DE1939754A1 - Electrolytic gold plating bath - Google Patents

Description

UV Philips ¹ Gloeilampenfabrieken, Eindhoven / Holland "ElektroIy ti sehes VergoIdungsbad"

The invention "relates to an electrolyte bath, with which gold or gold alloy deposits are obtained.

Known electrolytic gold plating baths contain a buffer system that is used during the gold deposition keeps the pH constant in a range between 3 and 8. This "buffer system" consists of one weak organic acid and an alkali salt thereof (U.S. Patent 2,905,601) or from partially neutralized inorganic polybasic acids and their alkali salts, (German patent 656 395).

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When using these known electrolyte baths: a regular correction of the pH value is necessary. E.g. a gold plating bath that is called The buffer system contains citric acid sodium nitrate » an addition of citric acid of around 1 kg per kg of gold precipitated from it. As a consequence, that the bath is ultimately unusable because of the far too high concentration of citrate.

The invention creates a bath that can be easily regenerated and from the pay of excellent and constant goodness can be cast down.

In an electrolyte bath for the deposition of sold or gold alloys, which is a soluble gold compound, a buffer and optionally one or more salts of metals, which are deposited as alloy components, is after the invention of the buffer on a salt of an inorganic acid and a metal, its hydroxide or a basic compound in the pH range between 3 and 8 precipitates, the corresponding hydroxide or the basic compound itself and optionally an alkali salt thereof or another inorganic acid.

Depending on the selected type and concentration of gold salt and the type and amount of the other components of the bath, the pH value will tend to increase or decrease. In the former case there is a trace of the when assembling a bath Hydroxyds required. When using the bath, a larger amount of hydroxide and the pH will be stabilized as long as there are still ions of the metal in question are present, and thus nor can hydroxide precipitate.

"HO 98 10/1 SO 7

In the latter case, an excess of hydroxide is required in the composition of the bath. In In this case the pH is stabilized as long as the entire amount of hydroxide has not yet been dissolved. According to a preferred embodiment, the electrolyte fluid is allowed to pass through continuously circulate a circuit containing a filter. If necessary, precipitating hydroxide is;

then always removed, thereby reducing the risk of an I.

Inclusion of this hydroxide in the ffold low level was eliminated. In the case described above, in which the pH of the bath has a tendency to increase, which necessitates the regular addition of metal hydroxide, the above-mentioned hydroxide or the basic compound is preferably not added to the bath, but rather placed on the filter that you see located in the circle through which the bath continuously circulates. Suitable metal salts, the hydroxide of which is precipitated at a pH value between 3 and β, are those of Al ⁺⁺⁺ (pH 3.5), Cr ⁺⁺⁺ (pH 4.5), Be ⁺⁺ (pH 6), rare Earth and Zn (pH 6.8). With the aid of the gilding bath according to the invention, a deposit of constant, undamaged quality is obtained.

It should be noted that from U.S. Patent 3 367 853 a gold plating bath is known from which a small amount of the hydroxide together with the Gold is precipitated, which gives the gold a greater hardness and a higher shine. In However, this bath uses a citrate together with citric acid as a buffer, whereby the pH of the bath is brought to a range where dam the mentioned metal salts with their hydroxide cannot exercise any buffering effect.

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The baths according to the invention are pure and do not cause any inclusion in the gold precipitate; When using aluminum alum aluminum hydroxide, Al could not be detected spectroscopically, ie that less than 0.003 fi of it is present in the gold.

According to an exemplary embodiment of an electrolytic Gold plating bath according to the invention contains a water-containing electrolyte per liter

12 g KAu (CN) ₂
150 g KAI (S0 ₄ ) ₂ . 12H ₂ O,

to which mixture an EOH solution was added until it became cloudy will. The pH is then around 3.5. This bath is at a temperature of 60-70 ° C and with. a current density of 0.5 A / dm is used.

Gold salt can regularly be added to an electrolyte of the type mentioned above, so that the composition of the bath is maintained. Hydrocyanic acid escapes and aluminum hydroxide precipitates, which is regularly removed by filtration during circulation. Al ₂ (SO,) «should be added.

Depending on how much gold is deposited from the bath, a total of 255 g of KAu (CN) ₂ can be added per liter to a bath liquid of the type mentioned above. The bath then contains 105 g / l K2 ^S0 4 ^ ³²¹⁴ the precipitate is 24 g Al (OH) ₅ . If the original concentrations in the gold bath are to be restored, 204 g Al ₂ (SO.) Are added at 80 ° C, after which it is cooled to 30 ° G, whereby potassium-aluminum alum crystallizes out until the con-

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concentration in the bath is 150 g (KAI (SO ₄ ) _2. 12HgO per idter.

During the entire service life of the bath, gold is of constant, undamaged quality without changing the pH value or the current yield,

Alloy deposits are obtained by adding salts of the base metals in question to the gold-plating bath. If 1 g / l of nickel sulfate (NiSO ^ .7H ₂ O) is added to this bath, a highly lustrous deposit of gold with a nickel content of about 1 $> is obtained. When 2 g / l of nickel sulfate is added, a pale colored gold alloy is obtained. By adding complexing agents (e.g. tartaric acid), the nickel concentration in the electrolyte can be selected to be higher, while the nickel concentration in the alloy deposit is still low. In this way, shiny, abrasion-resistant gold layers can be obtained with very low nickel contents in the precipitate.

In a similar way, Cd, Co, Ie, Gu and platinum metals can also be deposited at the same time.

The operating temperatures of these baths can be between Room temperature and 100 ° G vary. With the higher ones Temperatures can with the then achievable higher gold concentrations current densities of a few A / dm can be applied.

Patent claims:

0U9B10 / 1507

Claims (3)

Claims; 1. Electrolyte bath for depositing gold or gold alloys, which contains a soluble gold compound, a buffer and optionally one or more salts of metals that are deposited as alloy components, characterized in that the buffer consists of a salt of an inorganic acid and a metal, the Hydroxide or basic compound precipitates in the pH range between 3 and 8, the corresponding hydroxide or the basic compound itself and optionally an alkali salt of the same or another inorganic acid. 2. Electrolyte bath according to claim 1, characterized in that the liquid circulates continuously through a circuit containing a filter. 3. Electrolyte bath according to claim 2, characterized in that the excess of metal hydroxide or basic compound, which are reflected in the pH range between 3 and 8, is given to the filter which is in the circle through which the bath circulates continuously . 0 098 10/1507