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
  • C23C18/32—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron
  • C23C18/34—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents

Definitions

• ABSTRACT OF THE DISCLOSURE An improved process for chemical plating with alkaline aqueous plating baths containing a nickel and/or cobalt salt, a primary complexing agent such as ethylene diamine and a boron hydride compound is disclosed. The mprovement is directed to the regeneration of such plat mg baths, the same to be carried out in the plating bath itself and without interrupting the process.
• the improvement in accordance with the invention lies in the teaching to add to the bath during the plating process an aqueous solution containing a secondary complex formmg agent, the same being characterized in that it is volatile at the temperature at which the plating operation is being carried out; the primary complexing agent not being volatile at such temperature and further the secondary complexing agent being characterized in that it forms less stable complexes with the metal salt than does the primary complexing agent, together with a metal salt, i.e., nickel and/r cobalt salt.
• the present invention relates to a process for the regeneration of plating baths, containing boron hydride compounds as reducing agents.
• nickel or cobalt plating with the aid of boron hydride compounds especially the easily accessible sodium borohydride as reducing agent plating baths are used which contain, in addition to the reducing agent a nickel or cobalt salt, e.g. chloride, a complex forming agent, e.g. ethylene diamine, and an alkali metal hydroxide, e.g. sodium hydroxide as well as stabilizers etc.
• a nickel or cobalt salt e.g. chloride
• a complex forming agent e.g. ethylene diamine
• alkali metal hydroxide e.g. sodium hydroxide as well as stabilizers etc.
• the bath becomes enriched in alkali metal borate and alali metal salt (chloride) while the content of nickel salt and reducing agent falls.
• the bath must constantly be replenished with the reducing agent and with the metal to be deposited, added in the form of its complex salt, and at least a part of the byproducts must be removed.
• this may suitably be done by continuously removing from the plating bath a relatively small quantity of the bath liquid, removing borate and chloride from this by treating it with a solution of an alkaline earth metal salt and then adding nickel salt, alkali metal hydroxide and if necessary complex-forming agents; the regenerated solution can then be returned to the plating bath.
• This method is particularly advantageous for plants of medium to large size which operate continuously. In smaller units, on the other hand, which are operated intermittently, there is frequently a tendency to waive the regeneration plant and to discard the plating baths after they. have been used for some time. This method, however, is economical only if the bath can be utilized to its utmost.
• the invention relates to a process for chemical plating with alkaline aqueous plating baths containing nickel and/or cobalt salts, primary complex-forming agents as hereinafter defined and boron hydride compounds, the process which comprises adding to said baths during the plating process an aqueous solution with a secondary complex-forming agent as hereinafter defined, said agent having a lower complex stability and a higher volatility than the primary complex-forming agents and a nickel and/or cobalt salt at the rate at which these metal salts are reduced and deposited.
• a bath based on borohydride compounds used for chemical plating for example a nickel plating bath, consisting of a solution in'aqueous sodium hydroxide of ethylene diamine, sodium borohydride and nickel chloride, optionally with the addition of stabilizers, e.g. lead salts, which loses nickel salt in the course of the plating process but still contains about 1 mol per litre alkali metal hydroxide and reducing agents can be readjusted to the starting concentration by the addition of an aqueous solution of nickel chloride together with a volatile, weaker complcx-forming agent and can be operated in the same way as a freshly prepared bath.
• stabilizers e.g. lead salts
• Suitable complex-forming agents for the process of inventi0n-they shall be denoted as secondary complex-forming agents-are all amines or their aqueous solutions which are volatile at the temperature at which the plating bath operates, 40100 C. Accordingly e.g. ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, n-propylamine, iso-propyl amine, n-butylamine, iso-butylamine etc. can be used.
• the nickel salt/amine solution may be added to the bath in portions, for example after each batch has been plated, or the solution may be added continuously.
• the secondary complex-forming agents are used in such amounts that the corresponding nickel hexamine or cobalt tetramine complexes are formed, i.e. in molar ratios of Ni-amine of about 1:6 and of Co-amine of about 1:4. Minor deviations of these ratios are not harmful. Larger additions of amine are not useful for reason of economy.
• the alkali metal hydroxide which is also removed from the bath during the plating process is supplemented by the addition of a solution of alkali metal hydroxide, preferably simultaneously with the reducing agent.
• metal salts there can be used water-soluble nickel or cobalt salts such as nickel chloride, nickel sulfate, cobalt chloride or cobalt sulfate etc.
• borohydride compounds such as alkali metal borohydrides, preferably sodium borohydride, borazanes'or 'borazoles, substituted with hydrogen on the !boron atom.
• Fresh plating baths are prepared with complex-forming agents-primary complex-forming agents-which form more stable complexes with nickel and cobalt salts than the secondary complex-forming agents and which agents are not volatile under the temperature conditions of above 40 to C. used for the plating process.
• complex-forming agents e.g. ethylene diamine, triethylene tetramine, diethylene triamine', tetraethylene pentamine etc. can be used.
• the nickel salt concentration was lowered in the course of the plating process from an initial 7.5 g. Ni/l. to about 0.7 g. Ni/l.
• the nickel content was raised to the original value by the addition of a solution of 28 g. nickel chloride hexahydrate in 100' ml. of an approximately 24% ammonia solution.
• 9.5 g. sodium hydroxide were added.
• the apparent reduction yield, i.e. the yield corresponding'to the equation was 35% in this replenished bath as compared with 37% in the original bath. A similar yield was obtained even after a second and third renewal of the bath.
• the process of the invention is, however, not limited to discontinuously operated baths.
• continuously operating plating baths it is possible to put through the bath a quantity of nickel equal to ten times the original concentration before any regeneration with alkaline earth metal salts according to Belgian patent specification 618,098 becomes necessary.
• Example 1 Six chemical plating baths a, b, c, d, e and f of a volume of l l. and having the composilions: 3O g./l. nickel chloride, 40 g./l. sodium hydroxide, 60 g./l. ethylene diamine (approximately 98%), 3 g./l. sodium fluoride and 0.5 g./l. sodium borohydride are heated to 90 C.
• Four degreased and pickled iron plates each havmg a surface area of x 10 cm. are suspended in each bath. .
• the lead chloride solution containing 2 g. PbCl per litre is added dropwise at the rate of 40 ml./h.
• Portions of 0.5 g. sodium borohydride dissoved in approximately 50 ml. cooled bath solution are added to the plating bath at half-hourly intervals.
• Approximately 6 g. nickel have been deposited on the iron plates from each plating bath after 3 hours. The concentration of nickel has thus dropped to 20% of the original value in each bath.
• NiCl -6H O nickel chloride
• the nickel salt solutions are introduced, with cooling, into the various baths as follows: For bath a into 100 ml. methylamine, for bath [2 into 200 ml. dimethylamine, for bath 0 into 200 ml. trimethylamine, for bath d into 200 ml. 40% ethyla-mine, for bath e into 200 ml. 65% isopropylamine and for bath 1 into 200 ml. 96% n-butylamine. A clear solution is obtained only when the nickel salt solution is poured into methylamine. By adding this nickel-amine complex salt solution or suspension to the plating baths which have been cooled to room temperature, the nickel salt in the baths is readjusted to the original concentrations. The bath liquors obtained need not be filtered.
• ExampleZ 1 l. of a chemical plating bath consisting of 33 g./l. nickel sulfate, 87 g./l. triethylene tetramine and 40 g./l. sodium hydroxide is heated to 95 C. and two brass plates and two copper plates each having a surface of 10 cm. x10 cm. are suspended in the bath and 0.6 g. NaBI-L, dissolved in about 50 ml. bath solution is added. 20 ml. lead chloride solution containing 2 g. PbCl per 1. and 0.6 g. sodium borohydride dissolved in 50 ml. bath solution are added at 20 minute intervals to the plating bath. Plating is continued for a period of 3 hours. 4.75 g.
• Ni-B alloy are deposited on the four plates at the end of this time.
• 22.8 g. nickel sulfate (NiSO -7H O') are then dissolved in 50 cc. water and poured into 100 cc. ammonia solution (approximately 25% NH The nickel amine sulfate is then added to the plating bath, the bath is heated to the plating temperature and nickel plating is continued as described above. In the course of 3 hours, 4.90 g. Ni-B alloy are deposited on the plates. The coatings are smooth and bright.
• Example 3 0.6 g. sodium borohydride dissolved in 50 ml. bath solution is added to 1 litre of a plating bath of the composition 30 g./l. nickel chloride, 40 g./l. sodium hydroxide, g./l. ethylene diamine (98%) and 10 g./l. sodium fluoride, which is heated to 90 C., and two iron and two brass plates each having a surface of 10 cm. x 10 cm. are suspended in the bath. 20 ml. of a lead acetate solution containing 2 g. Pb(CH COO) per litre is continuously added dropwise over a period of 30 minutes. 0.6 g. NaBH dissolved in approximately 50 ml.
• the bath solution is added to the bath at half-hourly intervals.
• the plating time is 3 hours. At the end of this time, a total of 5.99 g. Ni-B alloy has been deposited on the plates.
• the plating bath is replenished by the. addition of 1300 cc. of a solution containing 24 g. NiCl -6H O and cc. conc. ammonium solution (approximately 25% NHg).
• the alkali content of the plating bath is readjusted with 40 cc. of sodium hydroxide solution containing 200 g. NaOH per 1. Nickel plating is then continued for 3 hours.
• the plated plates are then weighed back and the bath, which is now poor in nickel and alkali, is again replenished as described above and plating is again continued. This process is repeated altogether five times.
• the deposition of nickel over a plating time of 3 hours is in each case as follows.
• the plating bath need not be filtered.
• the coatings obtained on the plates are smooth and bright.
• Example 4 A chemical plating bath (volume 1 l.) of the composition 30 g./l. nickel chloride, 40 g./l. sodium hydroxide, 60 g./l. ethylene diamine, g./l. sodium fluoride and 0.6 g./l. sodium borohydride is operated at 90 C. Four metal plates each having a surface of 10 cm. x 10 cm. are suspended in the bath.
• Example 5 It is desired to coat chemically with an Ni-B alloy the inner walls of two steel pressure flasks provided with closure caps, as Well as the thread of the valves and the outer surfaces on which the caps sit.
• the plating temperature is 90 to 91 C. 60 g. NaBH in which approximately 200 cc. plating liquid are dissolved and 100 cc. lead acetate solution containing 3 g. lead acetate per litre are introduced in each case after 20 minutes through a glass funnel whose outlet level is adjustable.
• the plating time is 2.5 hours.
• the plating liquid is run oif.
• the steel flask is rinsed several times and then dried. Analysis of the depleted bath liquor indicated 1.2 g./l.
• NiCl -6H O NiCl -6H O.
• the used plating bath liquor is readjusted to the original concentration of 30 g. NiCl -6H O per litre by the addition of 317 g. nickel chloride dissolved in 1 litre conc. ammonia solution.
• the solution thus obtained is heated in the course of about half hour to C. 6 g. NaBHI are added and the solution is then filled into another steel flask which has been carefully degreased, pickled and rinsed and preheated in the water bath.
• Plating is carried out as described above. After a nickel plating time of 2.5 hours, no more nickel can be detected in the plating solution.
• Ni-B coating deposited on the inner wall of the flask is smooth, even and bright.
• the thickness of the layer is approximately 25 We claim:
• a process for chemical plating with an alkaline plating :bath containing a metal salt selected from the group consisting of nickel and cobalt salts, a primary complex forming agent selected from the group consisting of poly lower alkylene polyarnines and a boronhydride compound the improvement which comprises adding to said bath during the plating process an aqueous solution containing a secondary complex forming agent selected from the group consisting of ammonia, mono-, diand trialkyl amines, said secondary complexing agent being volatile at the temperature at which said plating process is being carried out, said primary complexing agent not being volatile at said temperature, said primary complexing agent forming more stable complexes with said metal salt than said secondary complexing agent and a metal salt selected from the group consisting of nickel and cobalt salts at a rate at which said metal salt is reduced and deposited.
• a metal salt selected from the group consisting of nickel and cobalt salts
• a primary complex forming agent selected from the group consisting of poly lower alkylene polyarnines
• said secondary complexing agent is selected from the group consisting of amines having from 1 to 4 carbon atoms and a boiling point of less than C.
• said secondary complexing agent is a member selected from the group consisting of methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, N-propylamine, isopropylamine, N-butylamine and isobutylamine.
• said salt is a member selected from the group consisting of nickel chloride, nickel sulfate, cobalt chloride and cobalt sulfate.

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• Mechanical Engineering (AREA)
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• Organic Chemistry (AREA)
• Chemically Coating (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Electroplating And Plating Baths Therefor (AREA)

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• 1963
  • 1963-07-22 DE DEF40295A patent/DE1237399B/de not_active Ceased
• 1964
  • 1964-06-12 CH CH770964A patent/CH441925A/de unknown
  • 1964-06-18 US US376207A patent/US3373054A/en not_active Expired - Lifetime
  • 1964-06-30 GB GB27018/64A patent/GB1006173A/en not_active Expired
  • 1964-07-20 BE BE650755D patent/BE650755A/xx unknown

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