Note: Descriptions are shown in the official language in which they were submitted.
, CA 02236933 1998-06-10
ELECTROPLATING OF LOW-STRESS NICKEL
- IR 3489 NP
BACKGROUND OF THE INVENTION
THIS APPLICATION C~AIMS THE BENEFIT OF UNITED STATES
PROVISIONAL APPLICATIC)N NUMBER 60/050,140 FILED ON June 1~,
1 997.
Field of Invention
The field of the invention relates to a bath for electroplating low-stress
nickel to conductive substrates and processes ~ltili7ing such baths.
Description of the Prior Art
Many industries provide corrosion resistance, decorative finishes and
electroformed coatings to conductive substrates by continuous or batch plating
the substrates with nickel in an electroplating coating bath.
Nickel s-llf~m~te baths are generally used when a low stress nickel
coating is required, such as in e lectroforming applications, or where the nickel
deposit will be subjected to exl:ernal stress. Nickel slllf~m~te solutions are
prefeITed over nickel sulfate solutions because (a) the mechanical properties ofthe slllf~m~te produced coating are superior to those formed from sulfate
solutions, (b) high rates of deposition are possible from the slllf:~m~te solution,
and (c) the deposit quality is less affected by variations in pH and current density.
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However, several issues need to be addressed when a nickel sul f~m~te bath is
used.
A typical nickel slllf~m~te solution contains nickel slllf~m~te (400 - 650
g/l), nickel chloride (5 - 20 gll) and boric acid (30 - 40 g/l). The operating pH is
between 3.5 - 4.5 and the temperature may vary from 35 - 50~C. Soluble nickel
s anodes are used to replenish the nickel which is plated on the cathode during
electrolysis. Current density varies from 0.5 - 30 A/dm2.
One of the issues with lhe use of a nickel sulfamate bath is stability of
the s1llf~m:~te ion.
The slllf~m~te ion is stable in neutral or slightly alkaline solution even at
elevated temperature. However, because of nickel hydroxide precipitation, these
solutions are not used at a pH greater than 5.
Hydrolysis of the slllf~m,3te ion may be a problem. The hydrolysis of
slllf~m~te is generally characterized by the formation of ammonium ions and a
bisulfa~te or sulfate anion:
H2NSO3-+H3O+ ~ NH4+ + HSO4-
The sulf:~m~te hydrolysis reaction has been investigated and has been
founcl to be at an increased rate at greater hydrogen ion concentrations (e.g.,
lower pHs). These investigators also found the slllf~m~te hydrolysis reaction
increases with an increase in temperature of the electrolyte; thus nickel
2 o sl~lf~m:~te solutions are commonly operated at lower temperatures than Watts
type nickel plating solution.
The slllf~m~te ion also decomposes at the anode, for example, at
insoluble anodes such as platinum and at passive nickel oxide electrodes. The
decomposition of sulfamate aE~pearS to produce several intermediates such as
2 5 sulfite, dithionate, azodisulfonate and another unknown species which may
effec-t the quality of the electrodeposited coating.
It would be desirable to have baths other than nickel slllf~m~te from
which to electrodeposit nickel.
- 2 -
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When choosing a nickel solution from which to deposit a layer of nickel
it is important to consider the resultant internal stress of the nickel coating.Stresses in nickel deposits range from -15,000 PSI (compressive) to about
+1 00,l~00 PSI (tensile). A high tensile stress may lead to cracking of the nickel
deposit particularly if the nickel is subjected to mechanical deforrnation (stresses
and strains) or elevated temper,ltures. Nickel electroforms such as those
produced from nickel sl-lf~m~te solutions may have warpage or change
dimensions when the substrate is removed if the nickel is in a state of tensile
stress. High tensile stresses may also lead to lower fatigue life of steels and
alllminllm alloys. Investigators have shown a twenty-two percent reduction in
0 the fatigue life of high strength~ steels if the nickel is deposited in a compressive
state but a fifty-nine percent reduction in fatigue life is the nickel is tensile
stressed. Similarly, aluminum alloys plated with a nickel in a tensile stress
exhibited a fifty-five percent reduction in fatigue life but only a ten percent
reduction if the nickel was compressively stressed.
Organic additives are commonly added to nickel solutions to reduce the
tensile stress of the deposits. ~rhe composition and concentration of the stressredùcers is dependent upon the nature of the nickel electrolyte (e.g., nickel
sulfate or nickel slllf~m~te). The effects of organic stress reducers on the
internal stress of nickel deposits from a nickel sulfate solution has been
examined. Additives which contain sulfur such as saccharin, naphthalene-1,5-
disul~onic acid and naphthalene trisulfonic acid are effective stress reducers.
Sulful cont~ining compounds and their influence on the internal stress in nickelcoatings has also been studied. Sodium benzene sulfonate, benzene sulfonamide
and sulfanilic acid reduce the iinternal stress but only benzene sulfonamide
2 5 imparts a compressive stress. However, p-amino benzene sulfonamide causes
the sl:ress to become very tensile in nickel deposits plated from sulfate solutions.
An article by Kudryavtsev et al. entitled Nickel Electrodeposition from
Methansulfonic Acid-Based ]Bath, Proceedings of American Electroplaters,
Surf:ace Finishin~, pages 837-841 (1996), compares electroplating nickel from
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a Ni(CH3SO3)2, also dçsignAte~l, NiMSA, to electroplating from a nickel
slllfam~te bath.
Kudryavtsev et al. disclose that disadvantages ol'the s~llf~m~le bath
include (1) the slllf~m~te bath being chemically unstable (2) slllfam~te starting
to decompose at 60~C but th~ baths run at 45 to 60~C, and (3) the bath being
very sensitive to impurities oi other metal ions, thus to prevent deterioration in
coatiing quality, reduction in cluctility and cathode current efficiency, the
maximum Fe which can be present in the bath is 20 mg/L~ maLximum Cu is 10
mg/l,, maximum Zn is 10 mg/L, maximum Pb is 2 mg/L and maximum Cr is
2 mg/L.
0 Kudryavtsev et al. disclose that the compositions they tested were
comprised of Ni(CH3SO3)2 1()0 to 400 g/l; H3BO3 17 to 40 g/l; saccharin, .01
to 1.~, g/l; and sodium lauryl sulfate, .02 to 0.5 g; and that the electroplating
process was at a pH of 0.8 to 2.0; temperature of 30 to 60~C; and a current
density (CD) of 0.5 to 39 A/drn2 . However, there are problems with
elecboplating using the Kudryavtsev et al. disclosed composition. First, since
sodium saccharin is extremely soluble in water but saccharic acid is not,
saccharic acid begins to crystallize when the processing pH is <2 and particles
of saccharic acid will be deposited with the electrodeposited nickel producing an
unacceptable coating. Second, Kudryavtsev et al. disclose that the Ni(CH3SO3)2
2 o composition tested resulted in a positive (tensile) internal stress and not th
desired negative (compression) internal stress.
Accordingly, the present invention seeks to obtain the advantages of
avoiding these and other difficulties encountered in the related art. These and
other advantages are obtained according to the present invention which is the
2 5 proviision of a process and cornposition of matter that substantially obviates one
or more of the limitations and disadvantages of the described prior processes
and compositions of matter of the related art.
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SUMMARY OF THE INVENTION
To achieve these and other advantages, and in accordance with the
purpose of the invention, as embodied and broadly described, the invention
comprises a composition of matter which allows the use of nickel alkane
sulfonic acid in an electrodepositing process to produce low-stress nickel
coatings having compressive stress.
One embodiment of the invention is a composition of matter for
producing low stress electrode~positing nickel coatings. The composition is an
acidic aqueous electroplating bath comprising a nickel alkane sulfonic acid and
a stress-reducing additive that imparts compressive stress to the coating.
0 Another embodiment of the present invention is a process for
prodwcing electrodeposited coatings by electroplating a cathodic conductive
substrate in a coating bath having an anode inserted therein, the bath consists
essentially of a nickel alkane sulfonic acid and a stress-reducing additive thatimparts a compressive stress to the coating, m:~int~ining the coating bath at a pH
from about 0 to about 5; and m~int~ining the current density on the substrate atfrom about l to about l00 A/dm2.
Another embodiment of the invention is a composition of matter for
replenishing a spent electropla.ting bath for producing low stress
electrodeposited nickel coatings, the spent bath initially cont~ining Ni(CH3SO3)2
2 o and a. stress-reducing additive that imparts a compressive skess to the coating,
the composition being a slurry comprising nickel carbonate and an aromatic
sulfonic acid.
The process and composition of the invention provide excellent nickel
coati:ngs on conductive substrates.
2 5 Detailed. Description of the Invention
The description whiich follows sets forth additional features and
advantages of the invention, and in part, will become apparent from the
description or learned by practice of the invention. The skilled artisan will
CA 02236933 1998-06-10
realize the objectives and other advantages of the invention obtained by the
process and composition of matter particularly pointed out in the written
descri.ption and claims hereof.
The electroplating baths of the present invention generally comprise a
mixh~re of from about 50 to ablout 600 grams/liter, preferably from about 150 to450 grams/liter, of a nickel alkane sulfonic acid; from about 0.5 to 15
gram,'liter, preferably 5 to 10 gram/liter, of a stress reducing additive that
imparts a compressive stress to the electrodeposited coating; optionally, from 0to about 100 grams/liter, preferably 20 to 40grams/liter, of a nickel halogen,
and, optionally, from 0 to about 60 grams/liter of a buffer.
Nickel Alkane Sulfonic Acids
The nickel alkane sulfonic acids include sulfonic acids of the formula
(R) (SO3)1~ where R and x are defined hereinafter.
The nickel alkane sulfonate comprises a water soluble compound by
whic~h it is meant that the compound is soluble in water at about room
temperature (about 20~C) or lower (about I O''C to about 20~C), and preferably
from these temperatures up to or slightly below the operating temperature of thebath, and has the formula:
Ni[(R)(SO3)X]y forrnula (A)
where x has a value from 1 to about 3; and
2 o y has a value from 1 to 2 so that y may be 1 when x is greater than 1.
R is an alkyl group having from 1 to about 15 carbon atoms and
especially 1 to about 7 carbon atoms including the straight chain and branch
chain isomers thereof such as methyl, ethyl, propyl, isopropyl, butyl, t-butyl,
isobutyl, pentyl, isopentyl, and the like. Hydroxy substituted alkyls, as alkyl is
2 5 defined herein, are also inclucled. Specific nickel salts in this regard comprise
nickel methane sulfonates, nic kel ethane sulfonates, nickel propane sulfonates,nickel isopropane sulfonates, nickel butane sulfonates, nickel isobutane
sulfonates, nickel t-butane sulfonates, nickel pentane sulfonates, nickel
isopentane sulfonates, and the like, as well as the hydroxy substituted
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compounds thereof. R also inc]Ludes cyclic, and heterocyclic hydrocarbon
substituents such as cycloaliphatic, unsatura~ed cycloaliphatic, and aromatic
groups having from 4 to about 16 carbon atoms and especially from about 6 to
about 14 carbon atoms including cyclobutyl, cyclobutenyl, cyclohexyl,
cyclohexenyl, cyclohexadienyl, cyclooctanyl, cyclooctadienyl.
The compound is present in sufficient quantity so that the concentration
of Ni~~~ is preferably 25 to 135; g/l, more preferably 50 to 100 gll, most
preferably about 80 g/l.
Preferred for use in the bath of the present invention is nickel methane
sulfonic acid - Ni(CH3SO3)2.
0 Alloys of Nickel
The invention also includes depositing alloys of nickel as the nickel
coating of the present invention, and can employ alkane sulfonate salts of the
alloying metals and nickel alkanesulfonates~ where in formula (A), the alloying
meta] will be substituted for "Ni", "y" has a value of 1 up to the valence of the
alloy ing metal, and "x" has the values given above.
Alloys of nickel may also be deposited employing alloying additives to
the coating bath in lieu of or in addition to the sulfonate alloying compounds
described herein. Any of the other Group IB, IIB, IIIA, IVA, IVB, VA, VB,
VIB, VIIB or VIIIB metals may be used as alloying metals. Mixtures of
2 o alloying metals from Group VIII and/or Group IIB or Cr or Mn may also be
prepared, especially the two component or three component alloys where the
alloying metal is present in the coating in an amount anywhere from about 0.1 toabout 20 percent by weight and especially from about 5 to about 15 percent by
weight. Examples include Ni.Zn, NiCr, NiFe, NiP, NiMn, NiSn and NiW.
2 5 The alloys are prepared by inserting the alloy metal into the coatingbaths either as an anode in a manner well known in the art or by adding a salt of
the alloying metal to the coating bath.
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Stress-Reducin~ Additive that Imparts Compressive Stress in Coatin~
A stress reducing additive that imparts a compressive stress to the
electrodeposited coating is present in the bath at a concentration of 0.5 to 15 g/l,
preferably 2 to 15 g/l, more preferably 5 to 10 g/l, and most preferably about 8g/l. IJsually the concentration of the additive will range from 5 to 20 % of theconcentration of the nickel ion present in the bath .
Useful additives include those known as being useful in Watts and
Slllf~m~te baths. Included are aromatic sulfonic acids in which the aromatic
group of compound may be any six membered ring or polynuclear ring having
from about 10 to about 14 carbon atoms, all of which are well known in the art.
0 Anywhere from one to about three sulfonate groups can be substituted on the
aromatic ring. Examples include aminobenzene sulfonic acid, benzene sulfonic
acid, benzene disulfonic acid, :napththylamine disulfonic acid, naphthalene
monosulfonic acid, naphthalene disulfonic acid, naphthalene trisulfonic acid,
naphl:hol monosulfonic acid and p-toluene sulfonic acid.
Other useful stress reducing additives include benzene sulfar~nide,
cysteine hydrochloride, saccharin (useful when the bath will be m~int~ined at a
pH > 2), p-toluene sulfonamide, thioacetamide, thiosernicarbazide and thiourea.
Preferred is naphthalene trisulfonic acid, especially 1,3,6-naphthalene
trisulfonic acid.
2 o Nickel Halo~en
When soluble nickel anodes are used in the process, the bath preferably
contains a nickel halogen, such as, for example, NiCI2 or NiBr2. The nickel
halogen aids in the dissolution of the soluble anode. The amount of nickel
halogen present in the bath is about 0 to 100 g/l, preferably 20 to 40 g/l.
2 s Other Additives to the Bath
It is also within the scope of the invention to adjust the bath by the
addil:ion of other components know to these skilled in the art. Such other
addil:ives include, for exarnple, 0 to about 6() g/l, preferably 35 to 45 g/l ofbuffers, such as boric acid and/or O to about 2 ml/l, preferably about 1 ml/l of a
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surfacl;ant, for example, sodium. Iauryl sulfate, to reduce surface tension and
prevent bubbling of hydrogen ~;as.
Electrodeposition according to the process takes place at a pH from
about 0 to about 5, preferably about 0.5 to about 4.5, and most preferably aboutpH 1 to4.
Current Densitv
The composition and process of the present invention operates at current
densities from about 1 Amps/dm2 to about 200 Amps/dm2 and preferably from
about 2 Amps/dm2 to about 30 Amps/dm2. In high speed plating such as on
steel strip, the preferred current density is about 50 Amps/dm2 to about 100
Amps/dm2.
Temperature
The process of the invention proceeds at temperatures from about room
temperature (20~C) to about 80~C, and preferably from about 30~C to about
70~C, and most preferably frorn about 40~C to about 60~C.
Agitation
In order to prevent "bu]ning" of high current density areas and provide
for more even temperature control of the solution, solution agitation may be
employed. Air agitation, mechanical stirring, pumping, cathode rod and other
2 o means of solution agitation are all satisfactory. Additionally, the solutions may
be operated without agitation.
In high speed plating ~uch as on steel strip, the agitation of the bath
preferably produces a flow rate of about 0.5 to S meters/sec.
E~epleni~hin~ Composition
2 5 When the process utilizes an insoluble anode, eventually the bath
solution will need to be replenished in order to have sufficient nickel present in
the bath to enable the electrodeposition of low-stress nickel. A suitable
composition for the replenishing the spent nickel alkane sulfonic acid and stress-
reduc:ing additive containing electroplating bath is a slurry comprising (a) nickel
g
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carbonate which replenishes the nickel and increases the pH of the bath, and (b)the stress reducing additive of the initial bath used to impart compressive stress
to the electrodeposit.
The slurry usually will contain 0.5 to 10 g/l, preferably 1.5 to 5 g/l, of
the stress reducing additive for every 1000 g/l of the nickel carbonate present in
the slurry. However, the amount of the stress reducing additive will be
dependent on the particular stress-reducing additive used in the slurry. For
example, if 1,3,6-naphthalene trisulfonic acid is the stress reducing agent the
amount will preferably be about 1 to 6 g/l, most preferably about 3 g/l per 1000g/l of nickel carbonate.
0 The amount of slurry added to the bath will be based on the Amp hoursto which the spend bath has been exposed and will be sufficient to maintain the
amo~mt of nickel in the bath at the concentration desired by the electroplater.
Anocles
The anodes useful in the process of the present invention include soluble
anodes, such as, for example, nickel foil, and insoluble anodes, such as, for
example, platinum and precious metal oxides.
The insoluble (inert) anodes used in this invention are insoluble (inert) in
the electrolyte solution and consist of either a solid anodic metal or metal
compound e.g., oxide, where the metals are of the Group IVB, VB, VIB, VIIB,
2 o VIIIB, and IB of the periodic table, or the anodes comprise the above-described
metals or their alloys mounted on support materials including, for example,
cheaper base metals from the Group IVB, VB, VIB, VIIB, and VIIIB metals and
their alloys, e.g., stainless steels. A preferred anode metal compound is iridium
diox:ide (IrO2). Alloy metals of IrO2 are preferably the metals of Group VIB and2 5 VII~" e.g, chromium, molybdenum, and nickel.
Insoluble anodes can be used to deposit any galvanic metal, in addition
to nickel. The metals that can be deposited are kno~vn to those skilled in the art
and include zinc, copper, lead., chromium, magnesium, tin, molybdenum and
alloys thereof.
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Substrate (cathode)
Electroplating proceeds in the manner described herein by
electrolytically coating a conductive substrate with the composition of the
invention, where the substrate (cathode) comprises any electrically conductive
substrate or polymer substrate, or insulating substrate (e.g., a polymeric
material, such as a synthetic polymeric substrate, or a ceramic substrate) coated
with a conductive material such as a metal or any art known conductive
substrates such as a carbon substrate.
Although the examples describe the electroplating process as one that is
conducted on a steel substrate, any conductive substrate may be employed
whether a polymer, plastic, pure metal, a metal alloy, and includes other iron-
alloy substrates or metals or alloys based on Groups IB, IIB, IIIA, IVA, IVB,
VA, VB, VIB, VIIB or VIIIB metals and elements, the alloys comprising
combi.nations of two or more of these metals and elements, especially the two orthree or four component combinations of metals and elements.
Process
Coating proceeds by passing a current between the anode in the
electrocoating bath to the cathode substrate in the bath for a period of time
sufficient to deposit the desired nickel coating on the cathode.
The various numerical -ranges describing the invention as set forth
2 o throuphout the specification also include any combination of the lower end of
the range with the higher end of the range set forth herein including, inter alia,
ranges of concentrations of compounds, ratios of these compounds to one
another, molecular weights, pH, current densities, temperatures, and the like, as
well as all whole number and/or fractional number values and ranges
2 5 encornpassed within these ranges.
Example l.
A bath was prepared cont~ining Ni(CH3SO3)2 (300 g/l) and 1,3,6-
naphthalene trisulfonic acid (7.5 g/l). No nickel halogen or buffer was added.
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The bath was employed to deposit a nickel coating on a steel plate using
a 1 liter plating vessel with mild air agitation at 50~C. The anode was a piece
of niclcel foil. The average current density was about 4 amp per sq. dm. The pH
of the bath at the start of platin~ was 3.5 and at the end of plating 2.1.
The deposition is carried out for 15 minutes to provide a coating 7 to 10
~m thick. The coating was smooth and semi-bright. The stress in the coating
was
-6000 PSI (compressive).
Example 2.
A bath was prepared cont~ining Ni(CH3SO3)2 (300 g/l); 1,3,6-
0 napht]~alene trisulfonic acid (7.5 g/l), NiC12 (40 g/l), and H3BO3 (45 g/l).
The bath was employed to deposit a nickel coating on a steel plate using
a 1 liter plating vessel with mild air agitation at 50~C. The anode was a piece
of nickel foil. The average current density was about 4 amp per sq. dm. The pH
of the bath at the start of plating was 3.5 and at the end of plating 3.4.
The deposition was carried out for 15 minutes to provide a coating 9 to
12 ,Lcm thick. The coating was smooth and semi-bright. The stress was -5200
PSI (compressive).
Example 3.
A bath was prepared cont~ining Ni(CH3SO3)2 (300 g/l), sodium
2 o saccharin (1 g/l), NiCI2 (40 g/l), and H3BO3 (45 g/l).
The bath was employed to deposit a nickel coating on a steel plate using
a 1 lil;er plating vessel with mild air agitation at 50~C. The anode was a pieceof nic:kel foil. The average culTent density was about 4 amp per sq. dm. The pH
of thc bath at the start of plating was 3.3 and at the end of plating 3.4.
2 5 The deposition was carried out for 30 minutes to provide a coating 19 to
23 ,urn thick. The coating was smooth and semi-bright. The stress was -2000
PSI compressive.
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Example 4
A bath was prepared contaiming Ni(CH3SO3)2 (300 g/l) and 1,3,6-naphthalene
trisulfonic acid (7.5 g/l) ). The bath was employed to deposit a nickel coating
on a steel plate using a 1 liter plating vessel with mild air agitation at 50~C.The anode was a piece of iridium oxide coated titanium. The average current
density was about 4 amp per sq. dm. The pH of the bath at the start of plating
was 1.8 and at the end of plating 1.7.
The deposition was carried out for 60 minutes to provide a coating 40 to
45 ,urn thick. The coating was smooth and semi-bright. The stress was -3200
PSI (compressive).
Example 5
A bath was prepared Cont~ininy Ni(CH3SO3)2 (300 g/l) and 1,3,6-naphthalene
trisulfonic acid (7.5 g/l) . The bath was employed to deposit a nickel coating on
a steel plate using a 1 liter plaling vessel with mild air agitation at 55 ~C. Two
anodes were used, a soluble nickel foil and a piece of iridium oxide coated
titanium. The average current density was about 5 amp per sq. dm. The pH of
the bath at the start of plating was 2.0 and at the end of plating 1.8.
The deposition was carried out for 30 minutes to provide a coating 18 to
22 ,um thick. The coating was smooth and semi-bright. The stress was -1500
PSI (compressive).
2 o Example 6
A nickel methanesulfonate solution was prepared by dissolving 150 g/l
NiCO3 into 70% MSA. After complete dissolution of the nickel carbonate, this
solution was filtered to remove any residual particulate matter. To this was
added 30 g/l boric acid, 5 g/l n~phth~lenetrisulfonic acid. This solution was
2 5 heated to 60~C to dissolve the boric acid. Upon cooling to room temperature,
the pH was adjusted to 2.0 with 70% MSA.
A. A steel coupon was anodically cleaned in 50 g/l NaOH followed by
water rinses. This was activated in 5% HCL, room temperature for five
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seconds. The steel was plated at 4 AJdm2 for 15 minutes. Tne panel was bright
and s:mooth. Cathode current e fficiency was 89.3%.
B. To this solution was added 10 g/l Al203 (150 mesh), mixed. A
second panel was pretreated as above and plated for 15 minutes. The panel was
bright and semi-smooth. The cathode efficiency was 90.2%. Sc~nning electron
microscopy showed co-deposition of the aluminum oxide particles in the nickel
matrix.
Example 7
A nickel methanesulfonate solution was prepared by dissolving 150 g/l
NiCC)3 into 70% MSA. After complete dissolution of the nickel carbonate, this
0 solution was filtered to remove any residual particulate matter. To this was
added 15 g/l nickel chloride, 30 g/l boric acid, 3 g/l napthlene trisulfonic acid.
This solution was heated to 60~C to dissolve the boric acid. Upon cooling to
room temperature, the pH was adjusted to 3.2 with 70% MSA.
A. A steel panel was pretreated as above and plated in the solution. The
panel was bright and smooth. Cathode current efficiency was 96%.
B. To this solution was added 2 g/l MoS2, molybdenum disulfide. This
mixed for 10 minutes. A steel panel was pretreated as above and plated. The
cathode efficiency was 94%. SEM analysis showed the presence of MoS2
particles.
2 o C. To a new nickel solution was added 2 g/l MoSi2. These particles
were allowed to mix in the nickel solution for lO minutes. A steel panel was
cleaned as above and plated in this solution. SEM analysis confirmed the
presence of MoSi2 in the nickel coating.
Example 8
2 5 A 5% aqueous solution of sulfamic acid was prepared and the pH was
adjusted to 3Ø A three electrode electrochemical setup was used to study the
oxidaLtion of the sulfamic acid. The counter-electrode was a IrO2 grid. The
reference electrode was silver,'silver chloride. The working electrode was
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iridium-coated titanium. The potential of this system was scanned, starting from-0.2 V, in the anodic direction. A large oxidation peak was seen at +0.3 V.
A 5% MSA solution W;lS prepared and the pH adjusted to 3.0 with
sodium bicarbonate. The same three-electrode system was used in this study.
No oxidation peak was observed at +0.3 V in this MSA solution.
Therefore, one can use insoluble anodes in the nickel methanesulfonate
electrolyte and experience no clegradation by-products. The use of insoluble
anodes in the sulfarnic acid solution will lead to breakdown products at the
anode.
Comparative Example 1
0 A bath was prepared containing Ni(CH3SO3)2 (300 g/l) and sodium
saccharin (I g/l). No nickel halogen was used.
The bath was employed to deposit a nickel coating on a steel plate using
a 1 liter plating vessel with mild air agitation at 50~C. The anode was a piece
of nickel foil. The average cu]Tent density was about 4 amp per sq. dm. The pH
of the bath at the start of plating was 3.3 and at the end of plating 1.7. A white
precipitate was seen in the plating solution at the end plating. This is saccharic
acid ~,vhich precipitated due to the drop in pH.
The deposition was calTied out for 30 minutes to provide a coating 17 to
23 ,urn thick. The coating was slightly rough and semi-bright. The stress was
2 o +4200 PSI tensile.
Comparative Examples 2 to 5
Five coatings of nicke] electroplated from baths cont~ining Ni(CH3SO3)2
were compared. Effects of H3 BO3, NiCl2, pH, CD and NTS (1,3,6-naphthalene
trisulfonic acid) on stress are studied. All processes are operated at 60~C.
- 15
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Swnmary of the Results
In absence of NTS, stress in all deposits were tensile. NTS is necessary
to ensure compressive stress.
ComparativeCol~lpal aLive Comparative Comparative Comparative
Bath Bath Bathbath l)f presentbath of present
2 3 4 invention invention
Ni(CH:3SO~)~ 300 g/l 300 g/l 300 g/l 300 g/l 300 g/l
NTS no no no 7.5 g/l 7.5 g/l
NiCl2 45 g/l 45 g/l 45 g/l 45 g/l no
H3B~3 no no 30 g/l 30 gA no
pH 4.5 1.2 1.47 1.47 1.21
CDdurin~Stress Stress Stress Stress Stress
Processof coatin~of coatin~of coating of coatin.~ of coating
4 Arnpldm2 +17,344 +17,759 ~20,115 -7,963 -7,543
8 Amp/dm2 +37,890 +16,947 +20,529. -7,445 -8,229
12 Amp/dm2 +30,282 +21,298 +19,996 -7,824 -8,465
20 Amp/dm2 +22,568 +25,078 +18,400 -9,335 -6,936
50 Amp/dm2 +19,263 +16,272 burn burn +380
slight burn
Throughout the specification, the inventors refer to various materials
used in their invention as based on certain components, and intend that they
contain substantially these components, or that these components comprise at
least the base components in these materials.
It will be apparent to those skilled in the art that various modifications
2 o and variations can be made to the composition and process of the invention
without departing from the spirit or scope of the invention. It is intended thatthese modifications and variations of this invention are to be included as part of
the invention, provided they come within the scope of the appended claims and
their equivalents.
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