Electroplating white palladium

© Start of patent period: 1984 02 15 Longest possible duration:

© Issued: 1984 09 25 © inventor:

© dependence:

375 965 © Pamphlets considered to delineate the prior art:

US-PS 4098656 US-PS 4066517 GB-PS 1035850 OE-OS 2943399 <26-0 3-1981I

Nr.375965

The invention relates to an electroplating bath for the deposition of white palladium metal on various surfaces. In particular, the invention relates to baths for forming thin coatings of white palladium metal.

As is already known, when conventional palladium baths are used, over 5 lines of gray color are formed. On the other hand, rhodium baths are known to form white coatings which are very useful in the jewelry and decoration industry. In view of the relatively high cost of rhodium compared to palladium, it would be highly desirable to be able to obtain a white coating from palladium baths to replace the rhodium coatings currently used. The previous attempts to form a white palladium metal coating were unsuccessful because the coating was not white enough for the intended purposes, for example as a replacement for the conventional white rhodium coatings. It would also be useful for commercial purposes to easily produce thin, white palladium metal coatings.

U.S. Patent No. 3,330,149 mentions the preparation of a white palladium coating. The electroplating bath according to this patent contains palladium chloride, ammonium phosphate, sodium phosphate or ammonia and optionally benzoic acid. The pH of the bath at work is not disclosed, although it is stated that ammonia is boiled off and the liquid, which was alkaline, becomes slightly acidic. As stated, benzoic acid is only optionally used, but it is further disclosed in the said patent that it bleaches the overcoat and makes it more noticeable on iron and steel.

Electroplating baths intended to improve the gloss of palladium or palladium alloy coatings on metal substrates are also already known, see, for example, U.S. Patent No. 4,098,656. According to this patent, the improved gloss is achieved by using both Class I and Class II organic brighteners in the bath and adjusting a pi value of 4.5 to 12.

In the drawing, the improved whiteness of palladium coatings obtainable according to the invention is explained in comparison to the prior art.

According to the invention, it has now been found that thin white palladium metal coatings can be obtained by using an electroplating bath formed by a bath-soluble palladium source and a bath-soluble ammonium salt as a conductive material. The bath must also contain ammonium hydroxide and a special kind of organic brightener. These components as well as the adjustment of the pi value to at least 8 are essential to achieve the desired whiteness of the palladium metal coating.

The invention thus provides a stable aqueous electroplating bath suitable for obtaining thin white palladium metal coatings which is characterized in that it consists essentially of (a) a bath-soluble source of pure palladium free of alloying elements in an amount, sufficient to provide from 0.1 to 20 g / l of palladium in the bath, (b) from 30 to 120 g / l of a bath-soluble conductive ammonium salt, (c) 1 to 5 g / l of an organic brightener from the group of nickel brighteners

Class I and II and (d) ammonium hydroxide in an amount sufficient to adjust and maintain the pH of the bath at the range of about 8 to 10, and optionally a buffer, ⁴⁵ With respect to the subject matters of U.S. Patent No. 4,098,656, U.S. Patent No. 4,066,517 and British Patent No. 1,035,850, comparative experiments were carried out, the results of which show that white palladium coatings of the present invention are obtained which are much more similar in appearance to rhodium are, than can be achieved according to the methods of the aforementioned PSEN. These test results are as follows:

Nr.375965

<td rowspan="2">example</td><td rowspan="2">source</td><td colspan="4">test conditions</td>

<td>Pd G/¹</td><td>Temp. ° C.</td><td>p_H</td><td>Dense ASF</td>

<td>1</td><td>Invention Example 1</td><td>2</td><td>22</td><td>9.0</td><td>10</td>

<td>2</td><td>U.S. Patent No. 4,066,517, Ex. 1</td><td>10</td><td>37.7</td><td>9.0</td><td>10</td>

<td>3</td><td>U.S. Patent No. 4,099,656. Ex. 1</td><td>10</td><td>50</td><td>8.5</td><td>5</td>

<td>4</td><td>British Patent No. 1,035,850 Ex. 1</td><td>11</td><td>30</td><td>8.5</td><td>6</td>

<td rowspan="2">example</td><td rowspan="2">source</td><td colspan="5">% Reflectance based on% rhodium metal reflectance</td>

<td>400 nm</td><td>500 nm</td><td>600 nm</td><td>70</td><td>0 nm</td>

<td>1</td><td>Invention Example 1</td><td>83</td><td>91</td><td>92</td><td></td><td>93</td>

<td>2</td><td>U.S. Patent No. 4,066,517, Ex. 1</td><td>77</td><td>84</td><td>86</td><td></td><td>86</td>

<td>3</td><td>U.S. Patent No. 4,098,656, Ex. 1</td><td>82</td><td>89</td><td>89</td><td></td><td>91</td>

<td>4</td><td>British Patent No. 1,035,850 Ex. 1</td><td>73</td><td>82</td><td>84</td><td></td><td>85</td>

Further comparative experiments were conducted with those methods closest to the results of the invention, with the palladium content of the baths reduced to 1 g / l in each bath tested, thus comparing the results obtained on the same palladium content basis. The results of these experiments were as follows:

<td rowspan="2">example</td><td colspan="4">% Reflectance based on% rhodium metal reflectance</td>

<td>400 nm</td><td>500 nm</td><td>600 nm</td><td>700 nm</td>

<td>1</td><td>92</td><td>94</td><td>93</td><td>94</td>

<td>3</td><td>73</td><td>82</td><td>88</td><td>91</td>

These results clearly show that when compared on the basis of the same palladium content, the baths according to the invention gave deposits which, in appearance, were significantly closer to rhodium than the other baths.

The use of the brightener in these baths not only increases the whiteness of the palladium metal coating but, unlike baths that do not contain brighteners, allows for thicker metal coatings without loss of the desired whiteness.

The palladium metal source in the electroplating bath of the present invention may be amine-complexed to any palladium, such as the nitrate, nitrite, chloride, sulfate and sulfite complex. Typical such useful complexes are palladium diaminodinitrite and palladamine chloride, with palladium diaminodinitrite being preferred. The palladium content of the plating bath is at least sufficient to deposit palladium on the substrate when the bath is electrolyzed, but is less than that which causes the coating to darken. Typically, the palladium concentration is about 0.1 to 20 g / l, with concentrations of about 1 to 6 g / l being preferred.

The conductive salt may be any soluble ammonium salt, such as ammonium sulfate, ammonium chloride, dibasic ammonium phosphate, and the like. Mixtures of such ammonium-containing inorganic salts can also be used. The proportion of conductive ammonium salt in the platinum bath is at least such as to impart sufficient conductivity to the bath to effect the electrolytic precipitation of palladium and to reach the maximum solubility of the salt in the bath. Typically, the conductive ammonium salt is present at a level of about 30 to 120 g / l, with levels of about 50 to 100 g / l being preferred.

The buffer is preferably ammonium biborate, as it also increases the whiteness of the coating. However, it is clear that other buffers such as sodium tetraborate and the like. can be used effectively in these baths. Also, buffers other than borates may be used, provided they maintain the pi value in the desired range of 8 to 10. The level of buffering agent or agent may be from 0 to about 50 g / l, preferably about 10 to 30 g / 1, amount.

Another essential material used in formulating the electroplating bath of the present invention is ammonium hydroxide. This compound is used in a proportion sufficient to raise the pH of the bath to the desired range, namely 8 to 10, preferably 9 to 9.5. In general, the ammonium hydroxide is used in proportions of about 10 to 50 ml / 1 plating bath.

The brighteners required in the bath are Class I and Class II nickel brighteners. Organic brighteners that can be used for the purposes of this invention are described in Modern Engineering, 2nd Ed., FA Lowenheim (Ed.), Page 272 et seq. (1963). , and Metal Finishing Guidebook &amp; Directory, 42nd ed., p. 358 ff. (1973). Such brighteners are described in column 1, line 2, through column 2, line 8, U.S. Patent No. 4,098,656. Specific organic brighteners that have been found to be particularly useful in the present invention are:

Class I nickel whitener:

saccharin

sodium benzene

benzenesulfonamide

phenolsulfonic

Methyl-bis (naphthalene) sulfonic acid

Nickel Brightener Class II:

2-Butyne-1,4-diol Benzaldehyde-o-sodium sulfonate 2-Butene-1,4-diol Allyl sulfonate

The concentration of the individual brighteners may be from about 1 to 5 g / l, preferably 1 to 3 g / l. Some compounds may fall under both Class I and Class II, but this does not affect their usefulness in the baths of the invention. In contrast to the requirement of US Pat. No. 4,098,656 that at least one brightener from each class of nickel brightener must be used, according to the invention only one organic brightener from one of these classes must be used to achieve the desired results.

As mentioned above, the electroplating baths of the present invention must be used at a pi of at least 8, preferably about 9 to 9.5.

The temperature of the palladium plating bath can be maintained between room temperature and 71 ° C. To avoid the evolution of excess ammonia from the solution, the plating temperature is preferably below about 54 ° C. Current densities of about 0.01 to 5 A / dm² are suitable for most purposes. For rack plating, a current density of 0.2 to 2 A / dm², preferably about 1 A / dm², be applied.

Another feature of the invention is that thin palladium coatings are formed to ensure the formation of a white coating. Thus, the coating thickness of about 0.01 to 1 μπι, preferably from 0.03 to 0.4 μπι vary.

The whiteness characteristic of the invention is determined as the reflectance of white light as measured by spectrophotometric techniques, such as using a Perkin Elmer 559 spectrophotometer and plating the coatings to be tested on 2.5χ 2.5 cm plates, labeled 0 0.1 mm (0.5 mil) copper and then pre-plated with 0.01 mm (0.5 mil) nickel, hereinafter referred to as nickel plated plates, to eliminate surface defects. The reflectivity of white light of these plates becomes the transmission type of 400 to 700 nm

- 5 No.375965 scanned against a Magnesiumoxydbezugsplatte. The sample coating scan is then compared to a similar scan of a rhodium coating.

<td>Preferred electroplating baths 8 according to the invention are as follows:</td><td>with a p ^ value of at least</td>

<td>component</td><td>concentration</td>

<td>Pd (NH₃)₂(NO₂)₂*</td><td>1 to 6 g / 1 (as Pd)</td>

<td>conductive salt</td><td>50 to 100 g / 1</td>

<td>Organic Brightener (Class I</td><td></td>

<td>or class II)</td><td>1 to 3 g / 1</td>

<td>ammonium hydroxide</td><td>10 to 50 ml / 1</td>

<td>buffer</td><td>0 to 50 g / 1</td>

<td>*) Palladiumdiaminodinitrit</td><td></td>

<td>The following examples are intended to illustrate the invention in more detail</td><td>but without them</td>

<td>should be limited.</td><td></td>

¹⁵ Example 1: A palladium electrolytic solution was prepared by dissolving the following ingredients in water:

<td>component</td><td>concentration</td>

<td>Palladiumdiaminodinitrit</td><td>2 g / 1 (as Pd)</td>

<td>dibasic ammonium phosphate</td><td>96g / 1</td>

<td>ammonium biborate</td><td>25g / 1</td>

<td>ammonium hydroxide</td><td>24 ml / 1</td>

<td>Benzaldehyde-o-sodium sulfonate</td><td>2g / 1</td>

The level of ammonium hydroxide used in the above formulation increased the p "value to about 9. The plating was carried out at a temperature of 22 ° C and with a current Π ₂₅ density of 1 A / dm² for 30 seconds on a nickel plated plate to give a white palladium-over-thickness of 0.25 to 0.35 μm thickness. The ammonium biborate acted as a buffer, keeping the pi value in the desired range and increasing the desired whiteness of the palladium metal coating obtained.

Example 2: A plating bath similar to Example 1 but using a different one

Brightener, was formulated as follows:

Component concentration

<td>Palladiumdiaminodinitrit</td><td>2</td><td>gfl (as Pd)</td>

<td>dibasic ammonium phosphate</td><td>96</td><td>g / 1</td>

<td>ammonium hydroxide</td><td>24</td><td>ml / 1</td>

<td>ammonium biborate</td><td>25</td><td>g / 1</td>

<td>2-butyne-l, 4-diol</td><td>2</td><td>g / 1</td>

The pi value was adjusted to 9 and the plating was carried out under the conditions described in Example 1, whereby a white palladium coating with a thickness of 0.25 to 0.35 pm

Nr.375965

- 6 was received. The reflectivity of the palladium metal coating on the nickel plated plate will be described later.

Example 3: A plating bath similar to Example 1 was formulated as follows, but using a class I nickel whitener.

<td>5</td><td>component</td><td>concentration</td>

<td></td><td>Palladiumdiaminodinitrit</td><td>1 g / 1 (as Pd)</td>

<td></td><td>dibasic ammonium phosphate</td><td>50g / 1</td>

<td></td><td>ammonium biborate</td><td>25g / 1</td>

<td></td><td>ammonium hydroxide</td><td>24 ml / 1</td>

<td>10</td><td>saccharin</td><td>2g / 1</td>

i

I

The aqueous solution contained sufficient ammonium hydroxide to afford the p_ßValue to 9 to 'ί increase. The plating was carried out under the conditions of Examples 1 and 2, wherein¹ a white palladium coating with a thickness of 0.25 to 0.35 gm was obtained. ;

In the following table, the reflectance of white light of the palladium coatings j on the nickel plated plates of Examples 1 to 3 with a rhodium coating on a nickel plated plate and with coatings prepared according to Example 3 of U.S. Patent No. 4,098,656 and U.S. Pat No. 3,330,149 (page 1, lines 77 to 102, and page 2, lines 1 to 8) were compared. The coatings of said US-PS had a thickness of 0.25 to 0.35 gm. The Perkin Elmer spectrophotometer and the above test method were used.

table

<td rowspan="2">coating</td><td colspan="4">% Reflectance</td>

<td>400 nm</td><td>500 nm</td><td>600 nm</td><td>700 nm</td>

<td>rhodium</td><td>80.5</td><td>85.0</td><td>88.5</td><td>90.5</td>

<td>U.S. Patent No. 4,098,656</td><td>60.0</td><td>71.5</td><td>78.0</td><td>80.5</td>

<td>U.S. Patent No. 3,330,149</td><td>51.5</td><td>60.0</td><td>66.5</td><td>72.0</td>

<td>example 1</td><td>67.0</td><td>78.0</td><td>83.0</td><td>85.0</td>

<td>Example 2</td><td>66.0</td><td>75.5</td><td>80.5</td><td>83.0</td>

<td>Example 3</td><td>67.0</td><td>77.0</td><td>81.5</td><td>83.5</td>

The above data shows that the electroplating baths of the present invention provide a significantly improved palladium metal coating as compared to the coatings of the two US patents referred to, which relates to the reflectance of white light. The visual difference of the whiteness is so significant that when used commercially, it makes the difference between

Acceptance and rejection can make.

When the above data is recorded, u.zw. % Reflectance versus wavelength, as in the drawing, the curve obtained shows the significance between the results obtained.

By means of a scanning electron microscope (SEM) micrographs of the coating prepared according to Example 1 30 and the coatings formed according to the two aforementioned US-PS were made. These micrographs show that the coatings according to US Pat. No. 3,330,149 are extensive dendritic

- 7 Nr.375965

Have deposits and a rough surface. The coatings of U.S. Patent No. 4,098,656, while exhibiting somewhat reduced dendrite growth, still possess significant surface roughness. In contrast, the coating of Example 1 is exceptionally smooth without any dendritic deposits. This further illustrates the unique properties of the coatings obtained according to the invention and shows the correlation between the smoothness of the coating and the reflectance of white light.