DE1771856C - Galvanic silver bath - Google Patents

Description

I 77! 856 <

1 2

The invention relates to a galvanic silver bath, silver coating improving organic Mitallver-

the dispersant and gloss additives contains, and added binding together with a wetting agent

with the high-gloss silver coatings of a thickness that always forms a sulforicmate radical as an anion.

of 50 microns and more is to be kept deposited, the cation of which, however, is optionally made of nickel,

should. 5 selenium, cobalt, iron or another signed

Metal can be used for silver-plating objects. Bai this organic Mitallim In general, aqueous solutions of silver potassium compounds are therefore primarily concerned with this double yanide, potassium cyanide and optionally ka- sulforicinate anion, while the metal cation is a lium carbonate used. In addition to these main v * - ': n- anything that increases the strength of the silver coating, which can be of the metal in terms of their quantity and quantity. The only BeUpbl in this one is If the proportions are precisely measured, the trap a silver bath with 300 to 3000 mg / 1 nickel-galvanic baths can also entsulforicinate other additives, that is to say with a nickel content of v = 60 to keep. 600 mg / 1 has been given, while over the for that

The most common additives in the bath silver coatings are amounts of cobalt sulfoein should give a special shine, 15 ricinat is not stated. This state of the art Sulfur compounds, such as carbon disulfide, or corresponding experiments with the addition of cobaitricinate Carbon disulfide condensed with acrolein, and even down to a cobalt content in the bath of Alkali xanthates, selenium or tellurium compounds at a rate of only 60 to 3CK) mg / 1 were extremely unsatisfactory turns. These connections are mostly used in results. Even a decrease in the cobalt present of surfactants, of which ao addition to 27 mg / 1 resulted in a specimen in which predominantly aliphatic alcohol sulfates or sodium - more than half of the silver-plated area does not Ricinoleate are used, added. Also showed gloss, so that just as little as that Polyglycols are one of these substances. well-known suggestion that any metal should not be considered glossy,

To improve the hardness of silver coatings but to use them as hardness builders, metals are also added to the bath in many cases, as the results with the cobaitricinate additives do not. These hardening additives are in particular antimony, bismuth, Indium, zinc, arsenic keeping a narrowly limited cobalt concentration or selenium, but they are usually not taken as between 1 and 13 mg / 1 in the silver bath, in order to find additives to improve the silver luster, this way flawless and especially because they are used for alone no shine-improving effect 30 have an excellent shine from the acquaintance as in some cases to get their combination with outgoing silver coverings,
organic substances, e.g. B. as in the case of the same- The silver ^{bath according to the invention l:} efert not only the timely use of antimony trichloride and a significantly improved gloss refinement and alkanolamines or of antimony tartrate or -gly- uniformization, but also offers zerat together with condensation products from 35 the previously non-existent possibility of Her-formaldehyde and naphthalene as dispersants. Position of high-gloss and flawless silver

With these known baths, depending on the coatings, a thickness of 50 microns and more

individual operating conditions more or less within a wide current density range, and it

shiny silver coatings can be obtained, but allows the silver-plating of objects of large size

only to a thickness below 20 microns. For thicker 40 dimensions and with relatively deep hollow

Coatings between 30 and 40 microns need to be cleared without the need for special aids

Interim refreshment of the coating, but also then required.

it is not possible to get flawless coatings on larger cobalt according to the invention in the form of objects, because either with bonds that are soluble in the silver bath, high current densities arise because of the low conductivity, especially as organomitallic complex compounds of the burn marks, or with low ones fertilize or as salts, preferably as cobalt sulfate, current densities the 20 micron thick layer of silver cobalt carbonate or cobalt potassium double cyanide.
takes on a milky or whitish appearance. The addition according to the invention is advantageous

For this reason, for example, the cobalt compounds together with 0.1 to 5 g / l of a

Silver plating of cutlery not directly in 50 naphthalene or benzene derivatives as a dispersant

such solutions are carried out, even not medium. This combination produces an additional one

while improving the operating conditions by improving gloss, because they are beneficial to the

Raising the bath temperature to about 30 ° C and through the orientation and size of the grains as well as the

continuous circulation of the electrolyte. Layering and thus on the structure of the silver

These disadvantages are reduced by the invention. As a particularly effective dispersing agent, according to the invention, the polymers from the polyol silver bath have proven to be particularly effective, which additionally contains 1 to 13 mg / 1 condensation of the sodium salt of an alkylnaphtha-cobalt in the form of an inorganic or organic linsulfonic acid or an alkylbenzenesulfonic acid water-soluble cobalt compound . grasslands.

Namely, it has been found that cobalt in so The main compound content in the silver bath this amount, even on particularly thick silver, corresponds essentially to the usual values, see above trains create a strong shine. With an addition that the silver bath IS up to 40 g / l silver (as a value of less than 1 mg / l the luster effect is non-potassium double yanide), 90 to 160 g / l free potassium sufficient and practically pointless. Even with more than cyanide and possibly IS up to 70 g / l potassium-13 mg / l, the gloss effect is less, because then 65 carbonate or an equivalent amount of potassium contains Cobalt acts as an impurity. can hold.

A silver bath has already become known, according to which, in addition to the gloss-improving agent

one above all the hardness and abrasion resistance of the invention, the silver bath can also be the usual ones

gloss-improving agents, such as sulfur compounds or antimony, tellurium, selenium or arsenic compounds, contain. Sometimes it also seems advisable to use surface-active, especially surface-active substances in the silver bath anion-active substances, e.g. B. alkyl sulfates to add.

The deposition is preferably carried out at a temperature between 14 and 35 ° C. and with a current density of 1 to 2 A / dm ^a and with gentle stirring of the silver bath.

The following examples 1 to 3 relate to comparative tests to demonstrate the technical progress associated with the silver bath according to the invention. Polished brass plates were used in all experiments. The deposition takes place in each case in a Hull cell within a treatment time of five minutes at a current density of 1.66 A / dm ² as well as at room temperature (20 to 22 ° C.) and with slow bath movement and better handling, coated with an ao colorless protective varnish, which, however, did not change its original appearance, in particular the silver sheen and possible stains.

example 1

It was initially worked with a known bath of the following composition:

Potassium silver cyanide 40 g / l

Potassium cyanide 150 g / l

Potassium carbonate 25 g / l

Antimony / glycerine complex 1.2 g / l

Condensation product from formaldehyde and Na naphthalene sulfonate .. lg / l

35

The specimen obtained from this had a milky color which made up about one quarter of the silver coating white-rimmed burn mark, caused by the peak effect in dpa zones of strong current densities was created.

A second test was then carried out with the same silver bath, but this time one according to the invention Cobalt addition of 2 mg / l (in the form of 10 mg / l cobalt sulfate) contained. With the one from this Bath with the cobalt additive according to the invention of the lower dose limit produced sample • piece the burn mark, like the blotchiness, was much smaller and less pronounced than in the aforementioned specimen.

A third attempt with the same silver bath again, but in this case a bit a higher cobalt addition of 4 mg / l (in the form of 24 mg / l cobalt / potassium double cyanide) resulted in a test piece without any; n burn mark and without white stain. This and that from the second attempt Test pieces were also characterized by the particularly pronounced purity and the radiant Shine of the silver coating, which is also due to the dosage range according to the invention The cobalt content of the relevant Silhjbäder is.

Example 2

Here it was assumed that someone was known Selenium-containing silver bath with the following composition:

Potassium silver cyanide 40 g / l

Potassium cyanide 130 g / l

Potassium carbonate 20 g / l

Selenium (as potassium selenide) 40 mg / 1

Condensation product from formaldehyde and Na-naphthalene sulfate

fonat 70 mg / 1

In the test piece obtained from this bath, the silver luster area was only Y _{4 of} the total area.

After 4 mg / 1 cobalt (in the form of 20 mg / 1 CoSO ₄ -7 H _a O) had been added to the same silver bath, a test piece was obtained in which the shiny silver area increased from V4 to ^a / _{t of} the total area ^a 5 had.

Example 3

In this case, a conventional silver bath of the following composition was assumed:

Potassium silver cyanide 33 g / l

Potassium cyanide 120 g / l

Potassium 7 g / l

Potassium carbonate 25 g / l

Antimony / GIyzenn complex 1.2 g / l

Condensation product of formaldehyde and Na naphthalene sulfonate lg / 1

The ^p robestück obtained from this bathroom without addition of cobalt showed about half the silver lining constituting, milky white rimmed burn as impact en3 peak effect in the zones starter current densities.

A second experiment with the otherwise identical silver bath, which, however, additionally contained about 6 mg / 1 cobalt (in the form of 18.8 mg / 1 anhydrous cobalt citrate, C0j (C _e H ₆ O,) ₂ ) yielded a test piece which the burn mark had almost completely disappeared.

A third experiment, again with the otherwise identical bath, this time containing 4 mg / l cobalt (in the form of cobalt tartrate, Co (C ₄ H ₄ O,) · 2.5H ₂ O), gave essentially the same result like the second attempt.

The following examples 4 to 7 serve to provide a better understanding of the invention.

Example 4 A silver bath of the following composition is made:

silver

(as silver potassium cyanide ..

free potassium cyanide

Alkali selenate Potassium carbonate Dispersants Carbon disulfide

Cobalt potassium double cyanide (= Cobalt content

to 40 g / l, preferably

to 65 g / l, preferably

to 150 g / l, preferably

0.5 to 10 g / l, preferably

to 70 g / l, preferably

0.1 to 5 g / l, preferably

to 20 mg / l, preferably

to 52 mg / l, preferably

to 13 mg / l, preferably

26 g / l 47 g / l) 140 g / l

4 g / l 35 g / l

0.5 g / l 12 mg / 1 16 mg / 1

4 mg / 1)

1 771 056

The potassium cyanide is distilled or deionized in Dissolved water, whereupon silver potassium cyanide, then potassium carbonate, while stirring gently added and the whole thing is passed through an activated carbon filter. Potassium selenate is then added one after the other, Carbon disulfide, the dispersant and cobalt potassium dcpp.'lcyanid added.

Operating conditions:
temperature

15 to 35 ° C, preferably 30 ⁰ C
Current density

1 to 2 A / dm ² , preferably 1.5 A / dm ²
slow stirring.

In this bath which the preferred amounts

of the specified compounds were under the above-mentioned most favorable operating conditions 40 minutes treated objects made of nickel silver, which were previously degreased and in an alkaline Solution had been coated with a thin silver film, which in a silver shock bath with higher Content of potassium cyanide and a soluble silver salt in an amount of a few grams per liter in a time of 1 to 2 minutes was applied.

ίο After 40 minutes of treatment in the silver bath the objects were sprayed on. They had a very shiny appearance on their entire surface, and it was not necessary, as has always been necessary in the past, to attach them to their cavities or protruding parts Post-treat parts.

Example 5

Silver 15 to 30 g / l, preferably 20 g / l

(as silver potassium cyanide .. 25 b.li 50 g / l, preferably 36 g / l)

Potassium cyanide 90 to 160 g / l, preferably 120 g / l

Potassium carbonate 15 to 25 g / l, preferably 20 g / l

Potassium 4 to 12 g / l, preferably 7 g / l

Dispersant 0.1 to 5 g / l, preferably 0.5 g / l

Antimony tartrate 1 to 20 g / l, preferably 3 g / l

Cobalt sulfate (7H ₂ O) 5 to 65 mg / 1, preferably 20 mg / 1

(= Cobalt content 1 to 13 mg / 1, preferably 4 mg / 1)

The operating conditions were the same as in Example 4 and the results were the same achieved.

Example 6

Silver 18 to 40 g / l, preferably 28 g / l

(as silver potassium cyanide .. 36 to 80 g / l, preferably 50.5 g / l)

Potassium cyanide 120 to 150 g / l, preferably 140 g / l

Potassium 4 to 12 g / l, preferably 6 g / l

Dispersant 0.1 to 5 g / l, preferably 0.2 g / l

anionic active agent 0.1 to 5 g / l, preferably 0.2 g / l

Tellurium oxide 0.01 to 1 g / l, preferably 0.1 / 0.3 g / l

Cobalt potassium double cyanide 4 to 52 mg / l, preferably 16 mg / l

(= Cobalt content .. 1 to 13 mg / 1, preferably 4 mg / 1)

Here, too, the operating conditions and results were the same as in the case of Example 4.

Example 7

Silver 18 to 35 g / l, preferably 26 g / l

(as silver potassium cyanide .. 30 to 65 g / l, preferably 47 g / l)

Potassium cyanide 120 to 150 g / l, preferably 140 g / l

Potassium carbonate 10 to 25 g / l, preferably 15 g / l

Potassium 4 to 12 g / l, preferably 7 g / l

Dispersant 0.1 to 5 g / l, preferably 0.2 g / l

anion active agent 0.1 to 5 g / l, preferably 0.2 g / l

Potassium selenium oxyanate 0.5 to 10 g / l, preferably 2 g / l

Cobalt sulfate 5 to 65 mg / l, preferably 20 mg / l

(= Cobalt content 1 to 13 mg / 1, preferably 4 nig / 1)

The operating conditions and results were the same as in the case of Example 4.

Claims (2)

Sponsorships: 1. Galvanic, dispersant and brightening additives containing cyanidic silver bath for Deposition of high-gloss silver coatings with a thickness of 50 microns and more, thereby marked that the bathroom in addition 1 to 13 mg / 1 cobalt in the form of a water-soluble inorganic or organic cobalt compound contains. 2. bath according to claim 1, characterized in that the bath as inorganic cobalt salts Cobalt sulfate, cobalt carbonate or cobalt potassium double cyanide contains.