U.S. patent application number 15/678771 was filed with the patent office on 2017-11-30 for chromium alloy coating with enhanced resistance to corrosion in calcium chloride environments.
The applicant listed for this patent is MacDermid Acumen, Inc.. Invention is credited to Stacey Handy, Masahiro Hara, Roderick D. Herdman, Kotaro Ishiwata, Tatsuya Nishiyama, Trevor Pearson, Toshiyuki Yamamoto.
Application Number | 20170342582 15/678771 |
Document ID | / |
Family ID | 42781304 |
Filed Date | 2017-11-30 |
United States Patent
Application |
20170342582 |
Kind Code |
A1 |
Herdman; Roderick D. ; et
al. |
November 30, 2017 |
Chromium Alloy Coating with Enhanced Resistance to Corrosion in
Calcium Chloride Environments
Abstract
The invention consists of a chromium electroplating solution
comprising a chromium electroplating solution comprising: (1) a
water soluble trivalent chromium salt; (2) at least one complexant
for trivalent chromium ions; (3) a source of hydrogen ions
sufficient to create a pH of from 2.8-4.2; (4) a pH buffering
compound; and (5) a sulfur-containing organic compound. The
chromium electroplating solution is usable in a method for
producing an adherent metallic coating on a decorative article,
such coating having enhanced resistance to corrosion in
environments containing calcium chloride.
Inventors: |
Herdman; Roderick D.;
(Staffordshire, GB) ; Handy; Stacey; (West
Midlands, GB) ; Pearson; Trevor; (West Midlands,
GB) ; Yamamoto; Toshiyuki; (Sanbu-Gun, JP) ;
Ishiwata; Kotaro; (Tokyo, JP) ; Hara; Masahiro;
(Kanagawa-Ken, JP) ; Nishiyama; Tatsuya;
(Kanagawa-Ken, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MacDermid Acumen, Inc. |
Waterbury |
CT |
US |
|
|
Family ID: |
42781304 |
Appl. No.: |
15/678771 |
Filed: |
August 16, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12409629 |
Mar 24, 2009 |
9765437 |
|
|
15678771 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D 5/14 20130101; C25D
3/10 20130101; C25D 3/06 20130101 |
International
Class: |
C25D 3/06 20060101
C25D003/06; C25D 5/14 20060101 C25D005/14; C25D 3/10 20060101
C25D003/10 |
Claims
1. A chromium electroplating solution comprising: a. a water
soluble trivalent chromium salt; b. a complexant for trivalent
chromium ions comprising a dicarboxylic acid and an amino
carboxylic acid; c. a pH buffering compound; and d. a
sulfur-containing organic compound; wherein the pH of the solution
is from about 2.8-4.2.
2. The chromium electroplating solution according to claim 1,
comprising a water-soluble trivalent salt of chloride or sulfate
selected from the group consisting of sodium, potassium and
ammonium salts of chloride or sulfate and combinations of one or
more of the foregoing.
3. The chromium electroplating solution according to claim 1,
wherein the water-soluble trivalent chromium salt is selected from
the group consisting of chromium sulfate, chromium chloride,
chromium methane sulfonate, and combinations of one or more of the
foregoing.
4. The chromium electroplating solution according to claim 1,
wherein sulfur-containing organic compound comprises a divalent
sulfur.
5. The chromium electroplating solution according to claim 1,
wherein the pH buffering compound is selected from the group
consisting of boric acid and salts thereof, acetic acid and salts
thereof, phosphoric acid and salts thereof, glycine and salts
thereof, and combinations of one or more of the foregoing.
6. The chromium electroplating solution according to claim 2,
wherein the sulfur-containing organic compound comprises divalent
sulfur.
7. The chromium electroplating solution according to claim 6,
wherein the sulfur-containing organic compound is selected from the
group consisting of sodium thiocyanate and other salts thereof,
sodium dimethyldithiocarbamate, dialkylthiocarbamate salts,
thiourea and derivatives thereof, sodium mercaptopropane sulfonate,
soluble mercaptoalkanesulfonate salts, and combinations of one or
more of the foregoing.
8. The chromium electroplating solution according to claim 1,
wherein the complexant for trivalent chromium ions is selected from
the group consisting of malic acid, aspartic acid, maleic acid,
succinic acid, glycine, soluble salts of any of the foregoing, and
combinations of one or more of the foregoing.
9. The chromium electroplating solution according to claim 1,
comprising an additional organic compound selected from the group
consisting of saccharin, sodium allyl sulfonate, 2-butyne-1,4-diol,
sodium 2-ethylhexyl sulfate, sodium dihexyl sulfosuccinate, other
water soluble salts of any of the foregoing and combinations of one
or more of the foregoing.
10. The chromium electroplating solution according to claim 1
wherein the concentration of the sulfur-containing organic compound
in the electroplating solution is such that the chromium deposit
produced by the electroplating solution comprises from 0.5% by
weight to 25% by weight of sulfur.
11-21. (canceled)
22. A method of depositing a corrosion resistant chromium alloy
coating on an article, the method comprising the steps of: a)
coating the article by electrolytic or electroless means with one
or more layers of metal or metal alloy, wherein said metal or metal
alloy comprises palladium, tin, copper or nickel; and thereafter b)
immersing the article as a cathode in a chromium electroplating
solution, wherein the chromium electroplating solution is prepared
by i) combining (a) a water soluble trivalent chromium salt; (b) at
least one complexant for trivalent chromium ions; and (c) a pH
buffering compound; and thereafter ii) purifying the solution; and
thereafter iii) adding at least one sulfur-containing organic
compound comprising a divalent sulfur and, optionally, at least one
additional additive to the purified solution; and c) passing an
electrical current through the chromium electroplating solution to
deposit a chromium alloy on the article; wherein the chromium
electroplating solution has a pH of about 2.8-4.0.
23. The method according to claim 28, wherein the chromium alloy
deposit comprises from 2% by weight to 20% by weight sulfur.
24. The method according to claim 28, wherein the chromium
electroplating solution is purified by treating the chromium
electroplating solution with hydrogen peroxide and activated carbon
and then filtering the purified solution.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to a method for
covering an article with an adherent metallic chromium-based
coating, preferably a decorative chromium coating. The
chromium-based coating of the invention renders the article more
corrosion resistant than traditional chromium deposits, especially
in environments containing calcium chloride.
BACKGROUND OF THE INVENTION
[0002] Chromium has long had a presence in industrial coatings. The
chemical and mechanical properties of chromium render it suitable
for a number of applications including engineering applications and
decorative applications. Engineering applications are generally
defined as applications where the chromium layer is relatively
thick (for example greater than 10 .mu.m) whereas decorative
applications normally have a thin layer of around 0.2-1.0 .mu.m. In
decorative applications the chromium deposit typically exhibits a
specular metallic finish with a slight bluish tint.
[0003] The current invention, in one embodiment, is directed
primarily to the application field of decorative coatings. The
properties of chromium that make it suitable for these decorative
applications include its attractive color and high hardness, which
even with thin coatings provides for some scratch resistance.
[0004] The most cost-effective method of depositing substantial
layers of chromium is electrodeposition which is traditionally used
to deposit chromium from electrolytes containing hexavalent
chromium compounds. Such electroplating baths have a poor
efficiency and, as such, the building up of thick chromium coatings
is not cost effective. Therefore, to provide resistance to the
elements and corrosion protection for the base substrate one
typical practice first applies a thick coating of nickel (normally
between 10 and 50 .mu.m) and then applies only a thin layer of
chromium over the top of this nickel coating. The nickel coating
may consist of a single layer or a combination of two, three or
even four distinct layers to provide for maximum corrosion
protection of the substrate material and to maintain the decorative
appearance of the coating. Depending on the substrate material of
the article, other pretreatment and metallic coatings layers may be
applied prior to the nickel undercoat, for example in the case of
parts manufactured from ABS or other non-conductive materials, or
from zinc diecast materials. Such treatments are generally well
known to those skilled in the art.
[0005] Typical commercial applications for these types of
decorative coatings include shop fittings, sanitary fittings (such
as taps, faucets and shower fixings) and automobile trim (such as
bumpers, door handles, grilles and other decorative trim), by way
of example and not limitation.
[0006] Traditionally the corrasion resistance of the aforementioned
nickel/chromium deposits has been measured by a method known as the
CASS test, applied according to the internationally recognized
standard ASTM B368. This consists of exposing the electroplated
articles to a corrosive fog spray (comprising aqueous sodium
chloride, copper chloride and acetic acid) in an enclosed chamber
at a temperature of 49.degree. C. After a set exposure time the
appearance of the articles is examined and the degree of their
corrosion protection is assessed according to ASTM B537.
[0007] The degree of corrosion protection required depends upon the
likely environment to be encountered by the electroplated article
(for example exterior or interior automotive trim). The typical
thicknesses and types of deposits recommended are summarized in the
ASTM standards B456 and B604. Typically automotive companies will
require parts for interior trim to be able to withstand 24 hours
exposure to CASS, whereas exterior parts will typically require
protection against exposure times of up to 72 hours.
[0008] Chloride-based environments are used for these corrosion
tests as chloride is an aggressively corrosive ion and during the
winter season it is normal practice to scatter sodium chloride on
roads in order to facilitate the melting of ice and snow in order
to make roads passable with a higher degree of safety. Thus the
exposure of exterior automobile components to chloride ions can be
very high.
[0009] In severe winter environments such as in northern Canada and
Russia, sodium chloride is not sufficiently effective at snow
melting and alternative salts have been used. Typical of these
alternative salts are calcium chloride and magnesium chloride.
[0010] In the last few years, it has become apparent to the
automotive industry that the use of calcium chloride represents a
particular problem for chromium coatings. It is found that in
environments where calcium chloride is used, salts can dry on the
exterior of automobiles in combination with soils and mud. When
this happens on a chromium coating, a particular type of
accelerated corrosion occurs and the chromium deposit is
effectively removed, leaving the nickel deposit exposed. This
reduces the corrosion protection of the entire combination coating,
and in addition, when the car is cleaned of these soils, the
chromium deposit then looks unattractive as it exhibits dark spots,
mottled appearance and yellow patches.
[0011] Thus automotive companies have a desire to improve the
resistance of the chromium coatings to environments containing
calcium chloride.
SUMMARY OF THE INVENTION
[0012] It is an object of the present invention to provide a
chromium electroplating electrolyte capable of producing a thin
corrosion resistant layer on a decorative article.
[0013] It is another object of the present invention to provide a
chromium alloy coating on a decorative article that provides
enhanced corrosion resistance, especially in environments
containing calcium chloride.
[0014] It is still another object of the present invention to
provide a chromium-sulfur alloy coating on a decorative article in
accordance with the present invention.
[0015] In one embodiment, the present invention relates generally
to an improved chromium electroplating bath comprising:
[0016] a. a water soluble trivalent chromium salt;
[0017] b. at least one complexant for trivalent chromium ions;
[0018] c. a source of hydrogen ions at a concentration sufficient
to establish a pH of 2.8-4.2;
[0019] d. a pH buffering compound; and
[0020] e. a sulfur-containing organic compound.
[0021] In another embodiment, the present invention relates
generally to a method of providing a corrosion resistant chromium
alloy coating on an article to provide improved corrosion
resistance thereon, the method comprising the steps of: [0022] (a)
Suitably cleaning and pretreating the article; [0023] (b) Coating
of the article by electrolytic or electroless means with one or
more of the following; palladium, tin, copper, nickel, or other
metal or alloy as desired and [0024] (c) Coating the article with a
deposit comprising a chromium-sulfur alloy as described herein to
achieve an attractive and corrosion resistant finish on the
article.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] For a fuller understanding of the invention, reference is
made to the following description taken in connection with the
accompanying FIGURE, in which:
[0026] FIG. 1 depicts the Pourbaix diagram for chromium.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The present invention relates generally to an improved
electroplating bath and method of providing a corrosion resistant
chromium alloy coating on an article to provide improved corrosion
resistance, especially in calcium chloride environments. In a
preferred embodiment, the chromium alloy coating is a
chromium-sulfur alloy coating.
[0028] The method generally comprises the following steps; [0029]
(a) Suitably cleaning and pretreating the article; [0030] (b)
Coating the article by electrolytic or electroless means with one
or more of the following; palladium, tin, copper, nickel, or other
metal as desired and [0031] (c) Coating the article with a deposit
comprising a chromium-sulfur alloy as described herein to achieve
an attractive and corrosion resistant finish on the article.
[0032] The inventors of the present invention have found that
chromium-sulfur coatings prepared in accordance with the present
invention provide enhanced corrosion protection in calcium chloride
environments as compared to traditional chromium coatings obtained
from hexavalent chromium electroplating baths.
[0033] Without wishing to be bound by theory, the inventors propose
that the hygroscopic nature of calcium chloride retains moisture in
the dried soils. This moisture allows for the dissolution into the
soils of atmospheric gases (primarily CO.sub.2, but also SO.sub.x
and NO.sub.x) which creates an acidic environment due to the
generation of hydrochloric acid by the following reaction schemes
Equation 1 and Equation 2;
CaCl.sub.2+2CO.sub.2+2H.sub.2O.fwdarw.Ca(HCO.sub.3).sub.2+2HCl
Equation 1
CaCl.sub.2+CO.sub.2+H.sub.2O.fwdarw.CaCO.sub.3+2HCl Equation 2
[0034] As seen in FIG. 1, which depicts the Pourbaix diagram for
chromium, in environments of a neutral pH, chromium has a stable
state of chromium (iii) oxide Cr.sub.2O.sub.3, but in mildly acidic
environments with a pH below about 4.8, chromium will dissolve from
the coating in the form of Cr(OH).sup.2+ according to Equation 3,
and below about 3.6 will dissolve as Cr.sup.3+ according to
Equation 4.
2Cr+4H.sup.++1.5O.sub.2.fwdarw.2Cr(OH).sup.2++H.sub.2O Equation
3
2Cr+6H.sup.+.fwdarw.2Cr.sup.3++3H.sub.2 Equation 4
[0035] Automotive companies have a desire to improve the resistance
of the chromium coatings to environments containing calcium
chloride, and have devised new testing methods in order to
artificially reproduce this corrosive environment. Currently there
is no standard test (for example to an ASTM standard such as
applies to CASS testing) and therefore each automotive manufacturer
has devised its own specific test. While these testing methods vary
in details, they are all based on the same principle and typically
involve the following steps; [0036] (a) mixing a small amount of
calcium chloride solution with kaolin to form a paste; [0037] (b)
applying a fixed amount of this paste to an area of the article
under test; [0038] (c) leaving the paste for a predetermined time
in an environment of fixed temperature and, optionally, fixed
humidity; [0039] (d) removing the paste by washing with water,
drying, and then assessing the appearance of the deposit; [0040]
(e) repeating steps (a) to (d) as desired.
[0041] When this type of test is applied to deposits of the present
invention it is surprisingly found that they have a considerably
improved corrosion resistance as compared to traditional chromium
coatings obtained from hexavalent chromium electroplating
baths.
[0042] The chromium deposits of the invention are typically
chromium-sulfur alloys and contain some co-deposited sulfur,
preferably in the form of sulfides. Again, without wishing to be
bound by theory, the inventors propose that the incorporation of
this co-deposited sulfur, preferably sulfides, into the deposit
renders the deposit more resistant to attack in the calcium
chloride environments. Typically the chromium deposits of this
invention contain between about 0.5 and 25% by weight of sulfur.
Preferably, the chromium deposits of this invention comprise
between about 2.0% by weight and 20% by weight sulfur. The
concentration of sulfur in the deposit can be adjusted by adjusting
the concentration of sulfur bearing compounds in the chromium
electroplating bath. Preferably, the concentration of the sulfur
bearing compounds in the chromium electroplating bath is from 0.001
to 10 g/1, most preferably from 0.01 to 2.5 g/l.
[0043] Typically the chromium electroplating electrolyte comprises
the following ingredients; [0044] (a) a water soluble trivalent
chromium salt; [0045] (b) additional inert water soluble salts to
improve solution conductivity; [0046] (c) a complexant for the
trivalent chromium ions; [0047] (d) hydrogen ions to provide a pH
of about 2.8-4.2; [0048] (e) a pH buffering compound; and [0049]
(f) a sulfur-containing organic compound, preferably containing
sulfur in the divalent form.
[0050] Typical examples of compounds usable in the composition of
the electrolytes according to the present invention are set forth
below although the current invention is not limited to deposits
obtained from electrolytes containing only the listed examples.
Various prior art chromium electroplating electrolytes are
described generally in Great Britain Patent No. 1488381, and U.S.
Pat. Nos. 4,157,945, 4,374,007, 4,448,648, 4,448,649, 4,432,843,
4,472,250 and 4,502,927, the subject matter of each of which is
herein incorporated by reference in its entirety.
[0051] The water soluble trivalent chromium salt is typically
selected from the group consisting of chromium sulfate, chromium
chloride, chromium methane sulfonate, and combinations of one or
more of the foregoing. Other similar water-soluble trivalent
chromium salts are also usable in the practice of the invention.
The concentration of the water-soluble trivalent chromium salt in
the chromium electroplating electrolyte is preferably in the range
of about 15 to about 125 grams per liter, more preferably in the
range of about 25 to about 80 grams per liter. Preferably the
concentration of chromium ions in the plating bath is from 5 to 20
g/l.
[0052] The additional inert water-soluble salt is typically one or
more water-soluble salts of chloride or sulfate, including for
example, the chloride or sulfate salts of sodium, potassium and
ammonium. In a preferred embodiment, the additional inert
water-soluble salts comprise one or more of sodium sulfate,
potassium sulfate, and ammonium sulfate, at a total concentration
of between about 100 and 300 grams per liter in the chromium
electroplating electrolyte.
[0053] The source of hydrogen ions is preferably selected from the
group consisting of sulfuric acid, acetic acid, hydrochloric acid,
phosphoric acid or other phosphoric containing acidic species, and
combinations of one or more of the foregoing. The hydrogen ion
concentration in the chromium plating bath should be sufficient to
achieve a pH of about 2.8-4.2.
[0054] The pH buffering compound is used to maintain the pH of the
electrolyte at the desired level and is typically selected from the
group consisting of boric acid and salts thereof, acetic acid and
salts thereof, phosphoric acid and salts thereof, glycine and salts
thereof, and combinations of one or more of the foregoing. The
concentration of the pH buffering compound in the electrolyte
solution is dependent on the desired pH of the electrolyte and is
typically in the range of about 50 to about 100 grams per liter. As
noted the pH of the plating bath should be in the range of about
2.8-4.2.
[0055] The source of the co-deposited sulfur, preferably sulfide,
contained in the deposits of the invention is the sulfur-containing
organic compounds in the electrolyte formulation. The
sulfur-containing organic compound is preferably selected from the
group consisting of sodium thiocyanate and other salts thereof,
sodium dimethyldithiocarbamate, other soluble
dialkyldithiocarbamate salts, thiourea and derivatives thereof
including, for example allylthiourea, sodium mercaptopropane
sulfonate, other soluble mercaptoalkanesulfonate salts, and
combinations of one or more of the foregoing. As discussed above,
the sulfur-containing organic compound preferably contains sulfur
in the divalent form such that the chromium deposit of the
invention is a chromium sulfur alloy containing co-deposited sulfur
in the form of sulfides. The sulfur-containing organic compound is
typically present in the chromium electroplating electrolyte at a
concentration capable of producing a concentration in the range of
about 0.5 and 25% by weight of sulfur in the chromium deposit.
Typically, the higher the concentration of the sulfur bearing
organic compound in the plating bath, the higher the concentration
of sulfur in the plated deposit. Preferably the concentration of
the sulfur bearing organic compound in the electroplating
electrolyte is from 0.001 to 10 g/l, most preferably from 0.01 to
2.5 g/l.
[0056] The complexant for trivalent chromium ions is typically
selected from dicarboxylic acids and suitable salts thereof and
aminocarboxylic acids and suitable salts thereof. Examples of these
dicarboxylic acids and aminocarboxylic acids include one or more of
malic acid, aspartic acid, maleic acid, succinic acid and glycine
by way of example and not limitation. The concentration of the one
or more complexants in the chromium plating bath is preferably in
the range of about 5 to about 40 grams per liter, more preferably
in the range of about 10 to 25 grams per liter.
[0057] In addition, although not required to produce deposits in
accordance with the present invention, other organic compounds may
also optionally be added to improve the aesthetic appearance of the
deposit and to lower the surface tension of the electrolyte.
Typically these compounds include saccharin, sodium allyl
sulfonate, 2-butyne-1,4-diol, sodium 2-ethylhexyl sulfate, sodium
dihexyl sulfosuccinate and other water-soluble salts of such
compounds, by way of example and not limitation.
EXAMPLES
[0058] The usefulness of the invention is demonstrated by the
following non-limiting examples.
[0059] In each of the examples, the thickness of the chromium
coating is determined by coulometric thickness testing.
[0060] The oxidation state of the sulfur in the deposits of
examples 1, 4 and 6 was determined by X-Ray Photoelectron
Spectroscopy (XPS).
[0061] Auger Electron Spectroscopy (AES) was used to determine the
composition of the deposit from Examples 1 through 5 and
Comparative Example 6. The composition FIGURE quoted is taken from
the bulk film to avoid the effects of surface oxidation on
compositional analysis.
[0062] The corrosion resistance of the deposits to a calcium
chloride environment is determined as follows; [0063] (a) 5 ml of a
saturated solution of calcium chloride at 40.degree. C. was mixed
with 3 g of kaolin to form a paste. [0064] (b) 80-100 mg of the
prepared paste was applied to the test panel, spread over a
circular test area of 15 mm diameter. [0065] (c) The test panel was
placed in an oven at 60.degree. C. for 48 hours. [0066] (d) After
48 hours the panels were removed, the dried paste was washed off
and the deposit appearance assessed for corrosion.
[0067] This test represents a typical calcium chloride test used by
a large automotive manufacturer.
[0068] Each test panel was tested in 3 different test areas and the
paste was freshly prepared for each test. The test panels were
allowed to stand for 14 days after plating before being tested.
Example 1
[0069] A trivalent chromium electroplating solution was prepared as
follows;
TABLE-US-00001 Basic chromium sulfate 65 g/l Malic acid 15 g/l
Sodium sulfate 35 g/l Ammonium sulfate 30 g/l Potassium sulfate 140
g/l Boric acid 90 g/l Sodium saccharin dehydrate 2.5 g/l Thiourea
10 mg/l Sodium dihexylsulfosuccinate 250 mg/l
[0070] Prior to adding the sodium saccharin dihydrate, thiourea and
sodium dihexylsulfosuccinate, the solution was purified by
treatment with 1 ml/l of 35% hydrogen peroxide and 1 g/l of
activated carbon, filtered and the pH adjusted to 3.3-3.5. A steel
panel was electroplated with three layers of nickel according to
ASTM B456 (semi-bright, bright and microporous nickel) and coated
with approximately 0.3 .mu.m chromium from the solution of example
2 by passing a current density of 10 A/dm.sup.2 for 12 minutes. The
electrolyte temperature was 60.degree. C. and a mixed metal oxide
(IrO.sub.2/Ta.sub.2O.sub.3) anode was used.
Example 2
[0071] A trivalent chromium electroplating solution was prepared as
follows;
TABLE-US-00002 Basic chromium sulfate 40 g/l Malic acid 9.0 g/l
Aspartic acid 1.0 g/l Sodium sulfate 180 g/l Boric acid 80 g/l
Sodium saccharin dehydrate 2.0 g/l Thiourea 10 mg/l Sodium
dihexylsulfosuccinate 250 mg/l
[0072] Prior to adding the sodium saccharin dihydrate, thiourea and
sodium dihexylsulfosuccinate, the solution was purified by
treatment with 1 ml/1 of 35% hydrogen peroxide and 1 g/l of
activated carbon, filtered and the pH adjusted to 3.3-3.5. A steel
panel was electroplated with three layers of nickel according to
ASTM B456 (semi-bright, bright and microporous nickel) and coated
with approximately 0.3 .mu.m chromium from the solution of example
3 by passing a current density of 10 A/dm.sup.2 for 12 minutes. The
electrolyte temperature was 60.degree. C. and a mixed metal oxide
(IrO.sub.2/Ta.sub.2O.sub.3) anode was used.
Example 3
[0073] A trivalent chromium electroplating solution was prepared as
follows;
TABLE-US-00003 Basic chromium sulfate 35 g/l Malic acid 8.5 g/l
Sodium sulfate 45 g/l Potassium sulfate 140 g/l Boric acid 90 g/l
Sodium saccharin dehydrate 3.0 g/l Thiourea 15 mg/l Sodium
dihexylsulfosuccinate 250 mg/l
[0074] Prior to adding the sodium saccharin dihydrate, thiourea and
sodium dihexylsulfosuccinate, the solution was purified by
treatment with 1 mill of 35% hydrogen peroxide and 1 g/l of
activated carbon, filtered and the pH adjusted to 3.3-3.5. A steel
panel was electroplated with three layers of nickel according to
ASTM B456 (semi-bright, bright and microporous nickel) and coated
with approximately 0.3 .mu.m chromium from the solution of example
4 by passing a current density of 10 A/dm.sup.2 for 10 minutes. The
electrolyte temperature was 60.degree. C. and a mixed metal oxide
(IrO.sub.2/Ta.sub.2O.sub.3) anode was used.
Example 4
[0075] A trivalent chromium electroplating solution was prepared as
follows;
TABLE-US-00004 Basic chromium sulfate 40 g/l Malic acid 9.0 g/l
Aspartic acid 15 g/l Sodium sulfate 50 g/l Potassium sulfate 140
g/l Boric acid 55 g/l Sodium saccharin dehydrate 3.0 g/l Sodium
thiocyanate 1.0 g/l Sodium dihexylsulfosuccinate 150 mg/l
[0076] Prior to adding the sodium saccharin dihydrate, sodium
thiocyanate and sodium dihexylsulfosuccinate, the solution was
purified by treatment with 1 ml/l of 35% hydrogen peroxide and 1
g/l of activated carbon, filtered and the pH adjusted to 3.3-3.5. A
steel panel was electroplated with three layers of nickel according
to ASTM B456 (semi-bright, bright and microporous nickel) and
coated with approximately 0.3 .mu.m chromium from the solution of
example 5 by passing a current density of 10 A/dm.sup.2 for 5
minutes. The electrolyte temperature was 60.degree. C. and a mixed
metal oxide (IrO.sub.2/Ta.sub.2O.sub.3) anode was used.
Example 5
[0077] A trivalent chromium electroplating solution was prepared as
follows;
TABLE-US-00005 Basic chromium sulfate 60 g/l Malic acid 12 g/l
Aspartic acid 1.0 g/l Sodium sulfate 35 g/l Ammonium sulfate 30 g/l
Potassium sulfate 140 g/l Boric acid 90 g/l Sodium saccharin
dehydrate 2.0 g/l Thiourea 10 mg/l Sodium thiocyanate 750 mg/l
Sodium dihexylsulfosuccinate 200 mg/l
[0078] Prior to adding the sodium saccharin dihydrate, thiourea,
sodium thiocyanate and sodium dihexylsulfosuccinate, the solution
was purified by treatment with 1 ml/l of 35% hydrogen peroxide and
1 g/l of activated carbon, filtered and the pH adjusted to 3.3-3.5.
A steel panel was electroplated with three layers of nickel
according to ASTM B456 (semi-bright, bright and microporous nickel)
and coated with approximately 0.3 .mu.m chromium from the solution
of example 6 by passing a current density of 10 A/dm.sup.2 for 12
minutes. The electrolyte temperature was 60.degree. C. and a mixed
metal oxide (IrO.sub.2/Ta.sub.2O.sub.3) anode was used.
Comparative Example 6
[0079] A chromium electroplating solution was created as
follows;
TABLE-US-00006 Chromium trioxide 225 g/l Sulfuric acid 1.0 g/l
Sodium hexafluorosilicate 1.0 g/l
[0080] This solution represents a typical decorative chromium
electroplating solution containing hexavalent chromium.
[0081] A steel panel was electroplated with three layers of nickel
according to ASTM B456 (semi-bright, bright and microporous nickel)
and coated with approximately 0.3 .mu.m chromium from the described
solution by passing a current density of 10 A/dm.sup.2 for 4
minutes.
[0082] The results from the examples are summarized below in Tables
1-4:
TABLE-US-00007 TABLE 1 Thickness Data Deposit thickness (.mu.m)
Example 1 0.23 Example 2 0.26 Example 3 0.22 Example 4 0.36 Example
5 0.41 Comparative 0.32 Example 6
TABLE-US-00008 TABLE 2 XPS Data Peak energy (eV) Peak Assignment
Relative Area (%) Example 3 162.1 sulfide 74 169.5 sulfate 26
Example 5 162.2 sulfide 92 169.0 sulfate 8 Comparative No sulfur
peak detected Example 6
TABLE-US-00009 TABLE 3 AES Compositional Analysis in % w/w Depth
(nm) Cr S C O N Example 1 50 87.7 4.8 3.7 1.3 2.5 Example 2 100
91.7 2.0 1.9 2.0 2.4 Example 3 100 89.1 4.0 2.7 2.0 2.2 Example 4
50 65.1 16.7 7.6 7.9 3.0 Example 5 50 66.4 22.0 9.2 1.2 1.2
Comparative 50 96.5 0.0 0.0 0.7 2.8 Example 6
[0083] Tables 2 and 3 demonstrate the presence of sulfur in the
deposits of the invention and that it is generally in the form of
sulfur (ii), and that sulfur is absent from the deposit of the
prior art obtained from a hexavalent electroplating bath.
TABLE-US-00010 TABLE 4 Corrosion Resistance of the Examples Degree
of corrosion Example 1 2 1 2 Example 2 2 2 2 Example 3 3 2 2
Example 4 1 1 1 Example 5 1 1 2 Comparative 3 4 3 Example 6 The
test panels are examined by viewing under indoor fluorescent
lighting at a distance of 30 cm and rated as follows; 1 = no
visible corrosion 2 = slight discoloration 3 = moderate
discoloration 4 = severe discoloration and some removal of chromium
coating 5 = complete removal of chromium coating
[0084] The results from the examples clearly show the improvements
provided by the deposits of the invention.
[0085] Finally, while the invention has been particularly shown and
described with respect to preferred embodiments thereof, it will be
understood that changes in form and details may be made therein
without departing from the scope and spirit of the invention.
* * * * *