DE3328067A1 - BATH AND METHOD FOR GALVANICALLY DEPOSITING DISPERSIONS CONTAINING PRECIOUS METAL AND METAL - Google Patents

Abstract

1. A bath for the electrolytic deposition of dispersion coatings of or containing a noble metal, which bath contains a noble metal compound, a solid lubricant, in particular but not exclusively graphite, a cross-linking agent and a gloss additive, characterized by a content of 1 to 10 g/l of a cobalt, nickel, or antimony salt of tartaric, citric or acetic acid.

Description

SIEMENS AKTIENGESELLSCHAFT Our mark

Berlin and Munich VPA 83 P 3 2 5 3 DE

Bath and process for the galvanic deposition of noble metal and noble metal-containing dispersion coatings

The invention relates to a bath for the galvanic deposition of noble metal and noble metal-containing dispersion coatings of solid lubricants, especially graphite, wetting agents and brightening additives Baths, as well as a method for the galvanic deposition of such coatings, which using such Bath is carried out.

Above all, the surfaces of workpieces coated with precious metals and alloys containing precious metals Contacts should have a high level of wear resistance, since the noble metal layer may rub through Malfunctions can be triggered.

In known processes and baths (DE-OS 30 32 469) for the galvanic deposition of gold dispersion coatings are the galvanic gold bears, the potassium gold cyanide, potassium cyanide, disodium phosphate and as a gloss additive Potassium silver cyanide (cyanidic alkaline baths) or potassium gold cyanide, potassium citrate, citric acid and Cobalt sulfate ((acidic gold baths) can be used as a gloss additive with a fine-grain solid lubricant, in particular graphite and an isoalkyl sulfate which is soluble in acidic and alkaline aqueous gold baths offset.

Td 2 Gr / 1.8.1983

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A cyanidic alkaline silver electrolyte containing 10 to 100 g / l graphite with a grain size of 1 to 10 μm, 0.02 to 5 g / l of a brightening additive and 0.05 to 2 g / l of a wetting agent for the production of silver graphite dispersion coatings is disclosed in US Pat DE-OS 25 43 known. The hardness of the silver-graphite dispersion coatings (HV 0.05) is in the range from 700 to 1000 N / mm ² . The wear of such dispersion layers is 1/10 or even less than that of pure silver under the same conditions.

• For many purposes, however, these properties are still not sufficient, especially with regard to wear resistance.
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The object of the invention is therefore a bath for the galvanic deposition of noble metal containing gloss additives and coatings containing precious metals with the help of which it is possible, in particular, to use simple and economical way to produce precious metal and precious metal-containing coatings that have improved wear resistance exhibit.

This object is achieved with graphite-containing noble metals and noble metal-containing metals that are customary in electroplating Baths according to the invention per liter an addition of 1 to 10 g / l of a cobalt, nickel or Contain antimony salts of tartaric, citric or acetic acid. The salts used according to the invention organic acids have a hardness-increasing effect.

The __ using a bath according to the invention produced dispersion coatings in particular silver / graphite, gold / graphite, palladium / graphite, palladium / nickel / Graphite coatings show increased hardness and an extraordinary improvement in wear resistance. In addition, there is a certain self-lubricating effect. It was surprising that the abrasion resistance of noble metal / graphite coating the hardness of which increases extremely sharply. For layers of gloss baths is the effect is particularly great. The addition of graphite and hardener results in a combination effect: wear resistance is increased by 2 to 3 orders of magnitude compared to normal silver coatings. Abrasion tests on samples made of copper sheet coated with silver or silver / graphite coatings this.

Additives suitable for carrying out the invention are potassium antimony (III) oxide tartrate, nickel (II acetate, Cobalt (II) citrate.

The invention also relates to a method for the galvanic deposition of noble metal and noble metal-containing dispersion coatings using a bath of the composition specified above, which is characterized in that the bath is at a temperature of 18 to 30 ⁰ C with a current density of 0.2 to 5 A / dm ^{2 is} operated.

The layers that can be achieved from a bath according to the invention can be obtained directly or using Interlayers - on steel, copper and copperIeg alloys, aluminum and aluminum alloys and nickel

get knocked down.
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The known noble metal and noble metal-containing electrolysis are suitable for the present invention. Particularly suitable ones contain potassium cyanide and the noble metal in the form of, for example, potassium silver cyanide. The electrolyte also contains fine-grain solid lubricants such as graphite and wetting agents such as Turkish red oils, sulfonated oleate esters, fatty alcohol sulfonates e.g. sodium lauryl sulfate, alkylarylsulfonates. The electrolyte can also contain a gloss additive, such as turkey red oil, carbon disulfide, sodium xantho genate, dithiocarbamate, sodium thiosulfate, sodium selenite.

The solid lubricant-containing obtained according to the invention Surface layers mainly containing graphite are widely used. For example, you can for plug connectors and on contact pieces of signaling and auxiliary switches.

The invention is explained in more detail by the following examples and the drawing.

example 1

From a bath (shiny silver bath) the following composition silver / graphite layers were deposited on a copper sheet.

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-C- Potassium silver cyanide 3328067 C ₁₂ H ₂₅ OSO ₃ Na 325 3OE Potassium cyanide VPA 85 P 46 g / i Potassium carbonate K [Ag (CN) ₂ ] CH ₄ KO Sb 75 g / i Sodium selenite KCN 20th g / i K ₂ CO ₃ Room temperature 2 g / i Na ₃ SeO ₃ 1 A / dm ² 75 g / i Graphite (grain size 0.1-5 μπι main amount 0.1-1 μπι) 10 μm 2 g / i Sodium Lauryl Sulphate 170 - 180 HV Solution of 154.8g 1.5% 16 g / i Potassium antimony (III) oxide tartrate Reibweq · up to in 11 water (18-30 ⁰ C) temperature Current density Layer thickness hardness Graphite content of the coating Abrasion test By-

rubbed: ^ 6 000 m

To test for abrasion resistance, an apparatus was used in which a contact rivet (silver rivet) is moved back and forth (one double stroke = 2 cm, length of the rubbing track) on the coated base body (copper plate with silver or silver graphite layer) under a certain load (100 cN) 1 cm, frequency: 1 double stroke / s). The friction path to the wear-through was, as already indicated above, \ 6000 m. For silver layers of Glanzbad without graphite and without hardener addition of the friction path was in contrast only 11.9 m.

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Example 2

Objects made of metal, e.g. electrical contacts, the surface of which is subject to wear and tear after a pretreatment and application that is customary in electroplating technology an intermediate nickel layer in an electrolyte of the following composition with a gold / graphite dispersion coating coated.

, 5 g / lAu)

Potassium gold cyanide K [Au (CN) ₂ ] 12th OSO ₃ Na g / l (8 Potassium cyanide KCN 35 g / i Disodium phosphate Na ₃ HPO ₄ 10 ₂ .4H ₂ O g / i Potassium silver cyanide K [Ag (CN) ₂ ] 0, 5-1 g / l 2-methyl pentyl sulfate C ₅ H ₁₀ (CH ₃ ) 15 g / l Graphite (0.1-1 μm) 80 g / l Nickel (II) acetate Ni (CH ₃ COO) 5 g / l PH value 11.5 temperature 20-25 ⁰ C Current density 0.4 A / dm ² Layer thickness 2 um

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Graphite content d. Coating 1% by weight

Compared to a bright gold bath without graphite and without the hardener addition nickel (II) acetate, the increase was the wear resistance about 2 orders of magnitude.

In the figure, a sliding contact is shown schematically, which is used as a blade contact in rotary switches for Low voltage can be used in particular in signaling and reporting technology.

83 P32 5 3DE

The two separable contacts 1, 2 of the sliding contact should for this purpose be as small as possible Interact with friction. In particular, should, conditionally due to manufacturing tolerances, in the event of a deviation from the predetermined actuation direction of the movable Contact on the one hand the friction can be reduced and on the other hand the closing or switching angle tolerance remain guaranteed.

In the embodiment shown in the figure, the two spherically shaped contact springs are. 1, 2 in pairs provided, the contacts 1,2 under the force of a spring or by natural springing with a certain contact force in the direction of arrow 3, 4 are pressed against each other. These two adjacent Contacts 1, 2 are from a. Contact knife 5 pushed apart, wherein the contact surfaces of the contacts 1, 2, the knife 5 between them while maintaining the Contact force. The start-up areas 1a, 2a and the drainage areas 1b and 2b are open during entry and exit The switch-off movement is loaded by the approach and drain flanks 5a, 5b of the contact blade 5. At the start-up and There is increased wear and tear, which

by coating the contact surfaces / using the bath according to the invention on the one hand by the lubricating effect achieved and on the other hand by the possible harder design of the galvanic coating. It is advantageous to coat the contact surfaces using the bath according to the invention, so that with the knife contact, even with a slight center offset in relation to the two contacts 1, 2 and thus due to the change in the wear point, a long service life can still be achieved.

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In so-called package switches with a large number of contact arrangements shown in the figure remains the driving or actuating force for the switch is low.

4 claims
1 figure

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Claims (4)

332806 VPA 83 P32 5 3 DE Claims 1 / bath for the galvanic deposition of precious metal and noble metal-containing dispersion coatings made from solid lubricants, in particular graphite, wetting agents and Baths containing brightener, characterized by a content of 1 to 10 g / l bath of a cobalt, nickel or antimony salt of tartaric, citric or acetic acid.
10 2. Bath according to claim 1, characterized by a content of 1 to 10 g / l bath potassium-antimony (III) oxide tartrate. 3. Process for the production of dispersion coatings with a bath according to claim 1, characterized in that it is deposited ^{at a temperature of 18 to 30 0} C and a current density of 0.2 to 5 A / dm ^2. 4. Use of a bath according to claim 1 for the production of precious metals and precious metals Graphite dispersion coatings on contact pieces of signaling and auxiliary switches.