US 3580820 A
Description (OCR text may contain errors)
United States Patent Int. c1. c231) /32, 5/46 US. Cl. 204-43 5 Claims ABSTRACT OF THE DISCLOSURE A palladium-nickel alloy plating bath is formed of a solution of palladium salt and a nickel salt in ammonia and a brightener in the nature of a sulfonate or a sulfonamide is added to the bath in which a metal is plated for approximately 30 minutes at a pH in the range of 7.5, temperature in the range of 30 C., and cathode current density in the range of 1 a./dm. without agitation.
DETAILED DESCRIPTION OF INVENTION The present invention relates to a palladium-nickel alloy plating bath.
In order to eliminate some drawbacks of conventional white metalplating comprising silver or nickel, palladiurn plating methods were developer (patent application Sho-39 No. 57,810). We have further succeeded in substituting a palladium-nickel alloy plating method as differentiated from palladium plating to lower the cost of the deposited layer and widen its application field. It is an object of the present invention to provide a palladiumnickel alloy plating bath which has high corrosion-resistance.
Generally palladium salt and nickel salt are soluble in ammonia solution to form amino complex salt wherein metal atom is coordinated with NH Complex salt is formed regardless of the nature of acidic radical used which will produce a palladium salt and a nickel salt which eventually forms a stable amino complex salt. It was found that when using a bath comprising amino complex salt of palladium salt and nickel salt thus formed, palladium and nickel codeposit in a form of solid solution alloy and a palladium-nickel alloy can be easily obtained. In addition, the bath for plating was found occasionally to have brightening effect, and such efiect is stabilized by adding brighteners such as naphthalenesulfonate and aromatic sulfonamide. Further examination revealed that the palladium content in the codeposited layer can be established on any point within the range of 30% and 90% by adjusting the composition of the bath or plating condition, that the so-plated surface obtained shows sufiicient brightness and corrosion-resistance and that accordingly this bath for plating satisfies said object of the invention.
Referring now to the present invention in more detail, the first composition of the bath for plating, comprises monosalt such as palladium chloride PdCl and complex salt such as palladous amino chloride Pd(NH Cl are used as supply sources for palladium. As for supply sources of nickel, nickel sulfate NiSo -7H O', nickel chloride NiCl '6H O etc. are used. When these palladium or nickel salts are put in aqueous solution of ammonia, the palladium and nickel salts are converted into the form of amino complex salt. Ammonium salt of inorganic acid or organic acid such as ammonium sulfate and ammonium citrate may be added. 'Ihese additions increase the solubility of palladium and nickel, by which stable dissolu- 3,580,820 Patented May 25, 1971 tion-.at relatively low pH is achieved. Electroconductivity of theibath is also improved and at the same time pH is stabilized by virtue of the product of NH.;+-NH buffer system in the bath. The concentration of palladium and nickel in the bath is controlled in such a manner that as to the quantity of palladium present is S to 30 g./l. and nickel is present in the same quantity i.e. 5 to 30 g./l. The alloy ratio of palladium and nickel in the deposited layer depends on the concentration ratio of palladium and nickel in the bath. As can be seen in the examples below, a combination of 20 g./l. of palladium and 10 g./l. of nickel produce alloy deposited layer comprising palladium in the amount of and alloy deposited layer composed of 60% of palladium is obtained with a combination of 10 g./l. of palladium and 10 g./l. of nickel. It is not only the concentration ratio of palladium and nickel that afiects the composition of the alloy deposited layer. Nevertheless other conditions such as pH of the bath, the temperature and cathode current density involve negligible problems because it is easy to keep these conditions constant during plating operation and except the pH of the bath the remaining conditions may be relatively varied without adversely affecting the desired results. Therefore desired the codeposited layer can be obtained if essentially the concentration of palladium and nickel in the bath and ratio thereof are controlled within the ranges defined.
By adding sulfo compositions such as naphthalenesulfonate or aromatic sulfonamide to said bath, a bright plating can be obtained. Discovery of these brighteners gave the bath great practical value. Examples of naphthalenesulfonate that can be used are given in the following.
(1) Sodium u-naphthalenesulfonate Sodium p-naphthalenesulfonate S|O3Na SOaNa (2) Sodium 1,S-naphthalenedisulfonate sioaNa SOaNa (3) Sodium 1,3,6-naphthalenetrisulfonate s oiNa S OzNa- -S OzNa These naphthalenesulfonates in which aromatic nucleus is combined with sulfonic radical show brightening effect regardless of the numbers of sulfonic radical and its joined position.
Examples of aromatic sulionamide that can be used are:
(1) Saccharin (2) Paratoluenesulfonamide In these sulfonamides the aromatic nucleus is combined with -SO NH- and its brightening eifect is caused by the presence of the SO NH.
The composition and internal stress of the deposited layer show no noticeable change by this bright plating. Satisfactory results can be obtained when said bath is operated at pH 7-10, temperature 15-40 C., cathode current density 0.5-1.5 ampere/dm using palladium or graphite anode. During plating concentration of palladium and nickel must be estimated by chemical analysis and always controlled properly. Supplies of deposition metal is elfectuated by adding said salt directly in the bath. While continuing plating the ammonium salt is gradually accumulated in the bath but it has no deleterious effect. The pH is adjusted by adding ammonia water and dilute sulphuric acid. Generally, lowering of pH tends to enlarge the deposition potential of nickel and increase the nickel content in the deposited layer. It sometimes occurs that palladium content in the deposited layer is not comprised within 30% and 90% owing to improper composition of the bath or plating condition. As the palladium content in the codeposited layer goes far from the range of 30 to 90%, solid solution of palladium and nickel is not formed completely and when applied thick plating plated surface loses its brightness and is easy to crack. Other plating conditions are the same with that of conventional method. There are no restriction as to the kind of the base metals.
The features and principles underlying the invention described above in connection with specific exemplifications will suggest to those skilled in the art many other modifications thereof.
EXAMPLE 1 A bath containing 20 g. of palladous amine chloride Pd(NH Cl 50 cc. of 28% ammonia water and 700 cc. of water was prepared. Then added ammonium sulfate of 50 g., nickel sulfate NiSO -7H O of 50 g. and water sufficient enough to form 1000 cc. of the bath.
A brass test piece was plated in said bath for 30 minutes at pH of 7.5, temperature 30 C., cathode current density 1 a./-dm. without agitation.
Alloy comprising palladium in 60% and nickel in 40% with white bright surface was obtained from this bath and deposited layer well adhered to the base.
EXAMPLE 2 Added 10 g. of sodium 1,3,6-naphthalene trisulfonate to the bath of Example 1, and plated for 30 minutes under the same condition with Example 1.
10p. of deposited layer with mirror polished surface was obtained. Hv=535 by Vickers hardness tester.
It was exposed to ammonia gas for 24 hours and dipped in artificial sea water for 6 days, after which there found no change at all.
EXAMPLE 3 A bath containing 40 g. of palladous ammine chloride Pd(NH Cl 50 cc. of 28% ammonia water and 700 cc.
4 of water was prepared. Then added ammonium sulfate of 50 g., nickel sulfate of 50 g., sodium saccharate NNa-2H2O of 5 g. and water until the bath attains 1000 cc.
A brass test piece was plated in said bath for 30 minutes at pH of 8.8, temperature 30 C., cathode current density 1 a./dm. without agitation.
Alloy comprising palladium in and nickel in 15% with mirror polished surface was obtained from this bath and there found no change after 24 hours exposure to ammonia gas and 6 days dip in artificial sea water.
What we claim is:
1. A palladium-nickel alloy plating bath having a pH of 7 to 10 composed of ammonia water containing 5 to 30 g./1. of palladium ions, and 5 to 30 g./ l. of nickel ions and an alkali metal naphthalenesulfonate in an amount effective for obtaining a bright palladium-nickel alloy electrodeposited layer in which palladium content is within 30 to thereof.
2. A palladium-nickel alloy plating bath having a pH of 7 to 10 composed of ammonia water containing 5 to 30 g./l. of palladium ions, 5 to 30 g./l. of nickel ions and a member of a group consisting of sodium tit-naphthalenesulfonate, sodium fl-naphthalene-sulfonate, sodium 1,5- naphthalene-disulfonate, and sodium 1,3,6-naphthalenetrisulfonate in an amount effective for obtaining a bright palladium-nickel alloy electrodeposited layer in which palladium content thereof is within 30 to 90%.
3. A palladium-nickel alloy plating bath having a pH of 7 to 10 composed of aqueous ammonia containing in solution a palladium amine complex salt incorporating 5 to 30 g./ 1. of palladium ions, a nickel amine complex salt incorporating 5 to 30 g./l. of nickel ions and, as brightener, an effective amount of sodium 1,3,6-naphthalenetrisulfonate whereby a bright palladium-nickel alloy electrodeposited layer having a palladium content between 30 and 90% may be obtained.
4. A palladium-nickel alloy plating bath in accordance with claim 3 wherein 10 grams of sodium 1,3,6-naphtha- 'lene-trisulfonate is added to the bath as a brightener for the palladium-nickel alloy.
5. A palladium-nickel alloy plating bath having a pH of 7 to 10 composed of aqueous ammonia containing in solution a salt incorporating 5 to 30 g./l. of palladium ions present in the form of palladium-amine chloride and a salt incorporating 5 to 30 g./l. of nickel ions present in the form of a member of a group selected from an amine nickel sulphate and an amine nickel chloride and a brightener comprising a member of a group consisting of sodium a-naphthalene-sulfonate, sodium ,B-naphthalene-sulfonate, sodium 1,S-naphthalenedisulfonate, sodium 1,3,6- naphthalene-trisulfonate in an amount effective for obtaining a palladium-nickel alloy electrodeposited layer in which the palladium content is within 30 to 90% thereof.
References Cited UNITED STATES PATENTS 1,981,715 11/1934 Atkinson 20447X 3,458,409 7/ 1969 Hayaski et a1 20447X FOREIGN PATENTS 958,685 5/ 1964 Great Britain 204-47 1,017,950 l/1966 Great Britain 204-47 OTHER REFERENCES Chemical Abstracts, vol. 45, 8317a (1951). R. H. Atkinson et al., Electrometallurgy (Supplement to the Metal Industry), pp. 595-598, June 9, 1933.
GERALD L. KAPLAN, Primary Examiner