US 3062666 A
Description (OCR text may contain errors)
3,062,666 BATH COMPOSITIONS FOR THE CHEMICAL REDUCTIVE PLATING F NICKEL-BORON AND COBALT-BORON ALLOYS Henry G. McLeod, St. Catharines, Ontario, Canada, as-
signor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Nov. 26, 1958, Ser. No. 776,420
- 3 Claims. (Cl.'106-1) This invention relates to chemical'plating of nickelboron and cobalt-boron alloys and more particularly it aired States Patent 0 relates .to improved stability in chemical plating baths I,
using amine-boranes as reductants.
In the copending application of T. Berzins, Serial No.
' 764,490, filed October 1, 1958, a process is disclosed for plating catalytic surfaces with nickel-boron and cobaltboron alloys in which the reductant is an amine-borane.
The amine-borane is also the source of the boron in the alloy plate. The plates thus obtained are bright, hard,
uniform in thickness, and exhibit excellent wear and corrosion resistance.
These properties make the plates useful both for decoration and protection of the substrate. 5
The plating bath contains, in addition to the amineborane, a water-soluble nickel or cobalt salt. The bath is maintained at a pH above 3.5 to minimize hydrolytic decomposition of the amine-borane and preferably below about 7 to-climinate the necessity for sequestering or complexing agents for the nickel or cobalt ions being reduced. A buffer is usually present in the bath to aid in maintaining the pH within the desired range, since the plating reaction liberates an acid. Salts of weak acids such as acetic, propionic, boric, etc. are elfective buffers for the plating bath.
Theoretically in a bath of this type, no metal is precipitated in the bulk of the bath and the plating is confined to the catalytic surface. In practice, however, these plating baths do tend to deposit metal spontaneously throughout the bath and on the container walls. This tendency is accelerated at increased nickel or cobalt ion concentration, at increased bath temperatures, and at increased reductant concentration.
A Simple plating bath formulation may contain 0.1 to 0.5 mole of nickel chloride or sulfate, 0.15 to 0.75 mole sodium acetate, and a reducing agent such as dimethylamine-borane at a concentration of 1 to 2 grams per liter. With a 0.5 molar nickel chloride solution, the bath produces much finely divided black nickel throughout the bath in to minutes of operation at 70-80 3,062,656 Patented Nov. 6, 1962 other object is to extend the operating life of a chemical plating bath. A still further object is to provide a chemical plating bath which deposits a smooth plate throughout the life of the bath.
These and other objects are attained by providing a chemical plating bath comprising an aqueous solution with a pH of 3.5 to about 7 containing an amine-borane as reductant, a water-soluble nickel or cobalt salt to provide nickel or cobalt ions, and a Water-soluble glycolate. An additional improvement in stability is obtained by providing about 140 parts per million of a soluble lead salt in the plating bath.
The glycolate may be added to the plating bath as glycolic acid and the pH then adjusted to the desired range by addition of a base, for example, an alkali metal hydroxide; or the glycolate may be added as ammonium glycolate or a water-soluble alkali metal or alkaline earth metal salt of glycolic acid. The pH may then be adjusted as required by addition of an acid or base.
stability to the plating bath, the actual form in which the glycolate is added is immaterial as long as a material antagonistic to the bath is not present in the glycolate composition.
The glycolate also functions as a buffer Since glycolic' acid is a relatively weak acid. Sufiicient glycolate may be added to provide all the buffering action required and thus replace the buffer, which is preferably present in the plating bath of the Berzins application, S.N. 764,490.
The glycolate may also be used in combination with other bufiering agents. Buffering systems usually do not contain materials such as cyanides, sulfides and thiocyfor example, the lead salt may be the acetate, chloride C. and pH of 4 to 5. A more dilute bath, for example,
The object of this invention is to improve the stability of chemical plating baths utilizing an amine-borane as the reductant. Another object is to provide additives which reduce the tendency of nickel or cobalt plating or sulfate. While lead ions show some improvement in bath stability in the absence of glycolate ion, the combination with the glycolate gives much better stability.
The invention is illustrated by the following examples which, however, are presented merely to show specific' bath compositions and are not to be considered limi-,
Example I A nickel plating bath was prepared by dissolving 25 g. (0.105 mole) of nickel chloride hexahydrate and 15 g. (0.15 mole) of sodium glycolate in sufiicient water to give 1 liter of solution. The pH was adjusted to 5.0 by addition of hydrochloric acid. The bath was operated in a glass beaker heated with an electric mantle. Dimethylamine-borane was used as the reductant at a concentration of 1 gram perliter of solution.
A steel object was placed in the bath and nickel-boron plated on it. The bath was maintained at -75 C. and was operated continuously until deposition of. black nickel precipitate occurred in the bath and on the beaker walls. This occurred after operation of the bath for 240 minutes.
Since the glycolate anion is the active ingredient conferring Example 2 A bath in which 21 g. (0.15 mole) of sodium acetate trihydrate replaced the sodium glycolate in Example 1 showed spontaneous deposition of nickel after 60 minutes operation under the same conditions as in Example 1.
' Example 3 as in Example 1 without spontaneous deposition of black nickel precipitate.
Example 4 A plating bath was prepared containing 0.1 mole nickel chloride, 0.1 mole sodium glycolate, and 0.1 mole sodium acetate per liter of solution. The pH was adjusted to 5.0. Dimethylamine-b orane was used as the reductant at a concentration of 1 gram per liter. The bath was operated as in Example 1. Spontaneous deposition of nickel occurred throughout the bath after 193 minutes.
When the sodium glycolate is replaced by the molar equivalent of sodium acetate, the bath shows spontaneous decomposition after about 60 minutes.
1 Example 5 A nickel plating bath was prepared containing 0.5 mole of nickel chloride and 0.75 mole glycolic acid. The pH was adjusted to 5.0 with sodium hydroxide and the volume of the bath adjusted to 1 liter. Dimethylamineborane was used as the reductant at a concentration of 1 gram per liter. Spontaneous deposition of nickel preq i pitate occurred after 117 minutes operation at 7075 C.
\ Example 6 A bath was prepared as in Example 5 except that 0.75 mole of sodium acetate replaced the glycolic acid. The pH was adjusted to 5.0 with hydrochloric acid. The bath showed spontaneous deposition of black nickel precipitate after 20 minutes operation at 70-l5 C.
Example 7 A bath similar to that in Example 5 containing 0.5 mole nickel chloride, 0.75 mole glycolic acid and 0.25
- mole boric acid with the initial pH adjusted to 5.0, ,de-
composed spontaneously after 130 minutes operation at 70-75 C. This example shows that boric acid, which is formed as the amine-borane reduces the nickel or cobalt cations, is not detrimental to the stability of the plating bath.
' Example 8 A bath as in Example 7 to which 20 parts per million of lead acetate were added produced black nickel throughout the bath after 297 minutes operation at 70-75 C.
Example 9 The use of succinic, lactic, formic, tartaric, malic and diglycolic acids individually as replacements for the glycolic acid in Example 5 provided essentially no improvement in bath stability over that obtained with acetic acid (see Example '6).
Example 10 of an auxiliary buffering agent. The glycolate anion is unique among the short chain organic acids in the stabilization of nickel and cobalt chemical plating baths containing an amine-borane as reductant. Likewise, the stabilizing effect of lead ion, especially in combination with a glycolate, is not obtained with other metal ions.
The glycolate concentration is preferably within the range of l to 3 moles for each mole of nickel or cobalt salt in the bath. Since the preferred concentration of nickel or cobalt ions is from 0.01 to 1 gram mole per liter of solution, the concentration of the glycolate is in the range of 0.01 to 3 gram moles per liter. Whenever the term ion, cation or anion is used herein, the term includes the total quantity of the element or radical present in the bath, both dissociated and undissociated. In other words, complete dissociation of the salts or acids is assumed where the concentration of ions is expressed in gram moles.
The concentration of lead salt in the bath is preferably within the range of l to about '40 parts per million. More can be used, if desired, but is not required; nor is it beneficial since the stability is not further improved by use of more than about 40 parts per million.
Nickel and cobalt ions may be introduced into the plating bath by adding the required amount of a watersoluble salt such as the chloride, sulfate, sulfamate, acetate, etc., of nickel or cobalt. The salts may be formed in situ by use of nickel or cobalt oxide in combination with the equivalent amount of an acid such as hydrochloric or sulfuric acid. If desired, the bath may contain both nickel and cobalt cations in which case a ternary nickel-cobalt-boron plate is obtained.
While the examples show only the use of dimethylamine-borane, a wide variety of amine-boranes may be used as reductants in chemical plating baths as described in Berzins application Serial No. 764,490. These include the boranes of primary, secondary and tertiary amines as well as diborane d ammoniate (2NH :B H and ammonia borane (NH zBH The concentration of aminepractical plating speeds and bath stability, concentra-- tions of amine-borane within the range of about 0.005 to 0.2 gram mole per liter are favourable.
The plating baths containing the glycolate or glycolateiead stabilizer may be operated at temperatures up to the boiling point of water. Since the rate of plating increases as the temperature increases, the bath will usually be operated at temperatures above 40 C. and preferably at a temperature of at least 60 C.
The materials whose surfaces catalyze the reduction of nickel or cobalt ions by amine-boranes include nickel, cobalt. iron, steel. aluminum, palladium. platinum, copper, brass, manganese, chromium, molybdenum, tungsten, titanium, silver, carbon and the like. Glass and plastic surfaces are in general non-catalytic but they can be made catalytic by methods known to those skilled in the art. For example. a glass article may first be dipned into a stannous chloride solution and then into a palladium chloride solution. A monolaver of palladium is thus produced which is catalytic to the reductive plating process.
Catalvtic surfaces of the above tvpes rnav be given a decorative or protective coating of nickel-boron or cobalt-boron bv immersion in the stabilized chemical plating baths of this invention.
1. An aqueous chemical plating bath having a pH within the range of 3.5 to about 7, the solutes in said bath consisting essentially of, per liter of said bath, about 0.005 to 0.2 gram mole of an amine-borane, 0.01 to 1 gram mole of a cation selected from the group consisting of nickel and cobalt ions, and 0.01 to 3 gram moles of glycolate anion.
2. An aqueous chemical plating bath buffered at a pH within the range of 3.5 to about- 7, the solutes in said bath consisting essentially of, per liter ofsaid bath,
about 0.005 to 0.2 gram mole of an a'mine-borane, 0.01 to 1 gram mole of a cation selected from the group consisting of nickel and cobalt ions, and an amount of a water-soluble compound selected from the group con- 7 sisting of glycolic acid, alkali metal glycolates, alkaline earth metal glycolates and ammonium glycolate, suflicient to provide 0.01 to 3 gram moles of glycolate anion. 3. An aqueous chemical plating bath buffered at a pH within the range of 3,5 to about 7, the solutes in said fbath consisting essentially of about 0.005 to 0.2 gram mole of an amine-borane per liter of said bath, 0.01 to 1 gram mole of a'cation selected from the group consisting of nickel and cobalt ions per liter of said bath, 0.01 to 3 gram moles of glycolate anion per liter of said bath, and from about 1 to about 40 parts per million based on said bath of a water-soluble lead salt.
OTHER REFERENCES I Hurd: Chemistry of the Hydride s, John Wiley an Sons, page 84, 1952.