceptance and rejection.

When the foregoing data are plotted, percentage reflectivity versus wavelength, as in the accompanying drawing, the resulting graph further reveals the significance of the results achieved by the practice of the present invention.

Scanning Electron Microscope (SEM) Micrographs were made of the deposit produced in Example 1 and those produced by the procedures of the Pilet et al and Deuber patents. The Micrographs show that the Pilet et al deposits have extensive dendritic deposit is and surface roughness. The Deuber deposits, while showing somewhat reduced dendritic growth than Pilet et al, still have considerable surface roughness. In contrast, the deposit from Example 1, is extremely smooth with no dendritic deposits. This further illustrates the unique properties of the deposits produced by the present invention and indicates the corellation between the smoothness of the deposit and its white light reflectivity.

The standard rhodium deposit referred to above was made as follows: The nickel plated panels were plated with rhodium in a rhodium plating bath containing 2 g/l of rhodium as phosphate and 20 ml/l of 98% sulphuric acid at 500 C, a current density of 2 ASD using moderate agitation and a plating time of 30 seconds to produce a deposit 0.05 to 0.1 microns thick.

Claims

1. A stable, aqueous electroplating bath suitable for obtaining thin, white deposits of palladium metal which comprises: (a) a bath soluble source of palladium (b) a bath soluble ammonium conductivity salt (c) a brightening amount of an organic brightener, and (d) ammonium hydroxide in an amount sufficient to adjust the pH to about 8 to 10; the source of palladium metal being present in an amount at least sufficient to deposit palladium on a substrate when the bath is electrolyzed but less than that which will cause darkening of the deposit and the ammonium conductivity salt being present in at least an amount that will provide sufficient conductivity to the bath to effect the palladium electrodeposition.

2. An electroplating bath as claimed in claim 1 in which the source of palladium is present in an amount sufficient to provide from 0.1 to 20 grams/litre palladium in the bath.

3. An electroplating bath as claimed in claim 2 in which the source of palladium is present in an amount sufficient to provide from 1 to 6 grams/litre palladium in the bath.

4. An electroplating bath as claimed in claim 1,2 or 3 in which the ammonium conductivity salt is present in an amount of from 30 to 120 grams/litre.

5. An electroplating bath as claimed in claim 4 in which the ammonium conductivity salt is present in an amount of from 50 .; 100 grams/litre.

6. An electroplating bath as claimed in any one of claims 1 to 5 in which the source of palladium is palladium diaminodinitrite.

7. An eiectroplating bath as claimed in any one of claims 1 to 6 in which ammonium conductivity salt comprises dibasic ammonium phosphate, ammonium chloride, ammonium sulphate or a mixture there af.

8. An electroplating bath as claimed in any one of claims 1 to 6 in which the ammonium conductivity salt comprises ammonium phosphate.

9. An electroplating bath as claimed in any one of claims 1 to 6 in which the ammonium conductivity salt comprises ammonium sulphate.

10. An aqueous palladium electroplating bath consisting essentially of a source of palladium ions in an amount to provide 1 to 6 g/l of palladium, a brightener in an amount of 1 to 3 girl, an ammonium conductivity salt in an amount of 50 to 100 g/l, and ammonium hydroxide in an amount to produce a pH of 8 to 10, and optionally a buffer.

11. An aqueous palladium electroplating bath consisting essentially of a source of palladium ions in an amount to provide 1 to 6 g/l of palladium, dibasic ammonium phosphate, ammonium chloride or ammonium sulphate as an ammonium conductivity salt in an amount of 50 to 100 g/l, a brightener in an amount of 1 to 3 g/l, and ammonium hydroxide in an amount to produce a pH of 8 to 10, and optionally, a buffer.

12. An aqueous palladium electroplating bath consisting essentially of a source of palladium ions in an amount to provide 1 to 6 g/l of palladium, dibasic ammonium phosphate, ammonium chloride or ammonium sulphate as an ammonium conductivity salt in an amount of 50 to 100 g/l, benzaldehycle-osodium sulphonate or 2-butyne-1,4-diol or saccharin as a brightener in an amount of 1 to 3 g/l and ammonium hydroxide in an amount to produce a pH of 8 to 10, and optionally a buffer.

13. An aqueous palladium electroplating bath consisting essentially of palladium diaminodinitrite, in an amount to provide 1 to 6 g/l of palladium, an ammonium conductivity salt in an amount of 50 to 100 g/l, a brightener in an amount of 1 to 3 g/l and ammonium hydroxide in an amount to produce a pH of 8 to 10, and optionally a buffer.

14. An aqueous palladium electroplating bath consisting essentially of palladium diaminodinitrite in an amount to provide 1 to 6 g/l of palladium, dibasic ammonium phosphate, ammonium chloride or dmmonium sulphate as an ammonium conductivity salt in an amount of 50 to 100 g/l, a brightener in an amount of 1 to 3 g/l and ammonium hydroxide in an amount to produce a pH of 8 to 10, and optionally a buffer.

1 5. An aqueous palladium electroplating bath consisting essentially of palladiiim diaminodinitrite, in an amount to provide 1 to 6 g/l of palladium, dibasic ammonium phosphate, ammonium chloride or ammonium sulphate as an ammonium conductivity salt in an amount of 50 to 100 g/l, benzaldehyde-o- sodium sulphonate or 2-butyne-1,4-diol or saccharin as a brightener in an amount of 1 to 3 g/i, and ammonium hydroxide in an amount to produce a pH of 8 to 10, and optionally a buffer.

1 6. An electroplating bath as claimed in any one of claims 1 to 1 5 which also contains a buffering agent.

1 7. An electroplating bath as claimed in claim 1 6 in which the buffering agent is ammonium biborate.

1 8. An electroplating bath as claimed in any one of claims 1 to 1 7 in which the organic brightener is present in an amount of 1 to 3 g/l.

19. An electroplating bath as claimed in any one of claims 1 to 1 9 in which the organic brightener comprises benzaldehyde-o-sodium sulphonate.

20. An electroplating bath as claimed in any one of claims 1 to 1 9 in which the organic brightener comprises saccharin.

21. An electroplating bath as claimed in any one of claims 1 to 20 in which the organic brightener comprises 2-butyne-1-1 ,4-diol.

22. An electroplating bath as claimed in any one of claims 1 to 21 in which the pH is adjusted to a range of 9 to 9.5.

23. An electroplating bath as claimed in Claim 1 substantially as specifically described herein with reference to any one of Examples 1,2 or 3.

24. A method of depositing white electrodeposits of palladium metal on a substrate which comprises passing an electric current through an electroplating bath as claimed in any one of claims 1 to 23 between a cathode and an anode, for a period of time sufficient to produce a palladium electro deposit having a thickness of from about 0.01 to 1.0 microns.