US2822294A

US2822294A - Chemical nickel plating processes and baths therefor

Info

Publication number: US2822294A
Application number: US569815A
Authority: US
Inventors: Gutzeit Gregoire; Talmey Paul; Warren G Lee
Original assignee: Gen Am Transport
Current assignee: General American Transportation Corp
Priority date: 1954-12-31
Filing date: 1956-03-06
Publication date: 1958-02-04
Anticipated expiration: 1975-02-04

Description

Feb. 4, 1958 G. GUTZEIT El AL CHEMICAL NICKEL PLATING PROCESSES AND BATHS THEREFOR Original Filed Dec. 51, 1954 2 Sheets-Sheet 2 p m N M m w M m w 0 Z 4 0 H W 0 "Wm m B d g m u m M N M 0 0 M r P w r C 0 3 N M L 0, P1. 8% 3 E H Q3 Q3 2 0 4. 2 a 3 3 3 2 2 2 P. 2

fi e Rt 0, wm m mm wywww mw 00 0 00 M m M G a B M m w U M m w 2 m NMPL 0, m 4 M, 0 2 M M. 6 .m,. V A 1 d .M J A a fl m L 0 0 w 7 7 BY P/mp/WE mp/ Pau/ Ta/mey Warren Lee JM 424%, W A mum;

United States Patent Office 2,822,294 Patented Feb. 4, 1958 CHEMICAL NICKEL PLATING PROCESSES AND BATHS THEREFOR Original application December 31, 1954, Serial No. 479,088. Divided and this application March 6, 1956, Serial No. 569,815

8 Claims. (Cl. 117-130) Paul Talmey, Barring- The present invention relates to improved processes of chemical nickel plating of catalytic materials employing baths of the nickel cation-hypophosphite anion type and to improved baths therefor, and more particularly to such processes and baths involving a continuous system of the character of that disclosed in U. S. Patent No. 2,658,839, granted on November 10, 1953, to Paul Talmey and William J. Crehan. This application is a division of the copending application of Gregoire Gutzeit, Paul Talmey and Warren G. Lee, Serial No. 479,088, filed December 31, 1954; and the last-mentioned application is, in turn, a continuation-in-part of the copending application of Gregoire Gutzeit, Paul Talmey and Warren G. Lee, Serial No. 478,492, filed December 29, 1954.

The chemical nickel plating of a catalytic material employing an aqueous bath of the nickel cation-hypophosphite anion type is based upon the catalytic reduction of nickel cations to metallic nickel and the corresponding oxidation of hypophosphite anions to phosphite anions with the evolution of hydrogen gas at the catalytic surface. The reactions take place when the body of catalytic material is immersed in the plating bath, and the exterior surface of the body of catalytic material is coated with nickel. The following elements are catalytic for the oxidation of hypophosphite anions and thus may be directly nickel plated: iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum. The following elements are examples of materials which may be nickel plated by virtue of the initial displacement deposition of nickel thereon either directly or through a galvanic effect: copper, silver, gold, beryllium, germanium, aluminum, carbon, vanadium, molybdenum, tungsten, chromium, selenium, titanium and uranium. The following elements are examples of non-catalytic materials which ordinarily may not be nickel plated: bismuth, cadmium, tin, lead and zinc. The activity of the catalytic materials varies considerably and the following elements are particularly good catalysts in the chemical nickel plating bath: iron, cobalt, nickel and palladium. The chemical nickel plating process is autocatalytic since both the original surface of the body being plated and the nickel metal that is deposited on the surface thereof are catalytic; and the reduction of the nickel cations to metallic nickel in the plating bath proceeds until all of the nickel cations have been reduced to metallic nickel, in the presence of an excess of hypophosphite anions, or until all of the hypophosphite anions have been oxidized to phosphite ions, in the presence of an excess of nickel cations.

In a batch plating process, the reactions are sloweddown rather rapidly as time proceeds because the anions, as contrasted with the cations, of the nickel salt that is dissolved in the plating bath combine with the hydrogen cations to form an acid, which, in turn, lowers the pH of the bath, and the reducing power of the hypophosphite anions is decreased as the pH value of the bath decreases. Moreover, there is a tendency for the early formation in the plating bath of a black precipitate that comprises a random chemical reduction of the nickel cations. Of

course, this formation of the black precipitate comprises a decomposition of the plating bath, and is particularly objectionable in that it causes the nickel deposit to be coarse, rough and frequently porous. Any fine solid particles suspended in the plating bath, or adhering to the walls of the plating vessel, at the plating temperature, initiate the formation of the black precipitate by acting as nuclei.

In a continuous plating process the reactions aremaintained substantially at their initial rates by the regeneration of the plating bath, i. e., by the adding thereto of soluble nickel-containing and hypophosphite-containing reagents, as well as an alkali for pH control; however, the problem of preventing the formation of black precipitate in the plating bath and the consequent decomposition thereof is the same as that previously mentioned. Moreover, another practical difficulty is encountered in the continuous plating process that is not encountered in the batch plating process in that there is a considerable buildup of the by-product phosphite therein as time proceeds and as a consequence of the cycling of the bath. More particularly, while nickel hypophosphite is readily soluble in an aqueous solution, nickel phosphite is much less soluble in an aqueous solution; whereby there is a tendency, as the phosphite concentration of the plating bath buildsup, for nickel phosphite to be precipitated therein, and thereby provide the solid particles that serve as nuclei for the formation of the black precipitate therein, previously mentioned. In passing, it is noted that the initiationof the precipitation of nickel phosphite in the plating bath is indicated by turbidity thereof, visible in a Tyndall beam.

In carrying out the chemical nickel plating process on a commercial scale, the continuous system disclosed in the Talmey and Crehan patent may be employed; which system involves periodic or continuous regeneration of the plating bath by the addition thereto of appropriate ingredients for the purpose of maintaining substantially constant the composition of the bath, as previously noted. More specifically in this system, there are provided a plating chamber and a reservoir; preferably one portion of the plating solution is stored at a relatively low temperature well below the boiling point thereof in the reservoir; and preferably another portion of the plating solution is held as a bath at a relatively high temperature slightly below the boiling point thereof in the plating chamber. The solution is continuously circulated at a low rate from the reservoir to the plating chamber and then back to the reservoir, the solution being heated substantially to the relatively high temperature after withdrawal thereof from the reservoir and before introduction thereof into the plating chamber, and the solution being cooled substantially to the relatively low temperature after withdrawal thereof from the plating chamber and before return thereof to the reservoir. The body that is to be nickel plated is immersed in the bath in the plating chamber and is subsequently withdrawn from the bath in the plating chamber after a time interval corresponding to the thickness of the nickel plating thereon that is desired; and during such time interval soluble reagents are added to the solution in the reservoir to maintain in the bath in the plating chamber during such time interval substantially the predetermined composition of the bath previously mentioned, so as to compensate for the ingredients of the bath that are exhausted during the time interval in the plating chamber. This regeneration of the solution in the reservoir consists essentially of adding thereto appropriate amounts of soluble nickel-containing and hypophosphite-containing reagents, as well as analkali for pH control, as previously noted.

In a plating bath of the nickel cation-hypophosphite anion type, the threshold of precipitation of the insoluble nickel phosphite begins when the (HPO concentration attains a value above the solubility of its simple nickel salt or its double nickel-alkali salt; i. e., above 0.03 to 0.07 m. p. 1.; and in order to obviate this defect, there are disclosed in the c'opending application of Gutzeit, Talmey and Lee, Serial No. 478,492, modified plating baths of the nickel cation-hypophosphite anion type containing both complexing agents and exalting additives. In these plating baths, the complexing agents serve to tie-up the nickel ions, thereby preventing precipitation of nickel phosphite until a high concentration of phosphite ions (about 1.0 m. p. l.) is reached in the plating bath in the continuous plating system; and the exalting additives serve to increase the normally low plating rates of these baths containing the complexed nickel ions. Among the complexing agents disclosed, those forming water-soluble chelates are most efiicien t; and, within that group, the hydroxycarboxylic acids have several practical advantages, such as: ready availability, low price and high buffering capacity.

More particularly, it is apparent that if the nickel ions are very strongly tied-up (i. e., if the chelate is very stable), they are actually removed from the plating process, and no longer available for deposition; whereas, if the complex bond energy is at a lower level, an equilibrium is reached between the dissociation rate of the nickel complex ion and the deposition rate of metallic nickel. The stability of nickel chelates with various hydroxycarboxylic acid additives is not only a function of the number of hydroxyl and carboxyl groups in the acid molecule, but also of molecular structure and steric factors, as may be better appreciated from a consideration of the structure of the more common of these acids:

Glycollic acid (hydroxyacetic acid) Hip-00011 H Malic acid (monohydroxysuc'cinic acid) H2 00'0H Lactic acid (alpha-hydroxypropionic acid) CH3 ire-AH GOOH Tartaric acid (dihydroxysuccinic acid) 11 'm z-ooon HO-GO0H Citric acid H:CCOOH BIO- -000H H: CO0H It is obvious that tartaric acid having two hydroxyl and two carboxylgroups will give the most stable complex; and it is also normal that glycollic and lactic acid complexes will show the least stability, both being monohydroxy-monocarboxylic acids. On the other hand, the lactic chelate of nickel is less stable than the glycollic complex; and this is due to a structural factor, i. e., the presence of an additional methyl group (CI-l Moreover, chelate stability is also determined by the number of carboxyl groups in the molecule so that the nickelmalic acid complex (a monohydroxy-dicarboxylic compound) is more stable than the corresponding chelates of both glycollic and lactic acids (monohydroxy-monocarboxylic acids), while the citric acid complex is them stable of all.

. Generally, if hydroxycarboxylic acids (instead of a non-chelating butler) are added to a chemical plating bath of the nickel cation-hypophosphite anion type in continuous operation, the resulting plating rate will be an inverse function of chelate stability; however, on the other hand, the more stable the nickel complex, the higher a phosphite ion concentration can be built up before precipitation of nickel nhosnhite occurs.

For the above reasons, the plating baths disclosed in the Gutzeit, Talmey and Lee application, Serial No. 478,492, comprise relatively stable complexing agents in combination with powerful exalting additives, dicarboxylic acids, aminocarboxylic acids and certain monocarboxylic acids (to increase the normally low plating rates of these baths).

The present invention is predicated upon the discovery that in a plating bath of the nickel cationhypophosphite anion type described, while the nickel chelating function of lactic acid is directly proportional to the concentration thereof in the bath, the effect thereof upon the plating rate of the bath is not inversely proportional to the concentration thereof (as is the general case with the other hydroxycarboxylic acids); rather within a given range of concentration, lactic acid is a definite exaltant in the bath, substantially increasing the plating rate thereof, together with the discovery that in the utilization of propionic acid as an exaltant in these lactic acid complexed plating baths synergistic exalting elfects are produced. The mechanism of these exalting efiects is not fully understood, but these effects are very pronounced; and are most unusual and entirely unexpected.

The general composition of a plating bath, in accordance with the present invention, essentially comprises an aqueous solution of a nickel salt, a hypophosphite, lactic acid or a salt thereof, and propionic acid or a salt thereof; wherein the absolute concentration of hypophosphite anions in the bath is in the range 0.15 to 1.20 m. p. 1., the ratio between nickel cations and hypophosphite anions in the bath expressed in molar concentration is within the range 0.25 to 1.60, the absolute concenration of lactic anions in the bath is in the range 0.25 to 0.45 m. p. 1., and the absolute concentration of propionic anions in the bath is within the range 0.025 to 0.045 m. p. l. The pH of the bath is normally in the range 4.0 to 5.6; and the bath is employed in the plating chamber of the continuous plating system at a'temperature above C., ordinarily slightly below the boiling point thereof and at about 97 to 99 C. The bath has a nickel plating rate of at least 1 mil/hour (0.001"/hour), or expressed in c. g. s. units, of at least 3.5 X l0 gm./crn. /min.; and no precipitation of nickel phospln'te takes place therein even at a phosphite ion concentration in some cases very close to 1.0 m. p. 1. Further, the plating appearance on both metals and non-metals is excellent (bright, smooth and non-porous); and adhesion of the nickel plating on both metallic and non-metallic bodies is excellent (no flaking of the nickel coating in bending, abrading and shock tests).

In accordance with the process of the present invention, the plating bath of the composition specified is preferably employed in the continuous plating system of the character previously described, whereby the lactic acid additive is present therein in the optimum range specified so that it serves both the complexing or chelating function with respect to the nickel ions and also the function of increasing the otherwise relatively low plating rate of the bath, and whereby the propionic acid additive is present therein in the optimum range specified so that it serves the function of further increasing disproportionately the plating rate of the bath. This complexing of the nickel cations'in the plating bath prevents the formation of precipitated phosphite therein, thereby rendering the bath of exceedingly long life in spite of the build-up of phosphite ions therein to a concentration even in excess of 1 molar. This complex of nickel in the plating bath is water-so1uble and of medium stability resulting in, a bond strong enough to prevent the nickel cations from forming insoluble nickel compounds, but having a stability constant low enough to release the nickel cations required for the nickel plating operation to efiect a plating rate of the bath of at least 3.5 l0 gm./cm. /min., as previously explained.

In view of the foregoing, it is the primary object of the present invention to provide an improved nickel plating process of the character described in which the reactions involved are carried out more efliciently and under more stable conditions (clarity of solution) than heretofore, thereby rendering the process more desirable from a commercial standpoint.

Another object of the invention is to provide an improved aqueous chemical nickel plating bath that may be employed with advantage in the practice of the improved process.

Another object of the invention is to provide an improved nickel plating process of the character described, that employs a plating bath of the nickel cation-hypophosphite anion type of the character specified, wherein the lactic acid substantially completely complexes all of the nickel cations in the bath, and wherein the combination of the lactic acid and the propionic acid substantially increases the plating rate thereof to at least 3.5 X gm./cm. /min.

A further object of the invention is to provide an improved nickel plating process of the continuous type involving an improved plating bath of the nickel cationhypophosphite anion type, so that the useful life of the bath is greatly extended in that it remains clear, notwithstanding the presence therein of a phosphite anion concentration approaching 1 molar.

A still further object of the invention is to provide an improved nickel plating bath of the character described that involves the combination of a novel range of lactic ion addition and a novel range of propionic ion addition.

These and other objects and advantages of the invention pertain to the particular arrangement of the steps of the plating process and of the composition of the plating bath, as will be understood from the foregoing and following description taken in connection with the accompanying drawings, in which:

Figure l is a curve illustrating the relationship between p'hosphite tolerance of a plating bath of the type described and the concentration of lactic acid contained therein;

Fig. 2 is two curves illustrating the relationship between phosphite tolerances of two plating baths of the type described and the pH thereof;

Fig. 3 is a curve illustrating the relationship between the plating rate of a plating 'bath of the type described and the pH thereof; and

Fig. 4 is two curves illustrating the relationship between the plating rates of the two plating baths of the type described and the concentration of phosphite therein.

In accordance with the process of the present invention, the article to be nickel plated and norm-ally having a catalytic surface is preferably prepared by mechanical cleaning, degreasing and light pickling substantially in accordance with standard practices in electroplating processes. For example, in the nickel plating of a steel article, it is customary to clean the rust and mill scale from the article, to degrease the article and then lightly to pickle the article in a suitable acid, such as hydrochloric acid. The article is then immersed in a suitable volume of the plating bath containing the proper proportions of nickel cations, hypophosphite anions, lactic ions and propionic ions, the pH of the bath having been, if necessary, adjusted to an optimum value by the addition of an appropriate acid or base, and the bath having been heated to a temperature just below its boiling point,

such as 99 C. at atmospheric pressure. Almost immediately, hydrogen bubbles are'formed on the catalytic surface of the steel article and escape in a steady stream from the plating bath, while the surface of the steel article is slowly coated with metallic nickel (containing some phosphorus). The steel article is subsequently removed from the bath after an appropriate time interval corresponding to the required thickness of the nickel coating deposited thereon that is desired; and ultimately the steel article is rinsed 0E with water, so that it is ready for use.

In the plating'bath, the nickel cations may be derived from nickel chloride, nickel sulfate, etc., or various combinations thereof; the hypophosphite anions may be de rived from sodium hypophosphite, potassium hypophosphite, etc., or various combinations thereof; the lactic ions may be derived from lactic acid, or various lactates, or various combinations thereof; and the propionic ions may be derived from propionic acid, or various propionates, or various combinations thereof. The desired pH of the bath is established by the eventual introduction thereinto of a suitable acid, such as hydrochloric acid, sulfuric acid, etc., or an alkali such as sodium hydroxide, sodium carbonate, sodium bicarbonate, etc.

The terms cation, anion and ion as employed herein, except where specifically noted, include the total quantity of the corresponding elements that are present in the plating bath, i. e., both undissociated and dissociated material. In other words, 100% dissociation is assumed when the terms noted are used in connection with molar ratios and concentrations in the plating bath.

In order to demonstrate the remarkable advantages ,of the plating baths of the present invention, several series of plating tests were conducted employing standard steel samples that had been given a standard pre-treatment. More particularly, steel samples (Dayton Rodgers) of 20 cm. total area were vapor degreased, cleaned by an alkaline soak and lightly pickled in 1:1 hydrochloric acid. The steel samples thus prepared were then plated at 98i C. in 50 cc. of different plating baths in 10-minute tests and involving a plating bath of the following fundamental composition:

BATH I Nickel ion (as nickel sulfate)"; m. p. l-.. 0.08 Hypophosphite ion (as sodium hypophosph lte -m. p. 1... 0.225 Lactic ion (as lactic acid) m. p. l 0.30

Utilizing plating Bath I containing various ones of the exaltants indicated, the following results were obtained, as set forth in the table below:

1 Bright and smooth.

Again utilizing plating Bath I, steel samples (pretreated in the manner previously explained) were plated in 60-minute tests, the plating bath containing various ones of the exaltants indicated, and with the results set forth in the table below:

From a comparison of'Tables IA and IE, it will be appreciated that propionic acid is a far better exaltant in the -minute rate test than the other soluble short chain aliphatic monocarboxylic acids, but that it is somewhat inferior in this regard to acetic acid in the 60- minute test. Nevertheless, propionic acid represents the preferred ,exaltantbecause acetic acid is easily volatilized, particularly through steam entrainment, and butyric acid and valeric acid are more expensive. Moreover, propionic acid is preferred for the additional reason that the structure thereof is quite similar to that of lactic acid, since lactic acid is of course alpha-hydroxypropion'ic acid. In these plating baths, the quantity of propionic anion required as an'exalting additive is about 10% of that of thelactic anions required as a complexing agent; whereby the ration Ni++/propionic anion should be preferably tate. The calcium salts of propionic, butyric and Valerie acids satisfy this condition, as do the calcium salts of lacticracidi At this point, it is mentioned that most common hydroxycarboxylic acids (malic, citric, tartaric, etc.) form insoluble calcium compounds.

In the continuous plating system, a similar plating test was performed involving a number of cycles of circulation of the body of plating solution and including periodic regeneration of the plating bath in the reservoir exteriorly of the plating chamber, as disclosed in the previously mentioned 'Talmey and Crehan patent. In this plating test, a number of cold rolled steel samples (1%" x 6" x 14 ga.) were employed that had been subjected to a pretreatment including vapor degreasing, alkaline soaking and pickling in 2:1 hydrochloric acid. In this plating test, the initial composition of the plating bath was as follows:

with caustic soda; and the specific results of this continuous plating test are set forth in the table below:

Table II Cycle No 1 2 3 4 5 6 7 8 9 10 Total weight gain (gm.) 6- 05 5. 6 6.1 5. 6 6. 0 2. 95 2. 90 3. 2.90 2.70 Plating rate, R X10 (gmJcrnfl/mrn). 3. 31 3. 3.19 3.45 3. 34 4. 00 3. 84 3. 61 3. 78 3. 65 Plating rate (mil/1m)--- 0. 94 0.99 0. 91 0.99 0. 95 1. 14 1.10 1.03 1.08 1. 04 Solution flow rate (co/1n 100 100 100 100 100 100 100 100 100 I 100 Plating time (121111.) 63 55 66 56 62 52 63 53 51 I itial pH 4. 70 4. 58 4.60 4. 7o 4. s5 4. so 4. 52 4.50 4. 50 4. 50 N1 added (gm. as NlSO4-6Ha0) 5. 6 5. 2 5. 7 5. 2 5. 6 2.70 2. 69 3. 10 2. 69 2. 50 NaHzPOq added (gm) 30 28 31 30 30 15 15 17 15 14 N aQH added (gm.) 7. 1 3.6 3. 6 4. 2 3. 6 3. 4 Additive (p p. 111.) Pl) 1 5 0 0. 5 0. 5 0 0. 5 0 Ni turnover (mol/l.). 0742 0.0820 0.0895 0. 0984 O. 1060 0.1130 Platmg appearance 0) 0) 0) '(l 1 Bright and smooth.

in the approximate range 1.5 to 2.5, since the Ni++/ lactic anion should preferably be in the approximate range 0.15 to 0.25. However, the bath may contain propionic anions in the approximate range 0.025 to 0.060 m. p. 1., since it may contain lactic anions in the approximate range 0.25 to 0.60 m. p. 1.

In plating operations involving plating baths of the nickel cation-hypophosphite anion type containing lactic ion as the complexing and exalting agent, the utilization of the simple short chain saturated monocarboxylic acids (propionic, butyn'c and valeric) is most advantageous in view ofthe solubility of the calcium salts thereof. More specifically, in the operation of the continuous plating system, after a relatively long time interval of pro duction plating, the phosphite concentration builds up to a point where a slight excess of (HPO despite the presence of a complexing agent, will result in nickel phosphiteprecipitation; in other words, a threshold isreached wherethe solubility of nickel phosphite, even in the presence of a nickel chelating agent, is exceeded. At this time, it becomes necessary to remove, by some method, the excess phosphite ion, as well as the excess sodium and sulfate ions that have accumulated as the result of regeneration. A simple and economical method ofachieving this objective is disclosed in the copending application of Paul Talmey, Gregoire Gutzeit and Donald E. Metheny, Serial No. 479,040, filed December 31, 1954, and involving the addition to the spent plating bath of a slight excess of calcium hydroxide, resulting in the precipitation of nickel phosphite, calcium phosphite and calcium sulfate; whereby, vfor practical reasons/it is highly desirable :to employ in .these plating .baths .an exaltant which is' not removed ;in.the '.-.above. described process, its calcium salt being soluble as is calcium lac- Incycles 1 to'S, inclusive, of this plating test, two of the panels specified having a total area of 290 cm. were plated; whereas in cycles6 to 10', inclusive, of this plating test, only one panel specified having a total area of cm. wasplated. In this plating test, the quality of the plating was excellent, particularly with respect to smoothness, lack of porosity and corrosion-resistance.

The phosphite tolerance of these plating baths of the nickel cation-hypophosphite anion type (also containing both lactic acid and propionic acid) is dependent substantially upon the concentration of lactic acid in the bath.

For example, a plating bath of this type was tested that had the following composition:

The results of these tests are set forth in the table below:

Table III Lactic ion Phosphite (m; vp. l.) tolerance (to. p. l.)

The results of these tests are also illustrated graphical: ly by the curve 11 in Fig. l; and it is noted that the phosphite tolerance of these baths is established substantially by the concentration of lactic acid therein. Also it will appear from the curve 11 of Fig. 1 that it is advantageous to use Bath III at the highest possible lactic ion concentration (consistent with good plating) in order to give the plating bath a long life in use. On the other hand, an increase in the lactic acid concentration above about 0.4 m. p. l. at substantially constant pH results in a marked decrease of the plating rate of a plating bath of this type.

This was demonstrated by a series of -minute plating tests employing steel samples (pretreated in the manner previously explained) and using a plating bath having the following composition:

BATH IV NiSo .6H O m. p. l 0.08 Na(I-I PO m. p. 1 0.225 Propionic acid m. p. l 0.03 Lactic acid variable Initial ph 4.6

The results of these plating tests are set forth in the table below:

Table IV Lactic acid (m. p. 1.) 0.10 0.20 0. 30 0. 40 0.50 Average plating rate (gm./

emfi/mmxloo s. 700 3.730 3.585 3.585 3.260 Final pH 3. 90 4.00 4.15 4.20 4.30

The plated samples were smooth and semi-bright; and it is noted that the final pH decreased from the initial pH in a manner inversely proportional to the lactic acid concentrations in the plating baths as a result of the buffering effect of the lactic acid.

From Table IX, it is apparent that the optimum lactic anion concentration in plating Bath IV (at a pH of 4.6) is about 0.4 m. p. 1. giving this plating bath a phosphite tolerance of 1.4 m. p. 1. In the use of the plating bath, if the plating rate can be sacrificed, a higher lactic anion concentration (for instance 0.5 m. p. 1.) can be used therein in order to achieve an overall saving in chemicals.

If the pH of a plating bath of this type is changed, the phosphite tolerance increases with increasing hydrogen ion concentration; however, the plating rate also decreases as the pH of the plating bath is lowered.

In order to demonstrate these facts, two plating baths were tested that had the compositions set forth below:

Lactic anion0.40 m. p. l

The results of these tests are respectively set forth in the tables below:

Table V Lactic anion0.30 m. p. 1.

pH Phosphlte tolerance .10 Table VI Lactic anion 0.40 m. p. 1.

Phosphite tolerance From a comparison of the results of these tests respectively set forth in Tables V and VI, and respectively employing plating Baths V and VI, it will be appreciated that the phosphite tolerance of a plating bath of this type is increased both with an increase in the concentration of lactic anion and with a decrease in the pH thereof.

The results of these tests are also illustrated graphically by the

respective curves

21 and 22 in Fig. 2.

In order to demonstrate the effect of pH variations upon the plating rate of a plating bath of this type, a: series of 10-minute plating tests were run employing steel samples of the character previously described and utilizing a bath of the composition set forth below:

The results of these plating tests are set forth in the table below:

Table VII pH 4. 70 4.60 4.50 Average plating rate (gm./cm. /min. 10 3.35 2. 94 2. 89

The results of these plating tests are also graphically illustrated by the curve 31 in Fig. 3.

Actually the matter of selecting the range of the lactic anion concentration and the pH of a plating bath of this character depends upon an economic problem in that a high phosphite tolerance lowers the cost of the chemicals per unit surface area nickel plated, while a high plating rate lowers the labor cost and amortization of the plant equipment. For practical purposes, a pH between 4.5 and 4.7 appears to be most desirable.

Further, it is pointed out that while a high phosphite tolerance is advantageous as noted above, the plating rate of a bath containing a high phosphite concentration is also impaired. This was demonstrated in two series of 10-minute plating tests that were run employing steel samples prepared in the manner previously explained and utilizing two baths having the compositions indicated below:

Identical to Bath VIII except that it contains:

Lactic anion-0.4O m. p. l.

The results of these plating tests are respectively set forth in the tables below:

Table VIII Lactic anion-0.30 m. p. I.

Phosphite concentration (m. p. l.)

10 Average plating rate (gm./cm. /mtn'.X10).--.

Table IX Lactic anion-0.40 in. p. l.

The results of these plating tests are also illustrated graphically by the

curves

41 and 42. in Fig. 4.

Thus it will be appreciated that as the phosphite conconcentration builds up in a plating bath of this type, as the plating bath is used in the continuous plating system, the plating rate of the bath declines. Accordingly, it will be appreciated that the level of concentration of the phosphite'in a plating bath of this type must be maintained as low as possible by employing continuous regeneration thereof during use, as disclosed in the previously-mentioned copending application of Paul Talmey, Gregoire Gutzeit and Donald E. Metheny. Otherwise, the plating bath must be discarded for further use, when about one-half to three-fourths of the phosphite tolerance thereof is reached, thereby to insure that in the plating operation, there is no formation of black precipitate in the plating bath.

in view of the foregoing, it is apparent that there has been provided an improved, process of chemical nickel plating, as well as improved plating baths therefor, wherein the baths are of the nickel cation-hypophosphite anion, type, and containing as a combination complexing agent and exalting additive a predetermined range of lactic acid and containing as a separate and independent exalting additive a simple short chain saturated aliphatic monocarboxylic acid, preferably propionic acid. These plating baths are particularly well-adapted for use in a continuous plating system, as they exhibit a fast plating rate, have an exceedingly long life, are productive of entirely satisfactory plating quality, and maintain nickel phosphite in solution in concentrations approaching one molar.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

Whatis claimed is:

l. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath consisting essentially of an aqueous solution of nickel ions, hypophosphite ions, 21 complexing agent selected from the group consisting of lactic acid and salts thereof, and an exalting additive selected from the group consisting of simple short chain saturated aliphatic monocarboxylic acids including 3 to 5 carbon atoms and salts thereof, wherein the absolute concentration ofhypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 1.60, the absolute concentration of lactic ions in said bath expressed in mole/liter is within the range 0.25 to 0.60, and the initial pH of said bath is within the approximate range 4.4 to 5.6.

2. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath consisting essentially of an aqueous solution of nickel ions, hypophosphite ions, a complexing. a-gcnt selected from the group consisting of lactic acid and salts thereof, and an exalting additive selected from the group consisting of propionic acid and salts thereof, wherein the absolute concentration.-of hypophosphite-ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 1.60, the absolute concentration of lactic ions in said. bath expressed in mole/liter is within the range 0.25 to. 0.60, and the initial pH of said bath is within the approximate range 4.4 to 5.6.

3. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath consisting essentially of an aqueous solution of nickel ions, hypophosphite ions, a complexing agent selected from the group consisting of lactic acid and salts thereof, and an exalting additive selected from the group consisting of propionic acid and salts thereof, wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range of 0.25 to 1.60, the absolute concentration of lactic ions in said bath expressed in mole/literis within the range 0.25 to 0.60, the absolute concentration of propionic ions in said bath expressed in mole/liter is within the range 0.025 to 0.060, and the initial pH of said bath is within the approximate range 4.4 to 5.6.

4. The process, of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, coper, silver, gold, palladium and platinum, which comprises contacting said body with a bath consisting essentially of an aqueous solution of nickel ions, hypophosphite ions, a complexing agent selected from the group consisting of lactic acid and salts thereof, and an exalting additive selected from the group consisting of propionic acid. andsalts thereof, wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 0.35, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 0.60, the absolute concentration of lactic ions in said bath expressedin mole/liter is within the range 0.25 to 0.45, the absolute concentration of propionic ions in said bath expressed in mole/liter is within the range 0.025 to 0.045, and the initial pH of said bath is within the approximate range 4.5 to 4.7.

5'. A bath for the chemical plating of a catalytic material with nickel consisting essentially of an aqueous solution of a nickel salt, a hypophosphite, a complexing agent selected from the group consisting of lactic acids and salts thereof, and an exalting additive selected from the group-consisting of propionic acid and salts thereof, wherein the absolute concentration of hypophosphite ions in said bath-expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 1.60, the absolute concentration of lactic ions in said bath expressed in mole/liter is within the range 0.25 to 0.60, the absolute concentration of propionic ions in said bath expressed inmole/liter is within the range 0.025 to 0.060, and the initial pH of said bath is within the approximate range 4.4 to 5.6. i

6. The process of chemically plating with nickel a body essentially comprising anelement selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath consisting essentially of an aqueous solution of nickel ions, hypophosphite ions, a complexing agent selected from the group consisting of lactic acid and salts thereof, and an exalting additive selected from the group consisting of simple short chain saturated aliphaticmonocarboxyl ic acids including 3 to 5 carbon atoms and salts thereof, wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 1.60, the absolute concentration of lactic ions in said bath expressed in mole/liter is within the range 0.25 to 0.45, and the initial pH of said bath is Within the approximate range 4.4 to 5.6.

7. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath consisting essentially of an aqueous solution of a nickel salt, a hypophosphite, a complexing agent selected from the group consisting of lactic acid and salts thereof, and an exalting additive selected from the group consisting of propionic acid and salts thereof, wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 1.60, the absolute concentration of lactic ions in said bath expressed in mole/liter is within the range 0.25 to 0.45, the absolute concentration of propionic ions in said bath expressed in mole/liter is within the range 0.025 to 0.045, and the initial pH of said bath is within the approximate range 4.4 to 5.6.

8. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath consisting essentially of an aqueous solution of nickel ions, hypophosphite ions, lactic ions and propionic ions, wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 1.60, the absolute concentration of lactic ions in said bath expressed in mole/liter is at least about 0.25, and the absolute concentration of propionic ions in said bath expressed in mole/liter is at least about 0.025.

No references cited.

Claims

1. THE PROCESS OF CHEMICALLY PLATING WITH NICKEL A BODY ESSENTIALLY COMPRISING AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF IRON, COBALT, NICKEL, ALUMINUM, COPPER, SILVER, GOLD, PALLADIUM AND PLATINUM, WHICH COMPRISES CONTACTING SAID BODY WITH A BATH CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF NICKEL IONS, HYPOPHOSPHITE IONS, A COMPLEXING AGENT SELECTED FROM THE GROUP CONSISTING OF LACTIC ACID AND SALTS THEREOF, AND AN EXALTING ADDITIVE SELECTED FROM THE GROUP CONSISTING OF SIMPLE SHORT CHAIN SATURATED ALIPHATIC MONOCARBOXYLIC ACIDS INCLUDING 3 TO 5 CARBON ATOMS AND SALTS THEREOF, WHEREIN THE ABSOLUTE CONCENTRATION OF HYPOPHOSPHITE IONS IN SAID BATH EXPRESSED IN MOL/LITER IS WITHIN THE RANGE 0.15 TO 1.20, THE RATION BETWEEN NICKEL IONS AND HYPOPHOSPHITE IONS IN SAID BATH EXPRESSED IN MOLAR CONCENTRATIONS IS WITHIN THE RANGE 0.25 TO 1.60, THE ABSOLUTE CONCENTRATION OF LACTIC IONS IN SAID BATH EXPRESSED IN MOLE/LITER IS WITHIN THE RANGE 0.25 TO 0.60, AND THE INITIAL PH OF SAID BATH IS WITHIN THE APPROXIMATE RANGE 4.4 TO 5.6.