Note: Descriptions are shown in the official language in which they were submitted.
3'76
Background of the Invention
Chrcmium electroplating baths are in widespread
commercial use for applying protective and decorative platings to
metal substrates. For the m~st part, commercial chrc~ium plating
solutions heretofore used employ hexavalent chrc~ium derived fram
ccmpounds such as chrcmic acid, for example, as the source of the
chromium constituent. Such hexavalent chrcmium electroplating
solutions have long been characterized as having limited covering
pGwer and excessive gassing p2xticularly around apertures in the
parts being plated which r,an result in in~mplete coverage. Such
hexavalent chrcmium plating solutions are also quite sensitive to
current interruptions resulting in so-called "whitewashing" of
the deposit~
Because of these and other problems including the
relative toxicity of hexavalent chrcmium, and asscciated waste
disposal problems, extensive work has been conducted m recent
years to develop chromium electrolytes incorporating trivalent
chramium providing numerous benefits over the hexavalent chrcmium
electrolytes heretofore kncwn. According to the present
invention a novel trivalent chrcmium electrolyte and process for
~
iZ~76
.. .~
depositm g chromium platings has been discovered by which bright
chramium deposits are produced having a color eq~livalent to that
obtained fram hexavalent chramium baths. m e electrolyte and
process of the present invention further provides electroplating
employing current densities which vary over a wide rangé without
producing the burning associated with deposits plated from
hexavalent ~h mmium plating baths; in which the electrolyte
composition minimizes or eliminates the evolution of mist or
noxious odors during the plating process; the electrolyte and
process provides for exoe llent coverage of the substrate and good
throwing power; current interruptions during the electroplating
cycle do not adversely affect the chromium deposit enabling parts
to be withdrawn from the electrolyte, inspected, and thereafter
returned to the b~th for continuation of the electroplating
cycle; the electr~lyte empl~ys low concentrations of chrcmium
thereby reducing the loss of chrcmium due to drag out; and waste
disposal of the chrcmium is facilitated in that the trivalent
chrcmium can readily be precipitated fram the waste solutions by
the addition of alkaline substances to raise the pH to about 8 or
above.
The electrolyte of the present invention further
incorporates one or more agents to prevent the formation of
detrimental concentrations of hexavalent chromium during bath
operation which heretofore has interfered with the efficient
electrodeposition of chromium from trivalent chromium plating
baths including the reduction in the efficiency and covering
power of the ~ath. In some instances, the buildup of detrimental
~L2~4376
hexavalent chromium has occurred to the extent that a cessation
in electrodepositon of chromium has occurred necessitating a
dumping and replacement of the electrolyte. In accordance with
a further discovery of the present invention, it has been found
that the addition of one or more of the additive agents
according to the electrolyte herein disclosed effects a
rejuvenation of an electrolyte contaminated with excessive
hexavalent chromium restoring the plating efficiency and
throwing po~er of such a bath and avoiding the costly and time
consuming step of dumping and replacing the electrolyte.
Summary of the Invention
The benefits and advantages of the present invention in
accordance with the composition aspects thereof are achieved by
an aqueous acidic electrolyte containing as its essential
constituents, controlled amounts of trivalent chromium, a
complexing agent present in an amount sufficient to form a
chromium complex, halide ions, ammonium ions and an additive
agent comprising metal ions selected from the group consisting
of neodymium, gold, silver, platinum, palladium, rhodium,
ir.idium, osmium, ruthenium~ rhenium, gallium, germanium,
indium, samarium, europium, gadolinium, terbium, dysporosium,
holmium, erbium, thulium, ytterbium, lutetium, praseodymium,
scandium, yttrium, lanthanum, titanium, hafnium, arsenic,
selenium, tellurium, cerium, uranium, and mixtures thereof)
present in an amount effective to maintain the concentration of
hexavalent chromium ions at a level below that at which
continued optimum efficiency and throwing power of the
electroplating bath is maintained. More particularly, the
electrolyte can broadly contain about 0.2 to about 0.8 molar
trivalent chromium ions, a formate and/or acetate complexing
agent present in an amount in relationship to the concentration
of the chromium constituent and typically present in a molar
ratio of complexing agent to chromium ions of about 1:1 to
``` ~Z~ 37~
t
about 3:1, a bath soluble and compatible salt or mixture of
salts of the additive metal ions present in a concentration of
at least about 0.001 gram per liter (g/l) up to about 30 g/l as
an agent to reduce the amount of any hexavalent chromium formed
during the electroplating process, ammonium ions as a secondary
complexing agent present in a molar ratio of ammonium to
chromium of about 2.0:1 to about 11:1, halide ions, preferably
chloride and bromide ions present ln a molar ratio of halide to
chromium ions of about 0.8:1- to about 10:1; one or a
combination of bath soluble salts to increase bath conductivity
comprising compatible simple salts of strong ac.ids such as
hydrochloric of sulfuric acid and alkaline earth, alkali and
ammonium salts thereof of which sodium fluoroborate comprises a
preferred conductivity salt, and hydrogen ions present to
provide an acidic electrolyte having a pH of about 2.5 up.to
about 5.5.
The.electrolyte may.optionally, but preferably, also
contain a buffering agent such as boric acid typically present
in a concentration of about 1 molar, a wetting agent present in
small but effective amounts of the types conventionally
employed in chromium or nickel plating baths as well as
controlled effective amounts of anti-foaming agents.
Additionally, the bath may incorporate another dissolved metal
as an optional constituent including iron, cobalt, nickel,
manganese, tungsten or the like in such instances in which a
chromium alloy deposit is desired.
In accordance with the process aspects of the present
invention, the electrodeposition of chromium on a conductive
substrate is performed employing the electrolyte at a temperature
9L3'76
. . .
t
ranging from about 15 to about 45C. The substrate is
cathodically charged and the chr3mium is deposited at current
densities ranging from about 50 to about 250 amperes per square
foot ~ASF) usually employing insoluble ancdes such as carbon,
platinized titanium or platinum. The substrat~, prior to
chromium plating, is subjected to oonventional pretreatments and
preferably is provided with a nickel plate over which the
chromium deposit is applied.
In accordance with a further process aspect of the
present invention, electrolytes of the trivalent chromium type
which have been rendered inoperative or inefficient due to the
accumulation of hexavalent chromium ions, are rejuvenated by the
addition of controlled effective amounts of the metal ion
additive agent to reduce the hexavalent chromium concentration to
levels below about 400 parts per million (ppm), and preferably
below 50 ppm at which efficient chrcmium plating can be resumed.
Additional benefits and advantages of the present
invention will be oome apparent upon a reading of the Description
of the Preferred Embodiments and the specific examples provided.
Description of the Preferred Embodiments
In accordance with the composition asFects of the
present invention, the trivalent chromium electr~lyte contains,
as one of its essential constituen~s, trivalent chrGmium ions
which may broadly range from about 0.2 to about 0.8 molar, and
preferably from about 0.4 to about 0.6 molar. Concen~rations of
3~7~
trivalent chromium below about 0.2 molar have been found to
pravide poor thrcwing power and poor coverage in so~e instances
whereas, concentrations in excess of about 0.8 molar have in some
instances resulted in precipitation of the chromium constituent
in the form of oomplex comFounds. For this reason it is
preferred to maintain the trivalent chramium ion concentration
within a range of about 0.2 to about 0.8 molar, and preferably
from about C.4 to akout 0.6 molar. The trivalent chromium ions
can be introduced in the form of any simple aqueous soluble and
compatible salt such as chrcmium chloride hexahydrate, chrcmium
sulfate, and the like. Preferably, the chrcmium ions are
introduced as chromium sulfate for econamic considerations.
A second essential constituent of the electrolyte is a
complexing agent for complexing the chromium constituent present
maintaining it in solution. The complexing agent employed should
be sufficiently stable and bound to the chramium ions to permit
electrodeposition thereof as well as to allaw precipitation of
the chrGmium during waste treatment of the effluents. The
camplexing agent may comprise formate ions, acetate ions or
mixtures of the two of which the formate ion is preferredO The
complexing agent can be employed in concentrations ranging from
about 0.2 up to about 2.4 molar as a function of the trivalent
chromium ions present. Ihe complexing agent is norm~lly employed
in a molar ratio of complexing agent to chromium ions of fmm
about 1:1 up to about 3:1 with ratios of about 1.5:1 to about 2:1
being preferred. Excessive amounts of the ccmplexing agent such
3~7~;
as formate ions are undesirable since such excesses have been
found in some instances to cause precipitation of the chromium
constituent as complex compounds.
A third essential constituent of the electrolyte
comprises one or a combination of metal ion additive agents in
the form of bath soluble and compatible salts present in an
amount which varies somewhat depending on the specific metal
ion or combination of metal ions employed. The broad and
preferred concentrations of the speci~ic metal ions is set
forth in Table 1.
TABLE 1
- CONCENTRATION, ~/l
METAL ION BROAD PREFERRED
_ _
Scandium 0.02-20 0.1-1
Yttrium 0.025-20 0.1-1
Lanthanum 0.01-20 0.1-1
Titanium - 0.01-20 0.1-1
Hafnium 0.015-15 0.1-1
Arsenic 0.025-10 0.1-1
Selenium 0.025-10 0.1-1
Tellurium 0.025-10 0.1-1
Cerium 0.002-10 0.05-1
Uranium 0.003-10 0.05-1
Gold 0 004~5 0.025-2
Silver 0.003-10 0.025-2
Platinum 0.002-10 0.025-1
Rhodium 0.002-10 0.025-1
Iridium 0.002-10 0.025-1
Osmium 0.001-10 0,02-1
Ruthenium 0.025-10 0O1-1
Rhenium 0.025-10 0.1-1
Gallium 0.060-10 0.1-1
Germanium 0.020-10 0.1-1
Indium 0.030-10 0.05 1
Samarium 0.020-10 0.05-1
E.uropium 0.020-10 0.05-1
Gadolinium 0.002-10 0.05-1
Terbium 0.002-10 0.05-1
Dysprosium 0.002-10 0.05-1
Holmium 0.002-10 0.05-1
~rbium 0.002-10 0.05-1
Thulium 0.002-10 0.05-1
Ytterbium 0.002-10 0.05-1
Lutetium 0.002-10 0.05-1
Praseodymium 0.002-10 0.05-1
NeodXymium 0,005-17 0.05 5
Palladium 0.002-lO 0.025-l
.~
~L~ 3~
Excess amounts of the metal ion additive agents do
appear to adversely affec-t the operation of the electrolyte in
some instances causing dark striations in the plate deposit and
a reduction in the plating rate. Typically and preferably,
metal ion concentrations are controlled within the preferred
ranges set forth in Table 1 which are satisfactory to maintain
the hexavalent chromium concentration in the electrolyte below
about 400 ppm, preferably below about 100 ppm, and more usually
from about O up to about 50 ppm at which optimium efficiency of
the bath is atta-ined.
The metal ion additive agent is introduced into the
electrolyte by any one of a variety of bath soluble and
compatible salts including those of only minimal solubility in
which event mixtures of such salts are employed to achieve the
required concentration.
For example, the neodymium additive agent is introduced
into the electrolyte by any one of a variety of neodymium salts
which do not adversely affect the chromium deposit and include,
for example neodymium trichloride (NdCl3), neodymium acetate
[Nd(C2H302)3 H20], neodumium bromate
[Nd(BrO3)3 9H20], neodymium tribromide (NdBr3),
neodymium trichloride hexahydrate (NdC13 6H20), and
neodymium sul~ate octahydrate [Nd2(S04)3 8H20], as
well as mixtures thereof.
7t~
In as much as the trivalent chramium salts, complexing
agent, and metal additive salts dc ~3t provide adequate bath
conductivity by themselves, it is preferred to further
incorporate in the electrolyte controlled amounts of conductivity
salts which typically co~prise salts of alkali metal or alkaline
earth metals and strong acids such as hydrochloric acid and
sulfuric acid. me inclusion of such conductivity salts is well
known in the art and their use mini~izes power dissipation during
the electroplating operation. Typical conductivity salts include
potassium and sodium sulfates and chlorides as well as ammonium
chloride and ammonium sulfate. A particularly satisfactory
conductivity salt is fluoboric acid and the aLkali metal,
aIkaline earth metal and a~moniumn bath soluble fluoro~orate
salts which introduce the fluoroborate ion in the h2th and which
has been found to further enhance the chrcmium deposit. Such
fluoroborate additives are preferably employed to provide a
fluoroborate ion concentration of from about 4 to about 300 g/l.
It is also typical to employ the metal salts of sulfamic and
methane sul~onic acid as a conductivity salt either alone or in
combination with inorganic conductivity salts. Such conductivity
salts or mixtures there~f are usually employed in amounts up to
~bout 400 g/l or higher to achieve the requisite electrolyte
conductivity and optimum chromium deposition.
It has also been observed that ammonium ions in the
electrolyte are beneficial in enhancing the efficiency of the
metal ion additive constituent for oon~erting hexavalent chramium
formed to the trivalent state. Particularly satisfactory result~
1~4~37~;
are achie~ed at molar ratios of total ammonium ion to chromium
ion ranging from about 2.0:1 up about 11:1, and preferably, from
about 3:1 to about 7:1. The ammonium ions can in part be
introduced as the ammonium salt of the complexing agent such as
ammonium ~ormate, for example, as well as in the form of
supplemental conductivity salts.
The effectivenss of t~e ~etal ion additive agent in
controlling hexavalent chrcmium formation is also enhanced by the
presence of halide ions in the bath of which chloride and bromide
ions are preferred. me use of a combination of chloride and
br~mude ions also inhibits the evolution of chlorine at the
anode. While iodine can also be employed as the halide
constituent, its relatively higher cost and low solubility render
it less desirable than chloride and brcmide. Generally, halide
concentrations of at least about 15 g/l have been found necessar~r
to achieve sustained efficient electrolyte operation. More
particularly, the halide concentration is controlled in
relationship to the chromium concentration present and is
controlled at a molar ratio of about 0.8:1 up to about 10:1
halide to chrcmlum, with a lar ratio of about 2:1 to about 4:1
being preferred.
In addition to the foregoing constituents, the bath may
optionally, but preferably also contain a buffering agent in an
amount of about 0.15 molar up to bath solubility, with amounts
typically ranging up to about 1 molar. Preferably the
concentration of the buffering agent is controlled fro~ about
~z~3~6
0.45 to about 0.75 molar calculated as boric acid. The use of
boric acid as well as the alkali metal and ammoniu~ salts thereof
as the buffering agent also is effective to introduce borate ions
in the electrolyte which have been found to improve the covering
power of the electrolyte. In accordance with a preferred
practioe, the borate ion concentration in the bath is controlled
at a level of at least abcut 10 g/l. The upper level is not
critical and concentrations as high as 60 g/l or higher can be
employed without any apparent harmful effect.
The bath further incorporates as an optional but
preferred constituent, a w~tting agent or mixture of wetting
agents of any of the types conventionally employed in nickel and
hexavalent chromium electrolytes. Such wetting agents or
surfactants may be anionic or cationic and are selected from
those which are compatible with the electrolyte and which do not
adversely affect the electrodeposition performance of the
chramium constituent. Typically, wetting agents which can be
satisfactorily employed include sulphosuccinates or sodium lauryl
sulfate and aLkyl ether .sulfates alone or in combination with
other ccmpatible anti-foamung agents such as octyl alcohol, for
example. The presence of such wetting agents has been found to
produce a clear chrcmium deposit eliminating dark mottled
deposits and providing for improved coverage in low current
density areas. While relatively high concentrations of such
wetting agents are not particularly harmful, concentrations
greater than about 1 gr~m per liter have been fcund in some
instances to prcduce a hazy deposit. Accordingly, the wetting
~Z~37~
t
agent when employed is usually controlled at concentrations less
than about 1 g/l, with amounts of about 0.05 to about 0.1 g/l
being typical.
It is also contemplated that the electrolyte can
contain other metals including iron, nanganese, and the like in
concent~ations of from O up to saturation or at levels below
saturation at which no adverse effect on the electrolyte occurs
in such instances in which it is desired to deposit chromium
alloy platings. When iron is employed, it is usually preferred
to maintain the conce~tration of iron at levels below about 0.5
5~1.
Ihe electrolyte further contains -a hydrogen ion
concentration sufficient to render the e]ectrolyte acidic. me
concentration of the hydroa,en ion is br~adly controlled to
provide a pH of from about 2.5 up to about 5.~ while a pH range
of about 2.8 to 3.5 is particularly satisfactory. The initial
adjustment of the electrolyte to within the desired pH range can
be achieved by the addition of any suitable acid or base
compatible with the bath constitutents of which hydrochloric or
sulfuric acid and/or D nium or sodium carbonate or hydroxide
are preferred. During the use of the plating solution, the
electrolyte has a tendency to beccme more acidic and appropriate
pH adjustments are effected by the addition of alkali metal and
D nium hydroxides and carbonates of which the am~onium salts
are preferred in that they si~ult~neously replenish the D nium
constituent in the bath~
3~g;
In accordanoe with the process aspects of the present
invention, the electrolyte a5 hereina~ove described is employed
at an operating temperature ranging from about 15 to about 45C,
preferably about 20 to about 30C. Current densities during
electroplating can range from about 50 to 250 ASF with densities
of about 75 to about 150 ASF being ~ore typical. The electrolyte
can be employed to plate chro~ium on conventional ferrous or
nickel substrates and on stainless steel as well as nonferrous
substrates such as aluminum and zinc. r~he electrolyte can also
be employed for -chromium plating plastic substrates which have
been subjected to a suitable pretreatment according to well-known
techniques to provide an electrically con~uctive coati~g
thereover such as a nickel or copper layer. Such plastics
include AES, polyolefin, PVC, and phenol-formaldehyde ~ol~mers.
me work pieces to be plated are subjected to conventional
pretreatments in accor~ance with prior art practices and the
process is particularly effective to deposit chramium platings on
conductive substrates which have been subjected to a prior nickel
plating operation.
During the electroplating operation, the work pieces
are cathcdically ch æged and the bath incorporates a suitable
anode of a material which will not adversely affect and which is
compatible with the electrolyte composition. For this purpose
anodes of an inert material such as carbon, for example, are
preferred although other inert anodes of platinized titanium or
platinum can also be employed. ~hen a chrcmium~iron alloy is to
be deposited, the anode may suitably ~e ccmprised of iron which
~z~ 6
.1
itself will serve as a source of the iron ions in the bath.
In accordance with a further aspect of the process of
the present invention, a rejuvenation of a trivalent electro-
lyte which has been rendered ineffective or inoperative due to
the high concentration of hexavalent chromium ions is achieved
by the addition of a controlled effective amount of the metal
ion additive agent. Depending upon the specific composition of
the trivalent electrolyte, it may also be necessary to add or
adjust other constituents in the bath within the broad usable
or preferred ranges as hereinbefore specified to achieve
optimum plating performance~ For example, the rejuvenant may
comprise a concentrate containing a suitable metal ion additive
agent salt in further combination with halide salts, ammonium
salts, borates, and conductivity salts as may be desired or
required. The addition of the metal ion additive agent can be
effected as a dry salt or as an aqueous concentrate in the
presence of agitation to achieve uniform mixing. The time
necessary to restore the electrolyte to efficient operation
will vary depending upon ~he concentration of the detrimental
hexavalent chromium present and will usually range from a
period of only five minutes up to about two or more hours. The
rejuvenation treatment can also advantageously employ an
electrolytic treatment of the bath following addition of the
rejuvenant by subjecting the bath to a low current density of
about 10 to about 50 ASF for a period of about 30 minutes to
about 24 hours to effect a conditioning or so-called "dummying"
of the bath before commercial plating operations are resumed.
The concentration of the metal ions to achieve rejuvenation
14
~ILZ~9~3~7f~
.,
can range within the same limuts as previously defined for the
operating electrolyte.
In order to further illustrate the cc~position and
process of the present invention, the following specific examples
are provided. It will be understood that the examples are
provided for illustrative puxposes and are not intended to ke
lLmiting of the invention as herein disclosed and as set forth in
the subjoined claims.
EX~LE 1
A trivalent chromium electrolyte is prepared having a
camposition as set forth below:
INGREDIENTCCNCENTRATICN, g/l
-
Cr+3 22
NH4COOH 40
NH4C1 150
4 50
H3BO3 50
Nd ions 0.05
Surfactant 0.1
The particular sequence of addition of the bath
constituents during bath makeup is not critical in achieving
satisfactory perfonmance. The trivalent ch mmium ions are
introduced in the form of chrcmium sulfa~e. m e neodymium ions
are introduced as neodymium trichloride. The surfactant employed
~Z~376
.,
comprises a mixture of dihexyl ester of sodium sulfo succinic
acid and sodium sulfate derivative of 2-ethyl-1-hexanol. The
operating temperature of the electrolyte is from 70 to about 80F
(21-27C) at cathode current densities of from about 100 to about
250 ASF and an anode current densit~ of about 50 ASF. The
electrolyte is employed using a graphite anode a* an anode to
cathode ratio of about 2:1. me electroplating bath is operated
employing a mild air and/or mechanical agitation. It has been
found advantageous to subject the bath to an electxolytic
preconditioning at a low current density, e.g. about 10 to about
50 ASF for a period UF to about 24 hours to achieve satisfactory
plating performance at the higher normal operating current
densities.
me electrolyte employed under the foregoing conditions
prcduced ~ull bright and uniform chroDium deposit having good to
execellent coverage over the current density ranges employed
including good coverage in the deep recess ~reas of the J-type
panels employed for test plating.
EXAMæLE 2
q~his example demonstrates the effectiveness of the
neodymium compound for rejuvenating trivalent chromium
electrolytes which have been rendered unacceptable or inoperative
because of an increase in hexavalent chro~iumn concentration to
an undesirable level. It has been found by test that the
progressive buildup of hexavalent chromium concentration will
eventually produce a skipping of the chrcmlum pkate and
16
~Z4~376
ultimately will result in the prevention of any chrcnium plate
deposit. Such tests employing typical trivalent chromium
electrolytes to which hexavalent chromium is intentionally added
has evidenced that a concentration of about 0.47 g/l of
hexa~alent chromium results in plating deposits having large
patches of dark chrcmuum plate and smaller areas which are
~ntirely unplated. As the hexavalent chromium concentration is
further increased to akout 0.55 g/l according to such tests,
further deposition of chromium on the substrate is completely
prevented. The hexavalent chrcmium concentration at which
plating ceases will vary scmewhat depending upon the specific
composition of the electrolyte.
In order to demonstrate a rejuvenation of a hexavalent
chromium contaminated electrolyte, a trivalent chromium bath is
prepared having the following ccmposition:
INGREDIENT ccNcENrRATIoN, g/1
Sodium fluoroborate 110
P~moniumn chloride 90
Boric acid 50
Ammonium formate 50
Cr+3 ions 26
Surfactant 0.1
me bath is adjusted to a pH between about 3.5 and 4.0
at a temperature of about 70 to about 80F. S-shaped nickel
plated test panels are plated in the bath at a current density of
4~3~
about 100 ASF. After each test run, the concentration of
hexavalent chromium ions is increased frcm substantially O in the
original bath by increments of about 0.1 g/l by the addition of
chromic acid. No detrimental effects in the chromium plating of
the test panels was observed through the range of hexavalent
ch mmium concentration of fm m 0.1 up to 0.4 g/1. However, as
the hexavalent chromium concentration was increased above 0.4 g/l
large dark chromium deposits along with small areas devoid of any
chrcmium deposit were observed on the test panels. As the
concentr~tion of hexavalent chromiun attained a level of 0.55 g/l
no further chromium deposit could be plated on the test panel.
Under such circumstances, it has heretofore been ccmmon
practice to dump the bath containing high hexavalent chromium
necessitating a makeup of a new bath which constitutes a costly
and time consuming operation.
To d~monstrate the rejuvenation aspects of the present
invention, neodymium ions were added in increments of about 0.55
g/l to the bath containing 0.55 g/l hexavalent chrcmium ions and
a plating of the test panels was re~umed under the conditions as
previously described.
me initial addition of 0.55 g/l neodymlum ions to the
bath contaminated with 0.55 g/l hexavalent chromium ions resulted
in a restoration of the efficiency of the chromium plating bath
producing a good chrcmium deposit of sood color and coverage
although hexavalent chrcmium ions were still de~ected as being
present in the bath.
'
t
EXAMPLE 3
` A basic trivalent chr~mium electrolyte is prepared
having a camposition as set forth below:
INGREDIENT CCNCEWT~A~ICN, g/l
Cr+3 22
NH4COOH 40
NH4C1 150
4 50
3 3 50
Surfactant 0.1
m e trivalent chrGmium ions are introduced in the form
of ch mmium sulfate. The surfactant employed ccmprises a mlxture
of dihexyl ester of scdium sulfo succinic acid and scdium sulfate
derivative of 2-ethyl-1-hexanol. Tb the foregoing basic
trivalent chromium electrolyte, controlled amounts of the
reducing metal ions are added in accordance with Examples 4
through 26 and 28 through 37.
EX~MPLE 4
To the trivalent chramium electrolyte of Example 3,
0.05 g/l of Gold ions are added in the form of gold chloride
(AuC13). The Gold ions can also be added to the electrolyte
employing alternati~e satisfactory bath soluble and compatible
gold ccmpounds including gold bromide (AuBr3), gold iodide (AuI)
as well as muxtures thereof.
19
~LZ~3~6
EX~MPLE 5
To the trivalent chrcmium electrolyte of Example 3,
0.05 g/l of Silver ions are added in the for.m of silver acetate
[Ag~C2H302)]. The Silver ions can also be added to the
electrolyte emplo~ing alternative satisfactory soluble and
compatible Silver compounds including silver tetraborate
~Ag2B407 2H20), silver chlorate (AgC103), silver perchlorate
(AgC104), silver fluogallate [Ag3(GaF6)lOH20], silver fluoride
(AgF), silver fluosilicate ~2SiF6-4H20) as well as mlxtures
thereof.
EXAMPLE 6
. .
To the trivalent chramium electrolyte of Example 3,
0.05 g/l of Platinum ions are added in the form of platinum
chloride (PtC14). m e Platinum ions can also be added to the
electrolyte employing alternative satisfactory bath soluble and
compatible Platinum compounds including platinum trichloride
(PtC13), platinum tetrachloride pentahydrate (PtC14-5H20),
platinum tetrafluoride (PtF4), platinum sulfate
[Pt[S04)2-4H20~ as well as mix*ures thereof.
EXAMPIE ~,
To the trivalent chrcmium electrolyte of Ex~mple 3,
0.05 g/l of Palladium ions are added in the form of palladium
chloride (PdC12). The Paladium ions can also be added to the
electrolyte employing alternative satisfactory bath soluble and
ccmpatible Palladium compounds including palladium chloride
dihydrate ~PdC12o2H20), palladium difluoride (PdF2), palladium
sulfate (PdS04-2H20) as ~ell as mixtures thereof.
; 2Q
, .
_ . _ .. . _ . ,, _, . . . . . . .
~2~ 376
EX~MpLE 8
Io the trivalent chromium electrolyte of Example 3,
0.05 g/l of Rhodium ions are added in the form of rhodium
chloride trihydrate (RhC13-3H20). The Rhodium ions can also
be added to the electrolyte employing alternative satisfactory
bath soluble and compatible Rhodium compounds including rhodium
sulfate hydrate [Rh2(SQ4)3~XH20], rhodium sulfite
[Rh2(S03)3-6H20] as well as mixtures thereof.
EX~IE 9
Tb the trivalent chromium electrolyte of Example 3,
0.05 g/l of Iridium ions are added in the form of iridium
tetrachloride (IrC14). The I~idium ions can also be added to
the electrolyte employing alternative satisfactory bath soluble
and compatible Iridium ccmpounds including iridium tribromide
(IrBr3-4H20), iridium tetrabromide (IrBr4), iridium dichloride
~IrC12), iridium tri-iodide ((IrI3), iridium sulfate
[Ir2(S04)3~XH20] as well as muxtures thereof.
EXPMPLE 10
Tb the trivalent chrQmium electrolyte of Ex~l~le 3,
0.05 g/l of Osmium ions are added in the form of osmium
trichloride (OsC13). me Osmium ions can also be added to the
electrolyte employing alternative satisfactory bath soluble and
ccmpatible Osmium comp~unds including osmium trichloride
trihydrate (OsC13-3H201, osmuum tetrachloride (OsC14),
osmium octafluoride (OsF8), osmium tetraoxide (0sO4) as well
as muxtures thereof.
. .
~2~t~3~6
EXAMPLE 11
: Tb the trivalent chromdum electrolyte of Example 3,
0.05 g/l of Ruthenium ions are added in the form of ruthenium
chloride trihydrate (RuC13-3H20). The Ruthenium ions can
also be added to the electrolyte employing alternative
satisfactory ~ath soluble and ccmpatible Ruthenium co~pounds
including ruthenium tetrachloride (RuC14-5H20), ruthenium
hydr~xide [Ru(OH)3], ruthenium tetroxide (Ru04) as well as
mixtures thereof.
EXAMPLE 12
To the trivalent chrGmium electrolyte of Example 3,
0.05 g/l of Rhenium ions are added in the form of rhe~ium
trichloride (ReC13). The Rhenium ions can also be added to the
electrolyte employing alternative satisfactory bath soluble and
compatible Rhenium ccmpounds including rhenium heptoxide
(Re207), rhenium tetrachloride (ReC14), rhenium hexachloride
(ReC16), rhenium hexafluoride (ReF6) as well as mixtures
thereof.
EXAMPLE 13
To the trivalent chromium electrolyte of Example 3,
0.05 g/l of Gallium ions are added in the form of gallium
trichloride (GaC13). The Gallium ions can also be added to
the electrolyte e~ploying alternative satisfactory bath
soluble and comFatible Gallium ccmpounds including
gallium acetate [Ga(C2H302)3], gallium tribromide
(GaBr3), gallium perchlorate [Ga(Cl04)3-6H20],
3~
gallium oxalate ~Ga2(C24)3 4H20]' gallium selenate
[Ga2(SeO4)3-22H2o], gallium sulfate [Ga2(S04)3], gallium
sulfate hyclrate [Ga2(S04)3~18H20] as well as mlxtures
thereof.
EXPMPLE 14
To the trivalent chr~mium electrolyte o'c Example 3 ,
0.05 g/l of Germanium ions are added in the form of germanium
c~loride (GeC14~. m e Germanium ions can also be added to the
electrolyte employing alternative satisfactory bath soluble and
cc~patible Germanium cc~ounds including ger~anium difluoride
(GeF2), germanium tetrafluoride (GeF4-3H20), germanium
diiodide (GeI2), germanium tetraiodide (GeI4), germanium dioxide
(G~02) as well as nuL~tu_es thereof.
EXA~PLE 15
To the trivalent chrGmium electrolyte of E~ample 3,
0.05 g/l of Indium ions are added in the form of indium chloride
(InC13). The Indium ions can also be added to the electrolyte
employing alternative satisfactory bath soluble and ccmpatible
Indium compounds including indium tribromide (Xn3r3), indium
perchlorate [In(C104)3-8H20], indium fluoride (InF3~3H20;
InF3~9H20),indium selenate [In2(SeO4)3. lOH20], indium sulfate
[In2(S04)3], indium sulfate nonahyarate [In2(S04)3~9H20],
y rng [In2(S04)3 H2S04 7H20~ as well
as mixtures thereof.
~ .
,
~'~4~3~7~
..
EX~MPLE 16
To the trivalent chrcmium electrolyte of EXample 3,
0005 g/l of Samariu~ ions are added in the form of sumarium
chloride hexahydrate (SmC13-6H20). The Samarium ions can
also be added to the electrolyte employ mg alternative
satisfactory bath soluble and compatible Samarium cc~pounds
including samarium acetate [Sm(C2H302)3-3H20], samarium
bromate [Sm(BrO3)3 9H20], samarium chloride (SmC13), samarium
sulfate [Sm2(S04~3-8H20], as well as mixtures thereof.
EX~MPLE 17
Tb the trivalent chromium electrolyte of Example 3,
0.05 g/l of Europium ions are added in the form of europium
sulfate octohydrate [Eu2(S04)3-8H20~. The Europium ions
can also be added to the electrolyte employing alternative
satisfactory bath soluble and compatible Europium ccmpounds
as well as mixtures thereof.
EXPMPLE 18
To the trivalent chrcmuum electrolyte of Example 3,
0.05 g/l of Gadolinium ions are added in the form of gadolinium
chloride hexahydrate (GdC13 6H20). The Gadolinium ions can
also be added to the electrolyte employing alternative
satisfactory bath soluble ~nd compatible Gadolinium compounds
including gadolinium acetate [Gd(C2H302~3 4H20]~ gadolinium
brcmide [GdBr3-6H~O], gadolinium chloride (GdC13), gadolinium
oxide (Gd203), g~dolinium selenate [Gd2(SeO4)3-8H20],
gadolinium sulfate [Gd2(S04)3], gadolinium sulfate octahydrate
[Gd2(S04)3-8H~O] as well as mixtures thereof.
24
~2~376
..
~E 19
Tb the trivalent chromium electrolyte of Example 3 ,
0.05 g/l of Terbium ions are added in the form of terbium
trichloride Hexahydrate (TbC13~6H2O). me Terbium ions can
also be added to the electrDlyte employing alternative
satisfactory bath soluble and compatible Terbium compounds
including terbium chloride (TbC13), terbium oxide (Tb203),
terbium sulfate ~Tb2(S04)3~8H20] as well as mixtures
thereof.
E~MPLE 20
To the trivalent chrcmium electrolyte of Example 3,
0.05 g/l of Dysprosium ions are added in the form of dysprosium
trichloride ~DyC13). The Dysprosium ions can also be added to
the electrolyte employing alternative satisfactory bath soluble
and compatible Dysprosium ccmpounds including dysprosium acetate
Y( 2 3 213 4H2O]' dysprosium brcmate [Dy(BrO3)3~9H2O],
dysprosium oxide (Dy2O3), dysprosium selenate [Dy~(SeO~)3~8H2O],
dysprosi~lm sulfate [Dy2(SO4)3~8H2Ol as well as mlxtures
thereof.
EX~MPLE 21
To the ~rivalent chr~mium electrolyte of Example 3,
0.05 g/l of Holmium ions are added in the form of holmium
trichloride hexahydrate (~oC13-6H2O3. The Holmium ions can
also be added to the electrolyte employing alternative
satisfactory bath soluble and ccmpatible Holmium ccmpounds
as well as mixtures thereof.
`` ~LZ~376
EXAMPLE 22
Tb the trivalent chromaum electrolyte of Example 3,
0.05 g/l of Erbium ions are added in the form of erbium
trichloride hexahydrate ~ErC13-6H20). The Erbium ions can
also be added to the electrolyte employing alternative
satisfactory bath soluble and ccmpatible Erbium ccmpounds
including erbium sulfate [Er2(S04)3), erbium sulfate
octahydrate [~r2(S04)3-8H20] as well as mixtures thereof.
EXAMP~E 23
To the trivalent chromium electrolyte of Example 3,
0.05 g/l of Thulium ions are added in the form of thulium
trichloride (ImC13). me mulium ions can also be added to th~
electrolyte employing alternative satisfactory bath soluble and
compatible mulium co~pounds as well as mixtures thereof.
EXAMPLE 24
To the trivalent chromium electrolyte of Example 3,
0.05 g/l of Ytterbium ions are added in the form of ytterbium
trichloride hexahydrate (YbC13~6H20). me Ytterbium ions can
i also be added to the electrolyte employing alternative
satisfactory bath soluble and compatible Ytterbium ccmpounds
including ytterbium acetate [Yb(C2H302)3~4H20]~ yt~erbium
sulfate [Yb2(S04)3], ytterbium sulfate octahydrate
[Yb2(S04)3-8H20~ as w~ell as mixtures thereof.
EXAMPLE 25
To the trivalent chrcmium electrolyte of Example 3,
0.05 g/l of Lutetium ions are added in the fonm of lutetium
26
_ ._ . _ . _ ... . ~ _ ., _ ,. . _ _ .. _ _ _ _ . . _ ~ .. ... _ . _., _ _ _ _ . _ . .. . _ .... _ . . .. .__ _ _ . . _ .
,
~244L37g~
sulfate octahydrate [Lu2(S04)3~8H20]. The Lutetium ions
can also be added to the electrolyte employing alternative
satisfactory bath soluble and compatible Lutetium compounds
as well as mixtures thereof.
EX~MPL~ 26
T~ the trivalent chromium electrolyte of Example 3 ,
0.05 g/l of Praseodymium ions are added in the form of
praseodymium sulfate octahvdrate [Pr2(S04)3-8H20]. The
Praseodymium ions can also be added to the electrolyte employing
alternative satisfactory bath soluble and comFatible Praseodymium
compounds including praseodymium acetate [Pr(C2~3C)2)3-3H20~,
praseodymuum bromate [Pr(BrO3)3-9H20~, praseodymium chloride
(PrC13), praseodymium chloride tPrcl3 7H20), praseodymium
selenate [Pr2tSeO4)3], praseodymium sulfate [Pr2tSO4)3],
praseodymium sulfate pentahydrate [Pr21S04)3-5H20] as well as
mixtures thereof.
EXAMPLE 27
This example demonstrates the effectiveness of the
metal ion reducing agents for rejuvenating trivalent chromium
electrolytes which have been rendered unacceptable or inoperative
because of an increase in hexavalent chronium concentration to an
undesirable level. It has been found by test that the
progressive buildup of hexavalent chromium concentration will
eventually produ oe a skipping of the chromium plate and
ultimately will result in the prevention of any chromium plate
deposit. Such tests employing typical trivalent chromium
~Z~376
t
electrolytes to which hexavalent chromium is intentionally added
has evidenced that a concentration of about 0.47 g/l of
hexavalent chromium results in plating deposits having large
patches of dark chromium plate and smaller areas which are
entirely unplated. As the hexavalent chromium concentration is
further increased to about 0.55 g/l according to such tests,
further deposition of chromium on the substrate is ccmpletely
prevented. me hexavalent chromium concentration at which
plating ceases will vary somewhat depending upon the specific
composition of the electrolyte.
In order to demonstrate a rejuvenation of a hexavalent
chromium contaminated electrolyte, a trivalent chrc~ium bath is
prepared having the follcwing composition:
INGREDIENr coNcENrRATIoN~ g/l
Sodium fluoroborate 110
~mmoniumn chloride 90
- Boric acid 50
Ammonium formate 50
Cr+3 ions 26
Surfactant 0.1
The bath is adjusted to a pH between about 3.5 and 4.0
at a temperature of about 70 to about 80F. S-shaped nickel
plated test panels are plated in the bath at a current density of
about 100 ASF. ~fter each test run, the concentration of
hexavalent chrcmium ions is increased from substantially 0 in the
original bath by increments of about 0.1 g/l by the addition of
lZ~ 6
chromic acid. Nb detrimental effect in the chrcmium plat mg of
the test panels was observed through the range of hexavalent
chrGmium concentration of frcm 0.1 up to 0.4 g/l. Hcwever, as
the hexavalent chromium concentration ~as increased above 0.4 g/l
large dark chrc~ium deposits along with small areas devoid of any
chrcmium deposit were observed on the test panels. As the
concentration of hexavalent chxcmium attained a level of 0.55 g/l
no further chrc~ium deposit could be plated on the test panel.
Under such circumstances, it has Xeretofore been csm~on
practice to dump the bath containing high hexavalent chromium
necessitating a makeup of a new bath which constitutes a costly
and time consuming operation.
Ib demonstrate the rejuvenation aspects of the present
invention, reducing metal ions as descriked in Examples 4 through
26 were added in incr~ments of akout 0.55 g/l to the bath
containing 0.55 g/l hexavalent chromium ions and a plating of the
test panels was resumed under the conditions as previously
described.
In each instance, the initial addition of 0.55 g/l of
the individual red-lcing metal ions to the bath contaminated with
0.55 g/l hexavalent chrcmium ions resulted in a restoratlon of
the efficiency of the chromium plating bath producing a good
chromium deposit of good color and coverage although h~avalent
chrcmium ions were still detected as being present in the bath.
2g
.
376
EXAMPLE 28
Tb the trivalent chromium electrolyte of Example 3 ,
0,05 g/l of scandium ions are added in the form of scandium
trichloride hexahydrate (ScC13 6H20). ffle scandium .ions can
also be added to the electrolyte employing alternative
satisfactory bath soluble and compatible scandium ccmpounds
including scandium chloride ~ScC13), scandium sulfate [Sc~(S04)3],
scandium sulfate pentahydrate [Sc2(S0~33-5H20], scandium sulfate
hexahydrate [Sc2(S04)3-6H20] as well as mixtures thereof.
EX~MPLE 29
Io the trivalent chromium electrolyte of Example 3,
O.05 g/l of yttrium ions are added in the form of yttrium
trichloride hexahydrate (YC13~6H20). The yttrium ions can
also be added to the electrolyte employing alternative
satisfactory bat~ soluble and compatible yttrium compounds
including yttrium acetate ~Y(c2H3o2)3.4H2o]~ yttrium
bronate [Y(BrO3)3-9H20], yttrium bromide ~YBr3), yttrium
~L24~3~6
bromide nonahydrate (YBr3 9H20), yttrium chloride (YCl3),
yttrium chloride monohydrate (YCl3-H20), yttrium iodide
(YI3), yttrium oxalate [ 2(C24)3-9H2]' yttrium
oxide (Y203), yttrium sulfate ~Y2(S04)3], yttrium
sulfate octahydrate [Y2(S04)3 8H20] as well as muxtures
thereof.
EXAMPLE 30
Tb the trivalent chromium electrolyte of Example 3 ,
0.05 g/l of lanthanum ions are added in the form of lanthanum
trichloride heptahydrate (LaCl3 ~I20). The lanthanum ions
can also be added to the electrolyte employing alternatlve
satisfactory bath soluble and ccmpatible lanthanum ccmpounds
including lanthanum acetate [La(C2H302)3-1~H20], lanthanum
brcmate [La(BrO3)3-9H20], lanthanum bromide (LaBr3-7H20),
lanthanum car~onate [La2(C03)3-8H2o], lanthanum chloride
(LaCl3~, lanthanum ~ydr~xide [La(QH)3~, lanthanum iodate
[La(I03)3], lanthanum molybdate [La(MbO4)3], lanthanum
oxide (La203), lanthanum sulfate [La2(S04)3], lanthanum
sulfate nonahydrate [La2(S04)3 9H20] as well as mixtures
thereof.
EXAMPLE 31
Tb the trivalent chrcmium electrolyte of Example 3 ,
0.05 g/l of titanium ions are added in the form of titanium
trichloride (TiCl3). me titanium ions can also be added to
the electrolyte e~ploying alternative satisfactory bath soluble
~Z4~3~;
and comçatible titanium compounds including titanium tribormide
tTiBr3-6H20), titanium tetrachloride (TiC14), titanium
trifluoride ~'riF3), titanium tetrafluoride ~TiF4), titanium
iodide (TiI4), titanium oxalate [Ti2~C204)3-10H20~, titam um
dioxide (TiO2-XH20) as well as mixtures thereof.
EXP~LE 32
To the trivalent chromium electrolyte of Example 3,
0.05 g/l of hafnium ions are added in the form of hafnium
oxychloride octahydrate (HfOC12-8H20). me hafnium ions can
also be added to the electrolyte employing alternative
satisfactory bath soluble and ccmpatible hafnium compounds and
mixtures thereof.
EXAMPLE 33
~ o the trivalent chrcmium electrolyte of Example 3,
0.05 g/l of arsenic ions are added in the form of arsenic oxide
(As205). The arsenic ions can also be added to the electrolyte
employing alternative satisfactory bath soluble and compatible
arsenic compcunds including arsenic pentafluoride (PsF5), arsenic
trioxide (As203) as well as mixture~ thereof.
" ~Z~4376
t
EX~MPLE ~4
Tb the trivalent chramium electrolyte af Example 3,
0.05 g/l of selenium ions are added in the form of sodium
selenate (Na2SeO4). The selenium ions can also be added to
the electrolyte emplaying alternative satisfactorv bath soluble
and ca~patible selenium compounds including sodium selenate
hydrate (Na2SeO4 lOH20), sodium selen}te ~Na2SeO3 5H20),
selenium dioxide (SeO2), potassium selenate(K2SeO4), potassium
selenite (K2SeO3) as well as mixtures thereof.
;
E~MPLE 35
To the trivalent chrcmium electrolyte of ExamDle 3,
0.05 g/l of tellurium ions are added in ~he form of sodium
tellurium oxide dihydrate ~Na2TeO42H20). The tellurium
ions can also ~e added to the electrolyte employing alternative
satisfactory bath soluble and compatible tellurium ccmounds
including potassium orthotellurate (K2H4Te & -3H20~, potassium
telluride (K2Tb), potassium tellurite (K2TeO3), sodium
orthotellurate (Na2H4TeO6), sodium tellurite (Na2TeO3) as well
as mixtures thereof.
EXAMPLE 36
To the trivalent chrcmium electrolyte of Example 3,
0.05 g/l of cerium ions are added in the fonm of cerium sulfate
(Ce2(S04)3). The cerium ions can also be added to the
electrolyte employing alternative satisfactory kath soluble and
f~37f~
..
aompatible cerium compounds including cerium acetate
ECe~C2H302)2], cerium bromate [Ce(BrO3)3-9H20], cerium carhonate
[Ce2(C03)3-5H20], cerium chloride (CeC13), cerium iodide
(CeI3~9H20), cerium molybdate [Ce2(MoO4)3], cerium selenate
[Ce2(SeO4)3], cerium sulfate tetrahydrate [Ce2(S04)3-4H~O],
cerium sulfate octahydrate [Ce2(S04)3~8H20], cerium sulfate
nonahydrate [Ce2~S04)3-9H20] as well as mixtures thereof.
, EXPMPLE 37
Tb the trivalent chromium electrolyte of Example 3 ,
0.05 g/l of uranium ions are added in the form of uranium
oxysulfate hydrate (U02(S04)-3-L~20). The uranium ions can
also be added to the electrolyte employing alternative
satisfactory bath soluble and ccmpatible uranium ccmpounds
including uranium trihromide (UBr3), uranium tetrabrcmide
(UBr5), uranium trichloride (UCl3), uranium tetrachloride
(UC14), uranium tetraiodide (UI4), uranvl acetate
[U02(C2H302)2-2H20~, uranyl bromide (U02Br2), uranyl chloride
(U02C12), uranyl formate [U02~CH02)2-H20]~ uranyl iodate
[U02(I03)2-H20~, uran~l oxalate [U02C204-3H20], uranyl sulfate
heptahydrate (2U02S04~7H20) as well as muxtures thereof.
34
124~376
The electrolytes of Examples 4 through 26 and 28
through 37 were employed at an operating temperature of
from about 70 to about 80F (21-27C) at cathode current
densities of from about 100 to about 250 ASF and an anode
current density of about 50 ASF. The electrolyte is
employed using a graphite anode at an anode to cathode
ratio of about 2:1. The electroplating bath is operated
employing mild air and/or mechanical agitation, In each
instance, it has been found advantageous to subject the
bath to an electrolytic preconditioning at a low current
density, e.g. about 10 to about 50 ASF for a period up to
about 24 hours to achieve satisfactory plating performance
at the higher normal operating current densities.
The electrolytes incorporating the additive metal
ions in accordance with Examples 4-26 and 28-37 under the
foregoing operating conditions produce full bright and
uniform chromium deposits having good to excellent coverage
over the current density ranges employed including good
coverage in the deep recess areas of the J-type panels
employed for test plating.
376
,, .
EX~MPLE 38
This example demDnstrates the effectiveness of the
metal ion additive agents for rejuvenating trivalent chromium
electrolytes which have been rendered unacceptable or inoperative
because of an increase in hexavalent chrom1um concentration to an
undesirable level. It has been found by test that the
progressive buildup of hexavalent chromium concentration will
eventually produ oe a skipping of the chrom~um plate and
ultLmately will result in the prevention of any chrcmium plate
deposit. Such tests employing typical trivalent chromium
electrolytes to which hexavalent chramium is intentionally added
has evidenc~d that a concentration of about 0.47 g/l- of
hexavalent chromium results in plating deposits having large
patches of dark chrcmium plate and s~aller areas which are
entirely unplated. As the hexavalent chromium concentration is
further increased to about O.55 g/l accord m g to such tests,
further deposition of chromium on the substrate i5 completely
prevented. ~he hexavalent chromlum concentration at which
plating ceases will vary somewhat depending upon the specific
ccmposition of the electrolyte.
In order to demonstrate a rejuvenation of a hexavalent
chromium contaminated electrolyte, a trivalent chro~ium bath is
prepared having the follcwing ccmposition:
36
~ Z'~ 7~
INGREDIENT CC~CENTRATION, g/l
Sodium fluoroborate 110
Ammoniurnn chloriae 90
Boric acid 50
Ammonium formate 50
Cr+3 ions - 26
Surfactant 0.1
The bath is adjusted to a pH between about 3.5 and 4.0
at a temperature of about 70 to about 80F. S-shaped nickel
plated test panels are plated in the bath at a current densitv of
about 100 ASF. After each test run, the concentration' of
hexavalent chrcmium ions is increased from substantially 0 in the
original bath by incre~ents o about 0.1 g/l by the addition of
chromic acid. No detrimental effect in the chrcmium plating of
the test panels was observed through the range of hexavalent
chrcmium concentration of frcm 0.1 up to 0.4 g/l. However, as
the hexavalent chranium concentration was increased above 0.4 g/l
large dark chrcmium deposits along with small areas devoid of any
chranium deposit were observed on the test panels. As the
concentration of hexavalent chrcmium attained a level of 0.55 g/l
no further chromium deposit could be plated on the test panel.
Under such circumstances, it has heretofore been ccm~,on
practice to dump the bath c~ntaining high hexavalent ch~xxnium
necessitating a maXeup of a new bath which constitutes a costly
and time consuming operation.
37
~Z~4~7~
Tb demonstrate the rejuvenation aspects of the present
invention, a~di~iv~ metal ions as described in EXamples28 through
37 were added in increments of about 0.55 g/l to the bath
containing 0.55 g/1 hexavalent chromium ions and a plating of the
test panels was resumed under the conditions as pr~viously
described.
In each instance, the initial addition of 0.55 g/l of
the individual additive metal ions to the bath contaminated with
0.55 g/l hexavalent chromium ions resulted in a restoration of
the efficiency of the chromium plating bath producing a good
chromium deposit of good color and coverage although hex~valent
chromium ions were still detected as being present in the bath.
While it will be apparent that the invention herein
disclosed is well calculated to achieve the benefits and
advantages as hereinabove set forth, it will be appreciated that
the invention is susceptible to modification, variation and
change without departing frGm the spirit thereof.
38
