U.S. patent application number 11/609672 was filed with the patent office on 2007-06-14 for process for deposition of crack-free and corrosion-resistant hard chromium and chromium alloy layers.
This patent application is currently assigned to ENTHONE INC.. Invention is credited to Matthias Kolner Strasse 54 a Bentele, Helmut Horsthemke.
Application Number | 20070131558 11/609672 |
Document ID | / |
Family ID | 37847008 |
Filed Date | 2007-06-14 |
United States Patent
Application |
20070131558 |
Kind Code |
A1 |
Horsthemke; Helmut ; et
al. |
June 14, 2007 |
PROCESS FOR DEPOSITION OF CRACK-FREE AND CORROSION-RESISTANT HARD
CHROMIUM AND CHROMIUM ALLOY LAYERS
Abstract
An electrolytic plating composition and related plating process
where the composition comprises chromium ions, a mineral acid,
halogen oxoanion, alkylsulfonic acid, and a source of sulfoacetic
acid for electrolytically coating a surface of a substrate with a
chromium layer or a chromium alloy layer.
Inventors: |
Horsthemke; Helmut;
(Solingen, DE) ; Bentele; Matthias Kolner Strasse 54
a; (Hilden, DE) |
Correspondence
Address: |
SENNIGER POWERS
ONE METROPOLITAN SQUARE
16TH FLOOR
ST LOUIS
MO
63102
US
|
Assignee: |
ENTHONE INC.
350 Frontage Road
West Haven
CT
06516
|
Family ID: |
37847008 |
Appl. No.: |
11/609672 |
Filed: |
December 12, 2006 |
Current U.S.
Class: |
205/283 |
Current CPC
Class: |
C25D 3/10 20130101 |
Class at
Publication: |
205/283 |
International
Class: |
C25D 3/04 20060101
C25D003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 2005 |
DE |
10 2005 059 367.4 |
Claims
1. A process for electrolytically coating a surface of a substrate
with a chromium-based layer, the process comprising: contacting the
surface of the substrate with an electrolytic plating composition
comprising a source of chromium ions, a mineral acid, a source of
halogen oxoanion, an alkylsulfonic acid, and a source of
sulfoacetic acid selected from the group consisting of sulfoacetic
acid, a sulfoacetate salt, a sulfoacetate ester, a sulfoacetate
anhydride, and a reactant which generates sulfoacetic acid; and
supplying an external source of electrons to electrolytically
deposit the chromium-based layer onto the surface of the
substrate.
2. The process of claim 1 wherein the halogen oxoanion is an alkali
metal salt or alkaline earth metal salt of the halogen oxoanion,
and the composition has an initial concentration of halogen
oxoanion between about 0.001 M and about 0.1 M.
3. The process of claim 2 wherein the salt of the halogen oxoanion
is selected from the group consisting of an iodate salt, a
periodate salt, a chlorate salt, a chlorite salt, a perchlorate
salt, a hypochlorite salt, a bromate salt, and combinations
thereof, and the composition has an initial concentration of
halogen oxoanion between about 0.001 M and about 0.1 M.
4. The process of claim 1 wherein: the source of chromium ions is
selected from the group consisting of chromium(VI) oxide; chromate
(CrO.sub.4.sup.2-) salts of sodium, potassium, and ammonium;
dichromate (Cr.sub.2O.sub.7.sup.2-) salts of sodium, potassium, and
ammonium; and combinations thereof; and the composition has an
initial concentration of chromium ions between about 0.5 M and
about 5 M; the source of halogen oxoanion is a salt selected from
the group consisting of an iodate salt, a periodate salt, a
chlorate salt, a chlorite salt, a perchlorate salt, a hypochlorite
salt, a bromate salt, and combinations thereof, and the composition
has an initial concentration of halogen oxoanion between about
0.001 M and about 0.1 M; the source of alkylsulfonic acid is
selected from the group consisting of methanesulfonic acid,
methanedisulfonic acid, ethylsulfonic acid, propylsulfonic acid,
salts thereof, and combinations thereof, and the composition has an
initial concentration of the alkylsulfonic acid of between about
0.01 and 0.1 M; the composition has an initial concentration of
sulfoacetic acid in the range of about 0.03 and about 0.3 M; and
the composition has a pH of less than 1.
5. The process of claim 1 wherein: the source of chromium ions is
selected from the group consisting of chromium(VI) oxide; chromate
(CrO.sub.4.sup.2-) salts of sodium, potassium, and ammonium;
dichromate (Cr.sub.2O.sub.7.sup.2-) salts of sodium, potassium, and
ammonium; and combinations thereof; and the composition has an
initial concentration of chromium ions between about 2 M and about
3 M; the source of halogen oxoanion is a salt selected from the
group consisting of an iodate salt, a periodate salt, a chlorate
salt, a chlorite salt, a perchlorate salt, a hypochlorite salt, a
bromate salt, and combinations thereof, and the composition has an
initial concentration of halogen oxoanion between about 0.007 M and
about 0.03 M; the source of alkylsulfonic acid is selected from the
group consisting of methanesulfonic acid, methanedisulfonic acid,
ethylsulfonic acid, propylsulfonic acid, salts thereof, and
combinations thereof, and the composition has an initial
concentration of the alkylsulfonic acid of between about 0.02 and
0.04 M; the composition has an initial concentration of sulfoacetic
acid in the range of about 0.06 and about 0.12 M; and the
composition has a pH of less than 1.
6. The process of claim 1 wherein the external source of electrons
provides a current density between about 20 A/dm.sup.2 and about
150 A/dm.sup.2.
7. The process of claim 1 wherein the electrolytic plating
composition has a temperature between about 20.degree. C. and about
90.degree. C.
8. The process of claim 1 wherein the chromium-based layer has a
hardness of more than 800 HV 0.1.
9. The process of claim 1 wherein the chromium-based layer has a
corrosion resistance of greater than 200 hours when tested
according to DIN 50021 SS.
10. An electrolytic plating composition for electrolytically
coating a surface of a substrate with a chromium layer or a
chromium alloy layer, the composition comprising: a source of
chromium ions; a mineral acid; a source of halogen oxoanion; a
source of alkylsulfonic acid; and a source of sulfoacetic acid
selected from the group consisting of sulfoacetic acid, a
sulfoacetate salt, a sulfoacetate ester, a sulfoacetate anhydride,
and a reactant which generates sulfoacetic acid.
11. The electrolytic plating composition of claim 10 wherein the
source of chromium ions is selected from the group consisting of
chromium(VI) oxide; chromate (CrO.sub.4.sup.2-) salts of sodium,
potassium, and ammonium; dichromate (Cr.sub.2O.sub.7.sup.2-) salts
of sodium, potassium, and ammonium; and combinations thereof.
12. The electrolytic plating composition of claim 10 wherein the
source of chromium ions has an initial concentration of chromium
ions between about 1M and about 4M.
13. The electrolytic plating composition of claim 10 wherein the
source of chromium ions is added to yield an initial concentration
of chromium ions between about 2 M and about 3 M.
14. The electrolytic plating composition of claim 10 wherein the
composition has an initial pH less than about 1.
15. The electrolytic plating composition of claim 10 wherein the
source of halogen oxoanion is an alkali metal salt or alkaline
earth metal salt of the halogen oxoanion.
16. The electrolytic plating composition of claim 15 wherein the
salt is selected from the group consisting of an iodate salt, a
periodate salt, a chlorate salt, a chlorite salt, a perchlorate
salt, a hypochlorite salt, a bromate salt, and combinations
thereof.
17. The electrolytic plating composition of claim 16 having an
initial concentration of halogen oxoanion between about 0.001 M and
about 0.1 M.
18. The electrolytic plating composition of claim 16 having an
initial concentration of halogen oxoanion between about 0.005 M and
about 0.08 M.
19. The electrolytic plating composition of claim 16 having an
initial concentration of halogen oxoanion between about 0.007 M and
about 0.03 M.
20. The electrolytic plating composition of claim 10 wherein the
source of alkylsulfonic acid is selected from the group consisting
of methanesulfonic acid, methanedisulfonic acid, ethylsulfonic
acid, propylsulfonic acid, salts thereof, and combinations
thereof.
21. The electrolytic plating composition of claim 20 wherein the
source of alkylsulfonic acid is added in an initial concentration
between about 0.015 M and about 0.06 M.
22. The electrolytic plating composition of claim 10 having an
initial concentration of sulfoacetic acid between about 0.03 M and
about 0.3 M.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to DE patent application
102005059367.4, filed Dec. 13, 2005.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a process for the deposition of
crack free and corrosion resistant hard chromium and chromium alloy
layers and an electrolytic chromium plating composition for
depositing chromium and chromium alloy layers.
[0003] Surfaces are coated through electrolytic plating for a
variety of reasons such as improving the surface properties in
terms of hardness, abrasivity, and corrosion resistance.
Additionally, surfaces can be coated for purely aesthetic reasons,
such as in decorative coating.
[0004] Chromium is a typical decorative and functional coating
layer deposited by electrolytic plating methods. Adjusting the
components and their concentrations in the electrolytic plating
composition can affect chromium layer properties such as hardness,
corrosion resistance, and brightness.
[0005] Electrolytic chromium plating compositions typically
comprise a source of hexavalent chromium and sulfuric acid for
depositing chromium over a base metal surface. The deposition
temperature is typically between 50.degree. C. and 70.degree. C.,
with current densities in the range of 30 A/dm.sup.2 to 50
A/dm.sup.2. Under these conditions, current efficiencies are
typically between 12% and 16%. German Patent Application DE 4302564
discloses that the addition of fluoride ions and alkylsulfonic
acids can increase the current efficiency up to 26%.
[0006] Besides adjusting the composition chemistry to affect the
properties of the chromium deposit, it is also possible to affect
the properties by adjusting the plating conditions. For example,
bright chromium layers are deposited at current densities between 2
A/dm.sup.2 and 8 A/dm.sup.2 and at a composition temperature of
about 30.degree. C., or at current densities between 3 A/dm.sup.2
and 18 A/dm.sup.2 and at a composition temperature of about
50.degree. C., or at current densities between 6 A/dm.sup.2 and 28
A/dm.sup.2 and at a composition temperature of about 50.degree. C.
Matte layers are deposited at current densities below 2 A/dm.sup.2
and at a composition temperature of about 30.degree. C. It is
possible to deposit matte layer at current densities up to about 6
A/dm.sup.2 by controlling the composition temperature.
[0007] A hot chrome process available from Enthone Inc. under the
trade name ANKORO 1141 can be used to plate a chromium layer having
a hardness of 700 HV 0.1. This process achieves current
efficiencies of about 10% at a composition temperature of
70.degree. C. Higher current efficiencies result in a layer which
cracks during mechanical processing.
[0008] European patent application EP 0073568 discloses an
electrolytic chromium plating composition capable of current
efficiencies of about 30% by adding a carboxylate to a chromium
composition also comprising potassium iodate as a halogen
source.
SUMMARY OF THE INVENTION
[0009] Among the various aspects of the invention may be noted an
electrolytic chromium plating composition and method for plating a
chromium layer or chromium alloy layer which is corrosion
resistant, crack free, and hard. The plating method is capable of
plating with a high current efficiency.
[0010] Briefly, therefore, the invention is directed to a process
for electrolytically coating a surface of a substrate with a
chromium-based layer, the process comprising contacting the surface
of the substrate with an electrolytic plating composition
comprising a source of chromium ions, a mineral acid, a source of
halogen oxoanion, an alkylsulfonic acid, and a source of
sulfoacetic acid selected from the group consisting of sulfoacetic
acid, a sulfoacetate salt, a sulfoacetate ester, a sulfoacetate
anhydride, and a reactant which generates sulfoacetic acid; and
supplying an external source of electrons to electrolytically
deposit the chromium-based layer onto the surface of the
substrate.
[0011] In another aspect the invention is directed to an
electrolytic plating composition for electrolytically coating a
surface of a substrate with a chromium layer or a chromium alloy
layer, the composition comprising a source of chromium ions; a
mineral acid; a source of halogen oxoanion; a source of
alkylsulfonic acid; and a source of sulfoacetic acid selected from
the group consisting of sulfoacetic acid, a sulfoacetate salt, a
sulfoacetate ester, a sulfoacetate anhydride, and a reactant which
generates sulfoacetic acid.
[0012] Other objects and features of the invention will be in part
apparent and in part pointed out hereinafter.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0013] This application claims priority to DE patent application
102005059367.4, filed Dec. 13, 2005, the entire disclosure of which
is incorporated by reference.
[0014] The electrolytic chromium plating composition and method of
the present invention is capable of plating a chromium layer or
chromium alloy layer which is corrosion resistant, crack free, and
hard. The plating method is capable of plating with a high current
efficiency, with current efficiencies greater than 30% typically
achieved.
[0015] The electrolytic chromium plating composition which can
plate a corrosion resistant, crack free, hard chromium layer at
high current efficiencies comprises a source of chromium ions, a
mineral acid, a source of halogen oxoanion, an alkylsulfonic acid,
and a source of sulfoacetic acid selected from the group consisting
of sulfoacetic acid, sulfoacetate salts, sulfoacetate esters,
sulfoacetate anhydride, and reactants which generate sulfoacetate.
When it is desirable to plate a chromium alloy layer, the
electrolytic chromium plating composition can comprise a source of
alloying metal ions, such as poly-anion forming metals, including
molybdenum, tungsten, vanadium.
[0016] The source of chromium ions provides hexavalent chromium
(chromium(VI) ions) to the electrolytic chromium plating
composition. Sources of hexavalent chromium include chromium(VI)
oxide (CrO.sub.3, commonly referred to as the anhydride of chromic
acid); chromate (CrO.sub.4.sup.2-) salts of sodium, potassium, and
ammonium; and dichromate (Cr.sub.2O.sub.7.sup.2-) salts of sodium,
potassium, and ammonium. A preferred source of hexavalent chromium
is CrO.sub.3 because CrO.sub.3 avoids introducing other metal ions
and cations in the plating bath, which may limit the conductivity
of the plating bath. The source of chromium ions can provide
hexavalent chromium into the electrolytic plating composition in an
initial concentration of at least about 0.5M. Preferably, the
source of chromium ions can provide hexavalent chromium into the
electrolytic plating composition in a concentration of at least
about 1M, more preferably at least about 2M. The concentration is
preferably at least about 0.5M to avoid loss conductivity in the
plating bath, necessitating a high plating voltage. The source of
chromium ions can provide hexavalent chromium into the electrolytic
plating composition in an initial concentration no greater than
about 5M, preferably no greater than about 4M, more preferably no
greater than about 3M. At higher concentrations than 5M, their may
be disadvantages related to high drag out rate from the plating
bath and increased cost. Accordingly, the source of chromium ions
can provide hexavalent chromium into the electrolytic plating
composition in a concentration between about 0.5M and about 5M,
preferably between about 1M and about 4M, even more preferably
between about 2M and about 3M. When CrO.sub.3 (M.W. 99.99 g/mol) is
the source of hexavalent chromium, these molar concentrations
correspond to concentrations of about 50 g/L to about 500 g/L,
preferably about 100 g/L to about 400 g/L, even more preferably
about 200 g/L to about 300 g/L in the electrolytic plating
composition.
[0017] A mineral acid can be added for pH adjustment. Preferably,
the pH of the electrolytic chromium plating composition is no
greater than about 1. In one embodiment a mineral acid suitable for
lowering the composition pH is preferably sulfuric acid.
[0018] A source of halogen oxoanion can be added to the
electrolytic chromium plating composition to increase the current
efficiency and improve the chromium layer properties. Although the
mechanism is not fully understood, it has been observed that the
absence of the halogen oxoanion results in significantly lower
current efficiency. The present invention is directd to a
combination of such anions that provide improved efficiency and
crack free deposits. The discovered catalyst and bath formulation
provides a desirable combination of deposit properties such as
relatively high hardness, crack free deposit, and improved
corrosion resistance. Sources of halogen oxoanion include bromo-oxy
compounds and iodo-oxy compounds. Exemplary bromo-oxy compounds
include bromate (BrO.sub.3.sup.-) and perbromate (BrO.sub.4.sup.-)
salts. The compounds can include bromate and perbromate alkali
metal and alkaline earth metal salts such as the salts of sodium,
potassium, magnesium, calcium, and barium. The compounds may also
include bromate and perbromate salts of ammonium and amines.
Bromate and perbromate may also be provided as acids. Exemplary
iodo-oxy compounds include iodate (IO.sub.3.sup.-) and periodate
(IO.sub.4.sup.-) salts. The compounds can include iodate and
periodate alkali metal and alkaline earth metal salts such as the
salts of lithium, sodium, potassium, magnesium, calcium, and
barium. The compounds may also include iodate and periodate salts
of ammonium and amines. Iodate and periodate may also be provided
as acids. The the source of halogen oxoanion be a bromide salt,
bromine, an iodide salt, or iodine, which could be oxidized in the
electrolytic chromium plating bath to the halogen oxoanion.
Chlorine oxoanions are also applicable, such as chlorates,
chlorites, perchlorates, hypochlorites, as well as chlorine and
chlorides which may be oxidized in the electrolytic chromium
plating bath to a chloro-oxoanion.
[0019] A preferred source of halogen oxoanion is potassium iodate.
Of the applicable halogen oxoanion, potassium iodate results in the
highest plating bath efficiency. The source of halogen oxoanion can
be added to the electrolytic chromium plating bath in an initial
concentration of at least about 0.001M, preferably at least about
0.005M, even more preferably at least about 0.007M. The source of
halogen oxoanion can be added to the electrolytic chromium plating
bath in an initial concentration of no greater than about 0.1M,
preferably no greater than about 0.08M, even more preferably no
greater than about 0.03M. Accordingly, the source of halogen
oxoanion can be added to the electrolytic chromium plating bath in
an initial concentration between about 0.001M and about 0.1 M,
preferably between about 0.005M and about 0.08M, even more
preferably between about 0.007M and about 0.03M. At concentrations
outside the range of between about 0.001M and about 0.1 M, the bath
experiences a loss of plating efficiency. At concentrations higher
than about 0.1M, there is the additional disadvantage of poor
adhesion of the chromium layer on the substrate. When potassium
iodate (KIO.sub.4, M.W. 230.00 g/mol) is the source of the halogen
oxoanion, these molar concentrations correspond to concentrations
of about 0.23 g/L to about 23 g/L, preferably about 1.15 g/L to
about 18.4 g/L, even more preferably about 1.61 g/L to about 6.9
g/L in the electrolytic plating composition.
[0020] The alkylsulfonic acid can be added to the electrolytic
chromium plating composition because its inclusion results in an
increase in the hardness of the deposited chromium layer without
impairing the current efficiency or deposition speed. The effect of
the alkylsulfonic acids on the plating mechanism is not fully
understood. It is thought that alkylsulfonic acids increase the
percentage of (100) oriented crystallites, providing higher
hardness than other crystal orientations. Alkylsulfonic acids for
use in the electrolytic plating compositions of the invention
typically have alkyl groups from one to four carbons, more
typically from one to two carbons. Alkylsulfonic acids can have
from one to four sulfonate groups, preferably from one to two
sulfonate groups. Exemplary alkylsulfonic acids include
methanesulfonic acid, methanedisulfonic acid, ethylsulfonic acid,
and propylsulfonic acid. Preferably, the alkylsulfonic acid is
methylsulfonic acid. The alkylsulfonic acid may be added to the
electrolytic chromium plating bath as a salt, typically, the
sodium, potassium, or ammonium salt. The alkylsulfonic acid can be
added to the electrolytic chromium plating bath in an initial
concentration of at least about 0.01 M, preferably at least about
0.015 M, even more preferably at least about 0.02 M. At
concentrations lower than about 0.01M, the plated chromium layer
may be less hard than desirable. The alkylsulfonic acid can be
added to the electrolytic chromium plating bath in an initial
concentration no greater than about 0.1 M, preferably no greater
than about 0.06 M, even more preferably no greater than about 0.04
M. At concentrations greater than about 0.1M, the plating bath
experiences a loss of plating efficiency, and cracks may develop in
the plated chromium layer. Accordingly, the alkylsulfonic acid can
be added to the electrolytic chromium plating bath in an initial
concentration between about 0.01 M and about 0.1 M, preferably
between about 0.015 M and about 0.06 M, even more preferably
between about 0.02 M and about 0.04 M.
[0021] The source of sulfoacetic acid can be added to increase the
current efficiency of the plating bath. The source of sulfoacetic
acid can be selected from sulfoacetic acid, sulfoacetate salts,
sulfoacetate esters, and sulfoacetate anhydride. Additionally, the
source of sulfoacetate can be a reactant which generates
sulfoacetate. Exemplary reactants which generate sulfoacetate in
the electrolytic chromium plating bath include
3-hydroxypropane-1-sulfonic acid, hydroxymethansulfonic acid, or
aldehydeomethanesulfonic acid. When these sources are used,
sulfoacetic acid is a degradation product of an oxidation process
of chromic acid. Preferably, the source of sulfoacetic acid is
sulfoactic acid in its pure form. The source of sulfoacetic acid
can be added to the electrolytic chromium plating bath in an
initial concentration of at least about 0.03 M, preferably at least
about 0.05M, more preferably at least about 0.06 M. At
concentrations lower than about 0.03M, the current efficiency in
the plating bath decreases. The source of sulfoacetic acid can be
added to the electrolytic chromium plating bath in an initial
concentration no greater than about 0.3 M, preferably no greater
than about 0.15 M, more preferably no greater than about 0.12 M. At
concentrations higher than about 0.3M, the chromium layer may
develop cracks and adhesion of the chromium layer to the substrate
suffers. Accordingly, the source of sulfoacetic acid can be added
to the electrolytic chromium plating bath in an initial
concentration between about 0.03 M and about 0.3 M, preferably
between about 0.05 M and about 0.15 M, more preferably between
about 0.06 M and about 0.12 M.
[0022] The method of the present invention may also be used to
plate chromium alloys. Typically, chromium may be plated in an
alloy with poly-anion forming metals, such as molybdenum, tungsten,
and vanadium. The concentration of the alloying metal may be added
to yield a chromium alloy layer having between about 0.1% and about
5%.
[0023] The invention further proposes a method for electrolytic
chromium plating, in which an electrolytic chromium plating
composition comprising the above mentioned components is used.
Substrates applicable for plating a hard chromium layer with the
compositions of the present invention include parts such as
pistons, cylinders, shocks, struts, and hydraulic shafts.
Substrates for decorative chromium plating include electrical
appliances and exterior car parts such as door handles, hub caps,
and bumpers. The base metal over which the chromium layer or
chromium layer alloy can be plated can be any conductive metal
substrate, but is typically steel, iron, copper, aluminum based
alloys, and stainless steel including casted metals. A particularly
preferred substrate is CK45 steel.
[0024] The cathode substrate, i.e., the part upon which the
chromium layer is deposited, and anode are electrically connected
by wiring and, respectively, to a rectifier (power supply). The
cathode substrate for direct or pulse current has a net negative
charge so that chromium(VI) ions in the electrolytic plating
composition are reduced at the cathode substrate forming plated
chromium metal on the cathode surface. An oxidation reaction takes
place at the anode. The cathode and anode may be horizontally or
vertically disposed in the plating tank.
[0025] During operation of the electrolytic plating system,
chromium metal is plated on the surface of a cathode substrate when
the rectifier is energized. A pulse current, direct current,
reverse periodic current, or other suitable current may be
employed. Preferably, plating is carried out by means of direct
current. The temperature of the electrolytic solution may be
maintained using a heater/cooler whereby electrolytic solution is
removed from the holding tank and flows through the heater/cooler
and then is recycled to the holding tank.
[0026] The electrolytic plating bath can be operated at any
temperature from about 20.degree. C. to about 90.degree. C.,
preferably from 45.degree. C. to about 65.degree. C. The electrical
current density is typically up to between about 20 A/dM.sup.2 and
about 500 A/dM.sup.2, more typically between about 20 A/dm.sup.2
and about 150 A/dm.sup.2. The deposition speed may vary between
about 0.2 .mu.m/min and about 60 .mu.m/min depending on current
densities applied, which is faster than conventional methods. At a
current density of about 50 A/dm.sup.2 and 55.degree. C., the
deposition speed is typically greater than about 1.3 .mu.m/min.
Current efficiencies typically between about 25% and about 40%,
with current efficiencies exceeding about 30% routinely achieved.
In a typical industrial application, the chromium layer may be
deposited to a thickness between about 2 .mu.m and about
200.mu.m.
[0027] The electrolytic chromium plating composition and
electrolytic plating method are capable of depositing hard chromium
layers. The Vickers Hardness values of the chromium layers are
typically between about 650 HV 0.1 and about 1100 HV 0.1, with
layers having hardness values exceeding about 800 HV 0.1 routinely
achieved. Moreover, the deposited chromium layers exhibit excellent
corrosion resistance. The corrosion resistance of a chromium layer
having a thickness of 25 .mu.m typically exceeds 200 hours under
the DIN 50021 SS standard test.
[0028] The following examples further illustrate the present
invention.
EXAMPLES 1-10
Electrolytic Chromium Plating Compositions
[0029] Ten electrolytic chromium plating compositions were prepared
including the additives of the present invention. Each composition
was used to plate an alloy layer over an inductively hardened CK45
steel substrate. The base electrolytic composition (included in all
10 compositions) contained chromium(VI) oxide (CrO.sub.3) in a
concentration of 280 g/L and sulfuric acid (H.sub.2SO.sub.4) in a
concentration of 2.8 g/L. The steel substrates were plated at
current of either 10A or 14A for 30 minutes, and the performance of
the electrolytic plating compositions were measured in terms of
current efficiency and deposition rate. The results are shown in
the following table. TABLE-US-00001 3-hydroxy propane-1-sulfonic
Halogen oxoanion Sulfonic Current Density Current Deposition Rate
No. acid (mL/L) concentration (g/L) acid (g/L) Current (A)
(A/dm.sup.2) Efficiency (%) (.mu.m/min) 1 8 0 0 10 50 37.3 1.396 2
10 2 0 10 50 37.07 1.388 3 10 3.4 0 14 70 36.76 n.d. 4 12 3.4 0 14
70 38.79 n.d. 5 8 2 0 10 50 40.23 1.506 6 8 2 0 14 70 37.33 2.010 7
10 2 0 14 70 39.67 n.d. 8 10 2 2.25 10 50 33.88 n.d. 9 10 3.4 2.25
10 50 35.68 1.335 10 10 3.4 2.25 14 70 37.36 1.958
[0030] n.d.=not determined
[0031] All deposited layers from Example Compositions 1-10 had
hardness greater than 800 HV 0.1, and a corrosion resistance
according to DIN 5002165 of more than 200 hours.
[0032] In view of the above, it will be seen that the several
objects of the invention are achieved and other advantageous
results attained.
[0033] When introducing elements of the present invention of the
preferred embodiment(s) thereof, the articles "a", "an", "the" and
"said" are intended to mean that there are one or more of the
elements. The terms "comprising", "including" and "having" are
intended to be inclusive and mean that there may be additional
elements other than the listed elements.
[0034] As various changes could be made in the above without
departing from the scope of the invention, it is intended that all
matter contained in the above description and shown in the
accompanying drawings shall be interpreted as illustrative and not
in a limiting sense.
* * * * *