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Патент USA US2512723

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Patented June 27, 1950
Richard 0. Hull, Lakewood, Ohio, assiznor to E. I.
du Pont de Nemours & Company, Wilmington,
Del., a corporation of Delaware
No Drawing. Application September 18, 1945.
Serial No. 617,167
4 Claims. (Cl. 204-54)
This'ikinvention relates to the electrodeposition
of tin and is more particularly directed to com- ‘
positions and processes for the electrodeposition
of tin employing a stannous compound and a salt
containing the radical Fe(CN)s.
Among the best tin-plating compositions are
small excess over that needed to react with iron
and copper is used, the ferricyanide or ferro
cyanide is not inactivated by the relatively large
amount of tin present.
Any acid-tin electrodepositing bath which con
those in which the tin is present as a stannous
tains part or all, and preferably at least a major
amount, of its tin as a stannous compound may
compound but unfortunately these plating com
be improved according to the present invention,
positions are none too stable. Dry compositions
when operated at pH 2 to 5 (preferably 2.5-4). ‘
containing a stannous compound become partly 10 There may preferably be used, for instance,
newly developed baths employing'stannous chlo
insoluble after extended storage, and electroplat
ing baths containing stannous compounds form
ride and sodium ?uoride. Numerous other prior
sludge. Sludge formation is a particularly great
art baths may similarly be used in which tin is
problem under the severe conditions of commer
present as stannous chloride, stannous sulfate,
cial employment of large volumes of solution 15 stannous ?uoride, phenol sulfonate or other
with considerable agitation of the solution.
stannous salts of sulfonic acids. Baths of these
It is an object of the present invention to pro
types frequently include acids such as hydro
vide tin electrodepositing compositions and baths ?uoric acid, hydrochloric acid, sulfuric acid, or
which contain stannous tin but which are of in
aromatic sulfonic acids. These baths may also
creased stability during storage and in commer 20 include organic addition agents and metal bright
cial use. It is a further object to provide elec
eners in the customary way, the important con
trodepositing baths which contain stannous tin
sideration for the purposes of the present inven
and which may be subjected to considerable agi
tion being that the bath contain tin in the form
tation without excessive sludging. It is a still
of a soluble stannous compound and any such
further object to provide stabilizing agents which 25 bath may be improved according to the teachings
are effective in small concentrations and which
produce no undesirable e?ects upon the tin de
posits. It is a still further object to provide tin
electrodepositing compositions which contain
of this invention.
While any acid, stannous electrodepositing
bath or composition may be improved according
to the present invention it will be found that the
stannous tin and which can be used by a plater 30 baths must have a pH of 2 to 5. Dry, solid elec
by simply adding the required amount of water.
Still further objects will become apparent here
trodepositing compositions should similarly be of
such composition that upon being dissolved in
water they will have a pH of 2 to 5.0, though
sometimes it will be found desirable to let the
The foregoing and other objects of the inven
tion are attained by the addition to an electro 35 pH of the resulting bath be adjusted by the ad
dition of a suitable acid.
depositing composition or bath containing stan
According to the invention, there may be used
nous tin of a sodium, potassium, or ammonium
an alkali ferricyanide or ferrocyanide, by which
ferricyanide or ferrocyanide.
I mean sodium, potassium, or ammonium ferri
It is not entirely clear by virtue of what ac
tion these agents exercise their bene?cial e?ects 40 cyanide or ferrocyanide. The ferricyanides are
generally preferable.
upon stannous plating baths. The soluble ferri
The amount of a bath-soluble ferricyanide or
cyanide or ferrocyanide appears to combine with.
ferrocyanide to use in a particular stannous bath
sequester, and nullify the effects of iron and cop
is related to the content of iron and copper.
per compounds which probably act as oxidation
catalysts for stannous tin. It is to be observed, 45 The ferricyanide or ferrocyanide should ordi
narily be used in at least an amount su?icient to
however, that even in the absence of iron and
take out any iron and copper which is present
copper the ferricyanide or ferrocyanide exercises
and to take outiron and copper which is carried
a stabilizing in?uence on a stannous electrode
into the bath by the article being plated. It is
positing bath. Whatever the cause of their e?i
cacy and without being committed, to any theory 50 desirable to maintain an additional small excess
to take ‘care of the iron and coppergbrought into
or explanation for their action it can simply be
the bath, as by steel strip being plated.
observed that a ferricvanide or ferrocyanide ex
From about 0.005 to 2 grams per liter of a
ercises a remarkable stabilizing~ in?uence upon a
bath-soluble ferricyanide or ferrocyanide may be
stannous electrodepositing bath or compo"ition.
It is particularly surprising that even when a 55 used under average conditions. More speci?cally
from about 0.01 to 0.5 gram per liter is preferred.
A bath in operation can most satisfactorily be
maintained with from about 0.01 ‘to 0.20 gram per
liter of a bath-soluble ierricyanide or ferrocya
A composition for maintenance will have a
somewhat diii'erent composition from that shown
above for initial preparation of a bath. Such a
be employed.
composition is as follows:
The amounts of ferricyanide and i'errocyanidc
above indicated are particularly applicable to
stannous tin baths which contain from about 15
to 45 grams per liter oi’ tin computed as the
metal in the form, of course. of a soluble com 10
pound. With more particular reference to the
preferred baths of the invention, the indicated
Per cent
Sodium ?uoride
Sodium bi?uoride________________________ __ 60
Potassium terricyanide ___________________ _. 10
While such a composition is ideal where high
anode efficiencies maintain the tin content of the
bath, the following composition is better where
amounts of ‘a ierricyanide or ferrocyanide are
employed with from about 30 to 90 grams per liter
of stannous chloride, or more speci?cally from 16 operating conditions lead to lower anode e?lcien
cies and sludge loss:
about 45 to '75 grams per liter of stannous chlo
Per cent
Example I
Stannous chloride__________________ __'____- 49
A tin electrodepositing bath was made up as
Sodium bi?uoride________________________ .. 49
Potassium ferricyanide ___________________ __ 2
Stannous chloride.- ____ --grams per liter__
Sodium ?uoride __________________ __do__l__
Sodium bi?uoride (NaHF'z) _______ _..do_..__
Sodium chloride ________________ __do..___'
Under still di?'erent conditions, first one and
211:; the other of the above may be used as de
As has been illustrated above, dry prepared
stannous electrodepositing compositions of the
present invention may be made up by including
Hydrochloric acid (20° Bé.)__cc. per liter__' 12.5
"Carborwax" 1500 ______ "grams per liter__
“Schae?er's” salt ________________ __do___-
Potassium ferricy'anide __________ -_do____
PH 2.5
a ierricyanide or terrocyanide together with the
stannous compound and any other desired elec
trodepositing ingredient. Thus part or all of the
materials to make up an electrodepositing bath
may be included in such a composition and may
The “Carbowax" 1500 is a polyethylene oxide
of molecular weight about 1500.
be used by the plater simply by adding water.
The above bath containing a ferricyanide ac
The composition may also be sold as concentrated
cording to the present invention was much more
solutions. For the purposes of the present inven
stable and formed far less sludge than a. bath 35 tion
it is important only that‘ a ierricyanide or
otherwise similar but omitting‘ the ferricyanide.
ierrocyanide be included with the stannous com
Similar results were obtained using the same
amount of potassium ferrocyanide instead of fer
A preferred composition for the preparation of
40 a bath of the invention may be made up using
Example If
about 37.5 to 60.19% or stannous chloride from
A stannous electrodeposlting bath of the pres
about 39.8 to 62.0% of an alkali ?uoride, and
ent invention was prepared with the following:
from about 0.01 to 0.5% of an alkali ferricyanide
Grams per liter
Stannous sulfate _______________________ ..- 88
Sodium ?uoride
or ierrocyanide.
While I have shown numerous illustrative proc
esses and compositions it will be understood that
the invention is not to be limited thereby but
that numerous stannous electrodepositing baths
and compositions may be prepared employing a
Beta naphthol-ethylene oxide ___________ __ 0.1
Potassium ferrocyanide _________________ __ 1.0 50 Ierricyanide or ferrocyanide without departing
from the spirit of this invention.
pH 2.0
Example III
This application is a continuation-in-part of
my co-pending application, Ser. No. 494,506, ?led
A dry prepared composition formulated accord
July 13, 1943. The latter application was aban
ing to the present invention was made up as fol
55 doned on September 2'7, 1945.
lows using anhydrous materials:
Sodium bi?uoride _____ __'_______________ __ 41
Sodium sulfate _________________________ __ '15
I claim:
Per cent
1. In a process for treating an aqueous, stan
Stannous chloride ______________________ -.. 45.5
nous plating bath of a pH from about 2 to 5, the
Sodium ?uoride
step comprising treating the bath with a slight
Sodium bi?uoride _____ __, ________________ __ 36.0
Potassium ferricyanide ___________________ __ 0.5
This composition is employed simply by dis
solving in the required amount of water to give
a bath like that of Example I. The pH will be
substantially correct. but may, if needed, be ad
justed. Addition agents, etc., may be added as
desired. Instead of using the blfiuoride, a corre
spondingly larger amount of ?uoride may be used
and the pH adjusted later to about pH 2.5 by
the use of an acid such as hydrochloric.
stead of using sodium ?uoride compositions such
as that shown, there may be used another- alkali
?uoride. When reference is made herein to an
excess over that required to precipitate copper
and iron of a compound selected from the group
consisting of alkali ferricyanides and ferrocya- ‘
2. In a process for the electrodeposition of tin,
the steps comprising effecting deposition from a
solution of a stannous compound at a. pH from
about 2 to 5 and which contains a slight excess
over that required to precipitate iron and copper
of a compound selected from the group consist
70 ing of alkali ferricyanides and ferrocyanides, and
thereafter during bath operation maintaining
dissolved in the bath a small amount of one of
said alkali compounds.
3. In the operation or an aqueous tin-plating
alkali ?uoride it will be understood that sodium.
potassium, or ammonium ?uoride or bi?uoride 7‘ bath which contains about 15 to 45 grams per
liter oi’ tin in the form of a stannous compound,
and which is at a pH from about 2 to 5, the step
comprising operating the bath while there is dis
solved therein from about 0.01 to 0.5 grams per
liter of a compound selected from the group con 5
sisting of alkali ferrlcyanides and ferrocyanides.
4. In the operation of an aqueous tin-plating
bath which contains about 15 to 45 grams per
The‘ following references are of record in the
tile of this patent:
Schulte __________ __ July 25, 1922
Schweikher ______ __ June 18, 1946
Schweikher ______ __ Sept. 10, 1946
liter of tin in the form of a stannous compound
and which is at a pH from about 2 to 5, the step HI
- comprising operating the bath while there is
dissolved therein from about .005 to 2 grams per
liter of a compound selected from the group con
sieting of alkali ferricyanides and terrocyanides.
Great Britain __________ __ of 1869
Germany _________ __ Jan. 18, 1939
“Transactions of The Electrochemical Society,”
15 vol. 23 (1913), pages 228 through 232. -
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