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Патент USA US2406189

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Patented Aug. 20,1946
. 2,406,189
um'rso s'm'rss PATENT I OFFICE
2,408,180
_
'Mn'rnon Foa m mmo
Nowell r. Blackburn, Niagara Falls, N. Y., assign
or to E. I. du Pont de Nemours & Company,
I Wilmington, Del., a corporation of Delaware
No Drawing. Application May 20, 1943,
Serial No. 487,813
7 Claims. (0]. 204-54)
2
This invention relates to the electroplating of
metals and particularly to the electrodeposition
of tin from alkali metal stannate electroplating
baths.
with high electrode e?iciencies.
.
In present commercial practice for the elec
troplating of tin, alkaline plating baths con- _
taining sodium stannataor potassium stannate
are commonly used. Although sodium stannate
electroplating baths may be operated- satisfac
torily at comparatively low current densities,
.
anodes may be operated at high current densities
,
The novel alloy anodes of'my invention may be
prepared by mixing molten tin with a molten
alkali metal and molding the mixture in the
desired form. For example, pure tin is heated in
an iron or silica crucible to approximately 270°
C. The required weightof alkali metal is then
added to the molten tin. It may be desirable to
utilize about 0.1 to 0.2% excess alkali metal to
compensate for possible loss through oxidation
such baths have the disadvantage that when it 1.0
is desired to operate at high current densities in
during the mixing and molding operation. .The
order to obtain high plating speed the anode
alkali metal is introduced under the surface of
e?lciency becomes so low as to make such baths
the molten tin, for example, by introducing the
unsatisfactory for commercial operation. Al 15 alkali metal under an inverted crucible held in
though sodium stannate electroplating baths
position under the surface of the molten tin.
have been successfully used at current densities
The mixture is agitated until all lumps have
up to about 50 A/SF, no method has been avail
disappeared, the surface skimmed to remove oxi
able hitherto by which these electroplating baths
dation products, and the melt poured into a mold
could be satisfactorily operated at current den 20 and allowed to cool.
sities substantially above 50 A/SF. In the case
In general, the methods vcommonly used for
of potassium stannate electroplating baths the ' the preparation of alkali metal alloys may be
di?lculty encountered in obtaining satisfactory
utilized in the preparation of my novel anodes.
anode efficiencies exists at even lower current
Preferably the molten mixture is protected by
densities and lack of a method for operating 25 an atmosphere of inert gas such as nitrogen in
_ such baths at high current densities has serious
ly hampered the commercial development of the
potassium stannate bath. Heretofore no method
has been available which would permit operation
of stannate electroplating baths at high current
densities with satisfactory anode efficiency, and
it has therefore been impossible to fully utilize
their potential capacity.
.
It is one of the objects of this invention to
provide a new and improved method for alkaline
tin plating. Another object is to provide an
electroplating bath for the electrodepositlon of
tin which will operate e?lciently at high current
order to avoid oxidation. The molten tin should
be heated to a temperature somewhat above the
melting point of the alloy to be formed.
‘
The concentration of alkali metal present in
so the
novel anodes of my invention may be varied
over a considerable range with satisfactory re
sults. Usually only relatively small amounts of
alkali metal are required, 1. e. 0.1 to 10% by
weight. I have found that amounts of sodium up
to 10% or of potassium up to 5% of the weight
of the alloy are sufficient for practical operation.
When concentrations of alkali metal greater than
10% by weight are utilized the solubility of the
anode in the plating solution tends to become
densities. A further object is to provide a novel
anode for alkali metal stannate electroplating 40 too high for satisfactory operation. Further
baths. These and other objects will be apparent '
more‘, substantially higher concentrations of
from the ensuing description of my invention.
alkali metal may decrease ' the mechanical
The above objects are attained in accordance
strength of the anode below practical limits.
with my invention by electroplating tin from an
The particular concentration of alkali metal to
alkali metal stannate plating bath having an 45 be used in any given plating bath will depend
anode or anodes comprising an alloy of tin and
upon the current density at which it is desired
one or more alkali metals. I have discovered
to operate. At low current densities concentra
that when a tin anode containing a relatively
tions of alkali metal as low as 0.1% may be suf
small amount of alkali metal is utilized in the
flcient to effect the required anode efficiency.
stannate plating bath, a surprising and unex 50 When it is desired to operate at high current
pected increase in anode efficiency is obtained
densities, for example, current densities of 100 to
and 'stannate plating baths utilizing these novel
150 A/SF, concentrations of alkali metal as high
3
4
. .
as 5% sodium or 4% potassium may be required
to obtain‘; the high anode eillciency necessary for
satisfactory operation.
new a
1.2% potassium-tin alloy anode vs. tin anode m
For example, I have
a sodium stannate plating bath
found that when a stannate plating bath con
taining 120 g./l. of sodium stannate and 15 g./l.
of sodium hydroxide is operated at 90° C. and
Percent emcienoy
Current dentisy in AIBF
at a current density of 100 A/SF, an anode e?l
1 . 27
potas
eiu?i
alloy
anode
ciency of 99% is obtained when the concentra
tion of sodium in the anode is 4.6%. Similarly,
in the operation of a stannate plating bath con-'
P3235“
95
M
89
.......... -.
67
. . . . .
. . . ..
M
. . . . .
. . _ . -
taining 135 g./l. of potassium stannate and 21
g./1. or potassium hydroxide at 90° C. and 125
A/SF, an anode e?iciency of 90% is obtained
when the concentration of potassium in the tin
‘TABLE 4
anode is 3.8%; and when the same bath is oper 15
ated at 150 A/SF using the same anode an anode
0.75% sodium-tin alloy anode vs; tin anode, in a
potassium stannate plating bath
e?lciency of 80% is obtained.
The following tables illustrate the high anode
Percent e?loiency
e?iciencies obtained by the use or my novel anode.
In obtaining these data sodium stannate baths 20
Current density in A/SF
contained ‘120 g./l. of sodium stannate and 15 .
g./l. of sodium hydroxide were used and the po
tassium stannate baths contained 135 g./l. of
sggi?gii
pm ‘In
alloy anode
‘mods
potassium stannate and 21 g./1. of potassium hy
droxide. These materials were dissolved in dis
tilled water and the plating baths were main
tained at 90° C.
i
'
'
97
80
_
i
B8
82
64
4o
..
70
E
53
I0
100 .................................... ..
.
In the tables and throughout the speci?ca
tion the term "anode e?lciency" refers to the
Anode e?iciencies were determined in a con
80 ventional manner. The plating solution was
anode e?lciency based on tetravalent tin.
Table 1 represents a comparison of the anode
placed in series with a silver coulometer for.
yeillciencies obtained with a pure tin anode and
measuring the current used. An accurate am
with sodium-tin alloy anodes over a current
meter was connected in series and a volt meter
density range of 35 to 150 A/SF in a sodium
was connected across the bus bars of the plating '
35
stannate plating bath. Table 2 represents a sim
bath. The temperature 01’ the plating bath was
ilar comparison of potassium-tin anodes with pure
maintained constant throughout the operation.
tin anodes in a potassium stannate plating bath.
The anodes used were cylindrical and had a diam
Table 3 illustrates a comparison of the results
eter 01' 1/2", a length of 31A" and an area of ap
obtained in using a potassium-tin anode and a
proximately 5% square inches. The anodes were
40
pure tin anode in a sodium stannate plating bath.
placed in the bath between two cathodes having
Table 4 shows a comparison of a sodium-tin anode
a total area equal tothat of the anode. The
with a pure tin anode in a potassium stannate
anodes were polarized before drying and weigh
plating bath.
ing and the coulometer cathode was air dried
TABLE 1
and weighed. The baths were operated suili
clently long to deposit from 2 to 3 grams oi
Axons EmcIENcY Comrmusorz
silver on the coulometer in each e?lciency run.
Several runs were made and average values taken.
Sodium-tin alloy anode vs. tin anode in sodium
Anodes were kept in a polarized condition at all
stannate plating bath
times by increasing the current density until
gasing was observed.
Current density in A/BF
Anode efficiencies were
calculated by means of the following formula:
Percent sodium
50
75
100
Ef? ciency = 6%
Percent e?lcicncy
where A=anode loss and C=coulometer gain.
‘0.275=-1S§g electroequivalent ratio
As illustrated in the foregoing tables, the
80 novel alloy anodes of my ‘invention are espe
TABLE 2
Potassium-tin alloy anode vs. tin anode in
potassium stannate plating bath '
Current density in A/SF
Percent potassium
manode
2s
60
75
100 ' ‘125
15ercent e?lciency
150
200
, cially effective in electroplating baths operated at
high current densities. However, these anodes
are also effective in increasing efficiency when
baths are operated at lower current densities in
65 which case concentrations of alkali metal as low
as 0.1% may be su?lcient to obtain balanced elec
trode efficiencies. Sodium-tin anodes may be
utilized in either sodium stannate or potassium
stannate baths and likewise the potassium-tin
70 anodes may be used in either electroplating bath.
Generally, I prefer toutilize sodium-tin anodes
since sodium is relatively inexpensive and is read- ~
ily obtainable.
Although I have described my invention with
particular reference to electroplating baths con
5
6
taining sodium stannate or potassium stannate '
sium stannate and potassium hydroxide with an
alloy anode comprising essentially tin and at least
one alkali metal, the total alkali metal content
utilizing alloy anodes comprising tin alloyed with
sodium or potassium or both, it is to be under
stood that other alkali metals may be utilized in
the novel anode of my invention, for example,
of said‘ anode being 0.1 to 10% by weight.
3. A process for electroplating tin which com~
prises electrolyzingan aqueous solution of sodium
stannate and sodium hydroxide with an alloy
out other alkali metals. Likewise, alkali metal
anode comprising essentially tin and at least one
- stannate baths other than sodium and potassium
alkali metal, the total-alkali metal content of said
may be utilized in practicing my invention.
10 anode being 0.1 to 10% by weight.
A major advantage in the anodes of my inven
4. A process for electroplating tin which com
tion is the increased ef?ciency obtained, particu
prises electrolyzing an aqueous solution of an
larly high anode e?iciencies at high current
alkali metal stannate and an alkali metal hydrox
densities. A further advantage is that my in
ide with an alloy anode comprising essentially tin
vention makes possible balanced electrode em 15 and 0.1 to 5% by weight of potassium.
ciencies over a wide current density range. Thus,
5., A process for electroplating tin which com
for example, whenever the anode e?iciency is
prises electrolyzing an aqueous solution of an al
somewhat. low, the use of alkali metal alloy'
kali metal stannate and an alkali metal hydrox
anodes makes it possible to obtain increased
ide with an alloy anode comprising essentially tin.
anode ei?ciency without adversely effecting cath
and 0.1 to 10% by weight of sodium.
ode e?iciency. These and other advantages will 20
6. A process for electroplating tin which com
be readily apparent to those skilled in the art.
prises electrolyzing an aqueous solution of potas
I claim: '
sium stannate and potassium hydroxide with an
1. A process for electroplating tin which com- I
alloy anode comprising essentially tin and 0.1 to
prises electrolyzing an aqueous solution of an al
5% by weight of potassium.
'>
25
kali metal stannate and an alkali metal hydrox
7. A process for electroplating tin which com
ide with an alloy anode comprising essentially tin
prises electrolyzing an aqueous solution of po
lithium or caesium, and these metals may be al
loyed with an anode containing tin with or with
tassium stannate and potassium hydroxide with
and at least one alkali metal, the total alkali r
an alloy anode comprising essentially tin and 0.1
metal content of said anode being 0.1 to 10% by '
weight.
30 to 10% by weight of sodium.
2. A process for electroplating tin which com
prises electrolyzing an aqueous solution of potas
"
’
NEWELL F. BLACKBURN.
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