DE2032868A1 - Galvanic process - Google Patents

Description

The invention relates to a method for the galvanic deposition of gold in methods that work with the use of baths _? which contain complex salts of gold and work at a pH in the range of about 5 »5 to 7.5. Such galvanic gold plating processes are familiar and widely used in practice. '

Since gold cyanide baths are used in most technical galvanic gold plating processes, especially those requiring strong coatings, the present invention is discussed below with specific reference to such baths, but the method according to the invention is generally applicable to gold baths in which the gold source of a complex salt is formed which contains the gold in the anion. For example , alkali gold sulfites have also been used in electroplating baths . -.

009883/1351

B-1016

The gold cyanide baths are generally aqueous solutions which contain an alkali or ammonium gold cyanide. The potassium gold cyanide, KAu (CN) ₂ , has been shown to be particularly effective and is readily available. The conventional baths also contain various salts that act as buffers and improve the conductivity and scattering power of the solution. Examples of compounds used for such purposes are water-soluble phosphates, sulfamates, borates, tartrates, citrates, acetates, formates and the like. The highly effective baths usually contain these compounds as sodium, potassium or ammonium salts. During the galvanic gold deposition ™ from the alkali gold cyanide bath, alkali cyanides, hydroxides and salts of buffering agents are formed and the pH of the bath tends to rise. With the continuation of the electroplating process, the gold deposited from the bath is usually supplemented or adjusted by adding alkali gold cyanide, and the pH value is usually adjusted by adding an acid such as phosphorus, polyphosphorus, sulfamine, lemon or Tartaric acid, discontinued. As a pure effect of the repeated additions of alkali gold salts and the subsequent deposition of gold from them and the addition of pH-adjusting substances to the bath, there is an accumulation of non-gold-containing alkali salts in the bath.

One of the major problems with operating such deposition processes is to maintain substantially uniform or constant levels of deposition in the bath. The gathering of alkali salts is a main factor that disturbs the equilibrium. It reduces the separation quality and the current efficiency, and the adverse effects become more pronounced while the solution of saturation approaches and crystallization occurs. At or near the saturation point of the alkali salt, a gold deposit of high roughness occurs.

One of the convenient bath monitoring methods is the measurement of the solution density. The density of the most effective bath is

009883/1951

Β-1016;. ■■ -

can be determined empirically for each method. The density will for galvanic work usually on the basis of the tree Expressed scale, and z. B. can when working with potassium gold cyanide as the gold source, the initial density of the most effective bath, determined at 65 ° C, in the range from about 8 to 20 Be lie. Once the effective working conditions are established, it is highly desirable to keep them constant. In conventional methods, however, the steady accumulation of alkali salts in the bath comes in the constant increasing form Density expresses.

The problems that usually arise in connection with the gold deposition are naturally stronger and increasingly difficult to overcome with increasing thickness of the desired deposit and are particularly important when a relatively strong gold deposition, e.g. B. is in the order of the ^large-3/1 IO mm and more, are needed. With thin rainfall there is usually enough bath entrainment or drag to retard salt buildup. In the end, however, the final deterioration of the bath occurs even with baths used for thin deposits. In the case of very strong gold precipitates, such as are required for electroplating work, the problem becomes particularly severe, since the baths have a higher concentration, the electroplating work is carried out at the highest possible current densities and the parts are carried out for a longer time, hours or even days instead of remain in the bathroom for minutes. During this time, the gold deposited from the bath is replenished and the pH value is maintained by continuously adding alkali gold cyanides and pH adjustment acid, without any reduction in the concurrent accumulation of salt due to the entrainment or dragging of the baths for electroforming work are generally operated continuously to form gold coatings from about 3/40 to 2 1/2 mm thick. On the other hand, as mentioned above,

009883/195 1

B-1016

with the accumulation of alkali salts in the bath, the precipitate tends to become rough and unusable.

The method according to the invention allows a continuous one Operation of the gold bath with a long lifetime with the formation of smooth gold coatings or deposits.

According to the invention, galvanic processes are used in which Gold is deposited from an aqueous bath that has an acidic or neutral pH, and gold is deposited as soluble complex gold contains, improved by replacing the gold deposited from the bath with an alkali metal-free, soluble one P ■ gold salt supplements or updates, whereby the alkali metal concentration of the bath is kept essentially constant during the separation work.

According to a special embodiment, according to the invention, in a mode of operation in which the deposited from the bath Gold is supplemented by the addition of a soluble alkali salt, the bath with an ammoniated cation exchange resin brought together to replace alkali metal ions with ammonium ions, and the ion-exchanged bath operated at a temperature of 60 to 90 ° C. In this way, sufficient alkali metal ions are removed, and an accumulation

Development of such ions in the bath is avoided. W.

As mentioned above, the method according to the invention is applicable to gold deposition processes in which the gold source is formed by a complex salt of the gold and the gold is in complex form in the anion. Potassium and sodium gold cyanide complex salts are most commonly used, and potassium gold cyanide is usually preferred because of its higher solubility. The gold content of the bath changes depending on the process, e.g. B. the gold content of conventional potassium gold cyanide baths is between 1 and 10 g / l and more. The baths can also contain other metals, e.g. B. Ag, Cu, Ni, Fe, Co and As, these too

"· - i \ - · 009883/1951

can form an alloy with the gold deposit or remain alloy-free, as long as such metals are not present as cations that would interfere with the ion exchange. The metals can ζ. B. exist as part of a complex anion, such as in an alkali (or ammonium) heavy metal cyanide. The agents added for buffering, improving conductivity, creating a gloss or otherwise improving the bath are familiar and can be used, for. B. in the form of alkali or ammonium salts. In such a bath, the alkali metal salts, which remain after the deposition of gold from the bath are subject, with the following additions of gold addition salt to the bath and the continuous removal of gold ä from the solution in the form of the gold precipitation accumulation. When the bath is brought together with the ammoniated ion exchange resin, the alkali metal salts in the bath are converted into ammonium salts, and in this way the alkali salts in the bath can be kept essentially constant during the separation work.

Any ammoniated cation exchange resin can be used as the cation exchange resin to replace the alkali metal ions in the bath with ammonium Find use that at temperatures from ambient temperature to about 95 ° C in the presence of the galvanic Bath is resistant. Preferably the resin is entirely in the ammonium form. However, you can also use a Resins having equilibrium, i.e. Resins work that Contain acid and ammonium, but these resins do not are preferred as they have problems in obtaining the right balance between pH control and alkali ion removal. Acid resins are not usable as they to a rapid drop in pH with precipitation of gold cyanide lead in the ion exchange resin column. examples for Cation exchange resins for the purposes of the invention are those Ammonium forms of highly sulfonated cation exchange hars Polystyrene ^ type and sulfonated © resin © of styrene-divinylbenaol » Misclipolyjnör-Typi, Suitable Kafclonenaue.tapschharze aind im

- - ■ 5 V-009883/1951

Trade available, ζ. B. under the names Amberlite IR-120 and IR-200, Decolite C-20, Dowex 50 and Ionac C-250.

In general, the resins are made or are commercially available in the sodium form. The sodium form of the resin is according to methods familiar converted into the ammonierte form "Z. B _0, the resin is usually first washed to remove sodium ions with aqueous acid, and then the acid-washed resin to treatment such. B. subjected to ammonium hydroxide to achieve the ammoniated form. *. ■

When carrying out the process according to the invention, the electroplating bath containing alkali metal ions is brought with 'the ammoniated cation exchange resin, e.g. B. by passing through a cation exchange column, replacing alkali metal with ammonium ions. The bath solution can be intermittently or continuously brought together with the ion exchange resin, and it is not necessary to completely exchange the alkali metals. All that is necessary is to remove enough alkali metal to prevent harmful build-up in the bath. The speed and strength of the ion exchange can be controlled within the scope of the specialist knowledge.

When the ammonium ion is exhausted, the ion exchange resin must be regenerated. B. after utilization of about 70 % of the exchange capacity, regenerated. It is also possible to provide more than one column in the separation system, so that the other column can be used during the exchange or regeneration of one column and the process can be carried out continuously.

The solution brought into contact with the carbon exchange resin is recirculated to the electroplating bath, which is kept at a temperature in the range of about 60 to 90, preferably -65

OT Q IU

009883/1951 *. '.

B-1016 '

to 70 ° C and at a pH of about 5.5 to 7.5, preferably Holds 6.0 to 6.5.

A high-quality precipitate is obtained at around 60 to 90 ° C, and the ammonium salts, e.g. B. NH ^ CN, tend to decompose with the release of NH ,, with an equilibrium adjusts with the formation of a solution with a minimum pH of about 5.5. The pH of the solution should not exceed about 7.5, since any carbonates present in the bath would otherwise * at a pH value of over about 7.5 with corresponding impairment the deposition process would remain in the solution. With familiar buffering agents such as phosphates, citrates or tartrates, the pH will be in the desired {

Area kept. It is preferable to give a certain amount of the buffering compounds as ammonium salts to facilitate the removal of ammonia, but on the other hand can the compounds, when used as alkali salts, are also converted into ammonium salts in contact with the cation exchange resin will.

When operating in accordance with the method of operation described above, the bath works, as the uniform Baume values maintained in it show, with essentially constant deposition values. The most effective Baume value, i.e. the one that delivers the greatest current yield under the working conditions, can be determined empirically for any given bath. Overall% Mäss the invention, the effective Baume value is preferably maintained to within ± 2 °.

In the drawings shows

Fig. 1 in a schematic representation of a for performing the Gold-plating apparatus suitable for the method according to the invention, FIG. 2 on a photomicrograph at a magnification of about 20O a section of a according to the method according to the invention obtained gold deposit and

Fig. 3 on a photomicrograph at about 20O times the magnification

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Β-1016

^% tion a section of a gold deposit obtained by a known method.

In the apparatus of FIG. 1, the separating trough 1 contains an aqueous solution of an alkali gold cyanide, e.g. B. KAu (CN) ₂ , formed gold bath 2. The insoluble anode 3 is made of platinum-coated titanium, while the part to be gold-plated, e.g. B. a prepared in an appropriate manner for the gilding mandrel, as a cathode. ¹ ! serves. When the cell is in operation, these electrodes are connected to a current source (not shown). A heating element 5 keeps the bath 2 at a temperature suitable for the formation of a good gold deposit and also for the release of ammonia from the bath, e.g. B. in the range of 60 to 90 ° C. From the bath 2, a line 6 provided with a pump 7 leads to the inlet end 8 of a cation exchange column 9> the ammoniated. Cation exchange resin 10 contains, e.g. B. a highly sulfonated polystyrene cation exchange resin in ammoniated form. The outlet 12 of the cation exchange column 9 is connected to the tank 1 via a line 11. To regulate the flow through line 6 and, if desired, discharge through the bypass line 1Ί directly to line 11, a valve 13 is provided.

For heavy gold precipitation, e.g. B. with a thickness of the order of 1 mm, the bath z. B. KAu (CN) ₂ in an amount of 36 g / l, dipotassium hydrogen phosphate of 50 g / l, dibasic potassium citrate of 15 g / l and ammonium citrate of 15 g / l. The bath has an initial pH of about 6.3 and a density, determined at 65 ° C, of about 11 Be.

When performing the deposition, the bath z. B. on ο

65 C and a current of about 0.1 to 1 A / dm is supplied to the bath. During gold deposition, the bath is continually replenished with gold by adding a solution of KAu (CN) _{2 to} it, this supplement salt being directly 4) 1 to 10 A / square foot - 8 - ·.

009883/1951

• g "2032808

to the bath or through the cation exchange resin first can circulate. In operation, the pump 7 circulates under Directing through the valve 13 part of the bath 2 through the line 6 to the cation exchange resin 10 and back through the Line 11 to bath 2. In the cation exchange resin, potassium ions are exchanged for ammonium ions, the alkali metal can be partially or completely exchanged for ammonium ions. Appropriate steering is within the scope of professional ability. It is preferable to exchange enough alkali metal ions to achieve the desired Baume value of the bath constant. The cation exchange treated Solution is then returned to the separation tank, in which the bath is caused by the ammonium ion concentration of the | recirculated solution and the buffering salts to pH is maintained in the range of about 5.5 to 7.5. The gold precipitate obtained under these conditions shows an extraordinary one good quality. It is smooth and dense, and you can also see precipitations of great thickness, of the order of magnitude of 1 mm and more, and of high quality.

FIGS. 2 and 3 show on the basis of photomicrographs at Etched sections of gold deposits, magnified about 200 times. The production of the gold precipitation samples is included takes place essentially in the manner described in the example. The Pig. 2 shows a sample of the according to the invention gold precipitate obtained and FIG. 3 that according to the prior art Technique preserved gold precipitation sample. Fig. 2 'shows the uniform profile and a fine-grain structure that the deposit obtained according to the invention has a smooth surface is what constitutes highly desirable properties. For example, with regard to the smooth surface, it can be stated that a Gold deposit formed by electroplating work is often machined to achieve the required surface finish is processed, and thereby must be removed all the more expensive gold to achieve the desired surface finish the more uneven the surface is, on the contrary

this is due to the clearly uneven profile that coarser grain structure and the cavities (showing porosity) in the precipitate of FIG. 3 obtained according to the prior art, which can be clearly seen.

example

In this example, which serves to further explain the invention, a generally accepted gold plating process is used of the prior art with the method according to the invention compared.

In the comparative experiments, an aqueous gold bath was used Solution of the following composition with a pH of 6.0 and an initial gold concentration of 24.6 g / l:

Compound Amount by weight, g / l potassium goid cyanide 36.0

Monobasic potassium phosphate 50.0

Dibasic potassium citrate -1 * 1.5

General test conditions:

Temperature, ⁰ C 65

pH 6.0 to 6.6

Movement rotating cylinder:

. . cathode

To accelerate the deposition, the tests were carried out at a current density of 1 A / dm ^{2 for} approximately 6 hours per day, with the bath being kept at 65 ° C. every night and over the weekends. Every day the end of the trial »

The cathode yield was determined at 0.5 and 0.7 A / dm, the Baume and pH values were recorded and the weight of the cathode was determined to determine the amount of money deposited by electroplating supplemented by KAu (CN) _2.

.- 10 - - V -; ■

00 98 83 / 19S1 '' ^:

a) Working method according to the state of the art

Using 1 1 solution and the above general Conditions and according to the above general procedure, a bath was used up to the deposition of about 2Ί0 g Gold operated. The pH of the solution was increased daily Addition of phosphoric acid discontinued.

The measured values for the cathode yield obtained in this test using the known procedure "

2 '

at 0.5 and 0.7 A / dm and the Baume value after the precipitation of the specified amounts of gold are given in Table I | called. '·

b ) ■ Mode of operation according to the invention

A gold plating cell was created using 1 liter of solution and the above general deposition conditions by circulating the gold bath during deposition through one containing an ammoniated cation exchange resin Column operated according to the invention. The bath was operated until approximately 200 grams of gold were deposited.

To produce the ammoniated resin, the column (height 6 dm, diameter 2 1/2 cm) was charged with 240 g of Amberlite IR-120, a highly sulfonated polystyrene-type cation exchange resin Ά from the Rohm and Haas Company, and the resin was first charged by passing 1, 23 1 10 / Siger HpSO ₁₁ subjected to an acid exchange through the column and then converted into the ammonia form by passing 1.25 1 tiger NH ^ OH through the acid-treated resin. During the execution of the present experiment, the resin was periodically regenerated when about 70 % of its capacity was used. The resin regeneration was carried out according to the same procedure that was used to convert it into the ammonia form for the first time.

009883/1951

B-1016

In this test using the working method measured values obtained according to the invention for the cathode yield at 0.5 and 0.7 A / dm and the Baume value after the suppression of the stated amounts of gold by dilution table II listed. J,.

tab hurry I * - Was standing of the technique - ₉ x) Baume value
% at 65 ° C total quantity
at Au-Nieder-
blow,
R (± 5 %) yield
at 0.5 A / dm
% pX) yield
, at 0.7 A / dm
% 11.0 ' 0 NM ⁺ > NM 12.0 25th 72.5 78.8 11.0 50 73.3 68.8 17.0 100 71.2. 68.1 ND ⁺⁾ 150 61.1 56.0 22.0 190 112.6 37.1 23.0 200 12.7 38.5 26th 2i0 30.0 33.1

+). ND = not determined

NM = Since a current yield of over 90 % for the first 8 hours of use was known for the initial composition of the bath, no measurement was made at this point. :

x) 5 or 7 A / square feet. -v

Tabel

- total quantity
at Au-Nieder-
blow,
κ (i 5 K) procedure according to the Invention - 00 NM 5 11.0 51 O Yield ₀ Yield ₅ Baume value
at 0.5 A / dm, at 0.7 A / dm, at 65 ° C 90 0 XS ⁺⁺⁾ ? 5 NM ⁺ * 77 1 XS 50 \ 93.3 .83, 8th 11.0 100 79.7 80, 9 XS
■ 150 91.2 - 12 -
9883/1 85.5

Jl '' ■ ": ■ , 20328

(Table II - Porting)

Total amount Yield ₀ Yield _o Baume value

on Au low at 0.5 A / dnT at 0.7 A / dar, at 65 ° C blow,

190 77.7 72.8 _t XS

200 91.8 89.8 11.0

♦ TNM = as in Table I.

XS = To exclude even the remote possibility excessively frequent sampling was avoided in the event of carryover from the bathroom.

As Table I shows, increases in the known process the Baume value of the solution progressively from 11 to 26, where i

the solution at this point becomes saturated with potassium phosphate and crystallization occurs. In addition, the current yield drops from an initial value of around 90 % to around 30 % . The results according to Table II show that in the method according to the invention the Baume value of the bath remains essentially constant throughout the entire experiment and the cathode yield remains at relatively high values. In contrast to the known method, in the method according to the invention, the pH value remains essentially constant during the entire experiment. there was and is no addition of phosphoric acid. '

When comparing the obtained with the two working methods,

Precipitation samples show that the quality of the sample obtained according to the invention is superior to the comparison sample, since the sample obtained according to the invention is significantly smoother and more smooth. The above photomicrographs show z. B. in comparison with the according to the known Vei * "drive precipitate obtained (Pig; 3) ^v fine-grained structure and smoother surface of the gemäös-der' invention prepared (FIG, 2)"

00 * 8 * 3/1951

Claims (1)

B-.1O16 July 2, 1970 Claims Process for the electrodeposition of gold from an aqueous bath that is acidic or neutral Has pH and contains gold as a soluble complex salt, characterized in that one of the Bath deposited gold with an alkali metal-free, soluble gold salt supplemented, and / or with supplement the gold deposited from the bath by adding a soluble alkali metal gold salt by bringing it together of the bath with an ammoniated cation exchange resin Alkali metal ions replaced by ammonium ions and the ion-exchanged bath at one temperature operates in the range from 60 to 90 ° C, and thereby the alkali concentration of the bath during the separation work holds essentially constant. 2. The method according to claim 1, characterized in that the cation exchange resin is an ammoniated form a highly sulfonated divinylbenzene-polystyrene mixture polymer or a highly sulfonated polystyrene polymer used. 3. The method according to claim 1 or 2, characterized in that the ammoniated cation exchange resin is regenerated after using about 70% of the exchange capacity » Ί, method according to one or more of claims 1 to 3.> characterized in that the bath is kept at 65 to 75 C. T5T ancestors according to one or mehrsran of claims 1 to H ₃ in one dasa the pH to 5 ₃ 5 holds to 7.5. · - in 0098 33/135 1 ^ B-1016 6. The method according to one or more of claims 1 to 5 » characterized in that a gold plating of about 3/40 to 2 1/2 mm thick. 7. The method according to one or more of claims 1 to 6, characterized by having the Baume value of the bath maintained at> 2 °. 8. The method according to one or more of claims 1 to 7 » characterized in that it is used as an alkali metal-containing Complementary salt uses an alkali gold cyanide. ' 9. The method according to claim 8, characterized in that KAu (CN) _{2 is} used as the alkali gold cyanide. 10. The method according to claim 8, characterized in that NaAu (CN) _{2 is} used as the alkali gold cyanide. - 15 - 009883/1951 Blank page