Note: Descriptions are shown in the official language in which they were submitted.
` S-1~,172
_ACI~GI~OUND ~F Tllr Nv~lrrI~N
This invcntion rclatcs to the art o~ platinc~ gold deposits.
More specifically, it relates to the electrodeposition of goId
deposits exhibiting improved brightness.
Numerous platiny baths have been proposed for the electro-
deposition of gold deposits. Foremost are those baths contain-
ing the gold as a cyanide complex, and those containing gold as
the sulfite complex. Pertinent to the cyanide baths are U.S.
Patent Nos. 2,905,601; 3,373,094; 2,765,269; 2,812,299; and
RE. 25,883. The sulfite comp]ex baths are described for
example in U.S. Patent Nos. 3,057,789 and 3,666,640.
The foregoing patents describe generally the parameters for
plating using the gold complex compounds, and describe various
brightening agents which may be included in the plating bathsO
Suggested brighteners include hydrazine and piperazine deriva-
tives, as well as small quantities of arsenic, antimony, and
selenium ions.
As generally practiced, the gold cyanide baths are adjusted
to a pH of 3.5 or greater. The sulite baths are adjusted to
a pH of ~rom 5.5 to 10.5 and often rely on the pres~nce o an
amine compound in order to maintain stability at the lower pH's.
SUMMARY OF THE INVENTION
According to the present invention, an aqueous gold plating
bath containing gold in the form of a complex is provided with
a quantity o an amido-polyphosphate compound sufficient to im-
prove the brightness of the deposits obtained by electroplating
therewith. In a preferred embodiment, the aqueous plating solu-
tion additionally contains at least l g/l of a polyphosphate
compound. In the case of a cyanide complex bath, a further im-
provement in bri:ghtness and an improvement of hardness in the
deposit can be obtained by urther including at least 0.0l g/l
of Gobalt or nickel ion.
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The invention relates to an aqueous gold electro-
plating bath containing gold in an electrodepositable form ~ ;
adjusted to a pH suitable for plating. The bath includes an
amido-polyphosphate compound differing from a normal poly~
phosphate compound in that one or more of the oxygen linkages
between phosphorus atoms is replaced by an -NH-linkage in a .
sufficient quantity to effect a brighter deposit. . -~
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T~L'. I'~ILED D~.~CRIrTION OF T~IE INVENTION
I;l accordance with the state of the art, ~old plating solu-
tions commonly contain between 1 and 100 g/l gold in the form
of a complex. In order to minimiæe losses due to draqout, the
concentration of gold is preferably maintained between 1 and 20
g/l. In the case of the sulfite complex, the gold is normally
provided as an ammonium, amine, or alkali metal gold sulfite.
In the case of the cyanide complex, the gold is normally pro-
vided in the form of an ammonium or alkali metal gold cyanide.
For solubility reasons, the potassium salts are the most pre-
ferred. Common alloying metals may also be present in the
solution.
The essential component of the plating baths of the pre-
sent invention is an amido-polyphosphate compound. This com-
pound differs from the normal polyphosphate compounds in thatone or more of the oxygen linkages between phosphorus atoms
has been replaced by an -NH- linkage. As is the case with
polyphosphate compounds, the amido-polyphosphates may be added
either as the ammonium or alkali salts. Compounds of this type
may be made in various ways, for example, by the reaction of
dry ammonia with a phosphoric anhydride compound as described
in U.S. Patent No. 2,122,122. These compounds may be made
by reacting anhydrous ammonia with phosphorus p~ntoxide and
heating the reaction mixture in the presence of excess anhy-
drous ammonia at a temperature of at least about 150C. fora sufficient period of time to effect a molecular condensation
with loss of ammonia from the product, forming a substantially
neutral product in which 'he atomic ratio of nitrogen to phos-
phorus is less than 1.5 to 1. The amido-polyphosphates have
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S-10,172
~ P2O5 equivalent phosphorus content o~ ~rom 65 to 80Q by weight-
and an NH3 equivalent amide nitrogen content of from about 5 to
12% by weight. Where thP ammonium salt is employed, the NH3
equivalent ammonium nitrogen content should be from about 8 to
22% by weight. One commercially available ammonium salt of an
amido-polyphosphate is sold by the Stauffer Chemical Company
under the trademar~ "Victamide". The product contains approxi-
mately 76~ P2Os equi~alent phosphorus, 7% NH3 e~uivalent amide
nitrogen, and 15.4% NH3 e~uivalent ammonium. The compound ex-
hibits an average phosphorus content of about 4 to 5 atoms per
molecule.
The precise concentration of the amido-polyphosphate
- compound in tha gold plating solution depends to some extent
on the nature and concentrations of the other components pre-
sent. It appears, however, that at least 1 g/l is necessary
to obtain any appreciable effect and a quantity in excess of
100 g/l does not provide any further improvement in brightness.
In general, sufficient brightening effect can be obtained by
employing quantities between 5 and 40 g/l.
In a preferred embodiment of this invention, it has -
been found desirable to include a polyphosphate compound in
the solution as well. The amido-polyphosphata and the poly-
phosphate apparently co-act in some matter to further enhance
the brightness of the dep~sit. When it is desired to nclude
the polyphosphate compound in the soiution, at least 1 g/l
should be included in order to obtain beneficial effects. Ex-
amples of suitable compounds include the ammonium and alkali
metal salts of the pyrophosphate, tripolyphosphate, and tetra-
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S-10,17~
metapolyphosphate anions. Quantities in excess of 20 g/l
are preferred.
When the platin~ solution contains the gold cyanide
complex in the acid pH range, a still further preferred emhodi-
ment is the inclusion of a small ~uantity of cobalt or nickel
in depositable form. While addition of the amido-polyphosphate
and the polyphosphate compound improve the brightness of the
deposit, the final inclusion of cobalt and nickel ion brings
the deposit to full brightness. The inclusion of cobalt or
nickel is thus preferred wherever brightness is of extreme im-
portance as in the case of jewelry manufacture. As demonstrated
in the examples, the inclusion of cobalt and nickel has the ad-
ditional advantage of improving the hardness of the gold deposit.
The precise concentration of cobalt and nickel ions re-
quired in order to obtain the foreoging advantages depends upon
the concentration of the other components of the solution. Since
it is desirable to minimize the amount of cobalt or nickel in
the final deposit, it is, of course, desirable to include no
more co~alt in the solution than is necessary to obtain the
desired brightness. The minimum cobalt concentration required
appears to vary in proportion to the concentration of the amido~
polyphosphate compound in the solution. Cobalt concentrations
of 100 mg/l and less have been found effective, whereas amounts
as high as 1.1 g/l have also been found effective without in-
2S creasing the cobalt content of the deposit beyond 0.5%.
In order to simplify reporting in the following examples, -
a numerical scale ha~ been adopted in order to describe the de-
gree of brightness exhibited by a gold deposit:
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5 10,172
1. Bright --- Details of a reflected imagQ
are distinct.
2. Semi-bright --- A reflected imag2 is visible,
though hazy.
3. Lustrous --- The deposit exhibits a low~level
reflectance, although details of an image are
not visible.
4. Dull, smooth yellow --- The deposit appears
smooth, although there is no ordered light
reflection.
5. Dull, yellow --- The deposit exhibits no
light reflection and gives a matte appear-
ance.
6. Brownish-yellow --- The deposit has lost its-
normal yellow color and gives a matte appear-
ance.
7. Dull, dark brown --- The deposit is dark brown
and gives a matte appearance~
EXAMPLE
,
A ~old plating bath was prepared as follows:
COMPONENT G/L
-- .
Au as Na3~Au(so3)2] 8
~a25O3 3Q
Ammonium amido-poly- 25
phosphate
NaOH to p~ 9.0
Plating on cathodic brass panel~ was performed at
approximately 120F. and 3 ASF with perî~dic replenishment
for a period of 6~1/2 hours. Deposits oh~ained exhibitad
an average visual rating of 2. Where th~ same bath was em-
ployed without the amido-polyphosphate, ~e visual rating of
: ~ -the deposit was 4.
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. E~AMPLE II
A gold plating bath was prepared as follOW5:
COMPONENT G/L
Au as KAu(CN)2 8
K2HPO~ 60
Ammonium amido-poly- 20
phosphate
H3PO4 to pH 7.0
Plating on cathodic brass panels at approximately 120F.
to 1~0F. and 3 ASF with periodic replenishment for a period of
i-l/2 days. Deposits obtained exhibited an average visual rat-
ing of 4O When the same bath was employed without the amido-
polyphosphate the visual rating of the deposit was 5.
EXA~PLE III
15. A gold plating bath was prepared as follows:
COMPONENT G/L
Au as Na3[Au(So3)2] 8
Na2S03 . 10
Ammonium amido-poly 20
phosphate
Na4P27 30 .
NaOH to pH 8.5
Plating was performed on cathodic brass panels at
approx~mately 120F. and 3 ASF with periodic replenishment
for a period of over two days. Deposits obtained exhibited
an average visual rating of 1. The use of the pyrophosphate
improves the visual quality as compared to the system con-
taining neither the amido-polyphosphate nor the pyrophosphate
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- (k ratin~3) ~nd as co;n~ared to the system containing onl~ the
amido-polyphosphate (2 rating) in E`xample I. Identical re-
sults were obtained where Na5P301o and Na4P40~2 were substi-
tuted for the sodium pyrophosphate. An additional advantage
is that t~e pyrophosphate permits one to maintain the bright-
ening effect for a longer period of time and buffers the solu-
tion to impart stability.
EXAMPLE IV
A gold plating bath was prepared as follows:
COMPONENT G~L
K4P~07 100
Ammonium amido-poly- 10
phosphate
Au as KAu(CN)2 8
Co as CoS0~7H20 0.1
H3P04 to pH 4.0
Plating was performed on cathodic brass panels at ap-
proximately 100F. and 10 ASF. The deposit exhibited a visual
rating of 1 compound tc a rating of 4 without the cobalt. As
the amido-polyphosphate concentration was increased, the con-
centration of cobalt required to produce a 1 rating gradually
increased. At an amido-polyphosphate content of 100 g/l the
cobalt concentration required to obtain a 1 rating was. in ex-
cess of 0.5 g/l, although lesser quantities did improve the
brightness to some extent. An analysis of the deposits obtain-
ed indicated a cobalt content not exceeding 0.5%. Similar re-
sults were obtained when nickel as NiS04-6H20 was used in place
of the cobalt.
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EXAMPLE V
A bath was prepared in ~xample 4 hut containing 25 g/l
amido-polyphosphate and 0.35 g/l cobalt. Plating was performed
under the conditions of the prior example and deposits exhibit-
ing a visual rating of 1 and containing from 0.2 to 0.3~ cobalt
were obtained. The Knoop hardness of these deposits was in
the range of 147-159. Without the inclusion of cobalt, hard-
ness values ranged from 60 to 90.
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