JPS5826436B2 - Electrolyte for gold plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of gold compounds, and more particularly to electrolytes for gold plating.

The invention is advantageous for the production of all reactants for electronic device and watch manufacturing, jewelery and radio technology.

The electrolytes known in the past are gold-plated electrolytes based on sodium or potassium salts of dianoauric acid, and gold-plated electrolytes containing potassium sulfate, potassium hydrogen phosphate, and alkali metal salts of ethylene diaminoacetic acid. Electrolytes, these are produced by anodic or chemical dissolution of gold in solutions of alkali metal cyanides.

The production and use of this type of electrolyte involves the generation of toxic components and requires rendering them harmless.

The above-mentioned known electrolytes can only provide a good-quality film if the film is thick.

Further, the production and use of the above-described known gold plating electrolytes are accompanied by problems in that it is difficult to recover gold from the used mother liquor and toxic components are generated.

The most widely used gold plating electrolytes are those based on disulfite oleate, ethylenediaminodisulfite oleate, and alkali metal sianodisulfite oleate; Properties are based on how they are created.

The method is to refine the aurichlorohydric and from the CI ion by converting it to a slightly soluble gold compound, i.e., ferric hydroxide or auric ammoniate.

The gold compound is treated with a solution of an alkali metal sulfite, and the sulfite complex formed in the solution is then stabilized.

The sparingly soluble gold compounds produced in this way have low stability and therefore partially generate metallic gold, which reduces the desired product yield.

This also prevents the production of highly concentrated electrolytes for gold plating that are stable during storage and use, thereby reducing the efficiency of the gold plating process.

A gold-plated electrolyte based on potassium disulfite oleate and having the following composition is known (
See U.S. Pat. No. 3,893,896]K3[Au(S03
)2]6.8-68 Na2H2Ed ta O,1-10
0 to 2SO41, 0-100 to 2HPO410-40 water residual (current density is Dk = 0.1-1.2 A/ dm”
; T = 18-80°C) This gold plating electrolyte has a uniform electrodeposition of 90%t and a current efficiency (yield current) of 70%.
80 factor 1, the storage period is about 4 months at a temperature of 25° C., and the Dk at the starting point of decomposition is 0.8 A/dm2 or more.

This electrolyte makes it possible to produce high-quality, fine-grained coatings, whose hardness ranges from 80 to 220/li/1ll1.
2, and its porosity is 25 to 30 pores//cd at a thickness of 15μ, and non-porous at a thickness of 5μ or less.

The process of producing this electrolyte is to treat the aurichlorohydric acid with an ammonia solution at pH 3 to 6 to give the basic auric ammoniate, followed by decanting the mother liquor and washing with hot water.

The resulting suspension was mixed with a warm solution of potassium sulfite (150 f/, l).

The resulting mixture is then heat-treated at a temperature range of 70-90° C. for 48-72 hours, and the alkali metal salt of ethylenediaminetetraacetic acid,
Add potassium sulfate and potassium hydrogen phosphate.

The resulting electrolyte is filtered to recover the partially precipitated metallic gold.

The yield of the gold plating electrolyte produced in this way is between 30 and 60%, calculated for metallic gold.

This known gold plating electrolyte has a reduced stability during storage and use and has unsatisfactory technical parameters.

The main objective of the invention is to provide a gold-plated electrolyte with improved technical parameters and high stability during storage and use.

The purpose was to create a composite gold compound with sulfite ions,
According to the present invention, μ-ethylene sia is added to a gold plating electrolyte containing an alkali metal salt of ethylenediaminetetraacetic acid, potassium hydrogen phosphate, potassium sulfate, and water as the composite gold compound having sulfite ions. This is achieved by a gold plating electrolyte characterized by containing hexapotassium bis(gold(I) sulfite) tetraacetate in the following component ratio (f/l).

μ-ethylenediaminetetraacetic acid hexapotassium bis(gold(I) sulfite) i 0.5-123.0 Ethylene cyanidetetraacetic acid alkali metal salt 17.8-140.0 Potassium sulfate 12.6-110.0 Hydrogen phosphate Potassium 4.7- 40.0 Water
The content of these components to be added to the remaining electrolyte is such that the content of hexapotassium bis(ferrous sulfite) μ-ethylenediaminotetraacetate is 10.5. If it is less than @/, /, the electrodeposition rate is insufficient, and on the other hand, the content is 123? It is determined by the fact that if the amount is more than /l, the quality of the coating is impaired.

The proportions of the alkali metal salts of ethylenediaminetetraacetic acid, potassium sulfide and potassium hydrogen phosphate influence the quality of the coating, especially its hardness, and these properties are influenced by the content of hexapotassium bis(ferric sulfite) determined.

The gold plating electrolyte according to the present invention contains the following components in the following proportions? /
It is desirable to include it in l.

μ-Ethylenediaminetetraacetic acid hexapotassium bis(ferrous sulfite) 10.5-25.0 Ethylenediaminetetraacetic acid disodium dipotassium salt
17.8-40.0 Potassium sulfate 12
．． 6-28.4 Potassium hydrogen phosphate 4.7-
10.4 Water Residual The above specified component amounts of the optimal gold plating electrolyte composition ensure maximum reliability during use.

Therefore, in the amount mentioned above, 2Na2Ed ta is converted into ethylenediaminetetraacetate ion Ke CAu (SOa) under the action of electric field force in the layer adjacent to the electrode.
2 Edta).

In this case, the electrochemical reaction only takes place in the double electrical layer, which prevents the complex from decomposing itself in solution and liberating the gold in powdered form.

The amount of 2S04 specified above makes the process conductivity of the solution acceptable.

2HPO in the amounts specified above. creates a buffering property in the medium.

The reason this is necessary is that the following reaction occurs at the anode, SO3"-+H2O-+e804"+
This is because oxidation of 2H and thus of the medium takes place, resulting in decomposition of the complex in solution.

The compositional nature of the gold plating electrolyte according to the present invention is given by its method of production.

To produce this electrolyte, a solution of ammonium hydrogen phosphate and a solution of gold hydrochloride are added simultaneously to water at a temperature of 7° to 95°C, even though the pH of the resulting suspension is It is added in a proportion that falls within the range of 4.5 to 6.0.

At the same time, a precipitate is formed consisting of bis-(dihydroquinephosphatomonohydroquinephosphato)ammonium aurate pentahydrate of the following formula:

(N')(4) 3 CAu (HPO4) 2(H2
PO4) 2].5H20 This precipitate is washed to remove chloride using the filtration method or the decanting method and added in portions to a solution consisting of potassium hydroxide and the alkali metal salt of ethylenediaminetetraacetic acid. .

The pH of this solution is 9-10 and the temperature range is 70-90°C.

Non-soluble complex (NH4) 3c Au (HPO
4) 2 (H2PO4) 21) When 5H20 reacts with this solution, partial dissolution of the precipitate occurs and a soluble ethylenediaminetetraacetate complex of trivalent gold is produced.

A pH 9 solution containing potassium sulfite and potassium hydroxide is then added to the resulting suspension.

The above-mentioned soluble complex reacts with sulfite ions, with the result that trivalent gold is reduced to monovalent gold and 6(A
A sulfite conjugate called u (5o3) 2Ed ta ) is produced.

All of these steps shift the equilibrium state of the precipitate toward dissolution, while the steps listed above eliminate the secondary reaction processes that decompose the monovalent gold complex into metallic gold. do.

The electrolyte yield calculated for gold is 86%.

This high yield of gold plating electrolyte according to the invention is due to the use of ammonium hydrogen phosphate for the precipitation of highly soluble complex gold compounds.

This precipitated product is (NH4) s CAu (HP −
0, )・(H2PO4)2]・5H20, and the reproducibility of the formation of the gold-plated electrolyte compared to the precipitated product obtained with ammonia and known as lightning, which has no permanent composition. do better

Complex (NH4)3 [human u (HPO4)2・(H2PO
4) 2].5H20 is more insoluble than ammonium hydrogen phosphate, which allows the gold to be completely precipitated.

This complex consists of a dense powder that is easily precipitated, compared to lightning which is very unstable and dangerous in wet conditions and especially unstable and dangerous in dry conditions. , does not decompose in either wet or dry conditions.

Therefore, instead of multiple decantations in the case of thunder metal, purification from chlorides can be accomplished by filtering and washing.

When the composite is subsequently dissolved, phosphate, which is a component of the gold plating electrolyte according to the invention, is passed into solution.

Therefore, choosing ammonium hydrogen phosphate as the precipitant results in less gold loss due to more complete precipitation and
Mechanical loss is reduced by filtration rather than multiple decantations, and the complex (NH < ) a [Au
(HPO4) 2 ・(H2PO4) 2) ・5H
The chemical stability of 20 prevents the presence of metallic gold in the precipitate, thereby reducing gold loss during subsequent operations.

The gold-plated electrolyte thus produced has the following composition Ef/l
have.

K61Au(SO3)2Ed ta) 10.5-12
3. 2 Na2Ed ta□ 17.
2SO412 to 8-140, 2HP0 to 6-110. 4.7-40 water
Desirable conditions for residual precipitation are as follows.

The temperature is in the range of 18 to 60°C, and the cathode current density Dk is Dk = 0.02-15. 0 A/dm2, and the anode is stainless steel, platinum, and graphite.

The gold plating electrolyte according to the present invention has a uniform electrodeposition property of 80 times 1.
The current efficiency is 80-90, the storage period is 12 months or more at a temperature of 25° C., and the starting point of electrolyte decomposition is Dk = 15 A/dm2.

This gold plating electrolyte produces a fine coating of high quality, with a Vickers hardness of 8o to 22Qkg/m*2 and a porosity of 15 to 20 pores/cm with a thickness of 15μ.
and is non-porous for thicknesses up to 5μ.

The gold plating electrolyte according to the invention has improved process parameters compared to known gold plating electrolytes, has higher stability during storage and use, and higher gold yield during production.

Some specific examples of gold plating electrolytes and methods of producing the same according to the present invention are listed below.

Example 1 5 t ammonium hydrogen phosphate is dissolved in 1500 rrLl and the solution is heated to a temperature of 85°C, then 3
While holding a bag for 0 minutes, add 76.3 p of aurichlorohydric acid, 151 nl of hydrochloric acid, and 250 rrd of water.
1 and a solution containing 35 f of ammonium hydrogen phosphate and 250 ml of water are added simultaneously.

The addition of these solutions must be carried out in such proportions that the pH value of the resulting suspension is equal to 6.0.

Precipitated (NH4)sCAu(HP-04)2
・(H2PO4)2 ]・5H20 is filtered and 50
Wash with 0rrtl of water and then mix with 200yrtl of water to make a suspension.

One portion of the suspension thus prepared (2o1rL
Add parts e) to the solution consisting of each part e).

This solution consists of 50,011 liters of water at a temperature of 70'C.
It is a solution containing 14 of divalent hydrate of ethylene cyanatetraacetic acid disodium salt and potassium hydroxide at pH 9.01.

A solution of 110 t of potassium sulfite in 50 111 l of water is added in portions (20-257 portions) into the resulting mixture for 20 minutes at 1 to completely dissolve the precipitate.

The resulting gold-plated electrolyte contains the following components in the following proportions? /l, and its concentration is suitable both for use on its own and for making less concentrated gold plating electrolytes.

KQ [Au(803)2 Ea ta) 1
23 to 2Na2Ed ta
52 to 2SO44°K2HPO440 Water The generation of an electrolyte with a low residual concentration is achieved by diluting a highly concentrated electrolyte with water and adding other components to that concentration, namely potassium sulfate, to 110? /l'! So, 40 f of potassium hydrogen phosphate
/l-! , and ethylenediaminetetraacetic acid disodium 2
This is done by adding potassium salt at 1401f/14.

The gold plating electrolyte of this example has the following characteristics.

Uniform electrodeposition: 90 coefficient Current efficiency: 80 coefficient Storage period at 25°C: 12 months or more Dk 1 at the starting point of decomposition: A/dm2 or more
When used on copper, nickel and hi-stainless steel substrates at OIA/dm2, non-porous coatings up to 7 microns thick are deposited at a rate of 5 microns/hour.

The optimal conditions for adhesion are as follows.

Temperature 2o0~60'C1Dk=0.2~0.6 A
/ dm2, deposition rate 8-14 μ/h.

The coatings obtained under this optimum condition are non-porous at a thickness of 1 of 5 microns and have a porosity of 15 to 2 pores/ctrl for thicker layers, depending on the deposition conditions.

Example 2 The following components are in the following proportion f? 6 [Au(803)2Ed ta] 10.5 to 2 N to produce a gold plating electrolyte containing 1/l
a2 Ed ta 17.8 to 2SO412,6 to 2HP0. 4.7 Wednesday
of the concentration of Example 1 with an amount of 85r/Ll remaining (this is (N)(
4) s [Au (HPO4)2 ・(H2PO4)2
] Precipitation of 5H20 is carried out at pH 4.5 and temperature 95°C and dissolution of the resulting precipitate is carried out at temperature 95°C.
915 ml of water (prepared according to Example 1 above except that it was carried out at 0° C. and pH 10).

Ethylenediaminotetraacetic acid disodium dipotassium salt 13
．． 4. @, potassium sulfate 9.3 @, potassium hydrogen phosphate 5
．． 32 was added and the solution was stirred at room temperature.

The resulting gold plating electrolyte has the following properties.

Uniform electrodeposition property 80% Current efficiency 80% Storage period at 25°C 12 months or more Starting point of decomposition Dk = 15 A/dm2
In the electrolyte made as described above, a rate of 12 μ/h, a temperature of 40'C, and Dk = 0, 4 A/d.
Deposition was carried out on brass, copper and nickel using m2.

A glossy coating with an original thickness of 50 μm was obtained.

The porosity is 15 pores/c4, and the Witzkers hardness is 22.
0 kg/lst.

Example 3 Add 667M of water to the concentration of 333M produced in Example 1 above.
By adding 11Ll of potassium sulfate, 97f of potassium sulfate, and 123t of disodium dipotassium salt of ethylenediaminotetraacetic acid, the following components were mixed in the following proportion f? A gold plating electrolyte was prepared containing 1/l.

KQ CAu (SOs)2 ED Na 2 K2 Ed ta 2SO4 to 2HP04 Water ta, l 48.7 40 10 18.7 Residual The resulting gold plating electrolyte has the following properties.

Uniform electrodeposition property 9o current efficiency
80 coefficient Storage period at 25℃ 12 months or more Starting point of decomposition Dk =
16.2 A/dm240℃ temperature, Dk = 0
．． Shiny coatings with a thickness of 100 μm were deposited on brass, nickel, bronze and stainless steel at a rate of 3 A/dm2.12 tt/h.

For brass, bronze and nickel, the coating was non-porous at a thickness of 1 of 5μ, and for stainless steel of the same thickness, the porosity was 5 pores/cr11.

Witzkaas hardness is 80 kg/mx2.

Example 4 The following components are given the following ratio f! In order to generate a gold plating electrolyte containing -/l, 2N was added to K6[Au(SO3)2Ed ta]18.9.
a2Ed ta 32.2 to 2
S0. 2H on 22.7
P0. 8.0 water
The remainder is 153 mJ of the concentration produced as in Example 1 above.
and ethylenediaminetetraacetic acid disodium dipotassium salt 23.4. 6.6 t of potassium sulfate and 1.9 t of potassium hydrogen phosphate were added, and water was added in 1 part to make 1 t.

The resulting gold plating electrolyte has the following properties.

Uniform electrodeposition property 9o current efficiency
84% Storage period at 25℃
Starting point of decomposition over 12 months Dk =
16 A/dm". Deposition was carried out from the electrolyte thus produced on brass, stainless steel substrates at a temperature of 45 DEG C. and Dk = 0.4 A/dm2.

The resulting coating has a porosity of 23 pores/cm over a thickness of 15 μm, and a Witzkars hardness of 165 g/cm.
It was 1lI2.

Example 5 Concentration 310rr produced as in Example 1 above
tl, ethylenediaminetetraacetic acid disodium dipotassium salt 23. @ and potassium sulfate 16.4. @ and 1 t of water
1. By adding the following ingredients in the following proportions?
A gold plating electrolyte was prepared containing 1/l.

Ka CAu (SO3) 2 Ed Na 2 K2 Ed ta 2SO4 to 2HPO4 Water ta) 25.0 40.0 28.4 12.4 Residual The resulting gold-plated electrolyte has the following properties. ing.

Uniform electrodeposition property 80 coefficient current efficiency
90% storage period at 25℃
Starting point of decomposition over 12 months Dk = 1
5.8 A/dm2 in the electrolyte thus produced at a temperature of 60'C and Dk = 0.2 A/d
Deposition was carried out on brass and stainless steel substrates at m2.

The resulting film has a porosity of 30 pores/cat in a thickness of 15μ, and a Vickers hardness of 100Ic.
It was 9/yrtx2.

Electrodeposition of gold with the electrolytes of Examples 1 to 5 was carried out in electrolytic cells of conventional design.

In all of the above examples, sulfuric acid was added to the spent electrolyte.
Addition at pH 1 below 4 followed by temperature 1 at 50-60°C
Gold is recycled from the spent electrolyte by heating it with water and filtering the precipitated powdered gold.

Claims (1)

[Claims] 1. Are the following components in the following proportions? An electrolytic solution for gold plating characterized by containing /, l. μ-Hexapotassium bis(gold(I) sulfite) 10.5-123.0 Ethylenediaminotetraacetic acid alkali metal salt 17.8-140.0 Potassium sulfate A 12.6-110.0 Phosphoric acid Potassium hydrogen 4.7- 40.0 water
Residue 2 What are the following proportions of the following components? The electrolytic solution for gold plating according to claim 1, which contains the electrolytic solution in an amount of /l. μ-Ethylenediaminotetraacetic acid hexapotassium bis(gold(I) sulfite) 10.5-25.0 Ethylenediaminotetraacetic acid disodium dipotassium salt
17.8-40.0 Potassium sulfate
12.6-28.4 Potassium hydrogen phosphate
4.7-10.4 Water remainder