Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/31—Coating with metals
  • C23C18/42—Coating with noble metals
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/31—Coating with metals
  • C23C18/38—Coating with copper

Definitions

• the invention relates to a method for the currentless deposition of silver or gold layers on surfaces of correspondingly less noble metals.
• Metal objects coated with silver or gold layers play in numerous fields of technology, such as in electrical engineering, in electronics, in the construction of medical devices, in restoration technology, in corrosion protection, in the jewelry industry, finishing technology, space travel, in mechanics, but also increasingly in teaching.
• GB-A-1411971 describes the electroless deposition of copper layers on steel by means of coating baths which contain a copper complex which is obtained by reacting copper (II) chloride with a nitrogenous base in the presence of HCl.
• the object of the invention is therefore to provide a method for the electroless deposition of silver and gold layers, which avoids the disadvantages shown and which enables the production of well-adhering layers with sufficient layer thicknesses. This object is achieved with the present invention.
• the invention relates to a method for the electroless deposition of silver or gold layers on correspondingly less noble metals by contacting the object to be coated with a coating bath which contains a metal complex which by reacting a chloride of monovalent silver or gold with a base which Complexation with which silver or gold is capable, and is available with hydrochloric acid.
• all compounds which can be protonated by the hydrochloric acid used to prepare the coating bath are suitable as bases capable of forming complexes with the metal to be deposited (i.e. silver or gold).
• bases capable of forming complexes with the metal to be deposited (i.e. silver or gold).
• preference is given to using bases which are easily protonated under the reaction conditions used.
• all metals which are less noble than the respective metal to be deposited can be used as the substrate for the metals to be deposited.
• particularly suitable substrate metals for silver are e.g. Zinc, iron, nickel, tin, lead and copper; and for gold e.g. Nickel, copper, silver, tin, zinc, lead, iron and platinum.
• the reaction of the metal chloride i.e. the silver or gold chloride
• the base and the hydrochloric acid can be done by simply mixing these components together.
• the reaction can be carried out without or in the presence of a solvent, and an excess of base can also serve as the solvent.
• the molar ratio base / metal chloride / hydrochloric acid is chosen so that the entire amount of metal chloride is dissolved in the reaction. It is expediently in the range from 1 to 40/1/1, but the molar value of the base and the hydrochloric acid can also be substantially higher, for example twice as high. The most favorable molar ratio depends in particular on the type of implementation.
• Suitable solvents are inert to the complex formation reaction, especially aprotic organic solvents, such as e.g. Carbon tetrachloride and especially acetone.
• the solvents have to be weaker basic than the base used. Under these conditions, a base, such as. As dimethylformamide, can be used as a solvent.
• the reaction is carried out at room temperature or with heating.
• basic cleavage products result in particular in the case of bases sensitive to hydrolysis, which in turn produce hydrochloride with hydrochloric acid and complex with the noble metal chloride.
• This case occurs e.g. when formamids are reacted with hydrochloric acid and metal chloride in the heat.
• Cleavage occurs in formic acid and amine, the latter then immediately reacts to form the hydrochloride, which is the actually complexing agent.
• the metal chloride is preferably added in finely powdered form; the hydrochloric acid can be added in liquid form or introduced in gaseous form.
• the z. B. according to one of the process variants (a), (b) or (c) reaction solution obtained, optionally after dilution with a suitable solvent, can be used directly as a coating bath (metal deposition solution).
• a suitable solvent an aprotic solvent which can be used for the reaction, such as, for example, acetone or carbon tetrachloride, or mixtures thereof
• a suitable solvent an aprotic solvent which can be used for the reaction, such as, for example, acetone or carbon tetrachloride, or mixtures thereof
• Solutions of silver complexes can e.g. B. can be kept almost unchanged over several years.
• the metal complexes can by diluting the reaction solutions with a poorly dissolving solvent, such as. B. with acetone.
• the coating bath can then be prepared from these complexes if necessary by dissolving them in a suitable solvent, e.g. in dimethylformamide.
• the dissolution usually takes place with slight warming, e.g. at 60 ° C. To avoid decomposition of the complex and to maintain the separation quality and stability, overheating should be avoided.
• a complex-forming component base, metal or hydrochloric acid
• base metal or hydrochloric acid
• reaction conditions such as the type of solvent. It is also possible to use two or more bases. Gold / silver mixtures can also be deposited.
• the selection, combination and quantitative ratio of the complex-forming components also depend on the desired deposition rate (reactivity) and selectivity of the coating bath. It was found that, as a rule, a decreasing base strength results in greater reactivity.
• the metal layers are deposited on the substrate by the methods customary for electroless deposition from coating baths, in particular by immersing the objects to be coated in the deposition bath.
• the objects to be coated can generally have any shape, which is determined in particular by the later intended use.
• the contacting can also be carried out by applying (brushing on, brushing) the coating solution (coating bath) onto the workpiece.
• the coating method it is advisable to use coating baths that are as concentrated as possible. This process can be repeated any number of times until the desired layer thickness is reached.
• This method will be particularly preferable if only parts of an object are to be coated (this requires a partial covering with a layer that is later easy to remove again with the immersion method) or if immersion is not possible or is only possible with difficulty, e.g. in restoration technology.
• the duration of the contact time depends primarily on the deposition speed and the desired layer thickness.
• the deposition process can be interrupted at any time (e.g. by removing the workpiece from the solution) and, after the coating has been assessed, it can be continued by contacting it again. This process can be repeated any number of times until the desired layer thickness is reached.
• residues of the coating bath are washed with a suitable solvent, e.g. with methanol, ethanol or acetone, and the workpiece is dried, e.g. by wiping with a cloth.
• the quality of the coating depends to a large extent on the deposition rate. Deposition that is too rapid (reactivity that is too high) generally results in a less adherent ⁇ amorphic> coating than with a coating bath of lower reactivity.
• Favorable coating times are between one minute and one hour.
• the deposition rate (reactivity) of the coating bath can be adjusted by suitable selection and combination of the complex-forming components. However, it is also dependent on the concentration of the metal complex in the coating bath and / or the acid concentration. As a rule, the rate of separation increases with increasing concentration of metal complex and acid. From very concentrated solutions, the deposition z. B. done in a few seconds.
• the complex-forming components in particular base and hydrochloric acid
• Selectivity is also related to reactivity.
• the deposition rate for a particular metal can be regulated by varying the amount of acid. A change in the concentration of the metal complexes usually only affects the deposition rate.
• the layer thicknesses that can be achieved are generally proportional to the metal complex concentration of the coating bath and the contact time.
• a suitable choice of the deposition conditions generally gives a layer thickness of 0.01 to 4 J.1m.
• the deposition can be followed by potential measurement. For example, by measuring the potential on a copper sheet, the final value of the coating (maximum coating) is displayed after four days. In order to measure the potential with as little feedback as possible, an electrometer amplifier was used (input current ⁇ 50 mA), and a silver wire was used as the reference potential. The initial potential was 100 mV and practically reached zero after the time specified above. The change in potential during the deposition process was recorded graphically with the aid of a recorder.
• a dropwise addition of concentrated acid enables an almost quantitative utilization of the complexed metal for the deposition from those which appear to be ⁇ exhausted> Coating baths can be achieved. Too large an amount of acid is recognized by an immediate precipitation of the silver still in solution as a halide, in the case of gold as a metal.
• the silver can be precipitated from the exhausted solutions by dilution with water as the halide or the gold by adding an aqueous iron (II) salt solution as the metal and sent to a recycling process. This makes it possible to keep the environmental impact low with the method according to the invention.
• a method is thus provided with which it is possible to produce easily adhering and corrosion-resistant coatings (e.g. gold-plating) in a very simple and rapid manner with layer thicknesses not previously achieved with currentless methods.
• the process can be carried out without great mechanical outlay and at room temperature, that is to say without much outlay in energy.
• Working at room temperature also makes it possible to coat objects where galvanic deposition or electroless coating with conventional baths was not possible due to their temperature sensitivity.
• simple recycling separation of the metals from the ⁇ exhausted> coating baths, distillation of the solvents
• the cyanide-free coating baths also avoid the problems with handling and waste disposal which occur with the known cyanide-containing coating baths.
• the use of non-toxic and difficultly volatile substances also enables the objects to be coated to be brought into safe contact by simply applying (brushing).
• the invention therefore also relates to coating baths for the electroless deposition of silver or gold layers on correspondingly less noble metals, containing a metal complex which, by reacting a chloride of monovalent silver or gold with a base which is capable of complexing with the metal, and with Hydrochloric acid is available.
• the invention further relates to metal complexes which can be obtained by reacting a chloride of monovalent silver or gold with a base which is capable of forming a complex with the metal and with hydrochloric acid, and subsequent precipitation from the reaction mixture.

Landscapes

• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemically Coating (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

Family

ID=6148063

Family Applications (1)

Country Status (6)

Cited By (2)

Families Citing this family (21)

Citations (1)

Family Cites Families (6)

• 1981
  • 1981-12-07 DE DE19813148330 patent/DE3148330A1/de not_active Withdrawn
• 1982
  • 1982-11-30 EP EP82111045A patent/EP0081183B1/de not_active Expired
  • 1982-11-30 AT AT82111045T patent/ATE27187T1/de not_active IP Right Cessation
  • 1982-11-30 DE DE8282111045T patent/DE3276334D1/de not_active Expired
  • 1982-12-06 CA CA000417092A patent/CA1236843A/en not_active Expired
  • 1982-12-07 JP JP57213471A patent/JPS58104168A/ja active Granted
• 1988
  • 1988-07-21 US US07/222,386 patent/US4908241A/en not_active Expired - Fee Related

Patent Citations (1)

Also Published As

Similar Documents

Legal Events