US2316303A - Semibright nickel deposition - Google Patents

Description

r a bright or mirror-likefinish were Patented Apr. 13, 1943 I UTE s A'I'ES -'r orries I 2.31am snmnmen'r NICKEL nsrnon Andrew Wesley, Plainfleld, N. 3., andliay Wil- ,liam Carey, Lynbrook, N. Y.,asslgnors to The International Nickel Company, Ina, New York, N; Y., a corporation'of Delaware Application au ust 30, 1959, Serial No. 292,696

6 Claims: (011 204-49) appearance. =In order to avoid the expense and disadvantages inherent in such prior art practice, many attempts have been made to produce nickel 1 coatings which were so smooth that no or only slight bufilng was required trbring out a high luster. Coatings which gave a specular reflection without bufilng were known in the art as bright whereas those which had the appearanceof a mirrored surface that had been breathed upon and which required only slight bufilng to produce designated semi-bright or blushed.", The art in recent years has attempted to produce bright depositsby the use of .brightening addition agents" in the electroplating bath. These agents were, genreally speaking, additions of organic or inorganic materials such as sulionated naphthalene or terpene compounds, albumins. cadmium salts and lead salts intended to give bright or semi-bright deposition-were of the bright nickel type; In the event'that an ordinary nickel plating bath were used it was customary to bufl the final nickel layer as well as the intermediate copper layer.

A serious difliculty accompanied the extensive buil'ing necessary to bring ordinary nickel platings to the bright'condition. As a resultpf this extensive buillng the tendency to cut through the plate at the corners and at raised portions "deposits directly in the bath. Even with the most recent improvements, this art suflered from several-disadvantages which limited the commercial usefulness of baths containing brightening addition agents. The chief disadvantage was the difllculty of maintaining the bath composition constant over a period of time. The brightening was appreciable. The semi-bright deposit of the present invention eliminates the necessity of extensive bufling and thus eliminates the danger of cutting through with its accompanying toll of rejects j l v There was a definite and well recognized need in the art fora methodof depositing single layer coatings of'nickel free from pits and smooth enough to buff-easily and which was not subject to the operating difllculties mentioned hereinabove. However, when attempts have been made to eliminate extensive buillng'and deposit nickel directlytcn iron, experts in the art advised against the use of a nickel chloride bath due to the poor 7 .bond formed between the coating and thecore plating peeling oifa metal which resulted in the short time after deposition.

We have invented a process of electrodepositing nickel free from pits and in such sniooth form that a high luster can be developed by slight bumng. In our novel and improved process an easily controlled electroplating solution composed substantially entirely of an aqueous solution of addition agents were not perfectly stable; were vdiilicult to maintain in constant "concentration in the bath, and in part are deposited on the ob- :Iect being plated. So much highly'skilled technical service had 'to be given to users of such baths that none of them was in widespread use in smaller plating shops. Other shortcomings of these processes were extreme brittleness oi the deposit, a pronounced tendency for development of pits in the deposit, and with some plating baths 7 the permissible variation in plating conditions such as temperature and current density was very narrow with the result that frequently only part of-therplated article would be bright as plated so that bufllng was required to develop a uniform bright finish.

Due to the difllculty of ionsmn'ciand' bunt-gt nickel chloride and boric acid in critical amounts is' used and the plating conditions including the hydrogen ion concentration temperature and current-density are controlled within critical limits properly correlated with the bath compoordinary matte electrodeposited nickel coatings j and of getting coatings ofnickel rree'r m. pits, meta, having a-nrei'erred it was common practiceto'use multiple coatings of nickel and copper and to confine the polishing sition to produce satisfactory and acceptable semi-bright nickel deposits. 7 It is an object of the present invention to provide semibright coatings of nickel which-may be brought to a high luster with only slight butt-r ing. a

' It is another object of the present invention to provide semi-bright deposits of nickel having a preferred crystallographic orientation with the 1 direction normal to the surface of the basis metal.

It 'is a further' obiect oi' the present invention.

to provides'emi-bright single layer coatlngs of nickel on othermetals such as iron, steel, brass,

. face and'a preponderance of crystals having their (I l I) face: developed in heavyldeposits.

,The invention also contemplates providing relatively thick, comparatively ductile coatings of electrodeposited nickel free from pits and having a grain size greater than 0.0001 mm. and which are so smooth that they may be brought to a high luster with slight bufling.

Other objects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a graph showing the result of a physical test for distinguishing between matte. semibright or bright deposits;

Fig.2 is a return reflection curve showing the intensity of reflected light at various angles from a heavy semi-bright nickel deposit; and

Figs. 3, 4 and 5 depict graphically the critical correlation between temperature and current density at pH values of 0.75, 1.0 and 2.0, respectively.

Generally speaking, the semi-bright nickel coatings of. the present invention may be obtained on any appropriate foundation metal or alloy. We prefer to use a plating bath containing principally nickel chloride and boric acid in aqueous solution without "brightening addition agents," and by properly correlating hydrogen ion concentration, current density and temperature within critical limits, as hereinafter described. The present invention makes it possible to produce directly thick deposits of semi-bright nickel so smooth that they require only slight bufling to be brought to a high luster. At the same time the deposits are satisfactory in respect to adherence, ductility, soundness and freedom from pits. The semi-bright nickel deposits of the present invention may be obtained directly on iron or steel,

and the nickel plating so produced adheres well and has no tendency to peel off and is suitable for subsequent plating with chromium or other metals.

In the preferred plating bath employed in the present chloride and boric acid are dissolved in water. Preferably the bath contains about 300 grams per liter of nickel chloride and about 30 grams per liter'of boric acid. No addition of brightening agents of any kind need be made to the present improved bath to obtain the desired semi-bright nickel deposits. The boric acid content may vary from more than about 35 grams per liter down to less than about 5 grams per liter. Satisfactory results may be obtained provided more than a critical minimum content of boric acid is presout. If boric acid is present in an amount less than 5 grams. the semi-bright nickel deposit is burned and unsatisfactory. Beyond about 35 grams of boric acid per liter, the solubility of boric acid at room temperature is exceeded and flakes of boric acid settle out when the bath is allowed to cool. About 35 grams of boric acid per liter represents a practical maximum for commercial and industrial operations but the present invention is not limited to this amount as an absolute maximum. Satisfactory results maystill be obtained when the boric acid concentration is substantially equal to saturation at the operating temperature. While the theoretical function or functions of boric acid in its unique cooperation and combination with nickel chloride in the bath are not thoroughly understood. it is believed that boric acid does serve to bufier the solution. Between the limits of about 260 grams and about .340 grams "of NiClz.6H2O per liter satisfactory Y semi-bright deposits are obtained. Either above invention, critical amounts of nickel or below these critical limits. matte deposits are formed.

The acidity limits for producing satisfactory semi-bright deposits having preferred crystallographic orientation with the nickel chloride-boric acid bath are within the limits of about pH=0.7 and about pH-=3.0 (electrometric). While satisfactory deposits are obtained from baths operated within these limits, we prefer to maintain a pH of about 1 when depositing semi-bright platings of nickel. The pH is maintained by additions of hydrochloric acid instead of the customary sulfuric acid. These limits are critical. Numerous experiments have demonstrated that satisfactory semi-bright deposits cannot be obtained with the above mentioned bath unless the pH value is less than 3.0. Below a pH of about 0.7. the cathode current efllciency becomes too low for satisfactory commercial operation.

Bath temperature and current density must be coordinated with each other and with the hydrogen ion concentration in order to dbtain the desired semi-bright deposit of nickel. These relationships are depicted graphically in Figs. 3, 4 and 5 in which the abscissa represents current density in amperes per square foot, and the ordinate is temperature in degrees Fahrenheit. The bath employed for each series of tests contained about 300 grams per liter of NiClaGHaO and about 30 grams per liter of boric acid with the pH and other plating conditions controlled ashereinafter set forth.

In'one series of tests, a constant pH of about 0.75 was maintained while'current density and bath temperature were varied. Current densities from very low values to more than 200 amperes per square foot were found to produce satisfactory semi-bright nickel deposits provided the bath temperature did not rise above a critical value indicated by the curve D in Fig. 3.

' Below the curve D satisfactory semi-bright deposits were obtained, but above the curve the deposits were matte. 1

The pH value was maintained at about 1.0 for a second series of tests in which both temperature and current density were varied. .Within the area defined by curves E and F in Fig. 4

' satisfactory semi-bright deposits were produced.

When the temperature lay above curve E at any particular current density the deposit was matte. Below curve F, the deposit is burned and unsatisfactory.

In Fig. 5, the results series of tests conducted at a pH of about 2.0.

The area between the curves G and H represents the conditions of temperature and current density which yield satisfactory semi-bright nickel deposits. Above curve G and below curve H the deposits are matte and burned respectively as described in connection with .Fig. 3.

It will be seen from a study of Figs. 3, 4 and 5 that the area defining the ranges of permissible temperatures and current densities decreases progressively as the pH rises. A fourth series of tests conducted at pH=3.0 demonstrated that the semi-bright area had substantially disappeared. While the operable range of pH is about 0.7 to about 3.0, practical limits for semi-bright plating on a commercial scale are about pH=0.75 and about pH=-2.0. Temperatures from about F. to about F. are satisfactory for commercial operation with current densities varying from about 20 to about 200 amperes per square foot. Current density, temperature and pH should preferably be so correlated as to fall well are plotted of a third 2,816,803 .within the semi-brightareas of ll'igs. s,- 4 and 5. A

It will be understood by those skilledin the art that lines of curves D, E, F, G andH actually represent areas of somewhat varying width.

' .In other words, for any given current density and pH, e. g., 140 amperes'per square foot and .pH= 1, the deposit does not suddenly change .from semi-bright to' mattewith a slight tempera-' ,ture change, e. g., from slightly less to slightly morethan 141525. (see Fig. 4). On the contrary, there is a relatively narrow temperature range over which the deposit changes rather rapidly from semi-bright to matte.

The following specific example is illustrative of the results that can be obtained by practicing I the present invention. An aqueous plating bath was prepared having the following composition:

'mchcmo about 300 grams per liter I HaBOa about 30 grams per liter Sufllcien't hydrochloric acid was added to the aqueous solution to adjust the pH to about 1.0.

A bagged, rolled, depolarized nickel anode was used and the solution was filtered continuously.

Slight'agitation of the bath was obtained by means of a gentle stream oi? air. The bath temperature was maintained at about 110 F. while a steel object was coated directly 'with nickel at a cathode current density of about 75 amperes per square foot. After about '19 minutes a semibright deposit about 0.001 inch thick had been formedwhich wastbrought to a high finish in a was illuminated by a narrow collimated beam of single bufling operation using a soft rag wheel treated with an ordinary 'grease coloring compound containing rouge. A bright, mirror-like surface was obtained at a given point in about 10 seconds.

white light of about 1500 foot candlesintensity,- incident upon the specimen at various known angles with respect to the surface of the specimen.

The intensity of the light reflected directly back from the specimen parallel tothe impinging beam of light was measured by an illuminometer. By

incident beam, data for curves correlating the angle of incidence (which in'this procedure is the same as the angle of reflection) and the intensity of the light reflected back along the path of the illuminating beam were obtained.

These data for typical matte, semi-bright and' bri ht specimens with coatings 0.001 inch thick are plotted in curves 1, J and K of Figure 1 which indicate quite different magnitudes and distribu-- more maxima in the curve with a maximum ob-- served intensity within the range of about 30 to about 600 foot candls when the incident light has an intensity of about 1500 foot candles, i. e.,

the maximum intensity of reflected light is about 2% to 40% of the incident light. Typical matte deposits, however. reflect light of less than 20 foot candles intensity under comparable conditions over a wide range of angles of incidence and reflection, i. e., about 1.5% or less.

Blight bumng of the semi-bright deposit, for

and in a plane normal to the table. The sample inclining the specimen at various angles to the .10

example, with a rag bufling wheel and ordinary The art recognizes three general classesof A nickel plating, viz., the ordinary white nickel,

bright nickel and semi-bright or blushed nickel. The term white" nickel has been used to describe the color of matte deposits and has no reference to any degree of brightness. A bright deposit is one wh ch gives a specular reflection of incident light and is mirror-like in appearance. Im-

, ages 01 objects seen in aflat surface coated with bright nickel appear clear and distinct. A dull or matte deposit is one whichrefiects so little light specularly that no images can be distinguished in a flat surface coated with matte nickel except at grazing angles of incidence. Instead of specular, there is diiiusereflection. A.semibright deposit is one approaching the smoothness of a bright deposit but falling somewhat short of light is reflected specularly that images of objects can be distinguished at fairly small angles of incidence, albeit not very clearly and with hazy, instead of sharp, edges.

In order to define more precisely the (inference between matte. semi-bright and bright deposits,

"return reflection measurements were made by the method originated by P. Bouger [Traite d'Qp. 'tique sur la Gradation de la Lumiere, Paris.

, Guerin and Delatour (1760),]. In obtaining these data, the specimen,- in the form ofaplanerec-.

' tang'ular piece of steel sheet coated with a nickel deposit about 0.001 inch thick, was placed at the -.center of a spectrometertable which permitted the angle of the test sample with respect to the rouge bumng compound for about 10 seconds, produced a bright, mirror-like finish at any particu{ lar spot. Deposits as thick as about 0.006 inch may be obtained readily by the process embodying our invention which are still semi-bright and readily polished with slight bufilng to bright,

T mitror-like finish.

niflcance of various typesof such curves. That.

In'evaluating the significance of the 'curve 01" Fig. 2 it is necessary to consider briefly the sigof a perfect reflector would have its maximum in-' a specular reflection of incident light. It appears I like a mirror that has Just'been lightly breathed on. The terms "blushed" and "milky are also used to describe semi-bright deposits. Enough v impinging light beam to be altered and measured tensity at 0 to the normal to the plane reflection and zero intensity for all other inclinations of the specimen. This would indicate that the faces ofall the small crystallites. were parallel to the specimen surface or'that the surface had been flowed into a plane as in polishing or that the crystallites were smaller than the wave length of the incident light. As the angles of the reflecting facets increased, this curve would broaden out, the peak intensity decreasing. This could continue until the limiting.case was reached, assuming, naturally, that the angular distribution of refleeting facets was perfectly haphazard, for which the intensity was constant for any angle of inci- 4 dence and reflection, i. e., each ordinate was the same, and the curve becamevery flat topped. If for any reason the facets tended to assume a par- 1 tic'ular angle we should expect to find a peak at this particular angle 01 incidence.

The general shape of all reflectivity'vs. angle I curves will vary in the manner indicated-above,

then, depending solely upon the angle that the facets of, the individual crystals make with the mean "plane" surface. An infinite number of variations'could be secured-however, by increasing the roughness of the surface. As this was done, two thingswould take place: mat, the efl'ective illumination of the surface would be decreased because only the hills would be lighted at most angles of incidence; and second, the incident light would be multiply reflected with some loss at each reflection, i. e., the hills" could block off the reflected light as well as the incident light and the surface would be considered dark. In addition to these obvious effects, it is possible toget a certain amount of extinction by interference.

The greater the amount of light absorbed. nattical reflection characteristics,'X-ray studies were made to determine the nature of the orientation of the crystals comprising the several types of deposits. These showed that the dark matte deposit had a random orientation and that thesemibright deposit had a strongly preferred orientation with the [II2] direction normal tothe plane of the specimen. Previous work had indicated that, with nickel, the (III) planes were developed in the plating process. With these planes developed in deposits having the l' I I2] direction normal to the plane ofthe sample, maxima in the optical return reflection would be expected at 19 2 to the normal which checks closely with the observations on the 0.0036 inch deposit discussed earlier. Thin deposits did not show two maxima in the ooptical reflection studies, but this may have been due to the lack of perfection in the (III) planes at this stage of the plating operation;

As stated above X-ray studies showed that the [I I2] direction of semi-bright deposits was normal to the plane of the specimen which means that the I I2) planes are parallel to the plane of the specimen; since the (III) facesmake only a small angle (i..e. 19 /2") with the (H2) planes, it is to be expectedthat the surface of the semibright electrodeposit is microscopically almost flat,

which accounts for the fact that only a slight amount of buffing is required to develop the degree of flatness required for a truly bright finish.

Departures from the plating conditions necessary for the production of the desired semi-bright plate with its highly preferred orientation caused a decrease in the percentage of crystals oriented with the [H21 normal to the plane of the specimen and the production of [H] and [I00] orientations, while still further departures in plating conditions cause the disappearance of the desired [H2] orientation and finally to a sensibly random orientation. This behavior causes incontaining 0.9 molar nickel. chloride, 0.1 molar" nickel sulfate and 0.6 molar boric acid. The plating conditions were pH 3.0,\current density 0.5 amp. per sq. drn. and room temperature. Bozorth says nothing in his article concerning the appearance of the deposit. It was made upon a small Typo of preferred orientation (dirvction normal to base) Sourci- OperatorA...,. Operator B.

Operator Operator!) Random.

Do. I)". Do.

It seems probable that the bright nickel deposits of commerce are bright primarily because their grain size is less than that of the wave length of visible light.

when metallographically prepared sections are examined, hence their grain sizes are greater than that of the wave length of visible light.

The existence of a high degree of preferred orientation with the II IZI direction normal to the plane of the sample is a unique distinguishing characteristic of the semi-bright deposits of the present invention. The dark matte deposists from" the same chloride bath all showed random orientation. The light matte deposits from the same bath show the presenceof several types of preferred orientations at the same time; a mixture of [I00], lIIO] and [H2] when made under border-line conditions, and [I00] and [I I0] if the deposits were formed under conditions quite remote from the critical conditions for semi-bright deposits.

To demonstrate in a-quantitatlve manner the importance of the present invention in producing an easily polished plate, determinations were made of the amount of nickel removed in buliing nickel plates of the same initialthickness on both sides.

It should be emphasized that both the matte and semi-bright plates whose polishing characteristics differed so markedly were produced in the same bath-one operated outside the semibright range and one within it.

The present application is a division in part and a continuation in part of our copending United States application Serial No. 248,146 filed December 29, 1938.

Although the present invention has been de- The semi-bright depositsv of the present invention show a definite structure scribed in combination with certain preferred embodiments thereof, it is to be understood that modifications and variations may be made as those skilled in .the artwill-readily understand.

It is to be understood that such variations and modifications are to be considered within the purview of the specification and the scope of the appended claims.

We claim:

1. As a new article of manufacture, a composit article comprising a metallic core'and an electrodeposited protective nickelous layer at least 0.0001 inch thick having a semi-bright finish containing grains of a size greater than 0.0001 millimeter, said grains having preferred crystallographic orientation with the [H2] direction substantially normal to the surface of the core.

1 [H21 direction practically normal to the surface 2. As a new article of manufacture, a com- I posite article comprising a metallic core and a thick electrodeposited nickelous protective layer,

said nickelous protective layer being about 0.0036 inch to about 0.006 inch thick, containing grains of a size greater than 0.0001 millimeter, having preferred crystallographic orientation with the [I I2] direction substantially normal to the surface of said core and havingtwo maxima of light reflectively at about 20 to the normal of said layer. I

3. As a new article ofmanufacture, a composite article comprising a-metallic core and a thin electrodeposited nickelous protective layer,

said nickelous protective layer being at least 0.0001'inch and less than 0.0036 inch thick, having one maximum of light reflectivity, having a preferred crystallographic orientation with the plane of said article and having a grain size greater than about 0.0001 millimeter.

4. As a new article of manufacture, a composite article having a ferrous core and a directly electroplated firmly adherent electrodepos'ited layer substantially of nickel, said layer of nickel being at least 0.0001 inch thick, containing grains of a size greater than 0.0001 millimeter, having a semi-bright finish and having a preferred crystallographic orientation with the [I I2] direction practically normal to the surface of said article.

5. As a newarticle of manufacture, a composite article consisting of a ferrous core and anelectrodeposited outer layer, said outer layer being I about 0.0036 inch to about 0.006 inch thick comprising substantially electrodeposited nickel having a grain. size greater than the wave length of visible light and said electrodeposited nickel havaunnizw WESLEY.

JAY WILLIAM CAREY.

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