Note: Descriptions are shown in the official language in which they were submitted.
~Z~14~
This is a divisional application of Canadian
application No. 389,254, filed November 2, 1981,which
relates to a trivalent chromium electrolyte and a process
employing vanadium reducing agent.
Chromium electroplating baths are in wide-
spread commercial use for applying protective and
decorative platings to metal substrates. For the most
part, commercial chromium plating solutions heretofore
used employ hexavalent chromium derived from compounds
such as chromic acid, for example, as the source of
the chromium constituent. Such hexavalent chromium
electroplating solutions have long been characteri~ed
as having limited covering power and excessive gassing
particularly around apertures in the parts being
plated which can result in incomplete coverage. Such
hexavalent chromium 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 chromium, and
associated waste disposal problems, extensive work has
been conducted in recent years to develop chromium
electrolytes incorporating trivalent chromium providing
numerous benefits over the hexavalent chromium electro-
lytes heretofore known. According to the invention of theparent application, a trivalent chromium electrolyte and
process for depositing chromium platings have been
'`'``
-- ~zo~
discovered by whieh bright ehromium deposits are pro-
dueed having a color equivalent to that obtained from
hexavalent ehromium baths. The eleetrolyte and proeess
of the parent application further provide electro-
plating employing eurrent densities whieh vary over awide range without producing the burning associated
with deposits plated from hexavalent ehromium plating
baths; in whieh the eleetrolyte eomposition minimizes
or eliminates the evolution of mist or noxious odors
during the plating proeess; the electrolyte and process
provide for excellent coverage of the substrate and
good throwing power; current interruptions during the
electroplating eyele do not adversely affeet the
chromium deposit enabling parts to be withdrawn from
the electrolyte, inspeeted, and thereafter returned to
the bath for eontinuation of the electroplating cycle;
the electrolyte employs low eoneentrations of chromium
thereby redueing the loss of ehromium due to drag-out;
and waste disposal of the ehromium is faeilitated in
that the trivalent ehromium ean readily be preeipitated
from the waste solutions by the addition of alkaline
substances to raise the pH to about 8 or above.
The electrolyte of the parent application
further ineorporates a redueing agent to prevent the
formation of detrimental concentrations of hexavalent
ehromium during bath operation whieh heretofore has
interfered with the efficient electrodeposition of
--2 --
lZ019~
chromium from trivalent chromium plating baths in-
cluding the reduction in the efficiency and covering
power of the bath. In some instances, the buildup of
detrimental hexavalent chromium has occurred to the
extent that a cessation in electrodeposition of
chromium has occurred necessitating a dumping and
replacement of the electrolyte. It has now been found,
in accordance with the invention of the present divi-
sional application, that the addition of the reducing
agent according to the electrolyte herein disclosed
effects a rejuvenation of an electrolyte contaminated
with excessive hexavalent chromium restoring the plating
efficiency and throwing power of such a bath and avoid-
ing the costly and time consuming step of dumping and
replacing the electrolyte.
The benefits and advantages of the invention
in accordance with the composition aspect 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 a reducing agent com-
prising vanadium ions 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 electro-
lyte can broadly contain about 0.2 to about 0.8
lZ0~4~:1
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 about 3:1, a bath
soluble and compatible vanadium salt present in a con-
centration to provide a vanadium ion concentration of
at least about 0.015 grams per liter (g/1) up to about
6.3 g/l as a reducing agent for 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 in a molar ratio of halide to chromium ions o~
about 0.8:1 to about 10:1; one or a combination of
bath soluble salts to increase bath conductivity com-
prising compatible simple salts of strong acids such
as hydrochloric or sulfuric acid and alkaline earth,
alkali and ammonium salts thereof of which sodium
fluoborate comprises a preferred conductivity salt,
and hydrogen ions present to provide an acidic electro-
lyte having a pH of about 2.5 up to about 5.5.
The electrolyte may optionally, but prefer-
ably, also contain a buffering agent such as boric
acid typically present in a concentration up to 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
--4--
12~)i4 11:
amounts of anti-foaming agents. Additionally, the bath
may incorporate other dissolved metals 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 a process aspect of
the invention, the electrodeposition of chromium
on a conductive substrate is performed employing the
electrolyte at a temperature ranging from about 15 to
about 45C. The substrate is cathodically charged and
the chromium is deposited at current densities ranging
from about 50 to about 250 amperes per square foot ~ASF)
usually employing insoluble anodes such as carbon,
platinized titanium or platinum. The substrate, prior to
chromium plating, is subjected to conventional pretreat-
ments and preferably is provided with a nickel plate
over which the chromium deposit is applied.
In accordance with a further process aspect of
the 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 vanadium reducing agent to reduce the
hexavalent chromium concentration to levels below about
25 100 parts per million (ppm), and preferably below 50 ppm
at which efficient chromium plating can be resumed.
Accordingly, the present divisional application
is directed toward a process for rejuvenating an aqueous
--5--
,,
~ lZ0141~
acidic trivalent chromium electrolyte whieh has been
impaired in effectiveness due to the contamination by
excessive quantities of hexavalent chromium, the electro-
lyte containing trivalent chromium ions, a complexing
agent for maintaining the trivalent chromium ions in
solution, halide ions, ammonium ions and hydrogen ions
to provide a pH on the acid side, which process comprises
the step of adding to the electrolyte a reducing agent
comprising vanadium ions in at least an amount sufficient
to reduce the concentration of hexavalent chromium ions
to a level which is not in excess of 0.4 grams/liter.
Additional benefits and advantages of the in-
ventions of both parent and divisional applications will
become apparent upon a reading of the following descrip-
tion of the preferred embodiments and the specificexamples provided.
In accordance with the composition aspect
of the invention, the trivalent chromium e~ectrolyte con-
tains, as one of its essential constituents, trivalent
chromium ions which may broadly range from about 0 2 to
about 0.8 molar, and preferably from about 0O4 to about
0.6 molar. Concentrations of trivalent chromium below
about 0.2 molar have been found to provide poor throwing
power and poor coverage in some instances whereas, concen-
trations in excess of about 0.8 molar have in someinstances resulted in precipitation of the chromium cons-
tituent in the form of complex compounds. For this
reason, it is preferred to maintain the trivalent chromium
--6--
--"` 120'~4i~
ion concentration within a range of about 0.2 to about 0.8
molar, and preferably from about 0.4 to about 0.6 molar.
The trivalent chromium ions can be introduced in the form
of any simple aqueous soluble and compatible salt such
as chromium chloride hexahydrate, chromium sulfate,
and the like. Preferably, the chromium ions are intro-
duced as chromium sulfate for economic considerations.
A second essential constituent of the electro-
lyte 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 chromium ions to permit electro-
deposition thereof as well as to allow precipitation
of the chromium during waste treatment of the effluents.
The complexing agent may comprise formate ions, acetate
ions or mixtures of the two of which the formate ion
is preferred. 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. The complexing agent is normally employed in
a molar ratio of complexing agent to chromium ions of
from 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 complexing agent such as formate ions are unde-
sirable since such excesses have been found in someinstances to cause precipitation of tne chromium con-
stituent as complex compounds.
A third essential constituent of the electro-
--` lZOl~
lyte comprises a reducing agent in the form of bath
soluble and compatible vanadium salts present in an
amount to provide a vanadium ion coneentration of at
least about 0.015 g/l up to about 6.3 g/l. Exeess
amounts of vanadium do appear to adversely effect the
operation of the electrolyte in some instances causing
dark striations in the plate deposit and a reduction
in the plating rate. Typieally and preferably,
vanadium eoneentrations of from about 0.2 up to about
1 g/l are satisfactory to maintain the hexavalent
chromium concentration in the electrolyte below about
100 ppm, and more usually from about 0 up to about 50
ppm at which optimum efficiency of the bath is attained.
The vanadium reducing agent is introduced
into the electrolyte by any one of a variety of vanadium
salts including those of only minimal solubility in
whieh event mixtures of sueh salts are employed to
achieve tne rec~uired eoncentration. The vanadium salt
may eomprise any one of a variety of salts which do not
adversely effect the chromium deposit and inelude, for
example, sodium metavanadate (NaVO3); sodium orthovana~
date (Na3VO4, Na3VO4-10H2O, Na3VO4-16H20); sodium pyro-
vanadate (Na4V2O7); vanadium pentoxide (V205); vanadyl
sulfate (VOSO4); vanadium trioxide (V203); vanadium
di-tri or tetra ehloride (VC12, VC13, VC14); vanadium
tri-fluoride (VF3.3H2O); vanadium tetrafluoride (VF4);
vanadium pentafluoride (VF5); vanadium oxy bromide
(VOBr); vanadium oxy di- or tri-bromide (VOBr2, VOBr3);
--8--
~z~
vanadium tribromide (VBr3), ammonium metavanddate
(NH4VO3); ammonium vanadium sulfate (NH4V(SO4)2.12H2O):
lithium metavanadate (LiVO3.2H2O; potassium metavana-
date (~VO3): thallium pyrovanadate (Tl4VO7), thallium
metavanadate (TlVO3), as well as mixtures thereof.
In as much as the trivalent chromium salts,
complexing agent, and vanadium salts do not provide
adequate bath conductivity by themselves, it is prefer-
red to further incorporate in the electrolyte control-
led amounts of conductivity additives which typicallycomprise salts of alkali metal or alkaline earth metals
and strong acids such as hydrochloric acid and sulfuric
acid, as well as the acids themselves. The inclusion of
such conductivity additives is well known in the art and
their use minimizes power dissipation during the elec-
troplating operation. Typical conductivity additives
include potassium and sodium sulfates and chlorid~s as
well as ammonium chloride and ammonium sulfate. A par-
ticularly satisfactory conductivity additi~e is fluobo-
ric acid and the alkali metal, alkaline earth metal andammonium bath soluble fluoborate salts which introduce
the fluoborate ion in the bath and which has been found
to further enhance the chromium deposit~ Such fluobo-
rate additives are preferably employed to provide a
fluoborate ion concentration of from about 4 to about
300 g/l. It is also typical to employ the metal salts
of sulfamic and methane sulfonic acid as a conductivity
salt either alone or in combination with inorganic con-
~Z014~l1
ductivity salts. Such conductivity salts or mixtures
thereof are usually employed in amounts up to about 300
g/l or higher to achieve the requisite electrolyte con-
ductivity and optimum chromium deposition.
It has also been observed that ammonium ions
in the electrolyte are heneficial in enhancing the
reducing efficiency of the vanadium constituent for
converting hexavalent chromium formed to the trivalent
state. Particularly satisfactory results are achieved
10 at molar ratios of total ammonium ion to chromium ion
ranging from about 2.0:1 up to 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 formate, for
15 example, as well as in the form of supplemental con-
ductivity salts.
The effectiveness of the vanadium reducing
agent in controlling hexavalent chromium formation is
also enhanced by the presence of halide ions in the
20 bath of which chloride and bromide ions are preferred.
The use of a combination of chloride and bromide ions
also inhibits the evolution of chlorine at the anode.
While iodine can also be employed as the halide con-
stituent, its relatively higher cost and low solubility
25 render it less desirable than chloride and bromide.
Generally, halide concentrations of at least about
15 g/l have been found necessary to achieve sustained
efficient electrolyte operation. More particularly, the
--10--
0~9Ll~
halide concentration is controlled in relationship to
the chromium concentration present and is controlled
at a molar ratio o~ about 0.8:1 up to about 10:1 halide
to chromium, with a molar ratio of about 2:1 to about
4:1 being preferred.
In addition to the foregoing constituents,
the bath optionally but preferably also contains a
buffering agent in an amount of about 0.15 molar up to
bath solubility, which amounts typically range up to
about 1 molar. Preferably the concentration of the
buffering agent is controlled from about 0.45 to about
0.75 molar calculated as boric acid. The use of boric
acid as well as the alkali metal and ammonium 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 electro-
lyte. In accordance with a preferred practice, the
borate ion concentration in the bath is controlled at
a level of at least about 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 wetting 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
--11--
, .,
0~L41~
cationic and are selected from those which are compatible
with the electrolyte and which do not adversely affect
the electrodeposition performance of the chromium
constituent. Typically, wetting agents which can be
satisfactorily employed include sulphosuccinates or
sodium lauryl sulfate and alkyl ether sulfates alone
or in comhination with other compatible anti-foaming
agents such as octyl alcohol, for example. The presence
of such wetting agents has been found to produce a
clear chromium deposit while eliminating dark mottled
deposits and providing for improved coverage in low
current density areas. While relatively high concen-
trations of such wettiny agents are not particularly
harmful, concentrations greater than about 1 gram per
liter have been found in some instances to produce a
hazy deposit. Accordingly, the wetting agent when
employed is usually controlled at concentrations less
than about 1 g/l, with amounts of about 0.05 to about
1 g/l being typical,,
It is also contemplated that the electrolyte
can contain other metals including iron, manganese, and
the like in concentrations of from 0 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 concentration of iron at levels below about 0.5 g/l.
The electrolyte further contains a hydrogen
- -12-
~zo~
ion concentration sufficient to render the electrolyte
acidic~ The concentration of the hydrogen ion is
broadly controlled to provide a pH of fxom about 2.5 up
to about 5.5 while a pH range of about 3.5 to 4.0 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 h~dro-
chloric or sulfuric acid and/or ammonium or sodium
carbonate or hydroxide are preferred. During plating,
the electrolyte has a tendency to become more acidic
and appropriate pH adjustments are effected so as to
maintain the pH within an optimum range for the parti-
cular bath components and concentrations used as well
as the nature of the substrate to be plated; this can
be done by the addition of-alkali..me..tal and ammonium
hydroxides and carbonates of which the ammonium salts
are preferred in that they simultaneously replenish
the ammonium constitutent in the bath.
In accordance with the process aspect
of the invention, the electrolyte as hereinabove des-
cribed is employed at an operating temperature ranging
from about 15 to about 45C, preferably about 20~ to
about 35C. Current densities during electroplating
25 can range from about 50 to 250 ASF with densities of
-13-
~'.
~ ~Z0~41~L
about 75 to about 125 ASF being more typical. The
electrolyte can be employed to plate chromium on con-
ventional ferrous or nickel substrates and on stainless
steel as well as nonferrous substrates such as aluminum
and zinc. The electrolyte can also be employed for
chromium plating plastic substrates which have been
- 13a -
.
. .,
~o~
subjected to a suitable pretreatment according to
well-known techniques to provide an electrically con-
auctive coating thereover such as a nickel or copper
layer. Such plastics include ABS, polyolefin, PVC,
and phenol-formaldehyde polymers. The work pieces to
be plated are subjected to conventional pretreatments
in accordance with prior art practic-es ana the process
is particularly effective to deposit chromium platings
on c~nductive substrates which have been subjected to
a prior nickel plating operation.
During the electroplating operation, the
work pieces are cathodically charged and the bath
incorporates a suitable anode of a material which will
not adversely ~f~ect and 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. When a
chromium-iron alloy is to be deposited, the anode may
suitably be comprised of iron which itself will serve
as a source of the iron ions in the bath.
In accordance with a further aspect of the
process of the invention, a rejuvenation of a tri-
valent electrolyte which has been rendered ineffective
or inoperative due to the high concentration of hexa-
valent chromium ions is achieved by the addition of a
controlled effective amount of the vanadium reducing
agent. Depending upon the specific composition of the
-14-
~L2(~
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 vanadium salt--in further combina-
tion with halide salts, ammonium salts, borates, and
conductivity salts as may be desired or required. The
addition of the vanadium reducing agent can be effected
as a dry salt or as an aqueous concentrate in the
presence of agitation to achieve uniform mi~ing. The
time necessary to restore the electrolyte to efficient
operation will vary depending upon the 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 30 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 vanadium ions to
achieve rejuvenation can range within the same limits
as previously defined for the operating electrolyte.
In order to further illustrate the composition
and process of the invention, the following specific
-` 120141~L
examples are provided. It will be understood that
the examples are provided for illustrative purposes
and are not intended to be limiting of the invention
as herein disclosed and as set forth in the subjoined
claims.
A series of trivalent chromium electrolytes
are prepared having compositions as set forth in Table 1.
-16-
20141~
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--17--
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-18-
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19--
120~
The particular se~uence of addition of the
bath constituents during bath make-up is not critical
in achieving satisfactory performance. In all of the
examples with the exception of Examples 34 and 35, the
trivalent chromium ions are introduced in the form of
chromium sulfate. In Examples 34 an'd 35, the trivalent
chromium constituent is introduced employing chromium
chIoride hexahydrate. In each of the examples, the
surfactant employed comprises a mixture of dihexyl
10 ester of sodium sulfo succinic acid and sodium sulfate
derivative of 2-ethyl-1-hexanol. The operating tempera-
ture of the exemplary electrolytes is from 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 electrolytes are employed using
a graphite anode at an anode to cathode ratio of about
2:1. The electroplating bath is operated employing a
mild air and/or mechanical agitation. It has been found
advantageous in some of the examplary bath formulations
20 to subject the bath to an electrolytic preconditioning
at a low current density, e.g. about 10 to about 30 ASF
for a period up to about 24 hours to achieve satisfactory
plating performance at the higher normal operating current
densities.
Each of Examples 1-36 employed under the foregoing
conditions produced full bright and uniform chromium de-
posits having good to excellent coverage over the current
density ranges employed including good coverage in the deep
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~L20~1~4~1
recess areas of the J-type panels employed for test plating.
EXAMPLE 37
-
This example demonstrates the effectiveness
of the vanadium compound for rejuvenating trivalent
chromium electrolytes which have been rendered un-
acceptable or inoperative because of-an increase in
hexavalent chromium concentration to an undesirable
level. It has been found by test that the progressive
build-up of hexavalent chromium concentration will
eventaully produce a skipping of the chromium plate
and ultimately will result in the prevention of any
chromium 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 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 O.S5 g/l according to such
tests, further deposition of chromium on the substrate
is completely prevented. The hexavalent chromium
concentration at which plating ceases will vary some-
what depending upon the specific composition of the
electrolyte.
3.20~
In order to demonstrate a rejuvenation of a
hexavalent chromium contaminated electrolyte, a triva-
lent chromium bath is prepared having the following
composition:
InqredientConcentration, q/l
Sodium fluoborate 110
Ammonium 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 80 to about 90~F.
S-shaped nickel plated test panels are plated in the
bath at a curxent density of about 100 ASF. After each
test run, the concentration of hexavalent chromium ions
is increased from substantially 0 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 were observed through the range of
hexavalent chromium concentration of from 0.1 up to
0.4 g/l. However, as the hexavalent chromium concen-
tration was increased a~ove 0.4 g/l large dark chromium
deposits along with small areas devoid of any chromium
deposit were observed on the test panels. As the
concentration of hexavalent chromium 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 common practice to dump the bath containing high
hexavalent chromium necessitating a make-up of a new
bath which constitutes a costl~ and ~ime consuming
operation.
To demonstrate the rejuvenation aspects of
10 the present invention, vanadium ions were added in
increments of about 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 conditons as previously
described. The addition of 0.55 g/l of vanadium ions
15 corresponds to 2.6 g/l of vanadyl sulfate and corres-
ponds to an incremental weight ratio addition of
vanadium ions to hexavalent chromium ions of about 1:1.
The initial addition of 0.55 g/l vanadium
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 hexavalent chromium ions were still detected
as being present in the bath.
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l~Q ~4:1~
The further addition of 0.55 g/l vanadium
ions produced a further improvement in the chromium
deposit and analysis indicates the presence of a small
amount of hexavalent chromium in the bath.
Finally, the addition of a further 0.55 g/l
vanadium ions for a total of 1.65 gjl vanadium ions to
the bath xesulted in an excel~ent chromium deposit and
an analysis for hexavalent chromium was negative. These
test results clearly demonstrate the efficacy of
10 vanadium as a rejuvenating agent for contaminated
trivalent chromium plating bathsO
EXAMPLE 38
In order to further demonstrate the process
for rejuvenating trivalent chromium baths contaminated
15 with hexavalent chromium, a trivalent chromium plating
bath is prepared of the composition as described in
Example 37 to which 1.65 g/l of hexavalent chromium is
aaded corresponding to a concentration approximately
three times the amount at which tests indicated a
20 deposition of chromium ceased.
A test panel is plated under conditions as
previously described in Example 37 clearly evidencing
complete failure to deposit any chromium on the test
panel. Thereafter, 4.95 g/l of vanadium ions corres-
25 ponding to 23.5 g/l of vanadyl sulfate is added to the
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~2~L4~;
bath which is calculated to reduce all of the hexavalent
chromium present to the trivalent state.
Following the addition of the vanadium reju-
venation agent, the bath under agitation was permitted
to stand for approximately ten minutes after which a
test panel was plated under the conditions as previous-
ly described in ~xample 37 It was observed that the
test panel exhibited a trace o~ chromium plate on the
surface thereof.
After waiting a total of forty-five minutes
following th~ vanadium addition to -the bath, a second
test panel is plated evidencing an improved chromium
plating with an increase in thickness and better
appearance.
The bath is thereafter electrolyæed at a low
current density of about 30 ASF for an additional three
hours and a third test panel is plated. The chromium
deposit is observed to he fully bright, of good color,
with some thin deposit in low current density areas.
The bath is further electrolyzed at a low
current density of 30 ASF for an additional seventeen
hour period after which a fourth test panel is plated
resulting in a chromium deposit of good thickness,
fully bright with thin areas in the low current densities.
The test solution is replenished to return it
to the concentration of the constituents as originally
provided prior to the hexavalent chromium and vanadium
addition including the addition of 3 g/l of trivalent
_ -25-
114~
chromium ions and a fifth test panel is plated. The re-
sultant panel is observed to have a fully bright chromium
plating of good color with substantially complete
coverage over the entire surface thereof including low
current density areas.
It should be appreciated that the efficacy
of the vanadium compound to rejuvenate trivalent chro-
mium baths contaminated with hexavalent chromium is
apparent for a wide variety of such trivalent chromium
electrolytes and is not specifically restricted to the
electrolyte as set forth in Examples 37 and 38.
