US2658841A

US2658841A - Process of chemical nickel plating and bath therefor

Info

Publication number: US2658841A
Application number: US194656A
Authority: US
Inventors: Gutzeit Gregoire; Krieg Abraham
Original assignee: General American Transportation Corp
Current assignee: General American Transportation Corp
Priority date: 1950-11-08
Filing date: 1950-11-08
Publication date: 1953-11-10
Anticipated expiration: 1970-11-10

Description

Nov. 10, 1953 GUTZEIT ETAL PROCESS OF CHEMICAL NICKEL PLATING AND BATH THEREFOR Filed Nov. 8, 1.950

7 Sheets-Sheet 1 Temperature C FIG I u &9 E E: k N $2 3 55 5 .5%

m v, 0.0 e

fb G A Nov. 10, 1953 e. GUTZEIT EAL 2,658,841

PROCESS OF CHEMICAL NICKEL PLATING AND BATH THEREFOR Filed Nov. 8, 1950 7 Sheets-Sheet 4 E a 26 (H P0 0.224 MO/E/LIIGI' g (0 11 02): 0. I20 Mole/Lifer E Inifial pH= 5.5 5 Q 22 Na J u m s g g 0 v/A=I0.0 g g t: 18-- i 6 E l I I I l l l l g g 012 014 0.6 010 1.0 /'.2 1.4 8 Ratio, Nickel Ions Hypophosphife Ions.

FIG. 6

g 54-- Q g} 52-- (H3PO2)= 0.224 Mole/Lifer 50- (Cg/I302 r= 0.120 Mole/Lifer Q) g Initial pH 5.5

Q on E uva 1 1; 44-- u L '5 g 42 32 I 40 E g 5 38+ V/A 20.0 0. 5 w g 36- E, 0 1 ois 055 017 0.9 /f/ 1'3 3 Ratio, Nickel Ions Hypophosphifefons. INVENTORS FIG 7 Gregoire Gufzeif BY Abraham Krie Nov. 10, 1953 G. GUTZEIT ETAL PROCESS OF CHEMICAL NICKEL PLATING AND BATH THEREFOR 7 Sheets-Sheet 5 Filed NOV. 8, 1950 4 r r I. 8 6 h H S L L n 2%. w m 0 0 M M m 0 :om Q h 8 0. 0 w- 6 H I 2 D. 2 0 F 0 0 H N 2 M m M .E II. I OH k w .N 0 m m :2 0

0 0 0 0 0 m 8 6 4 2 5335 B SE Q$ m BEE M 2 2 l I EQ\QE =5: 2 5 53 3 5 Bi m Ex s EEQ 39$:

FIG. 9

Abraham Krieg Affys.

Nov. 10, 1953 Filed Nov. 8, 0

Weight of Plating (Nickel 8 Nickel Phosphorus) Weight of Plating (Nickel 8 Nickel Phosphorus) Deposited in One Hour mg /cm Deposited in One Hour mg/cm G. GUTZEIT ETAL 2,658,841

PROCESS OF CHEMICAL NICKEL PLATING AND BATH THEREFOR 7 Sheets-Sheet 6 (cw/302) o./2o Mole/Liter (H P0 0.224 Mole /Liler 0.2 014 0. 6 o e i0 /.'2 [4 Ratio, Nickel Ions Hypophosphite Ions. F I 6.. IO

(HgPOgF 0.224 Mole Liter (0 H 0 0. I20 Mole Liter ICa J pH 4.7 W pH 5.0 2/

0 .2 0E4 0. 6 0E8 l .0 .2 If4 Ratio, Nickel Ions Hypophosphite Ions.

' ,INVENTORS [3 I Gregoire Gutzeit Abraham Krieg A ti ys.

Patented Nov. 10, 1953 PROCESS, OF CHEMICAL NICKEL PLATING AND LBATH THEREFOR Gregoire Gutzeit, Highland, and Abraham Krieg, Gary, Ind., assignors to General American Transportation Corporation,0hicago,- Ill., a.cr- .poration of New York Anplicationz Novemben 8, 1950, Serial "N051943656 12 Claims. (01.117-130) The present invent-ion: relates to processes -.of chemical nickel plating and -.to vbaths employed in carrying out such processes.

The purpose of the inventionis to provide a chemical plating :process. which will have :many advantages in commercial use over electroplating methods, including low cost of equipment, good adhesion of .the coating in the finished product, high corrosion resistance of .the coating, and a coating which is uniform, continuous and much harder.

Eiforts have heretofore: beenmade -.to obtain some of these desirable-results-by:coating processes but without su-fiicient success. to warrant the commercial use of the methods suggested. For example, it has been ::proposed' by Brenner and Riddell (Jour. Research,v NationalsBureau of Standards; vol. 37, -July. 1946, and vol. v3 9,; November, 1 947)thatcoatings ofnickel=may:be deposited upon --the surfaces of catalytic -metals, for example, mild .steekeby employing achemical reduction of nickelions froman-aqueousbath containing hypophosphiteions in thepresence of sodium: ions and. sulfate ions .andusing-sodium acetate as a buffer .tomaintain-the pH-of-the bath in the range ofiromal to 6,-the temperature of the .bath being maintained at about 190 -icen tigrade. For instance-,iBrenner and .Riddell: suggest a numberotbathse one of: which comprises nickel sulfate gms/liter) sodium: hypophosphite (10 .gms/Iiter), and sodium acetate (10 gms./liter). In all:of :.these .baths,- the ratio of nickel ions to hypophosphiteiions Ni l'fi-HPoz)" expressed in terms,-.-of molar concentrations was a. decimal fraction, sis approximately 1133 and the absoluteconcentrationof hypophosphite'ions is approximately 0.095 .mole/liter. Employing this bath Brenner, and :Riiddell .obtained the deposition of the nickel-uponathe surface of the; steel at a rate of 0.015zmillimeter per hour.

In such a chemical: plating process, thez-principal reaction,.in the presence of water, expressed in ionic .form is considered to the: i

the nickelionl and sodiumxhypophosphitezto providethe" hypophosphite ion:

certain advantages over "competitive electrolytic processes, it was z-found by them to :be-uneconomical, to produce deposits at -.a slow rate .and to lack control of the composition of the :deposits. It is considerably more expensive to carry out than the-competing:electrolyticprocesses due primarily to'the low nickel efliciency ofwthe reaction, i. e.,' therper cent of nickel actually deposited at completion, as related-to the total amount of nickel present in'the :bath initially.

Accordingly, it is a general object of the present invention toprovide an improved chemical nickel plating iprocess of the general character described, in which therreaction involved; is=.carried out in an efiicient manner which renders the process economical from a commercial; and industrial standpoint.

Another object: of :the' inventionxis to provide antimproved .aqueoustibath-lof thezgeneral character' described .that. may be employed with: ad vantage in carrying. .out. :the improved 2. process.

A further object of the invention is to provide an improved process of chemical nickel plating and an improved aqueous. bath thatsmay. be employed. in carrying: out thexprocess, whereby the surfaces of catalytic materials. may he. readily coated with nickel in a simpleandefficient manner and wherein .the nickel coatings ..are smooth and continuous andtare' of alowporosity and of high corrosion resistance and are intimately bonded tothe surf'aceof'the catalytic material.

A further object of: the 'invention is to provide an improved process of chemical nickel plating and an improved aqueous bath that may be employed in carrying out the processthatare adapted for the commercial coating of iron, steel and the like.

Further featuresof the-invention pertainto the particularl arrangement of the steps of: the processand to'the compositionofthe aqueous bath, whereby the above mentioned objectsof the invention andothers areattained.

The invention, both as to its organization and principle of operation, together with further objects and I advantages thereof,--will best be understood by-referenceto the following 'specificatioh taken -in connection with th'e accompanying drawings in which, i

Figure 1 shows the relative amounts of plating deposited-with changes-in temperature;

Fig. 2- shows the variationof the weight *of 1 plating depositedinsa given period with variation nickel ions .-tohypophosphite ions of the ratio of nickel ions tohypophosphit ions; Fig.3 shows the change .inthe .pH value after a given period with :vari'ation of the. ratio .iof

Fig. 4 shows the variation in the weight of the Fig. 6 shows the variation of the weight of the plating deposited with variation in the ratio of nickel ions to hypophosphite ions when using a higher ratio of bath volume to plating surface area than that employed in the tests recorded by the curves of Fig.

Fig. 7 shows the variation of the weight of the plating deposited with variation in the ratio of nickel ions to hypophosphite ions derived from sodium hypophosphite Fig. 8 shows the variation in nickel efiiciency, in per cent at completion, with variation in the ratio of nickel ions to hypophosphite ions;

Fig. 9 shows a series of curves illustrating the variation in the weight of the plating deposit with variation in the pH of the plating bath for different specified ratios of nickel ions to hypophosphite ions derived from sodium hypophosphite;

Fig. 10 shows the variation in weight of the plating deposit with variation in the ratio of nickel ions to hypophosphite ions derived from sodium hypophosphite for two specified pH values for the bath;

Figs. 11 and 12 show a series of curves illustrating the variation in the weight of the plating deposit with variation in the pH of the plating bath for different ratios of nickel ions to hypophosphite ions derived from calcium hypophosphite; and

Fig. 13 shows the variation of the weight of the nickel plating deposit with variation in the ratio of nickel ions to hypophosphite ions derived from calcium hypophosphite with the use of calcium acetate as a butter.

In accordance with the process of the present invention, the catalytic material that may be coated with nickel comprises any material in the solid phase which will initiate at its surface the reaction of

Equations

1 and 2 set forth above; i. e., a material which, when immersed in the bath, will cause the evolution of hydrogen gas at its own surface. amples of catalytic materialswhich may be nickel plated: copper, silver, gold, beryllium, boron, germanium, aluminum, thallium, silicon, carbon, vanadium, molybdenum, tungsten, chromium, selenium, tellurium, titanium, iron, cobalt, nickel, palladium and platinum; and the following elements are examples of noncatalytic materials which ordinarily may not be nickel plated: bismuth, cadmium, tin, lead and manganese. The

gassed nickel (containing some phosphorus).

The following elements are exthe nickel ions.

activity of these catalytic materials varies considerably. The following elements are particularly good catalysts in the chemical nickel plating bath hereinaiter set forth, viz: aluminum, carbon, chromium, cobalt, iron, nickel and palladium.

" Thus, the nickel plating process becomes autocatalytic, when both the original surface and the met-a1 that is deposited are catalytic, and the reduction of the nickel salt to metallic nickel in the bath in accordance with the reaction of Equation 2 proceeds until all of the nickel ions have been reduced to metallic nickel, in the presence of an excess of hypophosphite ions, or until 4 all of the hypophosphite ions have been oxidized to phosphite, in the presence of an excess of nickel ions. Actually the reaction of

Equations

1 and 2 is slowed down rather rapidly as time elapses, because the anions, as contrasted with the cations, of the nickel salt combine with the hydrogen cations to form an acid, which, in turn, lowers the pH of the bath tending to dissolve the nickel deposit. This reaction is considered to be:

Also, the reducing power of the hypophosphite ion is decreased as the pH value decreases. It is, therefore, important to prevent a rapid drop of the pH of the bath after initial adjustment thereof within its optimum range. This-can be achieved by various schemes both alone and in combination. For example, a soluble nickel salt of a weak acid, such as acetic acid, can be used both to provide nickel ions and to act as a buffer. Also, the pH of the bath can be corrected periodically by the addition of a weak alkali, such as sodium bicarbonate; or a buffer, such as sodium acetate or other alkali acetate, can be added to the bath.

In carrying out the process, the article to be plated and normally formed of the catalytic material is properly prepared by mechanically cleaning, degreasing and light pickling, according to the standard practice in electroplating processes. For example, in the nickel plating of a steel object, it is customary mechanically to clean the rust and mill scale from the object, to degrease the object, and then lightly to pickle the object in a suitable acid, such as HCl. The article is then immersed in a suitable volume of the aqueous bath containing the proper proportions of nickel ions, hypophosphite ions and a buffer, the pH of the bath having been first adjusted to an optimum value by the addition of a suitable acid, 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 can be observed forming on the catalytic surface of the steel object and escaping in a steady stream from the bath, while the surface of the steel object is slowly coated with The reaction is continued until the color of the bath (green at the start) shows the absence of nickel, or until the evolution of hydrogen gas stops.

A nickel plating bath, as indicated above, containing a soluble nickel salt, a soluble hypophosphite and a bufier, is only relatively stable; and even without the presence therein of a catalytic surface, it tends to decompose more or less rapidly by random chemical reduction of Specifically, the nickel ions are reduced as a fine amorphous, black powder, which, in turn, acts as a catalyst. The resulting precipitate is gray to black and contains various quantities of nickel, phosphorus and salts, depending on the conditions of formation. This spontaneous decomposition is a function of temperature, time and initial bath composisition; and insofar as the initial bath composition is concerned, the higher the ratio of hypophosphite ions to nickel ions and the higher the absolute concentration of hypophosphite ions, the more unstable is the bath. In other words, instead of a bath capable of controlled nickel deposition in the presence of a catalyst,

a high concentration of hypophosphite anions will produce the well-known purely chemical nonselective reduction of nickel ions. Under plating conditions, in the presence of a catalytic g ef and at an elevated temperature, thecontrolledchemical reduction of the nickel ions in the bath, thus depleting the bath. Also, the

presence of the black precipitate in the bath results in a dull, rough and uneven nickel coating upon the object that is undergoing the plat-- ingreactioni I v "In carrying=out the process, the-rateof catalytic reductionof nickel'ions tometallic nickel is-a function of temperature of the bath and.-

this function logarithmic; forexample, if the temperature ofthe bath is decreased from approximately 100 C; to-approximately 90 0., ithas been discovered that the plating rate drops approximately "52.5%. It is, therefore, important that thetemperature of the bath be maintained atthehighest possible temperature below the boiling point thereof under the prevailing conditions, which is under standard conditions a.

temperature of approximately 99C.. Tests have been made to determine the. weight of nickel deposited per hour by the method of the present inventionsat different temperaturesand the results between 930? and 100? C. have been plottedto form the curve l8 shownin Fig. 1 of the drawings.

While it is apparent that there is a definite relationship involving the plating, rate of the object in thebath between the volume of the bath. andv the, surface, area of the object, ithas been. -discovered.,.that the volume of. the bath also determines the: relative amount. of black precipitate that'is formed under otherwise similar conditions. Thus, as'the volume increases, the amount. of. black precipitate increases. Employing the notation: V/Af for the ratio b. tween the volume of the. bath expressed in cubic centimeters (cm3) and. the geometric surface been. found that certain alkaline cations that are thus introduced into the bath appear to retard the rate of nickelv deposition with respect to other cations. For example, barium ions ape pear to retard the rateof; nickel deposition with respectfto sodium; and potassium ions; Omthe other hand, certain cations that are thus introduced into the bath appear to accelerate the rate of nickel deposition with; respect to other cations.- Eor example, masn s u1n ns; app a to accelerate the rate:of nickel: deposition with respect to. sodium. and potassium ions. Ac.- cordingly, from afstandpoint of economy, sodium and. calcium hypophosphites: are recommended; and from a standpoint of: realizing the ma-ximumw rate of nickelv deposition, magnesiumhy:

pophosphiteis-recommended. a

' decomposition, is

In preparing the bath, the amounts or sol uble nickel salt and: soluble hypophosphite'that areemployed are such that both the ratio of nickel ions to hypophosphite ions and the abso I lute concentration of hypophosphite ions are initially established within optimum ranges.

The term ion'as employed herein includes thev total quantity of element or radical present in.-

the bath; i. e., both undissociated and dissociated material. In other words, dissociation is assumed when-the; term ionis used in connection with molar ratios and concentra.-. tions in the bath. The ratio between the nickel ions and the hypophosphite'ions, Ni++/(H2PO2)'-:,

; in terms of molar concentration may be ex- 'pressed as a decimal f'raction; and it has been discovered that the most favorable range ofthis fraction lies between 0.25 and 0.60. It has also been discovered that the required absolute concentration of the buffer anions, such as acetate ions, should be equivalent to two carboxyl groups per ion of nickel that can be reduced, as explained morefully hereinafter. For example, if a hypophosphite ion concentration of .225; mole/liter is chosen, the required absolute concentration of acetate ionsof the buflfer; ex-

pressed in mole/liter, would be apPrQXimately- The relationship betweenthe ratio,

This curve has been plotted phosphite ions was 0.035 mole/liter, as the- Brenner and Riddell baths derivedfrom'sodium hypophosphite, the absolute concentration of acetate ions was-0.120 mo1e/1iter, the. V/A-ratiowas /5; the temperature of the bath was approximately 9e 0., and "thinitial-pHof the bath was in the range of'frorn' 5.38 to 5.49. In Fig. 2- the abscissae show the ratio of nickel ionsto hypophosphitetions and the ordinates show the weight of the plating-deposited in-a period of'two' hours in milligrams-persquare centimeter. It will be observed that the highest 'plating rates were obtained when the ratio ofnickel ion s to hypophosphite tt 7 I In the zone where the -higest plating rate-Was -obtained, the coating -was als'o cf thebestquality. being bright andasmooth. The lower plating rates were characterized by a dull and rough coating: The zone where the coating was bright and smooth has been indicated in Fig. 2 b-y-the-nota tion be. and the zone where-the coating-was-dull and rough hasbeenind -icated by the notationdr.

In the event the .absol-uteconcentration of hypophosphiteions-in the bath is increased while maintaining constant the nickel ions to hypophosphite ions ratio, an increased ratecf nickel deposition is realized, until a region-is reached where the bath becomes unstable such that-spontaneous decomposition thereoftakes place with the resulting formation of theblack precipitate previously referred-to.

It has been discovered thatthe optimum absolute concentration ofghypophpsph-ite i'ons in the bath, 1, e., onethat will result in good-nickel-plating without an excessive ten rlency to spontaneous within-the range-0.15 mole/liter. to 0.35 mole/liter; and .approximately -0.22 5 mole/liter is recommended. Moreoverf'thespo sta'ntiabsolute concentration of hypophosphite with the results of V a test in which the object plated was formed of mild steel, the absolute concentration o f hypoio s sin the ran 5t 1-6Q-.,

ions is related to the ratio, Ni++/(l-Izl Oz)-, as

illustrated by the curve 22 shown in Fig. 3 which shows, with varying ratios of nickel ions to hypophosphite ions, the drop in pH value after three hours at 99 C. without a catalyst.

In these tests, represented by the curve 22 of Fig. 3, the absolute concentration of hypophosphite ions was 0.224 mole/liter; the absolute concentration of acetate ions was 0.120 mole/liter; the temperature of the bath was approximately 99 C.; and the initial pH of the bath was in the range 4.90 to 5.01. From Fig. 3, it will be observed that the minimum spontaneous decomposition, as determined by the drop in pH of the bath after three hours, occurred when the ratio was in the'range 0.25 to 0.60. Of course, it will be appreciated that the pH drop of the bath is a direct function of the spontaneous decomposition thereof, since the uncontrolled chemical reduction oi the nickel cation will produce the acid corresponding to the anion of the originally employed nickel salt in amounts corresponding to its mass. In these tests, as well as in the others herein referred to, the pl-I values were determined at room temperature.

It will be understood that the higher absolute hypophosphite ion concentrations yield higher rates of deposition of the nickel without materially impairing the stability of the both within the optimum Ni++/(H2POz) ratio. On the other hand, if the absolute concentration of hypophosphite ions is increased substantially above the optimum range (0.15 mole/liter to 0.35 mole/liter), both the amount of nickel plating obtained during a given period and the quality of coating are considerably decreased by virtue of the random chemical reduction of the nickel ions that takes place and produces the black precipitate which, in turn, causes roughness and porosity in the coating, as previously mentioned. This circumstance is illustrated by the curve 24 of Fig. 4 which shows as abscissae theconcentration of the bath and, as ordinates, the weight of the plating deposited in periods of two hours, in

milligrams per square centimeter.

In these tests, the results of which are plotted in Fig. 4, the object plated was formed of mild steel; the Ni++/(H2POz)- ratio was 0.330; the WA ratio was 100 cmfi/S cm.?; the temperature of the bath was approximately 99 0.; and the initial pH of the bath was approximately 5.0. 'These tests showed a maximum plating deposit with a hypophosphite concentration of 0.224 and :this coating was bright and smooth with only a ztrace of black precipitate but as the'concentraition increased the black precipitate increased very rapidly and the plating became very rough. As the hypophosphite ion concentration is decreased below the preferred value, the black precipitate is only a trace and the plating is good but dull in appearance.

For purposes of comparison and to demonstrate the advantages of the discoveries of the present invention, tests have been made using sodium hypophosphite and an absolute concentration of hypophosphite ion equal to that specified by Brenner and Riddell for their bath No. 4 (and in the same order of magnitudeas in'their other baths), viz., 0.095 moles per liter, in coating a mild steel sample with a fixed acetate concentrationof .120 mole/liter, at a V/A ratio of 50 cm. /20 cm. =2.5, at an initial pH of about.

5.5 and at abath temperature of 99 C. for a period of thirty minutes, withthe results which are shown by curve 26 in Fig. 5, where the abscissae show the ratio of nickel ions to hypophosphite ions and the ordinates show the weight of the plating deposited in milligrams per square centimeter. With this low nickel hypophosphite ion concentration, it was found that when the ratio of nickel ions was very low (between .179 and .368) there was no plating deposit. The plating was at a maximum when the ion ratio was .368 and it gradually decreased as this ratio increased. The plating was good until'the ratio of 1.325 was reached when it appeared slightly stained.

Using the same baths with sodium hypophosphite, these tests were repeated at a V/A ratio of 2.5 and at a temperature of 99 C. with the hypophosphite ion concentration constant at .224 mole/liter and the results are shown by the curve 28 in Fig. 5. Thus by substantially doubling the absolute hypophosphite ion concentration used by Brenner and Riddell, considerably higher rates of deposition can be obtained, while the stability of the baths is very little impaired at the optimum Ni '/(H2PO2) ratio. When the ratio of nickel ions to hypophosphite ions was in the range between 0.2 and 0.6, the nickel plating was good and very bright.

With the same absolute concentration of hypophosphite ion (.224 mole/liter) derived from sodium hypophosphite as in the tests represented by curve 20 in Fig. 5, and using a similar series of baths, but plating at a higher V/A ratio (50 cmfi/S cm?) :10, at a temperature or about 99 C., the amount of nickel deposited in 60 minutes, with an initial pH of 5.50, was as shown by the curve 30 in Fig. 6. At the lower ratios of nickel ions to hypophosphite ions the weight of the plating deposit was substantially greater and it was brightest and smoothest in the region represented by the peak of the curve.

On further tests, using again the same absolute concentration of hypophosphite ion (.224 mole/liter) derived from sodium hypophosphite and with the same baths, but plating at a still higher V/A ratio (100 cm. /5 cm?) at about 99 C. the amount of nickel deposited in two hours was as indicated by the curve 32 in Fig. 7. The deposit was dark and nonmetallio under the conditions represented by the beginning of the curve but was good at all other times. A study of the curves shown in Figs. 2, 5, 6 and 7 shows a defi-' nite maximum weight of deposit when the ratio N1++/ (HzlI- O2)- is between 0.25 and 0.6.

So faras nickel efficiency is concerned, i. e.,

the weight of available nickel deposited includ-' ing the nickel-phosphorus compound), it decreases as the ratio Ni /(H2PO2) increases as is shown by the curve 34 in Fig. 8, using the same bath as that employed for the experiments represented by the curve 25 in Fig. 5, and with a hypophosphite concentration of 0.095 mole/liter. The region of optimum ratio (between 0.25 and 0.60) 7 proved vastly superiorto that used by Brenner and Riddellf With an absolute hypophos-.

phite ion concentration} of .224 mole/liter the nickel efliciency at completion was 97.5% for a Ni++/'(H2PO2)2 ratio of .357 and 25.0% for a Ni++/(II2POz)z ratio of 1.33 (B. & Rh). As previously indicated, a low pH in the bath will increase the pressure of dissolution of thecatalyst (if the catalyst is acid soluble) and of the deposited nickel according to the Reaction 3 appearing above and will lower the reducing power of the hypophosphite; On the other-hand, a high pH tends to favor the formation and even? tual precipitation of basic nickel salt and to pro-.-

iiibtie criisting"-atthe' caitaiytic -"'iirf 'a*ce. sh'dwhfibove, the optimum 'platir'igre'sult' ith a simple bath containing nickel ions, hypoph'osphite ions and acetate ions 'p'an be obtained "15y usin a hypop'h'osphit'e ion concentration of around 0.2 mole/liter and a, I Iit+/(H2PQ 2)L ratio of about 11-25 to 0560, Plating solutions were prepared, according to these teachingsconteinihgolm II'lOl/Iilii or hypophosphiteionde- 1, rived from sodium hypophosphite-With variable Ni /(HZ'POZ) ratios and the usual 'bu'ffer con;- .cnt1a;ti0h (0.120 mole/liter); The iriitia-l pH was adjusted by the 'additionofia'cetic acid. usi 'a medium V/A "ratid of 50 c'rn. 'volume 0115 *cmfjarea'of catalyst oromjthedeposits ofnickel T minutes at '99 C, were as shown by the 'nickel deposited with .varying..ratios of nickel hypopiidsehite, "h'ave been "plotted "to "rori'n' the :gurves 42 and, respeotively shownin With the ratios o ni kei ionstogHypq hdspri te ions represented the peaks thep'iafing wasfal'so.thehrightestafid In g neral, the low'erjpH 'ir'aluje ap eared to 'gi 'e better is'filt'sbothasfto H afiib'itfitdflth. plat-'- rng'deposit arid its tr'ieh. a g 3 'fiie'iesults or test ilchlifaiiflielfi plotted to the Various 'curv's Shown in'F'i'gsJlto 10, inclusive, were made with sodium h'ypophosphite. For purposes of comparison, reference will now be made to testswh'ic the use or 'eaicmm h'i' p'f firstito jthe efiectjo'fkzariat'io "j plating path on the weight or ekefdepb ited a given period of. time when .plating 'with gal ic'iium hyp'o'phosphite aim "caljc'f' in a l tat e as a biifier, the results of tests are shown bi; thegcuryes 45, 48, iii) and EZshoWn-in Eigsi l liand lfi which record the eightfo'f the nickel-Ziepositeq in one ou "with IH/(m 0s) i-atios or .0268, 0.402, 0:313 and-1.34.0, respectively. I H p J The vjariat'ion in the weightof the nickel :de; posited with 'changeinjthia ratio .of then-icke l ions to hypophosphitefions, yvithgclifierent pH Values, when. the hypophosphitelis pderivedj om calcium hypophosphite iii-the presence of. calcium faoetate as a buffer is shown hy tests',=-the"results of which havebeen'plottedtoiorm the cur-yes 54 and in Fig. 13, where the abscissae indicatethe ratios or nickel ions to higpophosphitQiOHSifind the 'ordi'n'at'es show the ght in one hour in millig 7 The hypoph'osphite 1 011 concentration .224 mole/liter,- the V/Aratio-was 50 cm. /5 cm. and the acetate ion concentration was .120 mole/liter. The curve '5] shows the results when the pH of the-bath had a value of -eifl and the curve 56 e als n tershows the results whenthepHewas increased to 5.0. These results may be compared with those showmb y Fig. and also with those Fig. 7; which.represent-the-rsiilts of hypoph ph te ions de ived fib 'rlfsodiiiiii *i'i'yiabphbsphit'e, r v

"absolutequaritity' rfbiiirr ntjin"thep1atifig bath;f

y t qhy r s nfi sa orm fiefqfai i f r 't 'eP h n on woii-1lthereiore "decrease' 'rapidly elow h li fe mjfl e at -i ns? i ib Q 1 m ntfi 1f ksaf m w r nid w; eformdfduifi'ngtm plating 'operatio Q i i ma um mb n qf I dwh'ioh, in turn is afundtion F P'Q os'blfi flniav l- Thetheoretica' l needed bufier con'centrat n is "the ion of an organic acid eguivalent to two carbQXi L mu eriever ke i h t t-c ids sif xro tre b e, m e fija f fl "oiie mate dfifickel. An excess of buffer other hand, is objectionablefs'ince it iwill the'formation ofba's" "h'ickel salts. efp ir 'hfie h f mii ive the best "results maybe efi tee ing- -calcu fi To 'suniiiiai izefsjonie' of I the conclusionsj'which fm'ayf e tl'rawn from the foregoing disclosure, it I hes e that fijinjorder to obtain mgmetes bf gmke i'pl'at byri e fia' m n f qi l s iquebus c'idjgafth;without'excessive formatio or black Ipitate' uncontrolled, i andii ire;- =duot nofl nickel) the folldwing'coiiditions should z ulfi' d o of 'fii 'ckel ions to "hypoph osphfite io s in tn 31 1 should be between 0.25 nd "0160, depending 'uponj thespecific cation present. r

' 'IT e'co'ncentration of the bath in. hypqphos p M 319115 oi ldbe above 0.15 mole/liter and vewww .7

3. The-pptimum-initiai pH v alues'of the bath 'u'nderQthe conditions indicated in the two next preceding paragraphsare in the range between ligand 5.5 5, Foriins tance, with sodium hypo phosphite, f 'there are two optimuminitial pH va u s; 0 4.f6 0 .and 5.50 while when Calcium hypogphosphite is employed the optimum initial pH hufi'er 'co ncentrationfin the bath should be equivalent to two ceirboxyl groups for ev'e'ry nickel ion that can hedeposited. H V

5, The optimum ratio of solution volume of the bath topatalyt'ic material area (V/A) isbelow 1 0. I'tw i ll loe' understoodvthat the invention is not limited except' as "defined by the appended claims.

WQLcIaim: I 1. The process or chemically plating with nickel a solid blody essentie 11y comprising anfeleinentselec'te'd from the group consisting Ofcopper, silver,"gold aluminum, iron, cobalt, nickel, palladium and platinum, which oomprises jc'ontaictingsaid. body with a bath consisting essen} ti'ally of an aqueous "solution of a nickel saltra'n'd a hypophosphite, wherein the ratio between nickel ions and fl h pophosphite ions inesai'd bath expressed in insist concentrations is Within the range 0.25 to 0.61 wherein the absolutejconcen trat ion of hypophosphite ions in said bathe;- b i [l t 's., t t enew-1: t9 05%5, "andwhere the initial pH oi said bath is w hiii theap p r ximate range 4.5 to 5.6. H f

The process set-'jforth in claim 1, wherein said hathconsists essentially of an aqueous solution of a hickel salt stag hypophosphite and buff effo'rmof e salt of an 'organic acid;

,a solid body essentially comprising an element selected from the group consisting of copper,

silver, gold, aluminum, iron, cobalt, nickel, palladium and platinum, which comprises contacting said body with a bath consisting essentially .of an aqueous solution of a nickel salt and a hypophosphite and a buffer in the form of an alkaline acetate, wherein the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 0.60, wherein the absolute concentemperature of said bath is slightly below the boiling point thereof.

5. The process of chemically plating with nickel a solid body essentially comprising an ele ment selected from the group consisting of copper, silver, gold, aluminum, iron, cobalt, nickel, palladium and platinum, which comprises immersing said body in a bath consisting essentially of an aqueous solution of a nickel salt and a hypophosphite, wherein the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 0.60, wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 0.35, wherein the initial pH of said bath is within the approximate range 4.5 to 5.6, and wherein the ratio between the volume of said bath expressed in cm. and the surface area of said body expressed in cm. is not greater than 10.

6. A bath for the chemical plating of a catalytic material with nickel consisting essentially of an aqueous solution of a nickel salt and a hypophosphite, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations being within the range 0.25 to 0.60, the absolute concentration of hypophosphite ions in said bath expressed in mole/liter being within the range 0.15 to 0.35, and the initial pH of said bath being in the approximate range 4.5 to 5.6.

'7. A bath for the chemical plating of a catalytic material with nickel consisting essentially of an aqueous solution of a nickel salt and an alkaline hypophosphite and a buffer in the form of a salt of an organic acid, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations being within the range 0.25 to 0.60. the absolute concentration of hypophosphite ions in said bath expressed in mole/liter being within the range 0.15 to 0.35, the absolute concentration of said buffer in said bath being approximately two carboxyl groups for every nickel ion that can be deposited, and the initial pH of said bath being in the approximate range 4.5 to 5.6.

8. A bath for the chemical plating of a catalytic material with nickel consisting essentially of an aqueous solution of a nickel salt and an alkali hypophosphite and a buffer in the form of a salt of an organic acid, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations being within the range 0.25 to 0.60, the absolute concentration of hypophosphite ions in said bath expressed in mole/liter being within the range 0.15 to 0.35, the absolute concentration of said buffer in said bath being approximately two carboxyl groups for every nickel ion that can be deposited, and the initial pH of said bath being in the approximate range 4.5 to 5.6.

9. A bath for the chemical plating of a catalytic material with nickel consisting essentially of an aqueous solution of a nickel salt and an alkali earth hypophosphite and a loufier in the form of a salt of an organic acid, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations being within the range 0.25 to 0.60, the absolute concentration of hypophosphite ions in said bath expressed in mole/ liter being within the range 0.15 to 0.35, the absolute concentration of said buffer in said bath being approximately two carboxyl groups for every nickel ion that can be deposited, and the initial pH of said bath being in the approximate range 4.5 to 5.6.

10.v The process of chemically plating with nickel a solid body essentially comprising an element selected from the group consisting of copper, silver, gold, aluminum, iron, cobalt, nickel, palladium and platinum, which comprises contacting said body with a bath consisting essentially or an aqueous solution of a nickel salt and a hypophosphite, wherein the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 0.60, wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 0.35, and maintaining the pH of said bath within the approximate range 4.5 to 5.6.

11. The process of chemically plating with nickel a solid body essentially comprising an element selected from the group consisting of copper, silver, gold, aluminum, iron, cobalt, nickel, palladium and platinum, which comprises contacting said body with a bath consisting essen-- tially of an aqueous solution of a nickel salt and a hypophosphite, wherein the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 0.60, wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 0.35, and periodically correcting the pH of said bath by the addition thereto or a soluble alkali to maintain a value within the approximate range 4.5 to 5.6.

12. The process of chemically plating with nickel a solid body essentially comprising an element selected from the group consisting of copper, silver, gold, aluminum, iron, cobalt, nickel, palladium and platinum, which comprises contacting said body with an aqueous bath consisting essentially of nickel ions, alkaline ions, hypophosphite ions and acetate ions, wherein the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 0.60, wherein the absolute concentrations of hypophosphite ions and acetate ions in said bath expressed in mole/liter are respectively approximately 0.225 and 0.120, and wherein the initial pH of said bath is in the approximate range 4.5 to 5.6.

GREGOIRE GUTZEIT. ABRAHAM KRIEG.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,207,218 Roux Dec. 5, 1916 2,430,581 Pessel Nov. 11, 1947 2,532,283 Brenner V Dec. 5, 1950

Claims

1. THE PROCESS OF CHEMICALLY PLATING WITH NICKEL A SOLID BODY ESSENTIALLY COMPRISING AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF COPPER, SILVER, GOLD, ALUMINUM, IRON, COBALT, NICKEL, PALLADIUM AND PLATINUM, WHICH COMPRISES CONTACTING SAID BODY WITH A BATH CONSISTING ESSENTIALLY OF AN AQUEOUS SOLTUION OF A NICKEL SALT AND A HYPOPHOSPHITE, WHEREIN THE RATIO BETWEEN NICKEL IONS AND HYPOPHOSPHITE IONS IN SAID BATH EXPRESSED IN MOLAR CONCENTRATIONS IN WITHIN THE RANGE 0.25 TO 0.60, WHEREIN THE ABSOLUTE CONCENTRATION OF HYPOPHOSPHITE IONS IN SAID BATH EXPRESSED IN MOLE/LITER IS WITHIN THE RANGE 0.15 TO 0.35, AND WHEREIN THE INITIAL PH OF SAID BATH IS WITHIN THE APPROXIMATE RANGE 4.5 TO 5.6.