Electrodeposition of tin from sulfate electrolyte in the presence of synthanol, formalin, and propargyl alcohol

Article abstract of DOI:10.1023/A:1016148016754

The process of electrodeposition of tin from a sulfate electrolyte containing SnSO₄, H₂SO₄, synthanol, formalin, and propargyl alcohol was studied.

Full text of DOI:10.1023/A:1016148016754

Russian Journal of Applied Chemistry, Vol. 75, No. 2, 2002, pp. 219 222. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 2, 2002,
pp. 227 230.
Original Russian Text Copyright
2002 by Medvedev, Makrushin, Dubenkov.
APPLIED ELECTROCHEMISTRY
AND CORROSION PROTECTION OF METALS
Electrodeposition of Tin from Sulfate Electrolyte
in the Presence of Synthanol, Formalin, and Propargyl Alcohol
G. I. Medvedev, N. A. Makrushin, and A. N. Dubenkov
Novomoskovsk Institute of Mendeleev Russian University of Chemical Technology, Novomoskovsk, Russia
Received July 26, 2001
Abstract The process of electrodeposition of tin from a sulfate electrolyte containing SnSO4, H2SO4,
synthanol, formalin, and propargyl alcohol was studied.
Previously, electrodeposition of tin from a sulfate
electrolyte in the presence of organic additives has
been studied [1, 2]. It was shown that electrodeposi-
tion in an electrolyte containing synthanol and forma-
lin, together with 1,4-butanediol and 2-butene- and
2-butyne-1,4-diols, yields lustrous coatings. The pres-
ent communication reports the results obtained in
studying electrodeposition of tin from a sulfate acid
electrolyte in the presence of synthanol, formalin, and
propargyl alcohol.
P = 2.3a/2 hav log(H0 /Hi),
where a is the wave amplitude of the sinusoidal mic-
roprofile; hav the average coating thickness (10 m);
and H0 and Hi the initial and final amplitudes of
the sinusoidal microprofile, respectively.
The capacitance of the electric double layer was
measured in the course of electrolysis with a P-5021
ac bridge at a frequency of 30 kHz, using the series
equivalent scheme.
The investigation was carried out in an electrolyte
containing (g l ): SnSO4 10 50, and H2SO4 90 100.
The electrodeposition was done at 18 25 C with
and without electrolyte agitation by means of a mag-
netic rabble.
1
The organic substances were introduced into the elec-
trolyte in the following amounts: synthanol (DS-10)
1
1
1 4 g l , formalin (37% solution) 1 10 ml l , and
The effect of organic additives on the outward ap-
pearance of coatings was studied in an electrolyte con-
1
propargyl alcohol 1 15 ml l .
1
1
taining 50 g l SnSO4 and 100 g l H2SO4. It was
Tin was deposited onto copper substrates to a thick-
ness of 6 15 m. Polarization curves were measured
with a P-5828 potentiostat. The luster was measured
with an FB-2 photoelectric luster meter. The degree
of surface coverage with organic additives was
evaluated by the results of polarization measurements,
using the formula [3]
1
found that, with synthanol (1 4 g l ) added to the
electrolyte, dull coatings are obtained. With formalin
1
1
(1 10 ml l ), or propargyl alcohol (1 15 g l ), or
a mixture of these, poor-quality coatings are deposited.
The outward appearance of coatings is much im-
proved if propargyl alcohol is added to an electro-
1
lyte containing synthanol (2 3 g l ) and formalin
(6 8 ml l ). Data on the influence exerted by pro-
1
= 1
exp( E/b),
pargyl alcohol on the outward appearance of the coat-
ings are presented in the table.
where E is polarization, and b is the constant
appearing in the Tafel equation, determined from
polarization curves plotted in the E log ic co-
ordinates.
It can be seen that lustrous coatings are obtained
in the presence of propargyl alcohol. The widest range
of current densities at which lustrous coatings are
2
obtained (ic = 7 12 A dm ) is observed at propargyl
The leveling power P of the electrolytes was de-
termined directly by profilometric measurements of
the surface of samples with sinusoidal microprofile.
The P value was calculated using the formula [4]:
1
alcohol concentrations of 7 10 ml l .
With the formalin concentration outside the above
limits, silvery coatings are obtained. At synthanol
1070-4272/02/7502-0219 $27.00 2002 MAIK Nauka/Interperiodica

220
MEDVEDEV et al.
Effect of propargyl alcohol on the outward appearance of
tin coatings*
which hinders electrodeposition in an agitated elec-
trolyte.
In addition to the influence of organic substances,
the study was concerned with effect of the SnSO4
concentration on the working range of current den-
sities for obtaining lustrous coatings. The investiga-
1
2
cpa,** ml l
i, A dm
Outward appearance of coatings
1 3
1 5
6 11
12 13
1 5
Dull
Dull with luster along edges
Dull with burn-on
Dull
Dull with luster along edges
Lustrous
Lustrous with burn-on
Dull
Semilustrous
Lustrous
Lustrous with burn-on
Dull
Semilustrous
Lustrous
1
tion was carried out in an electrolyte containing 2 g l
1
1
synthanol, 6 ml l formalin, and 7 ml l propargyl
alcohol. It was found that lowering the SnSO4 con-
centration makes narrower the ic range in which
lustrous coatings are obtained. For example, lustrous
coatings are obtained in the ranges ic = 2 5 and 6
5 6
7 10
11 15
6 8
9 10
11 13
1 5
6
7 12
13
1 5
6 7
8 10
11 13
2
10 A dm at SnSO4 concentrations of, respectively,
1
10 20 and 30 g l . The H2SO4 concentration in the
1
electrolyte should be within 90 100 g l . At con-
1
centrations lower than 90 g l the electrolyte is un-
stable in operation and the ic range in which lustrous
coatings are obtained becomes narrower. At H2SO4
1
content exceeding 100 g l the range of current den-
Lustrous with burn-on
sities at which lustrous coatings are obtained remains
unchanged.
*
1
Electrolyte composition (g l ): SnSO 50, H SO 100,
synthanol 2; formalin 6 ml l ; mechanical agitation.
4
2
4
1
It should be noted that high-quality lustrous coat-
ings are only obtained in an agitated electrolyte, with
dull deposits formed otherwise.
**
c
is the concentration of propargyl alcohol.
pa
1
1
concentrations of less than 2 g l (1 g l ), the work-
ing interval of current densities for obtaining lustrous
coatings becomes much narrower. At synthanol con-
centrations exceeding 3 g l (4 g l ), the range of
current densities yielding lustrous coatings remains
unchanged, but electrolyte frothing is much enhanced,
The current efficiency (CE) by tin in electrolytes
yielding lustrous coatings decreases with increasing
ic and grows as the SnSO4 concentration becomes
1
1
1
higher. CE = 95 75% at SnSO4 content of 10 20 g l
2
and ic = 2 5 A dm , and CE = 95 90% at SnSO4
1
2
content of 30 50 g l and ic = 6 12 A dm .
To reveal the influence of organic substances on
electrodeposition of tin, cathodic polarization curves
were measured on a rotating disk electrode. As seen
in Fig. 1, the cathodic polarization is enhanced in
the presence of organic substances, with a plateau of
limiting current observed in the cathodic polarization
curve (curves 1 and 2). With the disk electrode rotated,
the ilim value grows and the cathodic polarization
decreases (curves 2 6). The limiting current in the
polarization curves is associated with adsorption of
organic substances and formation of an adsorption
layer on the cathode surface. This assumption is
confirmed by measurements of the capacitance of
the electric double layer. As seen in Fig. 1 (curves 7
and 8), introduction of organic substances into the
electrolyte makes the capacitance of the electric
Fig. 1. (1 6) Cathodic polarization curves of tin, measured
on a rotating disk electrode, and (7, 8) capacitance C of
double layer lower. At potentials Ec = 0.3
0.4 V,
electric double layer vs. electrode potential E in tin-plating
2
c
it decreases from 32 to 10 F cm . At higher cathode
potentials, organic substances are desorbed from
the electrode surface and the continuity of the adsorp-
tion layer is broken, which leads to an increase in
the electric double layer capacitance.
electrolytes. (i ) Current density. Electrolyte composition
c
1
(g l ): SnSO 50, H SO 100. (1, 7) electrolyte; (2, 8) 1 +
4
2
4
1
1
1
2 g l synthanol, 6 ml l formalin, and 7 ml l propargyl
alcohol; (3, 4, 5, 6) 2 at disk electrode rotation rates of,
respectively, 200, 500, 1000, and 2000 rpm.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 2 2002

ELECTRODEPOSITION OF TIN FROM SULFATE ELECTROLYTE
Figure 2 presents the degree of coating luster and
221
surface coverage as functions of the current density.
It can be seen that the degree of coating luster passes
through a maximum, and the coverage decreases
steadily, with increasing current density (curves 1
and 2). The value at ic yielding lustrous coatings
2
(ic = 7 12 A dm ) varies between 35.0 and 27.7%.
It should be noted that lustrous coatings can be ob-
tained in an electrolyte with organic additives only in
a certain range of ic and . Presumably, the optimal
values of these parameters correspond to the condi-
tions in which the growing deposit has the minimum
roughness.
Fig. 2. (1) Degree of coating luster, L, (2) surface coverage
The leveling power P was measured in a tin plating
electrolyte as a function of the cathode current density
(Fig. 2, curve 3). It can be seen that the tin plating
electrolyte with organic additives produces level-
ing effect. With increasing ic, the P value grows and,
, and (3) degree of leveling, P, vs. cathode current density
1
i . Electrolyte composition (g l ): SnSO 50, H SO 100,
c
4
2
4
1
1
synthanol 2; formalin 6 ml l ; propargyl alcohol 7 ml l
Mechanical agitation.
.
2
at ic = 10 11 A dm , passes through a maximum
over the microprofile. The probable reason is that
an adsorption layer of organic substances is formed
on the electrode surface. Intensification of the hy-
drodynamic mode affects the process of formation and
disintegration of such a layer. In this case, the rate of
tin deposition grows on all parts of the microprofile,
i.e., changes in such a way that this appears outwardly
just like a manifestation of the antileveling effect.
(P = 0.98). At present, the mechanism of surface
leveling is commonly explained in terms of the ad-
sorption-diffusion theory [4] whose main concepts are
as follows. All leveling additives inhibit electrodeposi-
tion of metals, with the degree of inhibition controlled
by diffusion as a result of the diffusion-controlled
expenditure of the additives in the course of electrol-
ysis. According to [4], polarization curves measured
at different rates of disk rotation on a rotating disk
electrode model qualitatively the cathodic process of
microprojections (fast rotation) or microdepressions
(slow rotation). The uneven accessibility of the micro-
profile is the reason for nonuniform distribution of
the supply rate of organic substances to different parts
of the microprofile. Since the inhibiting influence
exerted by leveling additives on the process of metal
electrodeposition grows with increasing rate of ad-
ditive’s diffusion toward the cathode (fast rotation),
this effect is manifested to a greater extent on micro-
projections, and to a lesser extent in microdepressions,
which leads to a nonuniform distribution of the elec-
trodeposition rate.
It should be noted that the same phenomenon is
observed in electrodeposition of a Sn Sb alloy from
a sulfate electrolyte in the presence of synthanol,
formalin, and 2-butyne-1,4-diol, or synthanol, for-
malin, and coumarin [5].
The leveling in an electrolyte, in which an adsorp-
tion layer of organic substances is present on the elec-
trode surface, can be accounted for on the assumption
that this layer disintegrates with increasing speed of
disk electrode rotation. This strips microprojections
to a greater extent as compared with microdepressions.
At the same time, a higher rate of supply of organic
substances to microprojections is observed with in-
creasing rate of electrode rotation, and the micro-
projections are more strongly inhibited than micro-
depressions, which leads to nonuniform distribution of
the metal electrodeposition rate over the microprofile
surface. The phenomenon of leveling is related to the
luster of electroplated coatings, since luster formation
is also a process of surface leveling. The leveling
eliminates large microirregularities 0.2 to 100 m and
more in size; in luster formation, very fine submicro-
irregularities (of size about 0.15 m and less) are
smoothed out [6].
It was proposed on the basis of this circumstance to
assess the action of various additives by measuring
the cathode potential in an electrolyte with additive(s)
in two agitation modes [4]. If the polarization grows
with increasing speed of electrode rotation, then it
would be expected that additive(s) will exert leveling
influence under the given conditions.
Analysis of the cathodic polarization curves in a tin
plating electrolyte, measured on a rotating disk elec-
trode (Fig. 1, curves 3 6), shows that they do not
model the distribution of the electrodeposition rate
Thus, submicro- and microirregularities of the cath-
ode surface are smoothed out in a tin plating elec-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 2 2002

222
MEDVEDEV et al.
trolyte containing synthanol, formalin, and propargyl
alcohol.
(3) The degree of coating luster and the electrode
surface coverage were measured in relation to the cur-
rent density. It is shown that, with increasing ic,
the degree of luster grows and passes through a max-
imum, and the surface coverage decreases. The cov-
erage varies between 35.0 and 27.7% in the range of
current densities yielding lustrous coatings.
Finally, it should be noted that the investigation
performed made it possible to develop a sulfate acid
tin-plating electrolyte of simple composition, which
yields lustrous leveled coatings. The electrolyte
1
composition is as follows (g l ): SnSO4 10 50,
H2SO4 90 100, synthanol (DS-10) 2 3; formalin
(4) The leveling power of a sulfate acid electro-
lyte with organic additives was studied. It is estab-
lished that, in simultaneous presence of synthanol,
formalin, and propargyl alcohol, the tin plating elec-
trolyte shows positive leveling whose amount depends
on ic.
1
(37% solution) 6 8 ml l ; propargyl alcohol 7
1
10 ml l . The process is performed with mechanical
2
agitation of the electrolyte, ic = 2 12 A dm . The
current efficiency is 75 95%.
Agitation with air impairs the stability of the elec-
trolyte operation because of the fast oxidation of the
electrolyte. The electrolyte temperature is 18 25 C.
Above 25 C, the working ic range in which lustrous
coatings are obtained becomes narrower, electrolyte
rapidly turns turbid, and a precipitate is formed on
the bath bottom, which impairs the quality of the coat-
ings obtained. The anodes should be made of pure
tin. To prevent electrolyte contamination with sludge,
the anodes are to be placed in sheaths of khlorin or
propylene fabric.
(5) The polarization curves obtained at different
rates of disk electrode rotation cannot model the dis-
tribution of the rate of tin electrodeposition over the
microprofile because of the sensitivity of the adsorp-
tion layer inhibiting the electrodeposition process to
the hydrodynamic mode.
REFERENCES
1. Medvedev, G.I. and Gorbunova, I.M., Zh. Prikl. Khim.,
1990, vol. 63, no. 4, pp. 807 812.
The electrolyte is adjusted with respect to SnSO4,
H2SO4, and formalin, according to chemical analysis
data [7]. The electrolyte adjustment with respect to
2. Medvedev, G.I. and Mashutina, G.G., Zh. Prikl. Khim.,
1992, vol. 65, no. 4, pp. 789 795.
1
synthanol should be done after 100 A h l is passed
3. Valentelis, L.Yu., Kamuntavichene, I.Yu., and Matu-
lis, Yu.Yu., Tr. Akad. Nauk LitSSR, Ser. B, 1970,
vol. 63, no. 4, pp. 129 136.
1
through the bath by adding 1 g l of synthanol. The
1
expenditure of propargyl alcohol is 0.01 ml A 1 h .
4. Kruglikov, S.S., Itogi nauki i tekhniki: Khimiya. Elek-
trokhimiya (Advances of Science and Technology:
Chemistry. Electrochemistry), Moscow: VINITI, 1965,
pp. 117 151.
CONCLUSIONS
(1) A study of tin electrodeposition from sulfate
acid electrolyte with organic additives demonstrated
that, in the case of simultaneous presence of syn-
thanol, formalin, and propargyl alcohol, lustrous coat-
5. Medvedev, G.I., Kruglikov, S.S., and Fursova, N.Yu.,
Gal’vanotekhn. Obrab. Poverkhn., 2000, vol. 7, no. 2,
pp. 25 29.
2
ings are formed at ic = 2 12 A dm , depending on
the SnSO4 concentration in the electrolyte.
6. Gnusin, N.P. and Kovarskii, N.Ya., Sherokhovatost’
elektroosazhdeniya poverkhnostei (Irregularity of
Electrodeposition on Surfaces), Novosibirsk: Nauka,
1970.
(2) Cathodic polarization curves were measured on
a rotating disk electrode. It was found that organic
substances inhibit electrodeposition of tin. In this
case, a plateau of limiting current is formed in the
polarization curve. With increasing speed of disk
electrode rotation, the limiting current grows and
the cathodic polarization decreases.
7. Vyacheslavov, P.M. and Shmeleva, N.M., Kontrol’
elektrolitov i pokrytii (Monitoring and Control of
Electrolytes and Coatings), Leningrad: Mashinostroe-
nie, 1965.
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