DE2315309A1 - GOLD BATH - Google Patents

Description

Patent attorneys: 2 3 1 P 4 U 3

Dr. ing. Watter AWte
Dr. Dieter F. Morf

Dr. Hans-Α. Brauns, 27. March 1975

I Munich 88, Pienzenaueratr. 28 B-1102

ENGELHARD MINERALS & CHEMICALS CORPORATION 450 Mountain Avenue, Murray Hill, NJ, V. St. A.

Gold bath

The galvanic deposition of gold from sulfite-gold complexes of alkali metals was described as early as 1842 (GB-PS 94-312; the more recent US-PS 3,05-789 and 3 4-75 292 relate to baths containing Sulphite-gold complexes for the formation of gold precipitates with a Knoop hardness of I30 to 200.

It has now been found that by adding a directed amount of a polycarboxylic acid together with a soluble Semi-metal receives shiny, ductile, pure precipitates with a controlled Knoop hardness of less than I30 and that by changing the proportions of the acid and semi-metal components mentioned, precipitates with a Knoop hardness below 90 can be obtained.

The gold electrolyte according to the invention for the formation of gold precipitates with a controlled Knoop hardness of less than 130 contains gold as a sulfite complex, an alkali sulfite, .ein

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Buffer and conductive salt and the combination of a polycarboxylic acid with a semi-metal brightener. The addition of a controlled amount of polycarboxylic acid and semimetal brightener leads to shiny, ductile, pure gold deposits with a Knoop hardness of less than I3O, and by changing the proportions of the named acid and semi-metal components, precipitates with a knoop Preserved hardness below 90.

Preferred embodiments are described below. The gold bath according to the invention contains

Gold as a sulfite complex 4-30

Alkali or ammonium buffer salt 10 - 200

Alkali sulfite 10 - 1 50

Polycarboxylic acid 0.025 - 1j5

Semi-metal brightener 0.0025 - 0.15

(as metal)

Alkali sal ζ in for setting

the bath pH value to 8 to 11 sufficient amount

The gold sulfite complex is selected from the group consisting of potassium gold sulfite, sodium gold sulfite and ammonium gold sulfite.

Examples of the alkali or ammonium buffer salts are Alkali or ammonium nitrates, borates, phosphates, sulfamates and pyrophosphates.

Sodium or potassium sulfites are used as alkali sulfites.

Examples of the polycarboxylic acids are succinic, malonic

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and oxalic acid and its derivatives such as maleic acid. The polycarboxylic acids For the purposes of the invention there are no hydroxypolycarboxylic acids such as citric or tartaric acid, their salts often used as a buffer or conductive agent in gold electrolytes Find.

Examples of the soluble salts of the semimetal are the soluble salts of antimony, arsenic, selenium and tellurium, such as Potassium antimony tartrate, arsenic trioxide, selenium than with alkali, like potassium or sodium hydroxide, neutralized selenic acid and tellurium as a soluble salt, like in potassium or Tellurium dioxide dissolved in sodium hydroxide.

Preferred as a combination of polyacrylic acid and hard metal " become oxalic acid and arsenic trioxide. The gloss-hardness control solution is obtained by allowing the arsenic trioxide to dissolve heated in an aqueous oxalic acid solution. It has been shown to increase or decrease the oxalic acid concentration in the brightener or electrolyte at e.g. B. same arsenic concentration galvanic precipitates of various hardnesses. The oxalic acid is preferably used together with the gloss-forming semi-metal added.

The following examples serve to further illustrate the invention.

example 1

To form solution A, 50 g of oxalic acid crystals and 10 g of arsenic were dissolved as arsenic trioxide in an amount of water sufficient to form Λ 1 solution.

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Gold as a sulfite complex 10 g / l

Potassium citrate '70 g / l

Sodium or potassium sulfite 25 g / l

Solution A ' ~ s 3 ml / 1

Ealiumhydroxid 'corresponding to pH-value

position on 9.0 to 9.5

The one at 0.5 A / dm (5 A / square foot) using a 25 g insert (Load) and the precipitate obtained in a thickness of over 0.05 mm had a Kno op hardness between 94- and 123. The precipitate was brilliant.

Example 2

To form solution B, sufficient water to form 1 liter of solution was mixed with 100 g of oxalic acid crystals and 10 g of arsenic dissolved as arsenic trioxide.

Gold as a sulfite complex 10 g / l

Potassium citrate 70 g / l

Sodium or potassium sulfite 25 g / l

Solution B 3 ml / 1

Potassium hydroxide according to the pH value

position on 9.0 to 9.5

The precipitate obtained at 0.5 A / dm using a 25 g insert and in a thickness of over 0.05 m. Had a Knoop hardness between 76 and 85. The precipitate was glossy.

Example 5

To form solution C, in sufficient water to form 1 liter of solution, 10 g of arsenic were added as. Arsenic trioxide solved.

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Bath;

Gold as a sulfite complex Potassium citrate Sodium or potassium sulfite Solution C

Potassium hydroxide according to pH-value

position on 9.0 to 9.5

The one at 0.5 A / dm using a 25 g insert

2315309 g / l 10 g / l 70 g / i ml / 1 3

and precipitate obtained to a thickness of over 0.05% had a Knoop hardness between 140 and 160. The precipitate was shiny.

B ei s ρ i e 1 -4

To form solution D, 100 g of oxalic acid were dissolved in sufficient water to form 1 liter of solution.

Bath:

Gold as a sulfite complex 10 g / l

Potassium citrate 70 g / l

Sodium or potassium sulfite 25 g / l

Solution "D 3 ml / 1

Potassium hydroxide according to pH-value

position on 9 »0 to 9.5

The precipitate obtained at 0.5 A / dm was brown and not very compact. On a hardness determination was waived.

The polycarboxylic acid-semimetal brightener combination becomes the bath in the ratio of polycarboxylic acid to semimetal added in the range of 4: 1 to 20: 1. For example, the ratio can be 5 J 1, whereby the precipitate is a Knoop hardness of 90 to 1JO, or preferably

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10: 1 j resulting in a Knoop hardness of the precipitate of less than 90.

The amount of such additive in the bath depends on the Working speed at which the bath is operated. The following example explains the use of the additive in a bath that is formulated to operate at substantial current densities, the current density being above that mentioned in Examples 1 to 4. To operation of the bath with such a higher current density it is necessary to increase the gold and aluminum citrate concentration.

Example 5

Gold as a sulfite complex '20 g / l

Potassium citrate 90 g / l

Uatrium or potassium sulfite 25 g / l Solution A £ from Example i) 6 ml / 1

Potassium hydroxide according to pH value

Setting from 9.0 to

'"9.5

2 This bath produced soft, pure gold precipitate at 2.2 A / dm with a Knoop hardness of 95 to 100.

As the following example explains, the above result Ratios of polycarboxylic acid to semi-metal salζ in one Bath containing alkali metal gold cyanide as a source of gold does not have the same reduction in hardness.

Example 6

Gold as potassium gold cyanide 10 g / l

Potassium citrate 70 g / l

Potassium dihydrogenphosphate JO g / l

Solution A (from Example 1) -3 ml / 1

'H ₃₅ PO ₄ or KOH according to pH value

^ Position on 6.5

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- O -

A precipitate deposited at 0.5 A / dm had one Knodp hardness of 140.

The following example further shows that you can use no the combination additive according to the invention, d. H. if the polyearboxylic acid (oxalic acid) is omitted, the same Hardness as in example 6 is obtained:

Example 7

Gold as potassium gold cyanide. 10 g / l

- Potassium citrate 70 g / l

Potassium dihydrogenphosphate JO g / l

Arsenic as arsenic trioxide 30 mg / 1

H ₃ JPO ₂ , or KOH according to pH value adjustment

^p * position to 6.5

A precipitate deposited at 0.5 A / dm had a Knoop hardness of 140.

The results of Example 6 show that the hardness controlling additive only see its effect in the non-cyanide Groldbädera unfolds.

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Claims (1)

2 . ? 3 1 5 3 O 9 Pa t e η t a n s .ρ rüche 1. Gold bath with a content of gold as a sulfite complex, Alkali or ammonium buffer salt, alkali sulfite and the Combination of polyearboxylic acid and semi-metal brightener in the ratio of polycarboxylic acid to semimetal in the range from 4: 1 to 20: 1. 2. Gold bath with a content a) from 4 to J> 0 g / l of gold as a sulfite complex, b) from 10 to 200 g / l of alkali or ammonium buffer salt, c) from 10 to 150 g / l of alkali sulfite, d) from 0.025 to 1.5 g / l of polyearboxylic acid, e) from 0.0025 to 0.15 g / l of semi-metal brightener, as metal, and of alkali metal salt in one for Adjustment of the pH value to 8 to 11 sufficient quantity. 3. Gold bath with a content a) from 4 to 3 ° g / 1 of gold sulfite complex from the group Potassium gold sulfite, sodium gold sulfite and ammonium gold sulfite, b) from 10 to 200 g / l of buffer salt from the group of alkali or ammonium citrate, borate, phosphate, sulfamate and pyrophosphate, c) from 10 to 150 g / l of alkali sulfite from the group Potassium sulfite and sodium sulfite, d) from 0.025 to 1> 5 g / 1 ⁸ ^ - polycarboxylic acid from the group of succinic, malonic and oxalic acid, e) from 0.0025 to 0.15 g / l of semi-metal brighteners, as metal, from the group arsenic, antimony, selenium and tellurium,. and of alkali salt in one to adjust the pH of the bath to 8 to 11 sufficient amount. - 8 - ■ 309841/1083 4 ·. Bath according to claim 31, characterized in that the Polycarboxylic acid oxalic acid and the semi-metal brightener Arsenic trioxide is. 5 «bath according to claim 3, characterized in that the combination of polyearboxylic acid and semimetal brightener with a ratio of carboxylic acid to half-metal gloss former is in the range of 4: 1 to 20: 1. 6. Bath according to claim 3 *, characterized in that the combination of polycarboxylic acid and semimetal brightener is present with a ratio of polyearboxylic acid to semimetal brightener of 5 ^: 1, the gold deposited from the bath having a Knoop hardness of 90 to 130 Has. 7 · bath according to claim 3i, characterized in that the Combination of polycarboxylic acid and semi-metal brightener with a ratio of polycarboxylic acid to semimetal brightener of 10; 1 is present, where the gold deposited from the bath has a Knoop hardness of less than 90. 8. Bath according to claim 3 »characterized in that the alkali salt potassium hydroxide used for pH adjustment is. 3 0 9 8 4 1/1