US2371123A - Electrolytic deposition - Google Patents

Description

March 13, 1945. P. AMUNDSEN I ELECTROLYTIC DEPOSITION OF NICKEL Filed Oct. 23, 1959 BY 9 W M 8 I Tom/Era Patented Mar. 13,1945 2,371,123

ELECTROLYTIC DEPOSITION .OF NICKEL Paul L. Amundsen, Detroit, Mich., assignor to Parker-Wolverine Company, Detroit, Micln, a corporation of Michigan Application October 23, 1939, Serial No. 300,709

3 Claims. (01. 204-49) This invention relates to a method of nickel plating, and more particularly relates to a method of electrolytically depositing nickel at relativelyhigh current densities which makes possible filtering devices are not only expensive but many of them have an extremely short life when used in extremely acid solutions.

Cast nickel, such as is conventionally used for nickel anodea-corrodes' far better than sheets of the utilization of an anode structure of electro 5 electrolytic nickel under ordinary plating condilr't e ckel. tions, but the corrosion of even the best anodes Numerous attempts have been made in the past is far from satisfactory and it is quite convento electrolytically deposit nickel employing an antional to use bags surrounding each of the anodes .ode of electrolytic nickel. Electrolytic nickel is in order to prevent as far as possible the deleconsiderablyfreer from impurities than cast nickterious effects resulting from the release of loose el such as is commonly employed as an anode and nickel from the anode during la Pl ing r it is also very much cheaper. Consequently. in tion. plating operations where substantial amounts of The. present invention has for its object the nickel are consumed, material savings may be provision of a method of electrolytically depositeffected by use of electrolytic nickel as an anode l6 s n e pl yi a bath w h m y. f if such anode were wholly satisfactory in all sired, be extremely acid having a cathode ourother respects. rent density which, if desired, may be extremely Electrolytic nickel has heretofore proven highly high and at the same time emp a anode nsatisfactory when employed as an anode in an of electrolytic nickel without at the same time enelectro-plating bath and the unsatisfactory na- 2 countering the deleteriousefiects of unsatisfacture of the results normally obtained is materitory corrosion mentioned above. ally increased as the current density at which ,Still further, the invention contemplates a the plating operationis conducted is increased. a method of electrolytically depositing nickel Obviously large scale plating operations. where which inherently results not only in a substantial very substantial quantities of nickel are used, are saving in the cost of the anode nickel, but one usually carried on at very high current densities, which results in a cathode-deposit which is more and, consequently, in the particular, plating opnearly pure, less porous and, therefore, more conerations where large amounts of nickel are berosion resistant, than deposits obtained by meth ing consumed, and where the savings by the use ods of electrolytically depositing nickel hereto of electrolytic nickel are most important, elecfore known. trolytic nickel anodes may be expected to corrode While it will be readily understood by reference in a most unsatisfactory manner. to the'following description and the accompany- When electrolytic nickel is employed as an aning drawing that substantial departures and ode at relatively high current density, that is in variations may be made in the selection of apexcess of 20 amperes per square 001; of anode paratus to practice the method, the apparatussurface, the surface of electrolytic nickel corrodes and description of the method following are here unevenly creating a sponge-like structure which in specifically d rib d as m ly illustrative o results in the release of relatively large fragments one embodiment of the invention which has been or particles 'of loose nickel. Some of these parfound particularly satisfactory for commercial ticles drop to the bottom of the plating tank' 40 plating operations. forming a sludge and resulting in considerable Referring to the drawing, the figure shown is loss of nickel. Other particles are carried over a more or less di ramm Sectional w tekeii bodily to the cathode and produce a roughnessof transversely through a conventional plating tank the electrolytic deposit on the article being illustrating suitable apparatus for practicing the plated. This latter efiect is particularly undesirnovel method described below. able in decorative plating operations and partic'u- In order to simplify the description of the presl y so in plating operations employing addient invention, the term electrolytic nickel as tion agents intended to producea bright, lustrous used n e p f cation and l ms h r in is cathode deposit, V intended to refer to substantially pure nickel The undesirable effects of this type, of corrosion which has been electrolyti lly refined and which. may in some cases be partially reduced by placafter electrodeposition, has not been subject to ing the anodes in bags or by the employment of any thermal "treatment, that is, has not been other filtering devices disposed in the bath bemelted. a tween the anode and the cathode, However, such The k 5 i8 015 em r i ml 68 is substantially filled with a solution 2 described in detail below. The anodes employed comprise baskets or containers 3 of conventional construction which may be formed of .wire mesh in which anode structure as a whole.

The bags 6 are substantially filled with small sections of electrolytic sheet nickel 8 which are packed against the surface of the sheet 1 and completely surrounded by the bag 8. The work 10 to be plated is hung on conventional plating racks II which are supported by means of a hook l2 on a rod is which rod forms the opposite sideof the plating circuit.

Conventional commercial nickel plating operations are generally carried on at cathode current densities of less than 80 to 90 amperes per square foot. It is obvious that in commercial plating operations, it is extremely desirable to maintain relatively high cathode current densi- "ties in order to reduce as far as is reasonably possible the plating'time, that is, to deposit as much nickel on the work as is reasonably possible within as short a time as possible. Consequently, many commercial nickel plating operations are carried on at current densities in excess of 50 amperes per square foot and it is generally understood that it is desirable to maintain vision of an electrolytic anode structure having an extremely large surface area with respect to the area of the cathode employed in the plating operation whereby commercial plating operations can be carried on employing relatively high cathode. current densities and at the same time maintaining the average current density on the anode the current density in excess of 20 amperes per square foot on the work being plated.

It will be obvious that in the event the a egate areaof the anode which is exposed to the a solution is substantially equal to the aggregate area of the work to which the plating is applied,

the anode current density will be substantially equal to the cathode current density and in the eventit is necessary to maintain a current density of 20 amperes per square foot or higher on the work being plated, the anode current density will also be in excess of 20 amperes per square foot.

In the past it has been appreciated that electrolytic nickel does not corrode satisfactorily and knowledge of this fact has resulted in the develsome of which drops into the bottom of, the tank to form a sludge and some ofwhich is'carried to the cathode causing roughness in the finished deposit.

sufilciently low to produce extremely satisfactory corrosion of the anode.

As is illustrated in the drawing. the anodes comprise a sheet of electrolytic nickel I extending from top to bottom of the basket 3 and extending throughout substantially the entire transverse width of the basket. This sheet of nickel is preferably placed on the side of the basket away from the cathode in order that the sheet itself will be exposed to current density even lower than the current density to which the fragments of nickel I are exposed. The bag 6 is filled with fragments of electrolytic nickel,

satisfactory results having been obtained by uti-' llzation of conventional nickel squares. These nickel squares are furnished to the trade in suitable sizes and thicknesses and extremely satisfactory results have been obtained by employing squares approximately one inch square and about one-quarter inch thick. Inany event, however, the fragments of nickel making up the bulk of the anode should be sufilciently small and numerous so that the aggregate surface area of the anode structure as a whole exposed to the elec-' trolyte will be many times the aggregate surface area of the work being plated.

Manifestly, it is not absolutely essential that the rubber covered baskets I be employed in order to practice the method herein described. The nickel fragments might obviously be piled in a heap either directly on the bottom. of the tank or in any other suitable receptacle so long as these 10 fragments collectively serve to constitute an anode structure having an aggregate eifective area many times the area of the cathode. v

In the above description, and in the description that follows, numerous references are made to the cathode current density to whichthev work being plated is exposed and also reference is made to the anode current density,- that is, the

current density towhich the surface of the anode structure is exposed. It will be readily sppreciated that in both the case of the anode and the cathode, the current density will not be absolutely uniform throughout the entire exposed surface of each'member but, on the other hand.

the current densitywill be relatively high on some It hasbeen found, however, that "extremely satisfactory corrosion of electrolytic nickel may be obtainedif the current density at which the corrosion takes place is extremely low, preferably less than three amp res p r square foot.

In general, it may be stated that it has been found that the lower the current density at which electrolytic nickel is corroded, the more 'satisfactory is thenature of-the corrosion. The present invention, therefore, contemplatesthe proportions and relatively low on other portions and for the purposes of the present description. the terms anode current density" and "cathode current density" are intended-to define the average anode current density or the average cathode :current density as the case may be. It will be .further appreciated that in this connection that good plating practice dictates that the anode and the cathode be formed and disposed to each other in such a way as to maintain the current density on the various portions of each member as near the average current density as is possible within reasonable limitations.

The particular solution-of the bath 2 may be least one-tenth normal and preferably between one-third and one-hall normal.

One, form of bath which has been found satisfactory for use in practicing the present method may be constituted as follows:

- Grams per liter Nickel chloride 40 Nickel sulphate 300 Boric acid 30 To the above may be added any suitable organic or inorganic brightening agents as may be desired in order to improve the luster of the cathode deposit.

The pH of the bath may be regulated within any reasonable limits and, similarly, the temperature at which the plating operation is conducted may be varied.

It has been observed that nascent chlorine is formed during corrosion in accordance with the methods described above and that this nascent chlorine-to a large extent dissolves in the bath.

It is recognized that chlorine acts as an effective anti-pitting and purifying agent in nickel plating solutions and, therefore, it is' believed that the presence of this chlorine adjacent the anode structure contributes materially to the beneficial results obtained by use or the method herein described.

In supplying current to the bath, sumcient current is preferably supplied in order that the cathode current density will be maintained above twenty amperes per square foot and preferably fifty to eighty amperes per square foot. As has been described above, the anode structure employed is so constructed and arranged with respect to the cathode that the anode current density employed when plating even at a cathode current density of eighty amperes per square foot will. under no circumstances exceed three amperes per foot and preferably be maintained in the neighborhood of one ampere per square foot or less.

It will be readily appreciated that the specific embodiment of the invention described'above is merely illustrative oi one form which the invention may take and substantial departures from v the above described specific method may be made 5 bath.

falling within the scope of the invention as set I forth in the following claims.

rent density thereon to below about three amperes per square foot.

2. The method of electrolytically depositing nickel which comprises passing suflicient electric current tron an anode to a cathode in an aqueous bath to produce an average cathode current density in excess of twenty amperes per square 1 foot, maintaining in solution in said bath a con.- centration oi nickel chloride of at least one-tenth normal, said bath comprising essentially nickel sulphate and boric acid in addition to said nickel chloride, and maintaining in said bath an anode of electrolytic nickel in divided form of suflicient effective surface area many times the area of the cathode to-produce thereon an anode current density of not more than about three amperes per square foot.

3. The method of electrolytically depositing nickel which comprises passing electric current from an anode to a cathode in an aqueous bath containing in solution therein nickel chloride in a concentration in excess of one-tenth normal,

said electric current being sufficiently strong to create upon said cathode an average current density of at least twenty amperes persquare foot, maintaining in said bath an anode structure of electrolytic nickel having a surfacearea at least ten times the area of the cathode in said PAUL L. AMUNDSEN.

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