Note: Descriptions are shown in the official language in which they were submitted.
~8352~ 912,333
CADMIUM ELEC~ROPLA~ING BATH
A variety o~ electrolytic baths ~or electroplating
cadmium on metallic substrates have been employed in the past.
These baths typically utilize sulfates and cyanides as the pri-
mary electrolytes ~herein. Cyanide baths, while proving ef-
~ective in a commercial sense, have significant objectionablefeatures, not the least of which are toxicity of the bath com-
ponents and difficulty of waste disposal due to the cyanide ion
therein.
Heretofore available sulfate-based baths, while over-
coming many of the objectionable features of the cyanide baths,have been found to exhibit relatively low throwing power and
poor efficiency at low current densities, resulting in an in-
crease of metal in the bath upon continued bath operation.
~urthermore, most of the sulfate-based baths contain such com-
ponents as ammonium ions and chelating agents. Such components,
because of their ability to complex with heavy metal ions, sig- ;
nificantly increase the difficulty of eliminating heavy metals
from spent baths.
A chloride based cadmium bath, which has overcome ';
many of the problems of the sulfate baths, and has been popular
commercially, is disclosed in U. S. Patent 3,577,327. However,
this bath also contains ammonium ions and chelating agents,
e.g. ethylenediaminetetracetic acid (EDTA), nitriloacetic acid
(NTA) and citric acid in the bath. Thus, removal of heavy
metals from spent baths is similarly difficult and expensive
waste treatment procedures and equipment must be utilized.
In U. S. Patent No. 3,826,722 there is disclosed an
acid cadmium sulfate bath which does not contain ammonium ions
or chelating agents therein. However, the effectiveness of the
bath is dependent upon the inclusion of a thiosemicarbazone
constituent. It is believed that this compound is somewhat
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unstable in strong acid solutions, and upon continued use in
an electrolytic bath may result in cadmium deposits which are
dull in appearance over an appreciable cathode current density
range. Sul~ur contamination of the bath from breakdown of this
thiosemicarbazone compound on extended use can also prevent
bright-dipping of the work piece subsequent to cadmium deposi-
tion.
In accordance with the invention, there is provided
an aqueous acidic electrolytic bath composition sui~able for
electroplating cadmium on a metal-surfaced substrate comprising
about 5 to about 75 grams per liter o~ cadmium ion~ a free acid
selected ~rom the group consisting of sulfuric and fluoboric
acids or mixtures thereof at a concentration of from about 0.4N
to about 4.ON, and a surfactant combination comprising about -
0.5 to about 20.0 grams per liter of a cationic polyoxyalkyl-
ated amine and about 0.5 to about 10.0 grams per liter of an
anionic surfactant. Preferably, the bath also contains from
about 0.05 to about 2.0 grams per liter of at least one non-
sulfur containing brightener.
The present bath eliminates the necessity for objec-
tionable ammonium ion and/or chelating agents thereby simpli-
fying waste treatment procedures for heavy metal removal.
Utiliæation of the preferred components in the invention pro-
vides a bath exhibiting high cathode current efficiency and
superior bright throwing power in recessed areas of the cath-
ode. The bath is capable of producing bright, smooth, fine-
grained cadmium deposits over a wide cathode current density
range upon continued electrolysis.
As previously noted~ the components which are essen-
tial for satisfactory operation of the bath of the present in-
vention to provide smooth, flne-grained, relatively bright
cadmium deposits include cadmium ions, a free acid, and the
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~83522
surfactant combination.
The bath may contain from about 5 to 75 grams per liter
of cadmium ion, and pre~erably con~ains about 8 ~o about 55 grams
per liter. Cadmium ion concentrations higher than about 75 grams
per liter may tend to produce a coarse, grainy and spongy deposit
at low cathode current densities, whereas baths containing less
than about 5 grams of cadmium ion per liter result in hazy, non-
uniform, non-bright deposits and exhibit low cathode current ef-
ficiency. The cadmium ion can be conveniently furnished from
soluble cadmium sulfate or cadmium fluoborate salts or from
cadmium oxide, the ]atter being capable of forming a soluble cad-
mium salt in combination with anions normally otherwise introduced.
The concentration of free acid selected from the group
consisting of sulfuric and/or fluoboric may range from about o.4N
to about 4.ON with from about 0.75N to about 2.5N being preferred.
Use of less than o.4N acid concentration may produce a poorly con- ` -
ductive bath which is operative only over a narrow range of current
density, thereby producing deposits of somewhat marginal quality.
Raising the free acid concentration beyond about 4.oN provides
minimal additional increase in current density, and at the same
time may tend to provide reduced cathode current ef~iciency.
The cationic surfactants useful herein are polyoxy-
alkylated amines. Exemplary compounds within this class, and com~
~f~on~ ecn
mercially available, include "El~ d" C-25, tradename ~or a
tertiary amine having one coconut fatty alkyl group and two poly-
oxyethylene groups attached to the amino nitrogen, available from
the Armak Company; "Polyrad" 1110, tradename for a dehydroabietyl-
amine-ethylene oxide adduct, available from the Hercules Powder
Company; and "Tetronic" 504, tradename for a polyoxypropylene/
polyoxyethylene diamine, available from BAS~ Wyandotte Company.
The concentration of cationic surfactants should be from about
0.5 grams per liter to about 20 grams per liter with from about
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2.0 to about 15.0 grams per liter being preferred. Below about
0.5 grams per liter, the cadmium deposit tends to be coarse and
dark, with no apparent grain refinement. At elevated concentra-
tions, i.e. above about 20 grams per liter, the solubility limits
of the surfactant in the bath may be exceeded.
The anionic surfactants useful herein in combination
with the cationic surfactants hereinbefore defined include con-
densed naphthalene sulfonic acids or their corresponding salts, and
long chain, i.e. at least 8 carbon atoms, alcohol sulfates.
The naphthalene sulfonates are formed from naphthalene
and sulfonic acid, usually condensed in the presence of a lower
aldehyde such as formaldehyde, and their molecular weight may
vary considerably. The most useful sulfonates are those having
a molecular weight of from about 400 to about 1,200 with from 600
to 900 being preferred.
Exemplary compounds fâlling within the above classes of
materials, and commercially available, include "Lomar" NC0, trade-
name for the sodium salt of naphthalene sulfonic acid, available
from the Diamond Shamrock Chemical Company; "Daxad" 11, tradename
for a condensed haphthalene sulfonic acid, available from the
W. R. Grace & Company; "Blanco't, tradename for a condensed naph-
thalene sulfonic acid, available from the GAF Corporation;
"Darvan" No. 1, tradename for a condensed naphthalene sulfonic
acid, available from the R. T. Vanderbuilt Company; "Duponol" 80,
25 tradename for the sodium salt of octyl alcohol sulfate, availabIe -
~rom the E. I. du Pont Company; and "Duponol" SN, tradename for
a mixture of sodium salts of long chain alcohol sulfates, avail-
able from the E. I. du Pont Company. The anionic surfactant
should be present in a concentration of from 0.5 gram per liter
to about 10.0 grams per liter with a range of 2.0 to 5.0 grams
per liter being preferred. Below 0.5 gram per liter, the cadmium
deposit tends to be coarse and dark with no apparent grain refine-
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ment. No advantage is gained by exceeding 10.0 grams per liter,
and foaming of the bath becomes excessive.
The electrolytic bath of the present invention desir-
ably and preferably includes non-sulfur containing organic
brighteners to develop uniform specular brightness over a wide
plating current density range. Brighteners which have been
~ound to impart beneficial effects on the bath of the present in-
vention include aryl aldehydes, e.g. anisic aldehyde, ring halo-
genated aryl aldehydes; e.g. orthochlorobenzaldehyde, 2,4-di-
chlorobenzaldehyde, and 2,6-dichlorobenzaldehyde; heterocyclic
aldehydes, e.g. thiophene aldehyde, aryl olefinic-conjugated ;
ketones, e.g. benzylidine acetone, and heterocyclic carboxylic
acids, e.g. nicotinic acid and isonicotinic acid.
It has been determined that a combination or condensate
15 of aminoguanidine bicarbonate and an aryl aldehyde can be util- ;
ized as a brightener herein. Aryl aldehydes such as ethyl vanil-
lin veratraldehyde, 2,5-dimethoxyl aldehyde, glutar aldehyde,
tolyl aldehyde, etc., when admixed with aminoguanidine bicar-
bonate in the bath or when condensated therewith prior to being
added to the bath impart full brightness to the cadmium deposit
over a useful cathode current density range. Benzoylpyridine is
another compound capable of use as a brightener herein.
The preferred brighteners are orthochlorobenzaldehyde,
2,4-dichlorobenzaldehyde and nicotinic acid. The brighteners
~5 may be employed singly or in combination within the concentra-
tion range of from about 0.05 gram per liter to about 2.0 grams
per liter, and preferably from 0.1 gram per liter to about 1.0
gram per liter.
To extend the bright plating range at very low cath-
ode current densities, e.g. at about 0.2 ampere per square deci-
meter, it may be desirable to include from about 0.2 gram per
liter to about 2.0 grams per liter of additives such as beta-
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1~835;22
naphthol and 4-chloro-1-naphthol.
Bath temperatures generally range from about 15C to
about 35C with an optimum temperature being dependent on the
type of plating being undertaken. At higher temperatures, the
cathode current efficiency is good but somewhat dull deposits
may be produced as the bright throwing power is reduced. Lower
temperatures, below about 15 C, tend to reduce cathode current
efficiency.
The invention will now be further exemplified by the
following specific non-limiting examples of electrolytic solu-
tions. Unless otherwise specified, all parts are by weight and
a standard 267 ml Hull cell was utilized at bath temperatures of
22 to 24~C with a 3 ampere cathode current for 3 minu~es.
Example 1
An aqueous electrolytic bath was prepared containing
per liter 28 grams of cadmium sulfate, 8 percent by volume of
66 Baume sulfuric acid, 3. 75 grams of "Tetronic" 504 and 2 . 25
grams of "Lomar" NCO. A smooth, fine-grained, uniform dull semi-
bright cadmium deposit was obtained on the Hull panel over a ~-
current density range of 0.01 to 8.0 amperes per square decimeter.
Example 2
A bath was prepared as per Example 1 with the exception
that 0. 3 gram per liter of benzoylpyridine was added to the bath.
The cadmium deposit was fully bright from current densities of
0 . 01 to 4 . 0 amperes per square decimeter, and from 4.0 to 8 . o am-
peres per square decimeter the deposit was bright with slightly
hazy strips noted.
Example 3
An aqueous bath was prepared containing per liter 39
grams of cadmium sulfate, 8 percent by volume of 66C Baume sul-
furic acid, 3.75 grams of "Tetronic" 504~ 2.25 grams of "Lomar"
NCO, 0.3 gram of benzoylpyridine and 0. 28 gram of orthochloro-
10~3~;;22
benzaldehyde. The deposit was bright at current densities rang-
ing ~rom 0.1 to 4.0 amperes per square decimeter.
Example 4
An aqueous bath was prepared containing per liter 39
grams of cadmium sul~ate, 8 percent by volume of 66 Baume sul-
furic acid, 4.0 grams of "Ethomeen" C-25, 0.9 gram of "Polyrad"
lllO, 3.8 grams of "DuPonol" SN, 0.1 gram of beta-naphthol, 0.375
gram of nicotinic acid and 0.28 gram of orthochlorobenzaldehyde.
Bright cadmium deposits were obtained over current densities
ranging from 1.6 to 8.o amperes per square decimeter.
Example 5
An aqueous electroplating bath was prepared containing
per liter 39 grams of cadmium sulfate, 5 percent by volume of 66
Baume sulfuric acid, l.l grams of "Polyrad" lllO, l.l grams of
"Lomar" NC0, 3.7 grams of "DuPonol" 80, 0.37 gram o~ nicotinic
acid and 0.28 gram of orthochlorobenzaldehyde. A bright cadmium
deposit was obtained on the Hull panel at current densities rang-
ing from 0.4 to 8.o amperes per square decimeter.
Example 6
A condensate was prepared by mixing 1.4 grams of amino-
guanidine bicarbonate with 1.8 grams of ethyl vanillin in lO0 ml
of "Cellosolve" and 50 ml water. To this solution were added 5
ml of 60 Baume sulfuric acid and the solution was stirred over-
night at 70C.
An aqueous bath was prepared containing per liter 30
grams of cadmium oxide, 2.5 percent by volume of 66 Baume sul-
furic acid, lO percent by volume of fluoboric acid (47 percent
by weight aqueous solution), 3.5 grams of "Ethomeen" T/25, 60
grams of "Lomar" NCO and 15 ml of the condensate solution.
3`0 Utilizing a 2-ampere panel for 5 minutes, a fully
bright cadmium deposit was obtained at current densities of from
0.10 to 6.o amperes per square decimeter.
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Example 7
An aqueous bath was prepared containing per liter 30
grams of cadmium oxide, 2.5 percent by volume of 66 Baume sul-
furic acid, 10 percent by volume of fluoboric acid (47 percent
by weight aqueous solution), 3.5 grams of "Ethomeen" T/25, 7.5
grams of "Duponol" 80 and 22 ml of the condensate solution of
Example 6. Utilizing a 2-ampere panel ~or 5 minutes, a fully
bright deposit was obtained at current densities of from 0.01 to
2.0 amperes per square decimeter, and a semi-bright deposit was
obtained from 2.0 to 6.o amperes per square decimeter.
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