GB2090869A - White palladium deposit - Google Patents

Abstract

The deposit of palladium metal is characterized by a white colour having average white light reflectivity values, determined by spectrophotometric methods. ranging from about 78 to 95% of the average white light reflectivity of rhodium metal deposits at the same wavelengths and further characterized by being smooth and substantially free of dendritic deposits. The deposit may be obtained by electroplating, utilizing baths comprising a source of palladium metal, an ammonium conductivity salt, ammonium hydroxide to provide a pH of 5 to 10 and optionally an organic and a nickel containing inorganic brightener. <IMAGE>

Description

SPECIFICATION White palladium electrodeposit The present invention relates to thin white palladium metal electrodeposits on conventionai substrates, which deposits have the appearance of white rhodium.

As is known in the art, conventional palladium electrodeposits are grey in colour. Rhodium electrodeposits, on the other hand, are white and 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 will 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 ammonia, 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 a Class I and a Class II organic brightener and an adjusted pH range of from 4.5 to 12.

In accordance with the present invention, unique white palladium metal electroplated deposits are formed on a suitable substrate. These deposits are characterized by average white light reflectivity values which range from about 78 to 95%, preferably from about 82 to 95%, of the average white light reflectivity of rhodium at the same wavelengths. These deposits are further characterized as being very smooth and substantially free of dendritic deposits.

Using known spectrophotometric methods and apparatus, such as the Perkin-Elmer 559 Spectrophotometer, palladium and rhodium deposits are scanned over the visible light spectrum of from 400 to 700 nanometers.

Based on the average white light reflectivity of rhodium metal, the following minimum percentage values were obtained for the white palladium metal deposits of this invention: Based on the percentage Rhodium Metal Reflectivity Nanometers Broad, % Preferred, % 400 at least 78 at least 83 500 at least 88 at least 92 600 at least 90 at least 94 700 at least 91 at least 94 These unique white palladium deposits are formed on any suitable substrate, such as steel, nickel, copper, zinc or precious or noble metals. The deposits have a thickness of from about 0.01 to 1.0 micron, with thickness of about 0.03 to 0.04 microns being preferred.

In determining the whiteness characteristics of these deposits, as set forth above, these are quantified in terms of white light reflectivity measured by spectrophotometric methods. These were measured using a Perkin-Elmer 559 spectrophotometer, although other similar instruments can be used. The deposits to be measured were plated over 1 inch by 1 inch (2.5 x 2.5 cms) steel panels that had been preplated with 0.5 mils of copper and then with 0.5 mils of nickel, to eliminate surface imperfections. These panels are hereinafter referred to as the nickel plated panels.

The white light reflectivity of the deposits on these panels were scanned in the transmittance mode from 400 to 700 nanometers against a magnesium oxide reference plate. The scan of the sample deposits of the present invention were then compared to a similar scan of a rhodium deposit to obtain the percentage reflectivity values given above.

As will be described hereinafter, these unique white palladium metal deposits can be obtained by utilizing certain prescribed palladium metal-containing electroplating baths.

Electroplating baths and processes which may be employed to produce the unique white palladium deposits are described in detail in co-pending U.S. Patent Applications Serial No. 21 7,31 8, G.B. Serial Number 8137924, U.S. Serial No.217319, G.B. Serial Number 8137926 and U.S. Serial No. 217,316, G.B. Serial Number 8137925, filed on 17th December 1980. Attention is directed to these three copending G.B. applications for further details of the processes described therein and their disclosures are incorporated by reference.

In general, these electroplating baths are stable aqueous solutions containing a bath soluble source of palladium, a bath soluble ammonium conductivity salt and one or more additional components, including ammonium hydroxide to adjust the bath pH to the desired level within a pH range of 5 to 10; buffers, to maintain the desired bath pH; chloride ions; an organic brightener and a nickel containing inorganic brightener.

The bath soluble source of palladium may be any palladium amine complex, such as the nitrate, nitrite, chloride, sulphate or sulphite complexes. Typical of such complexes which may be used are palladium diaminodinitrite and palladosamine chloride. The amount of palladium in the 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/iitre, with concentrations of about 1 to 6 grams/litre being preferred.

The ammonium conductivity salt in the bath may be any bath soluble ammonium-containing inorganic salt, such as dibasic ammonium phosphate, ammonium sulphate, or ammonium chloride.

Mixtures of such salts may also be used. The amount of the ammonium conductivity salt in the plating bath will be at least that which will provide sufficient conductivity to the bath to effect the palladium eiectrodeposition, up to the maximum solubility of the salt in the bath. Typically, the ammonium conductivity salt will be present in an amount of about 25 to 120 grams/litre, with amounts of about 30 to 100 grams/litre being preferred.

Typical of preferred electroplating baths which may be used are the following: Component Concentration Pd(NH3)2(NO2)2* 1 to 6 gl (as Pd) Conductivity Salt 50 to 100 g/l Ammonium Hydroxide 10 to 50 ml/l Buffer O to 50 g/I * Palladium diaminodinitrite Bath pH 9-9.5 Component Concentration Palladosamina Chloride 1 to 6 g/l (as Pd) Conductivity Salt 30 to 70 g/l Potassium Chloride 10 to 20 9/ Organic Brightener 1 to 3 g/l Inorganic Brightener 0.2 to 0.5 g/I Ammonium Hydroxide O to 1 5 ml/l Bath pH 5-8 Component Concentration Pd(NH3)2(NO2)2 1 to 6 g/l (as Pd) Conductivity Salt 50 to 100 g/l Organic Brightener (Class I or II) 1 to 3 g/I Ammonium Hydroxide 10 to 50 ml/l Buffer 0 two 50 9/ * Palladium diaminodinitrite Bath pH 9-9.5 In the plating process using these baths, the temperature of the palladium plating bath may be maintained between room temperature and 1 600F (71 aC). In order to avoid the emission of excess ammonia, the plating temperature will be preferably below about 1 300F (540C). For many purposes operations at room temperature are preferred. Current densities from about 0.1 to 50 ASF (i.e., 0.01 to 5.4 A/dm2) are suitable. Typically, current densities of from 2 to 20 (0.22 to 2.2 ASD) and preferably about 10 ASF (1.1 ASD) may be employed.

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 whiteness of the palladium electrodeposits 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 6; line C for Example 5; line D for Example 1; line E for Deuber and line F for Pilet.

In each of the examples white palladium deposit 0.25-0.35 microns thick was produced.

EXAMPLE I A palladium electrolyte solution was prepared by dissolving the following ingredients in water: Component Concentration Palladium Diaminodinitrite 2 g/l (as Pd) Dibasic Ammonium Phosphate 95 g/l Ammonium Hydroxide 24 ml/l The amount of ammonium hydroxide used in the above formulation adjusted the pH to about 9.2.

Plating was performed at ambient temperature, a current density of 10 ASG (1.1 ASD) and for 45 seconds on the nickel plated panel.

EXAMPLE 2 A plating bath similar to Example 1, but with the use of a buffer, was formulated as follows: Component Concentration Palladium Diaminodinitrite 2 g/l (as Pd) Dibasic Ammonium Phosphate 96 g/l Ammonium Hydroxide 24 mlil Ammonium Biborate . 25 g/l The amount of ammonium hydroxide used in this formulation also adjusted the pH to about 9.2.

Plating was performed at ambient temperature, a current density of 10 ASF (1.1 ASD), and for 45 seconds on the nickel plated panel. The ammonium biborate acted as a buffer to maintain the pH at the desired level.

EXAMPLE 3 The plating bath was similar to that of Example 2, with the exception that sodium tetraborate was used as the buffering agent. The formulation was as follows: Component Concentration Palladium Diaminodinitrite 4 g/l (as Pd) Monobasic Ammonium Phosphate 50 g/l Ammonium Hydroxide 24 ml/l Sodium Tetraborate 25 g/l The aqueous solution contained sufficient ammonium hydroxide to adjust the pH to 9. The plating operations were carried out under the same conditions as Examples l and 2.

EXAMPLE 4 A palladium electrolyte solution was prepared by dissolving the following ingredients in water: Component Concentration Palladosamine Chloride 2 g/l (as Pd) Ammonium Sulphate 60 g/l Potassium Chloride 1 5 g/I Benzaldehyde-o-sodium sulphonate 2 g/l Ammonium Nickel Sulphate 0.5 g/I The pH of the plating bath was 5.5 to 7 during plating operations at a temperature of 45--55"C and a current density of 10-20 ASF (1.1 to 2.2 ASD) on the nickel plated panel.

EXAMPLE 5 A plating bath, somewhat similar to that of Example 4, was formulated as follows: Component Concentration Palladosamine Chloride 2 g/l (as Pd) Ammonium Sulphate 30 g/l Potassium Chloride 15 g/l Ammonium Hydroxide 8 ml/l Benzaldehyde-o-sodium sulphonate 2 g/I Nickel Sulphate 0.2 g/l The pH of the plating bath ranged from 5.5 to 7 during operations at a temperature of 500C and a current density of 4-1 5 ASF (0.43 to 1.6 ASD) on the nickel plated panel.

EXAMPLE 6 A palladium electrolytic solution was prepared by dissolving the following ingredients in water: Component Concentration Palladium Diaminodinitrite 2 g/l (as Pd) Pibasic Ammonium Phosphate 96 g/l Ammonium Biborate 25 g/l Ammonium Hydroxide 24 ml/i Benzaldehyde-o-sodium sulphonate 2 g/l 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), and for 30 seconds on the nickel plated panel 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 7 A plating bath similar to that of Example 6, 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 6.

EXAMPLE 8 A plating bath similar to that of Example 6, with the exception that a Class I nickel brightening agent was utilized and was made up 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 2 g/l The aqueous solution contained sufficient ammonium hydroxide to raise the pH to 9. The plating operation was carried out under the same conditions as for Examples 6 and 7.

In the following table the white light reflectivity of the palladium deposits on the nickel plated panels of Examples 1 to 8 was compared with a standard rhodium deposit (made as described below) on the 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 Pilet and Deuber deposits, like those of Examples 1-8, had a thickness of 0.25-0.35 microns. As described above, the Perkin-Elmer 559 Spectrometer was employed. More specifically, the scanning of the various nickel plated panels, which were coated with the metal deposits vvas carried out in the transmittance mode over the visible light spectrum of from 400 to 700 nanameters against a magnesium oxide reference plate.

TABLE % Reflectivity Deposit 400 nm 500 nm 600 nm 700 nm 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 63.5 75.0 80.0 82.5 Example 2 64.5 75.5 81.0 83.5 Example 3 63.0 74.5 80.0 83.0 Example 4 66.0 76.5 81.5 84.0 Example 5 67.0 77.0 82.0 84.5 Example 6 67.0 78.0 83.0 85.0 Example 7 66.0 75.5 80.5 83.0 Example 8 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 make the difference between acceptance and rejection.

When representative examples of the foregoing data pertaining to the present invention are plotted, percentage reflectivity versus wavelength, against a rhodium metal deposit as well as the palladium metal deposits of Deuber and Pilet, the resulting graph as in the accompanying drawing reveals the significance between the palladium metal deposits of the present invention and the prior art deposits.

Scanning Electron Microscope (SEM) micrographs were made of the deposits produced in Examples 2, 4 and 6 produced by the procedures of the Pilet et al and Deuber patents. These micrographs show that the Pilet et al deposits has extensive dendritic deposits and surface roughness.

The Deuber deposit, while showing somewhat reduced dendritic growth than Pilet et al, still has considerable surface roughness. In contrast, the deposits from Examples 2, 4 and 6 ranged from smooth to extremely smooth, with no dendritic deposits in the samples from Examples 2 and 6. The sample from Example 4 did have very small amounts of dendrites but these were much less than those in the Deuber deposit and the overall surface smoothness was noticeably greater. This further illustrates the unique properties of the white palladium deposits of the present invention and indicates the correlation between the smoothness of the deposit and its white light reflectivity.

The deposits of the present invention also have a white light reflectivity profile against the standard magnesium oxide reference plate (as defined herein) of a comparative % reflectivity as a percentage of the % reflectivity of the said rhodium deposit of at least 75% especially at least 76% e.g.

78% to 84% at 400 nm, a comparative % reflectivity of at least 85% especially at least 86% e.g. 87% to 92% at 500 nm, a comparative % reflectivity of at least 88.5% especially at least 89% e.g. 90% to 94% at 600 nm and a comparative % reflectivity of at least 89% especially at least 90% e.g. 91 to 94% at 700 nm.

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.

Figures 2 and 3 are from Scanning Electron photomicrographs, Figure 2 taken at 900 to the surface and Figure 3 at a 300 angle.

Figure 2 is of the Deuber Ex. 3 deposit described above showing dendrites 10 and was taken at 20 K fold magnification.

Figure 3 is typical of deposits in accordance with the present invention as described above with reference to Exs. 2, 4, and 6 and shows platelets 20 indicative of high reflectivity to white light. It was taken at 10 K fold magnification.

Claims (5)

1. A product comprising a substrate having thereon a white palladium metal deposit the said palladium metal deposit being characterized by being smooth and substantially free of dendritic deposits and by having average white light reflectivity values, determined by spectrophotometric meal-:, ranging from about 78 to 95S'o of the average white light reflectivity values of rhodium metal measured at the same wavelengths.

2. A product as claimed in claim 1 in which the light reflectivity values are spectrophotometrically measured over a spectrum of from 400 to 700 nanometers.

3. A white palladium deposit substantially free of dendritic deposits and having a white light reflectivity profile against the standard rhodium deposit (as defined herein) of a comparative % reflectivity as a percentage of the % reflectivity of the said rhodium deposit of at least 75% at 400 nm, a comparative % reflectivity of at least 85% at 500 nm, a comparative % reflectivity of at least 88.5% at 600 nm, and a comparative % reflectivity of at least 89% at 700 nm.

4. A product as claimed in claim 1 or 3 in which the deposit has a thickness of from 0.01 to 1.0 microns.

5. A product as claimed in claim 4 in which the deposit has a thickness of from 0.03 to 0.4 microns.