September, 1954 issue of Plating
Nickel Plating From the Sulfamate Bath
Presented at the Forty-First Annual Convention of the American Electroplaters’ Society,
July 13, 1954.
Richard C. Barrett, Barrett Chemical Products Company, Shelton, Connecticut.
Nickel plating from sulfamate solutions was first announced in 1938 by Piontellil and Cambri in Italy. Although Piontelli and his co-workers2, 3, 4, 5, 6, 7, 8, 9, 10 continued to report regularly upon their progress of plating from sulfamate solutions during the subsequent ten years, the bulk of their research was confined to the development of bath formulae for plating or electrowinning of lead.
Co-incidental with the announcement11 of
a commercial source of production of sulfamic acid in this country during
the late 1930’s, further interest was aroused domestically and several
descriptions only of laboratory interest were published by Choguill,12 Mathers,13 and Forney.14 In 1940 a patent was issued to Cupery15 covering the plating of copper, nickel, and lead from sulfamate electrolytes.
During the ensuing ten years after the granting of the Cupery patent, no further published data- upon nickel plating from sulfamate baths appeared on record until 1950 when Barrett16 described a bath introduced to the electrotype industry late in 1949. As far as is known, this event marked the first reduction to practice in this country of any sulfamate plating bath for the electrodeposition of nickel upon a commercial scale.
Within the five-year period following 1949, more than 60 commercial sulfamate nickel plating baths were installed, comprising more than 50,000 gallons of solution. Such magnitude has made possible the collection of a large backlog of operating performance data, some of which are reported in this paper.
This new activity also encouraged further papers in the technical journals on sulfamate nickel plating as evidenced by the published discussions of Peters,17 Gurnham,18 and Barrett.19 Recently, Diggin20 presented a paper before the Fourth International Conference on Electrodeposition and Metal Finishing at London, in which he describes a nickel sulfamate-chloride bath.
The few references in the literature to sulfamate plating baths, the meager knowledge of the properties of the relatively new sulfamic acid, and the early high cost of the acid combined with a short supply of nickel during the years of World War II and continuing thereafter discouraged active-interest in any new nickel plating process.
Because of many desirable physical properties of nickel deposits plated from sulfamate baths, particularly with reference to low internal stress and the significance of stress upon premature fatigue failure, the aircraft industry as well as others are now actively evaluating the sulfamate nickel plating bath. It is predicted that sulfamate nickel plating will eventually be as common as the familiar Watts nickel.
DESCRIPTION OF SOLUTIONS
Any description of sulfamate plating baths must of necessity start with a description of the unique properties of sulfamic acid and its salts.
Sulfamic acid is a white crystalline inorganic solid, nonhygroscopic and nonvolatile. It may be conveniently handled and stored. In strength and chemical structure it is very similar to sulfuric acid.11
and maintenance has been reduced to a minimum
in the sulfamate nickel plating bath. Because
of the simplicity of the bath composition, in
which the sole nickel salt comprises more than
90 percent of the dissolved solids, routine analysis
need be no more complicated than the taking of
a hydrometer reading. The accompanying chart
(Fig. 2) indicates the relationship between specific
gravity or degrees Baumé at 70° F
and nickel metal concentration at specified boric
Boric acid control is not critical and it is sufficient to analyze for this constituent only at monthly intervals, using standard analytical methods for the determination of boric acid. The pH should be checked periodically, preferably daily, with any good color comparator or electric pH meter. In normal operation, pH tends to rise slowly with use and may be adjusted quickly with small additions of sulfamic acid.
sulfamate nickel plating bath has a very
low sensitivity to contamination, in many
instances tolerating much higher amounts
of metallic and organic impurities than other
conventional nickel plating baths. Good engineering
practice is to provide for solution circulation
with continuous electrolytic purification
at low current density either in compartmented
tanks or separate cells, in lieu of which
to ”dummy” periodically during
shut-down time. In applications involving
extra heavy deposits, continuous filtration
is advised. Activated carbon should not be
used as it will remove the organic wetting
agent or stress reducer (SNSR). Severe cases
of organic pollution can be removed by the
usual activated carbon treatment along with
subsequent replenishment of the addition
nickel plating solutions can be used
with any equipment normally used with
high chloride Watts’ nickel solutions,
providing however that lead be excluded
from contact with the solution. Lead
sulfamate is very soluble, and lead must
not, therefore, be used for heating coils
and thermostat control bulbs.
Anodes must be of 99 percent plus purity and rolled depolarized or electrolytic sheet and should be bagged, preferably with Vinyon type bags. Anode corrosion is 100 percent without the need for chloride-ion to promote corrosion. Although other investigators of nickel sulfamate plating solutions have advocated use of chlorides in their bath composition, it is considered highly undesirable because chlorides promote excessively stressed deposits.
STRESS AND ITS CONTROL
Many- industries in recent years have used electroplating processes as engineering tools to solve production problems rather than merely as a means to obtaining a decorative finish. A few examples are: electroforming of complicated shapes (wave guides); salvage of worn or mis-machined parts by heavy build-up of deposits; hard cladding of soft metals for abrasion resistance; manufacture of phonograph record stampers and printing plates; reproduction of surfaces such as human skin texture in prosthetics for artificial limbs and-for grain of simulated leathers; electroforming of denture models; production of finely perforated screen cloth; heavy cladding of pipe, chemical reaction vessels, and storage tanks. The literature is replete with references to such engineered applications of heavy nickel plating.
has been common knowledge for years that in
general nickel deposits have been plagued with
high values of internal tensile stress which
have been recorded as much as 60,000 psi from
all chloride and high chloride Watts’ baths.
Many authors have discussed in detail the importance of stress effects upon the quality of electroplating and within recent years have described several instruments for accurately measuring the stress of a deposit. 22, 23, 24, 25, 26 Excessively high stresses can cause peeling, cracking, crazing, warping, blistering, distortion, shrinkage, and even complete destruction and failure of plated metals either as structural units or as protective coatings.
only do highly tensile stressed plated
coatings fail within themselves, but they
also induce premature fatigue failure of
the underlying base metal upon which they
are laid down. The aspects of fatigue failure
caused by electroplating has become a major
problem with the aircraft industry where
premature failures cannot be tolerated
at any cost. These same stresses can also
lead to the phenomenon known as ”stress corrosion” which
accelerates corrosion failures of many
articles having decorative plate such as
automobile bumpers and bumper guards.
Early in 1947 the author initiated research to discover a nickel plating bath which might produce nickel deposits low in stress without the use of certain organic addition agents. Hundreds of stress measurements were made on over 1,000 different nickel plating baths during a two-year period. The only bath which showed a pronounced decrease in stress of all those tested was the basic sulfamate nickel formula.
Plotted curves showing the relation of stress to current density are shown in accompanying graphs (Figs. 3, 4 and 5) and indicate the true stress of deposits made both from the basic sulfamate nickel bath as well as baths containing organic stress reducing agents (SNSR). The dashed line curve in Fig. 3 is replotted from data given by Diggin20 and is included for purposes of comparing sulfamate baths operating with chlorides as opposed to those without chlorides.
All stress measurements were made with a Brenner-Senderoff Spiral Contractometer, an instrument admirably suited to accurate checking upon values of stress in plated coatings and which has been thoroughly described previously.27 Because stress varies with thickness, all measurements were taken at the uniform plated thickness of 0.0006 inch as determined by ampere minutes of plating time and checked for accuracy periodically with Magne-gage readings.
Variations in temperature, pH, and nickel metal content of the bath caused corresponding variations in recorded stress values. Except for the extremes of minimum and maximum, the stress variations were insignificant or within the experimental error of measurement.
In general the effects of all of the bath variables upon stress can be summarized in the following manner:
has slight minimum at pH 4.0. Increases
slowly at lower pH values and sharply
at values above 6.0.
content—No appreciable effect
decreases with increase of
bath temperature and increases
with drop in temperature, usually
not more than a total of plus
or minus 5,000 psi for the
rises sharply and linearly
with increasing chloride
3,000 psi for each 10 percent
increase of chloride as
with increase of current
reduces the rate
of increase of
stress with increase
of current density.
the range of
The stress reducer (SNSR) used in the sulfamate nickel bath to produce compressive stressed deposits is completely stable over long periods of bath operation and is lost only gradually through drag-out and codeposition. There being no chemical analytical control for this material, it is necessary to control the effects of this addition agent with a stress measuring instrument.
HIGH CURRENT DENSITY OPERATION AT LOW TEMPERATURE
In certain types of electroforming operations, it is necessary to plate upon temperature sensitive materials such as wax, plastic, and low fusing point alloys, and in most cases the base material must be removed later by melting out, preferably in hot water or hot ail.
Heretofore, nickel plating bath formulae suitable for plating at room- temperatures and having reasonably good stress characteristics have been those containing ammonium salts and, because of high pH operation, have been limited to current densities usually under 15 asf.
sulfamate nickel bath can be successfully
used at maximum current densities of 60-75
asf at temperatures ranging from 80-100° F,
giving approximately a fourfold or better
increase in speed. Previously cited references16, 17, 18,19 have indicated how this higher speed at low temperatures helped immeasurably to correct production bottlenecks in the electrotyping industry.
it is well known that hardness of nickel
deposits increase with decreased bath
operating temperature. Sulfamate nickel
baths can be operated as hard nickel
baths at 90-100° F with but a slight
sacrifice in limiting current density.
IMPROVEMENT OF FATIGUE STRENGTH OF UNDERLYING BASE METAL
It has been demonstrated that plated
coatings of tensile stress cause premature
fatigue failures in the base metals upon the
plated coating’s failure from stress
cracking.28, 29 Since the majority of fatigue failures originate at the surface, any weakness of a surface condition can be detrimental to life under fatigue conditions.
The aircraft industry in particular is very concerned with effects of plated coatings upon reduction of fatigue strength of steel and aluminum alloys.
Unpublished data have indicated that Watts nickel plating baths giving deposits with high tensile stress can cause as much as 46 percent reduction in fatigue strength of underlying steel, whereas nickel deposited in compression causes no reduction and in some instances slight (5-7 percent) gains in fatigue strength.
Almen,29 has shown conclusively that fatigue fractures cannot originate and cracks cannot propagate in compressively stressed material and that tensile stressed surfaces as thin as 0.0003 inch can be seriously considered a threat to early failure of a part.
Sulfamate nickel plating has been tested thoroughly over a period of two years by two major aircraft engine producers and has been found acceptable for plating parts without endangering their fatigue resistance. In certain cases, heavy nickel plate under compression has been used to increase materially fatigue life by protection of surfaces from nicks, scratches, or dents which might rapidly lead to fatigue failure. Two examples of such application is protection of the leading edges of propeller blades and jet engine compressor blades from small stone abrasions with heavy cladding of hard nickel under 2,500,000 psi compressive stress.
Deposits from sulfamate nickel plating baths have in general a very
fine grain structure, and as a result the deposits are very smooth and ductile
and have a slight sheen in appearance. The color is much whiter than any deposits
from baths containing chlorides and indicates a higher purity of nickel without
Tensile strengths range from
60,000 psi to 130,000 psi, depending upon the conditions under which
a bath is operated. Correspondingly,
ductility ranges from 30 percent elongation in 2 inches to a low of 6 percent
elongation at a hardness of 550VHN.
Hardness can be controlled
in the range of 200 VHN to 550 VHN with reproducibility by use of recommended
agents and shifting of operating conditions.
High pH and low temperature operation of the basic bath will produce the
hardest deposits without appreciable stress.
A complete resume with
collected data will be made the subject of a later paper upon the
physical properties of sulfamate nickel deposits.
Sulfamate nickel deposited
under compressive stress and with certain addition agents will have
very good levelling power. Brush surface
have indicated a reduction in surface roughness from 120 microinches
RMS to 7 microinches RMS for a deposit 0.0015 inches thick. The need
smooth, relatively hard nickel coating is reduced considerably by such
In conclusion, the author wishes to acknowledge and thank the
many people who have helped to contribute some of the data used in
this paper: Mr.
and Mr. Robert Ruddock for tensile strength, elongation, and other
physical property measurements; Mr. I. Friedman of Curtiss-Wright
for stress data; Mr. Moeller of Pratt & Whitney aircraft
for fatigue measurements; and the E. I. DuPont de Nemours & Co:
for use of their charts and data on sulfamic acid.
- L. Cambri & R.
Piontelli, Rend. reale ist. Lamb 72, 128 (1938).
- L. Cambri & R.
Piontelli, Ital. patent 268,824, (1938).
- R. Piontelli, Chimico e
industrla (Milan), 22, 65 (1940).
- R. Piontelli, Ital. patents
381,860 (1940); 388,932 (1941).
- R. Piontelli, Ric. Sci.
Ital., 11, 246 (1940).
- R. Piontelli, ibid. 12,
- R. Piontelli & G.
F. Patuzzi, Metallurgia Italiana, 34, 215 (1942).
- R. Piontelli, Korr.
Metallsch., 19,110 (1943).
- R. Piontelli, 3rd International
Conference on Electrodeposition, London, 1947.
- R. Piontelli, J. Electrochem.
Soc., 94, 106 (1948).
- M. E. Cupery, Ind. Eng.
Chem. 30, 320 (1938).
- H. S. Chogtull, C. A.,
34, 5351 (1940); Trans. Kansas Acad.
42, 213 (1939).
- F. C. Mathers & R.
B. Forney, Trans. Elect. Chem.
Soc., 78, 420 (1940).
- R. B.
Forney & F. C. Mathers, Trans. Elect. Chem.
Soc., 76, 371 (1939).
- M. E.
Cupery, U. S. Patent 2,318,592 (May 11, 1943).
- R. C. Barrett,
Electrotypers & Stereotypers Bull., 36, 55 (1950).
- E. I. Peters,
ibid., 38, 96 (1952). -
- C. F. Gurnham, Product
FinishinB, 18, 54
- R. C. Barrett,
Electrotypers & Stereotypers
Mag., June 1954.
- M. B. Diggin,
- E. Divers & T.
Haga, J. Chem. Soc.,
69, 1634-54 (1896).
- G. G. Stoney, Proc.
Royal Soc. (London)
A82, 172 (1909)-.
- B. Martin, Proc.
Amer. Ej lectroplaters
p. 206 (1944).
Phillips & F. L. Clifton, Proc. Amer. Electroplaters’ Soc.,
34, 97 (1947).
G. Soderberg & A. K. Graham, ibid., 74 (1947).
- A. Brenner & S.
Senderoff, J. Research Bur. Stds., 42, 89 (1949).
- A. Brenner & S.
Senderoff, Proc. Amer. Electroplaters Soc., 35, 53 (1948).
J. Love, Monograph
1403, Inst. of Metals
Monograph & Report
MR. EDWIN R. BOWERMAN
(Sylvania Electric Products, Flushing, N.- Y.): Can electroformed
printing plates be prepared consistently
of 625 Vickers
plus or minus 50? If so, what modification of bath would
MR. BARRETT: 625 Vickers is
a little high. We can consistently hold 550 to 575 Vickers. The modifications
necessary to achieve
use of an organic addition agent that is perfectly stable
and a change in the operating
conditions. We generally shift to a high pH operating range
and low temperature.
MR. ARMAND G. CHARRON (Texas
Instruments, Inc., Dallas, Texas): In plating aluminum parts, do you
put this sulfamate
is the conventional method of plating aluminum used?
BARRETT: We use the conventional method of plating, using a zincate
treatment. We do know of -one particular
where laying sulfamate nickel directly on aluminum
without zincate is used.
MR. CHARRON: Do you think
you could also use this one-step method when either vapor blast or
MR. BARRETT: In the particular
case mentioned, a vapor or mechanical blast is used. The interlocking
condition helps to
keep the nickel in
place as well as the compressive stress of the
which makes it lay down as
MR. CHARRON: Do you feel it
MR. BARRETT: It is, in this
particular case, but that is only a thin coating. I would not recommend
MR. A. D. SQUITERO (Hanson-Van
Winkle-Munning Company, Matawan, N. J.): Was the chloride
by the dotted line,
primarily on the tensile
MR. BARRETT: Yes.
Then-you feel that the additions of chloride will always produce
MR. BARRETT: Very definitely.
SQUITERO: Can your process continuously produce a deposit in compressive
in the presence
MR. BARRETT: Only in
the presence of organic addition agents. Without
3000 psi for each
10 percent increase
of chloride content.
What are your objections to the use of chlorides?
MR. BARRETT: Chlorides
raise the tensile stress of nickel deposits
This is approximately
psi for each
10 percent increase of chloride
as nickel chloride.
WEISMAN (Curtiss Wright Corporation, Caldwell,
You showed a slide-near
the end of your lecture
inducer blades. A great many
requests have been made by
department to use various
aluminum and magnesium
in order to reduce
wear on certain parts in
our propeller assemblies.
In contacting men who were
influential in developing
and applying the
methods for plating
and aluminum, recommendations
coatings of chromium or
nickel should not be plated on parts
used in high
stress applications. You
mentioned that there
was an application
of approximately 0.015
inch of nickel, which is
coating. We have been
reluctant to suggest
the plating of thick nickel
or chromium coatings on
or magnesium parts
for the reason
plating separation from
parts subjected to operation under
conditions of stress.
would like to have your
opinion on this point.
MR. BARRETT: If nickel
is laid down in compressive
a crack can
propagate in the compressive
fact. To protect the
sensitive surfaces of some metals
hard nickel coatings.
fact, one aircraft
company has put as much
as 0.030 inch of hard
nickel on the leading
increased the life
span of those
to 400 hours.
Is it true that the
magnesium will represent
other words, if you
have a zinc immersion method
for preparing your
metals, is it true that the final
strength will be governed
by the strength of
that particular intermediate
Yes, that would definitely determine
are bake tested in
an oven for an
hour at approximately 250° to
WEISMAN: Have you
had any experience
in the use
the plating of
MR. A. ADAMS (Armalite
now in effect
on bright nickel
Have you tried any
If so, how
did the results
to Watts type
bright nickel solution?
MR. BARRETT: Our laboratory has developed a bright nickel sulfamate bath with compressive stress that will be announced very soon. It is more stable than a Watts type solution.