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 electroless deposition of noble metal layers on surfaces of base metals.
• Metal objects coated with precious metal layers play in numerous fields of technology, such as. B. 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 in teaching to an increasing extent.
• the object of the invention is therefore to provide a method for the electroless deposition of noble metal 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 process for the electroless deposition of noble metal layers on correspondingly less noble metals by contacting the object to be coated with a coating bath, which is characterized in that a coating bath is used which contains a noble metal complex which is obtained by reacting a monovalent noble metal halide with a base , which is capable of complexing with the noble metal, and a hydrohalic acid is obtained.
• Monovalent noble metal halides suitable for the preparation of the coating bath are preferably noble metal bromides, noble metal iodides and noble metal chlorides.
• Monovalent precious metal halides are those of copper and primarily silver and gold.
• all compounds which can be protonated by the hydrohalic acid used to prepare the coating bath are suitable as bases capable of forming complexes with the metal to be deposited.
• bases which are easily protonated under the reaction conditions used.
• basic nitrogen-containing compounds such as, in particular, ammonia and amines, such as, for example, are particularly well suited for complex formation.
• B formamide, N-methylformamide, N-iso propylformamide, N-cyclohexylformamide, N- (2,4-dimethyl-pentyl-3) -formamide, N, N-dimethylformamide, N, N-diethylformamide, N-methylacetamide, N-ethylacetamide, N, N-diethylacetamide or propionamide; Urea derivatives, such as. B. N, N'-dimethylurea or N, N-dimethylurea; basic nitrogen heterocycles, such as. B.
• hydrocarbons and halogenated hydrocarbons such as. B. benzene, 1,2-dichlorobenzene, 1,2,3-trichlorobenzene, chlorobenzene or cyclohexane; of alcohols such as B. methanol, ethanol, propanol, 2-propanol, 2-methylpropanol, 1-butanol, 2-butanol, diethylene glycol, triethylene glycol, glycerin, cyclohexanol, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether or triethylene glycol dimethyl ether; of ethers such as B.
• diisoamyl ether diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or dioxane; of ketones, e.g. B. acetone, acetylacetone, methyl isopropyl ketone, diisopropyl ketone or cyclohexanone; of carboxylic acid esters, such as. B. acetic acid 'methyl ester, propionic acid ethyl ester, acetoacetic ester or phthalic acid dimethyl ester; of carbonitriles, such as. B.
• ketones e.g. B. acetone, acetylacetone, methyl isopropyl ketone, diisopropyl ketone or cyclohexanone
• carboxylic acid esters such as. B. acetic acid 'methyl ester, propionic acid ethyl ester, acetoacetic ester or
• benzonitrile benzyl cyanide, propionitrile, iso-butyronitrile or acetonitrile; or also of sulfur compounds, such as. B. dimethyl sulfoxide, sulfolane, thiosemicarbazide, thiobenzamide or N-phenyl-thiourea possible.
• sulfur compounds such as. B. dimethyl sulfoxide, sulfolane, thiosemicarbazide, thiobenzamide or N-phenyl-thiourea possible.
• hydrogen chloride comes as hydrohalic acids
• Hydrogen, hydrogen bromide and hydrogen iodide in question their suitability generally increases with increasing atomic weight of the halogen.
• the choice of the most suitable acid also depends on the other components, in particular on the pK b value of the base or the pK s value of its conjugate acid, but also on the other reaction conditions.
• all metals which are less noble than the respective metal to be deposited can be used as the substrate for the noble metals to be deposited.
• particularly suitable substrate metals for copper are e.g. B. zinc, iron and lead; for silver z. B. zinc, iron, nickel, tin, lead and copper; and for gold z. B. nickel, copper and silver.
• the reaction of the noble metal halide with the base and the hydrohalic acid can be carried out 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 / noble metal halide / hydrohalic acid is chosen so that the entire amount of noble metal halide 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 hydrohalic 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, especially aprotic, organic solutions to the complex formation reaction medium, such as B. carbon tetrachloride and especially acetone.
• the solvents have to be weaker basic than the base used. Under these conditions, a base, such as dimethylformamide, can also 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 hydrochlorides with hydrohalic acid and complex with the noble metal halide.
• This case occurs e.g. B. when formamides are reacted in the heat with hydrohalic acid and noble metal halide.
• Cleavage occurs in formic acid and amine, the latter then immediately reacts to form the hydrochloride, which is the actually complexing agent.
• the noble metal halide is preferably added in finely powdered form; the hydrohalic 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
• acetone or carbon tetrachloride or mixtures thereof
• Solutions of silver complexes can e.g. B. can be kept almost unchanged over several years.
• the noble metal complexes can be diluted with a poorly dissolving solvent, such as. B. with acetone. From these complexes, the coating bath can then, if necessary, by dissolving in a suitable solvent, such as. B. in dimethylformamide. The dissolution is usually done with gentle heating, e.g. B. 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 hydrohalic acid) depends in particular on the type of the other complex-forming components, on the type of metal to be deposited, but also on the type of metal substrate onto which it is deposited, and on the reaction conditions used , such as B. the type of solvent. It is also possible to use two or more bases and / or two or more hydrohalic acids. 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 acid strength, a decreasing ion diameter of the halide ion in the metal salt, and a decreasing base strength result in a greater reactivity ("strong deposition solution”). On the other hand, such very reactive "strong deposition solutions” (e.g., very weakly basic amine / metal chloride / hydrochloric acid) on very base metals (such as, for example, on zinc or tin) result in poorly adhering coatings than less reactive "weak deposition solutions "(e.g.
• the gold coating of a zinc foil with a solution of pyridine / gold (I) iodide / hydrochloric acid adheres e.g. B. better than with a solution of N, N-dimethylformamide / gold (I) iodide / hydrochloric acid.
• the noble 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 formed by applying, instead of dipping the workpiece in the coating (brushing, B epinseln) of the coating solution (plating) on the workpiece take place.
• this 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 possible only with difficulty, e.g. B. 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 with a suitable solvent such as. B. with methanol, ethanol or acetone, removed and the workpiece dried, for. B. by wiping with a cloth.
• the quality of the coating depends to a large extent on the rate of deposition. Deposition that is too rapid (reactivity that is too high) generally results in a poorly adhering “amorphous” 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 noble metal complex in the coating bath and / or the acid concentration. As a rule, the deposition rate increases with increasing concentration of the noble metal complex and acid. From very concentrated solutions, the deposition z. B. done in a few seconds.
• the complex-forming components in particular that of base and hydrohalic acid, it is also possible to obtain coating solutions with which only certain metals are selectively coated. Selectivity is also closely related to reactivity. So z. B. the deposition rate for a particular metal can be regulated by varying the amount of acid. A change in the concentration of the noble metal complexes usually only affects the deposition rate.
• the layer thicknesses that can be achieved are generally proportional to the noble metal complex concentration of the coating bath and the contact time.
• a suitable choice of the deposition conditions generally gives a layer thickness of 0.1 to 4 ⁇ m.
• the deposition (layer thickness) can be followed by measuring the potential. So z. B. the final value of the coating (maximum coating) is displayed after four days by measuring the potential on a copper sheet. In order to measure the potential with as little feedback as possible, an electrometer amplifier was used (input current ⁇ 5o mA), and a silver wire was used as the reference potential. The initial potential was 100 mV and practically reached a zero value after the time specified above. The potential Changes during the deposition process were recorded graphically with the help of a recorder.
• a dropwise addition of concentrated acid enables an almost quantitative utilization of the complexed metal for the deposition from the. coating baths appearing to be "exhausted". Too large an amount of acid is recognized by an immediate precipitation of the metal still in solution as a halide, in the case of gold as a metal.
• the metal 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 fed 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 in a very simple and rapid manner to produce well-adhering and corrosion-resistant coatings (for example gold-plating) with layer thicknesses which have hitherto not been 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.
• the cyanide-free coating baths also result in the known coating baths in the cyanide-containing coating baths avoiding problems in handling and waste disposal.
• 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 noble metal layers on correspondingly less noble metals, which are characterized in that they contain a metal complex which is reacted by reacting a monovalent noble metal halide with a base which is capable of complexing with the noble metal, and a hydrohalic acid are available.
• Another object of the invention are: by reacting a monovalent noble metal halogen with a base which is capable of complexing with the noble metal, and a noble metal complex which is obtainable with hydrohalic acid.
• the melting points (in ° C., with decomposition) are listed below for some noble metal complexes according to the invention, which were obtained in crystallized form by diluting the reaction mixture with acetone.
• the following examples illustrate the invention without restricting it.
• the dry iron object to be coppered which has been freed of oxide and other impurities, is immersed in the solution shown under a) at room temperature for 2 minutes, removed from the solution and polished with a cloth.
• the layer thickness of the copper covering is 0.2 ⁇ m. In order to achieve greater layer thicknesses, the iron object can be immersed, removed and polished as often and as long (up to several hours). In this way it is possible to continuously monitor the growth of the covering.
• the dry copper object to be silvered which has been freed from oxide and other impurities, is immersed in the solution shown under a) for 10 minutes, removed from the solution and polished with a cloth.
• the thickness of the silver coating is approximately 1 ⁇ m. In order to achieve greater layer thicknesses, the procedure described in Example 1 b) can be followed.
• the dry copper or silver object to be gold-plated which has been freed from oxide and other impurities, is immersed in the solution shown under a) for one hour, then removed from the solution and polished with a cloth.
• the thickness of the gold plating is approximately 0.5 ⁇ m.
• the coating can be interrupted at any time within this one hour in order to check and observe the coating process (possibly to measure). For further coating, the procedure described in Example 1 b) can be followed.
• the coating baths can be used as long as until they are exhausted, it should be noted that the coating speed is directly proportional to the concentration of the metal complex still present in the solution.
• the finished article can be used to remove traces of the coating bath, e.g. B. with acetone, ethanol, methanol, mineral spirits or water.

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• 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)

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• 1981
  • 1981-12-07 DE DE19813148330 patent/DE3148330A1/de not_active Withdrawn
• 1982
  • 1982-11-30 DE DE8282111045T patent/DE3276334D1/de not_active Expired
  • 1982-11-30 AT AT82111045T patent/ATE27187T1/de not_active IP Right Cessation
  • 1982-11-30 EP EP82111045A patent/EP0081183B1/fr not_active Expired
  • 1982-12-06 CA CA000417092A patent/CA1236843A/fr 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

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