US3335027A - Nickel plating - Google Patents

Description

Aug. 8, 1967 5 g, JR" ET AL 3,335,027

' NICKEL PLATING Filed July 17, 1964 AP, mm EFFECT OF CARBON D/SULF/DE F o 20 CONCENTRATION o/v REACT/0N WITH 25mm /w (0014 AT 25% 1 I0 I 229% O 45 l0 I5 so 4' o CARBON D/SULF/DE, VOLUME 4o Fl 2 REACT/0N RA rEs 0F 25mm gm? /w (0024 WITH VARIOUS CONCENTRATIONS 3 OF CARBON D/SULF/DE AT 25 0 2o 5AM. H. PITTS Jr.

5 MILTON A. THOMPSON INVENTORS 5 IO :5 2o 25 BY TIME, MINUTES A T'TORNEY United States Patent 3,335,027 NICKEL PLATING Sam H. Pitts, Jr., Arvada, and Milton A. Thompson,

Boulder, Colo., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed July 17, 1964, Ser. No. 383,533 Claims. (Cl. 117-107.2)

ABSTRACT OF THE DISCLOSURE A nickel carbonyl plating process and resulting coating, wherein vapor of Ni(CO) and CS may provide coatings at room temperatures.

The present invention relates to nickel plating, and more particularly to a new and improved method of vapor plating with nickel carbonyl, and to the nickel coating produced thereby.

While the utilization of nickel carbonyl 'gas or vapor (actually nickel tetracarbonyl, Ni(CO) decomposition to form nickel coatings or platings possess a number of advantages over other methods, there have been objections to its employment. For example, in some instances its use is deemed unsatisfactory due to relatively high temperatures required to obtain decomposition, which temperatures may damage, destroy or otherwise objectionably affect the article to be plated. This temperature difli why has been reduced by mixing with the Ni(CO) a quantity of hydrogen monosulphide (-H S), which appreciably lowers the decomposition temperature. However, the decomposition temperature has still been excessive for some uses and it has been attempted to lower the Ni(CO) decomposition temperature by addition of oxygen or water vapor (0 or H O vapor) to the Ni(CO) -H S mixture, but this introduces the complication of requiring a third constituent and controlling means therefor and, further, platings or coatings formed by employing a mixture of H 8 and Ni(CO) have been found to lack optimum physical characteristics.

The present invention aims to overcome or minimize the above and other difficulties by providing a new vapor mixture, namely, Ni(CO) and carbon disulfide (CS and method to plate surfaces with highly improved coatings, all without the necessity of employing higher than ordinary room temperatures.

An object of the present invention is to provide improvements in nickel plating.

Another object of the invention is to provide improvements in nickel plating operative at room temperatures.

Another object of the invention is to provide nickel plating improvements which furnish enhanced nickel coatings.

Still another object of the invention is to provide improved nickel coatings of greater thickness.

A still further object of the invention is to provide a nickel coating method which is faster than previous methods and in which there is obtained more efiicient utilization of Ni(CO) A still further object of the present invention is to provide nickel coating improvements wherein accumulation of by-products has little or no objectionable effect.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiments about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

The embodiments of the invention illustrated or described are not intended to be exhaustive nor to limit the 3,335,027 Patented Aug. 8, 1967 invention to the precise forms disclosed, but are chosen in order to best explain the principles of the invention and their application in practical use to thereby enable others skilled in the art to best utilize the invention in various embodiments 'and modifications as are best adapted to the particular use contemplated.

In the accompanying drawing:

FIG. 1 is a largely diagrammatic representation of apparatus that may be employed to perform the process;

FIG. 2 is a graphical representation illustrating the effect of various CS concentrations in reaction with Ni-(CO) and FIG. 3 is a graphical representation illustrating re-action rates of Ni(CO) with various concentrations of CS Stated briefly, in investigating disadvantages of previous nickel carbonyl plating methods, compositions, and resulting platings it was discovered that a mixture of CS gas or vapor with Ni(CO) gas or vapor provided, at room temperatures (around 20 C. to 30 0.), rapid decomposition of Ni(CO) and very desirable nickel coatings on the surfaces of objects.

Any appropriate apparatus may be utilized in carrying out the process. By way of example, and with reference to FIG. 1, a bell jar or reaction vessel 2 may be sealed against an O-ring to a stainless steel base plate 4, which is in turn fitted with suitable conduit connections for evacuation of the vessel and for gas chargings thereinto. The reaction vessel may be clamped down against the ring or retained by external atmospheric pressure, as desired, dependent upon pressures within the vessel. A motor driven fan or magnetic electric stirrer (not shown) may be provided, if desired, to facilitate gas or vapor mixing in the vessel, and pressure measuring equipment such as a mercury manometer 5 may communicate with the interior of the vessel. An object or objects with surfaces to be plated is placed inside the vessel. After evacuation of air from the vessel by a vent conduit 7, CS may be admitted or charged therein via a conduit 8 and control valve from a supply flask or bottle 10 and thereafter the Ni(CO) gas through another conduit 11 and control valve from another flask or bottle 12. Because of the toxic nature of Ni(CO) care should be taken in handling it and hence it may be desired to enclose the entire system in a hood (not shown) which has appreciable air flow therethrough, and to connect an evacuation conduit 13 from the vessel to a heated (e.g., by an electrical heating tape 9) decomposition chamber 14 filled with Pyrex glass beads and a filter 15 filled with glass Wool, both the chamber and filter being interposed between the ves sel and the vessel evacuation pump 16 so that vapor leaving the vessel passes through the decomposition chamber and filter.

In decomposition, the mixtures of CS and Ni(CO).; appear to effect a pressure increase in the range of about one to 2.5 times that of the initial mixture. Hence the decomposition reaction may generally be observed by noting pressure changes within the vessel and graphically represented by plotting pressure against time. In some specialized case-s, e.-g., in the plating of finely divided particulate matter, the pressure may be about one times that of the Ni(CO) charge even though infrared analysis shows complete Ni(CO) conversion; usually however, on

'objects with less surface area, pressure increase is about conversion of Ni(CO) when 13 to 15 or higher volume percent CS is employed down to no reaction as the CS concentration reaches esentially zero (see FIG. 2). Higher CS concentrations are not detrimental to decomposition or conversion of Ni(CO) but do not appear to be particularly advantageous.

The quantity of Ni(CO) is not critical, but for safety reasons, limitations of equipment should be considered. The equipment should withstand a minimum pressure increase of about 2.5 times the Ni(CO) charge. In a bell jar system with only external atmospheric pressure holding down the jar or vessel, the maximum Ni(CO) charge should,'of course, be such that any subsequent internal pressure increases will be less than the external atmospheric pressure, in order that the vessel not be released.

Up to about 6% to 7% water vapor or 18% air, by volume, in the vreaction mixture appear to have no promoting effect on the decomposition reaction.

In FIG. 2 the curve illustrates the effect of CS concentrations upon the reaction of Ni(CO) with an initial pressure of 25 mm. of mercury, in about a one liter capacity reaction vessel and at a room temperature of about 25 C. The ordinate shows pressure increase, this being an indicator of conversion of Ni(CO) to nickel and CO. It may be noted that from zero CS concentration the curve slopes upwardly to level off at around 16% to 18% CS by volume, thus showing that adding greater amounts of CS does not appreciably increase the pressure, and hence the nickel yield. There is nothing critical in the 25 mm. Ni(CO) pressure referred to in connection with FIGS. 2 and 3, this being used merely as exemplary; the reaction and method work just as well at other convenient pressures.

FIG. 3 shows the effect of various concentrations of CS on the reaction rate of Ni(CO) initial pressure of the latter being 25 mm. of mercury, as in FIG. 2.

When employing Ni(CO) at anywhere from around 20 mm. to 50 mm. of mercury in an evacuated vessel and a concentration of CS around 13% to 15% by volume, infrared spectrographic analyses of residual gas indicates that essentially all the CS is consumed and that there is obtained about a 98% to 100% conversion of Ni(CO) By way of comparison, based upon observed pressure change and the theoretical 1 to 4 volume increase for decomposition of Ni(CO) and with H S reactions employing 100 mm. of Ni(CO)., and reaction times two to three times longer than for the CS reactions, H S with Ni(CO) has been found to give only about 2% to conversion.

Another major improvement by use of CS with Ni(CO) as compared with H 8 is that with the former, accumulation of by-products, e.g., CO, has no appreciable objectionable elfect on the reaction; the reaction goes to completion without hindrance, whereas with the latter, accumulation of CO is a reaction-governing step that causes a retardation of plating. With CS -Ni(CO) vapor, the nickel formation occurs rapidly, the majority of the reaction occurring within as little as one to four minutes.

Nickel coatings or platings may be built up by admitting successive quantities or passes of CS and Ni(CO) to a reaction vessel until a desired cumulative thickness is obtained on an object. It has been found, by

interferometric thickness measurements, that with the present improvement, plating thicknesses three to four times greater are obtained by use of CS as compared with use of H 8, a single layer thickness from the CS mixture reaction lying in the range of 1700 to 2100 Angstroms using 25 mm. Ni(CO) in a 1-liter system, as compared With only from about 400 to 600 Angstroms obtained by the H 8 mixture.

With the CS mixture, eight to ten layers of nickel may be successively applied without evidence of peeling, whereas with the H 8 mixture the nickel has been found brittle, with cracking and peeling occurring after deposit of only two or three nickel layers. Metallic plating from the CS reaction analyses about 80% to 82% nickel, the balance being made up of sulphur, carbon, hydrogen, and oxygen.

The mechanism of the reaction between the CS and Ni(CO) in a vapor mixture is not wholly understood; but it is currently thought that a new complex is formed. It does not appear to be entirely of catalytic nature, but whatever it may be the nickel pl-atings and results achieved by mixtures of CS and Ni(CO) vapors are greatly superior to those resulting from previously known mixtures.

It will be seen that the present invention provides a new and improved method of obtaining nickel coatings or films, as well as greatly improved nickel coatings themselves. The method is relatively simple, rapid, makes more eflicient use of Ni(CO) than heretofore, and may be effected at room temperatures.

As various changes may be made in the form, construction and arrangement of the parts herein without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matter herein is to be interpreted as illustrative and not in a limiting sense.

We claim:

1. The method of nickel plating a surface of an object comprising exposing said surface to a vapor of Ni(CO) and CS 2. The method as claimed in claim 1, wherein temperature of vapor is from about 20 C. to about 30 C.

3. The method as claimed in claim 1, wherein said CS comprises about 13% to 15% by volume of said vapor.

4. The method as claimed in claim 1, wherein said Ni(CO) is at an initial pressure of from about 20 to 50 millimeters of mercury.

5. An improved object having a surface coated with a plurality of layers of nickel by the process of claim 1, and wherein said layers are of enhanced adherence and resistant to peeling and cracking.

References Cited UNITED STATES PATENTS 2,798,051 7/1957 Bicek 117107.2 X 2,881,094 4/1959 Hoover 117l07.2 2,886,468 5/1959 Hoover et al. 117107.2 2,921,871 1/1960 Cummins 117107.2 X 3,086,881 4/1963 Jenkin l17l07.2 X

ALFRED L. LEAVITT, Primary Examiner. A. GOLIAN, Assistant Examiner.

Claims (1)

1. THE METHOD OF NICKEL PLATING A SURFACE OF AN OBJECT COMPRISING EXPOSING SAID SURFACE TO A VAPOR OF NI(CO)4 AND CS2.

Images