Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/62—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of gold
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/48—Electroplating: Baths therefor from solutions of gold

Definitions

• This invention relates to an electrolyte and to a process for plating gold.
• the invention can be advantageously employed in any gold plating process, but is especially suitable for the gold plating of small parts according to the barrel plating process, for example.
• Small products because of the work required to rack each separate product, are more effectively plated by a barrel plating process.
• the distribution of the plating obtained by conventional plating baths is uneven and such products must be excessively plated in some parts to obtain the minimum thickness of plating required in the parts where the distribution is poor. Since gold is expensive, the cost of plating by baths with poor distribution is excessive.
• This invention is based on the discovery that the addition of certain limited amounts of soluble thallium compounds to acid gold plating baths of the type having a pH between 3 and 6, improves the metal distribution of the deposit and simultaneously improves the smoothness, color and brightness of the deposit obtained.
• the gold is added to the acid gold baths in the form of alkali gold cyanide, preferably potassium gold cyanide.
• the gold can be present in amounts of l to 75 g./l. calculated as gold.
• the baths contain conducting and buffering compounds and are adjusted to a pH of 3 to 6 by selecting a partially neutralized compound of a weak acid as the conducting media or by adding acid to the solution 'which contains a substantially neutral compound of a relatively weak acid.
• the minimum amount of conducting and buffering compound should be about 5 g./l.
• the maximum amount of acid and compound is not critical as long as the bath is adjusted to the pH range of 3 to 6 and as long as the resultant solution is not supersaturated at the temperature to be employed for electroplating.
• the addition agent for the present invention is especially useful for the production of pure gold deposits, but can also be employed with alloy deposits.
• ice tions it is possible to obtain smooth, bright yellow deposits of 24 karat gold, having a Knoop hardness, with a 25 gram load, within a range of to 145, for example.
• the alum is preferably added in the proportion of from 1 g./l. to 100 g./l.
• the thallium compound is added in an amount to provide about 1 mg. to 25 g. of thallium, calculated as the metal, in the bath.
• Suitable thallium compounds are the thallous and thallic sulfates, thallium alum, thallium chloride, nitrate, fiuosilicate, or other water soluble thallium compounds.
• the improved bath is operated at current densities of 0.1 to 10 amp/din. and at temperatures of about 20 C. to 90 C.
• the bath comprises the following ingredients, within the range specified:
• the alum added may be defined as a compound obtained by crystallizing the sulfates of aluminum, chromium and gallium with the sul; fates of ammonium, cesium, potassium, rubidium, sodium and thallium and with water in which the molar ratio is 1:1:24 and where M is the monovalent metal and M' is the trivalent metal.
• Potassium gold cyanide (calculated as g0ld)8 g./l. Thallium sulfate300 mg./l.
• a multiplicity of small parts having a head of about 1 cm. diameter and several thin leads extending from the 7 head were introduced into a conventional barrel plating device and plated in this solution at a current density of about 0.1 amp./dm. and at F. Parts placed in this solution to an average of 0.000050" thickness are smooth, lemon yellow and semi-bright and pass prescribed tests as follows:
• the device is heated to 410 C. and a pellet of gold-silicon eutectic is placed on the surface of the gold electroplate.
• the eutectic alloys with the gold plate and forms, when satisfactory, a smooth adherent melt which is not foamy, frothy or discolored.
• Beta-ray backscatter measurements show that the gold deposit is approximately the same thickness throughout the part.
• Gold as potassium gold cyanide-8 g./l.
• Thallium as the sulfate-2V2 mg./l.
• Phosphoric acid to a pH4.3
• a polished brass panel was electroplated in this solution at a current density of about 0.3 amps./dm. at 60 C.
• a deposit of about 3 microns was smooth lemon-yellow and bright-although not as bright as the original brass panel.
• a similar bath made without the addition of the thallium produced a deposit at the same thickness which had a dull, orange-brown appearance.
• Gold deposits to thicknesses of 30-50 microns were also produced from this thallium containing bath. These were lemon-yellow in color, rather than the orange-yellow appearance of gold.
• An improved aqueous electrolytic gold plating bath especially useful in barrel plating comprising:
• Gold (added as alkali gold cyanide)1-75 g./l.
• Conducting and bufiering compounds selected from partially neutralized weak acids-5 to 400 g./l. (saturated).
• conducting and buffering compounds are a mixture of partially neutralized weak, stable, organic acids and phosphates.
• a process of plating gold especially useful for small parts of irregular shape comprising electrolyzing at a cur- 4 rent density of about 0.1 to 10 amp./dm. and at a temperature of about 20 C. to C., an aqueous bath of the following components:
• Gold (added as alkali gold cyanide)-l-75 g./l.
• Conducting and buffering compounds selected from partially neutralized weak acids-5400 g./l. (saturation).
• a process as claimed in claim 8 wherein the conducting and bufiering compounds are mixtures of partially neutralized weak, stable, organic acids.
• a process as claimed in claim 8 wherein the conducting and buifering compounds are alkali phosphates.
• conducting and buffering compounds are a mixture of partially neutralized 'weak, stable, organic acids and phosphates.
• An aqueous electrolyte for the electrodeposition of pure gold comprising 1 to 75 g./l. of gold (added as an alkali gold cyanide), 5 to 400 g./l. (saturation) of conducting and buffering compounds selected from partially neutralized weak acids, and 0.001 to 25 g./l. of thallium (added as a water soluble compound), the pH of the electrolyte being adjusted to the range of from about 3 to about 6.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=24309474

Family Applications (1)

Country Status (4)

Cited By (4)

Family Cites Families (2)

• 1966
  • 1966-09-07 US US577618A patent/US3562120A/en not_active Expired - Lifetime
• 1967
  • 1967-08-01 GB GB35230/67A patent/GB1200110A/en not_active Expired
  • 1967-09-04 CH CH1240967A patent/CH476114A/fr not_active IP Right Cessation
  • 1967-09-06 DE DE1967S0111697 patent/DE1621169B1/de active Pending

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