ADDITIVE FOR SILVER-PALLADIUM ALLOY ELECTROLYTES

Abstract

The present invention relates to an electrolyte containing suitable reducing agents for adjusting the composition of silver-palladium layers. Furthermore, these reducing agents contribute to improving the layer appearance and to increasing the luminance (L value, CIE Lab) of the deposited layers. The present invention also discloses a method for the electrolytic deposition of silver-rich silver-palladium alloys. The alloys can be deposited on conductive surfaces over a wide current density range.

Claims

1. Cyanide-free, acidic and aqueous electrolyte for the electrolytic deposition of bright silver-palladium alloys with a predominantly silver content which in its dissolved form contains the following components: a) a silver compound in a concentration of 1-300 g/l silver; b) a palladium compound in a concentration of 0.1-100 g/l palladium; c) a tellurium and/or selenium compound in a concentration of 0.002-10 g/l tellurium and/or selenium, based on the total amount of tellurium and selenium in the electrolyte; d) urea and/or urea derivatives in a concentration of 0.05-1.5 mol/l, based on the total amount of urea and urea derivatives in the electrolyte and/or one or more amino acids, selected from the group consisting of alanine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, lysine, leucine, methionine, phenylalanine, phenylglycine, proline, serine, tyrosine and valine in a concentration of 0.005-0.5 mol/l, based on the total amount of amino acids in the electrolyte; e) at least one sulfonic acid in a concentration of 0.25-4.75 mol/l, based on the total amount of sulfonic acids; f) at least one reducing agent selected from the group of formic acid, oxalic acid, ascorbic acid, hydrazine, hexamethylenetetramine, salts and/or esters of sulfurous acid, gaseous sulfites, sulfinic acids and their salts and/or esters, formaldehyde, sodium formaldehyde sulfoxylate, benzaldehyde, benzaldehyde derivatives, hydroxybenzenes and their esters, polyphenols and their esters, phenolsulfonic acids and their salts and/or esters, and glutathione and also its salts and/or esters in a concentration of 1-100 mmol/l, based on the total amount of these reducing agents.

2. Electrolyte according to claim 1, wherein the silver compound is selected from silver nitrate, silver carbonate, silver methanesulfonate, silver chloride and silver oxide,

3. Electrolyte according to claim 1, wherein the palladium compound is selected from palladium hydroxide, palladium chloride, palladium glycinate, palladium methanesulfonate and palladium sulfate.

4. Electrolyte according to claim 1, wherein the selenium and/or tellurium compounds are selected from tellurites, selenites, tellurous acid, selenious acid, telluric acid, selenate and also tellurate.

5. Electrolyte according to claim 1, wherein the -amino acid is selected from alanine, glycine and valine.

6. Electrolyte according to claim 1, wherein component (d) is urea.

7. Electrolyte according to claim 1, wherein the at least one sulfonic acid is selected from ethanesulfonic acid, propanesulfonic acid, benzenesulfonic acid, and methanesulfonic acid.

8. Electrolyte according to claim 1, wherein the at least one reducing agent is selected from hydroxyphenols, ascorbic acid and salts and/or esters of sulfurous acid.

9. Method for the electrolytic deposition of silver-palladium layers predominantly containing silver from an electrolyte according to claim 1, wherein an electrically conductive substrate is immersed in the electrolyte and a flow of current established between an anode in contact with the electrolyte and the substrate as cathode.

10. Method according to claim 9, wherein the electrolyte temperature is 25 to 70 C.

11. Method according to claim 9, wherein the current is between 0.5 and 20 A/dm.sup.2 during electrolysis.

12. Method according to claim 9, wherein the pH value is set to a constant value of <2 during electrolysis.

Description

EMBODIMENTS

[0067] Various basic electrolytes were prepared and in each case a reducing agent in two different concentrations added. From these electrolytes, both with and without a reducing agent, silver-palladium layers were then deposited, characterized and compared to each other.

Embodiment 1

[0068] Basic Electrolyte:

[0069] 100 ml/l methanesulfonic acid 70%

[0070] 3 g/l glycine

[0071] 10 g/l palladium (as palladium hydroxide)

[0072] 5 g/l silver (as silver nitrate)

[0073] 0.5 g/l tellurium (as tellurous acid)

[0074] Reducing Agents: [0075] 0 g/l sodium formaldehyde sulfoxylate [0076] 0.95 g/l sodium formaldehyde sulfoxylate (8 mmol) [0077] 7.1 g/l sodium formaldehyde sulfoxylate (40 mmol)

[0078] Temperature: 30 C.

[0079] Anodes: PtTi

[0080] The palladium content of the deposited layers was measured using an X-ray fluorescence analysis method (XRF) (Fischerscope XDV-SDD, software WIN-FTM Version 6.28-S-PDM).

[0081] Measurement Results for Palladium Content:

TABLE-US-00001 Sodium formaldehyde sulfoxylate content [g/l] Current density [A/dm.sup.2] Pd content [wt %] 0 1 4.2 0 2 3.2 0 3 3.0 0.95 1 5.7 0.95 2 3.5 0.95 3 3.4 4.7 1 9.1 4.7 2 6.8 4.7 3 5.4

[0082] FIG. 1 shows the results of palladium content measurement.

[0083] The brightness of the deposited layers was measured in the form of the L* value according to CIEL*a*b.

[0084] Measurement Results:

TABLE-US-00002 Sodium formaldehyde sulfoxylate content [g/l] Current density [A/dm.sup.2] Brightness [L*] 0 1 78.3 0 2 73.4 0 3 73.0 0.95 1 73.6 0.95 2 83.0 0.95 3 80.5 4.7 1 75.6 4.7 2 77.2 4.7 3 78.8

Embodiment 2

[0085] Basic Electrolyte:

[0086] 80 ml/l methanesulfonic acid 70%

[0087] 5 g/l urea

[0088] 10 g/l palladium (as palladium chloride)

[0089] 6 g/l silver (as silver methanesulfonate)

[0090] 1.0 g/l tellurium (as potassium tellurite)

[0091] Reducing Agents: [0092] 0 g/l ascorbic acid [0093] 0.14 g/l ascorbic acid [0094] 0.42 g/l ascorbic acid

[0095] Temperature: 60 C.

[0096] Anodes: PtTi

[0097] The palladium content of the deposited layers was measured using an X-ray fluorescence analysis method (XRF).

[0098] Measurement Results for Palladium Content:

TABLE-US-00003 Ascorbic acid content [g/l] Current density [A/dm.sup.2] Pd content [wt %] 0 1 3.8 0 2 2.9 0 3 2.7 0.14 1 4.2 0.14 2 3.1 0.14 3 2.7 0.42 1 5.3 0.42 2 3.6 0.42 3 3.3

[0099] FIG. 2 shows the results of palladium content measurement.

[0100] The brightness of the deposited layers was measured in the form of the L* value according to CIEL*a*b.

[0101] Measurement Results for Brightness:

TABLE-US-00004 Ascorbic acid content [g/l] Current density [A/dm.sup.2] Brightness [L*] 0 1 81.8 0 2 67.9 0 3 64.5 0.14 1 83.6 0.14 2 76.6 0.14 3 71.0 0.42 1 83.0 0.42 2 79.0 0.42 3 73.6

Embodiment 3

[0102] Basic Electrolyte:

[0103] 100 ml/l methanesulfonic acid 70%

[0104] 5 g/l valine

[0105] 12 g/l palladium (as palladium hydroxide)

[0106] 25 g/l silver (as silver nitrate)

[0107] 1.5 g/l tellurium (as tellurous acid)

[0108] Reducing Agents: [0109] 0 g/l hydroquinone [0110] 0.5 g/l hydroquinone [0111] 1 g/l hydroquinone

[0112] Temperature: 60 C.

[0113] Anodes: Graphite

[0114] The palladium content of the deposited layers was measured using an X-ray fluorescence analysis method (XRF).

[0115] Measurement Results for Palladium Content:

TABLE-US-00005 Hydroquinone content [g/l] Current density [A/dm.sup.2] Pd content [wt %] 0 1 1.4 0 2 2.9 0 3 2.8 0.5 1 6.8 0.5 2 5.5 0.5 3 6.0 1.0 1 16.8 1.0 2 15.0 1.0 3 14.4

[0116] FIG. 3 shows the results of palladium content measurement.

[0117] The brightness of the deposited layers was measured in the form of the L* value according to CIEL*a*b.

[0118] Measurement Results for Brightness:

TABLE-US-00006 Hydroquinone content [g/l] Current density [A/dm.sup.2] Brightness [L*] 0 1 81.7 0 2 77.8 0 3 72.5 0.5 1 83.1 0.5 2 81.6 0.5 3 77.1 1.0 1 76.5 1.0 2 77.7 1.0 3 73.8

Embodiment 4

[0119] Basic Electrolyte:

[0120] 200 ml/l methanesulfonic acid 70%

[0121] 2 g/l glycine

[0122] 15 g/l palladium (as palladium sulfate)

[0123] 8 g/l silver (as silver carbonate)

[0124] 0.5 g/l tellurium (as tellurous acid)

[0125] Reducing Agents: [0126] 0 g/l sodium sulfite [0127] 1 g/l sodium sulfite [0128] 2 g/l sodium sulfite

[0129] Temperature: 40 C.

[0130] Anodes: PtTi

[0131] The palladium content of the deposited layers was measured using an X-ray fluorescence analysis method (XRF).

[0132] Measurement Results for Palladium Content:

TABLE-US-00007 Sodium sulfite content [g/l] Current density [A/dm.sup.2] Pd content [wt %] 0 1 6.2 0 2 4.9 0 3 3.5 1.0 1 10.0 1.0 2 8.1 1.0 3 8.1 2.0 1 15.6 2.0 2 12.3 2.0 3 11.7

[0133] FIG. 4 shows the results of palladium content measurement.

[0134] The brightness of the deposited layers was measured in the form of the L* value according to CIEL*a*b.

[0135] Measurement Results for Brightness:

TABLE-US-00008 Sodium sulfite content [g/l] Current density [A/dm.sup.2] Brightness [L*] 0 1 80.0 0 2 76.3 0 3 71.1 1.0 1 81.8 1.0 2 82.2 1.0 3 81.2 2.0 1 78.4 2.0 2 77.8 2.0 3 78.3