A study of the kinetics of tin electrodeposition from sulfate electrolyte with organic additives

Article abstract of DOI:10.1023/A:1020988206160

The method of Faraday impedance was applied to study the kinetics of tin electrodeposition from a sulfate electrolyte in the simultaneous presence of syntanol DS-10, formalin (37% solution), and benzyl alcohol.

Full text of DOI:10.1023/A:1020988206160

Russian Journal of Applied Chemistry, Vol. 75, No. 8, 2002, pp. 1234 1236. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 8, 2002,
pp. 1260 1262.
Original Russian Text Copyright
2002 by Medvedev, Makrushin.
APPLIED ELECTROCHEMISTRY
AND CORROSION PROTECTION OF METALS
A Study of the Kinetics of Tin Electrodeposition from Sulfate
Electrolyte with Organic Additives
G. I. Medvedev and N. A. Makrushin
Novomoskovsk Institute, Mendeleev Russian University of Chemical Technology, Novomoskovsk, Tula oblast, Russia
Received January 15, 2002
Abstract The method of Faraday impedance was applied to study the kinetics of tin electrodeposition from
a sulfate electrolyte in the simultaneous presence of syntanol DS-10, formalin (37% solution), and benzyl
alcohol.
Previously, the kinetics of tin electrodeposition
from a sulfate electrolyte in the presence of syntanol
DS-10 has been studied [1]. Dull tin coatings have
been obtained in this electrolyte. It has been shown
that the kinetics of tin electrodeposition depends on
the electrode potential and is gaverned by a hetero-
geneous and a homogeneous chemical reactions.
show that C decreases with increasing frequency and
is constant in the range 30 50 kHz. It was assumed
on the basis of this fact that the differential capaci-
tance measured at these frequencies is the capacitance
of the electrical double layer (EDL).
The measurements were done using a series equiv-
alent circuit. The Cb and Rb values obtained with
an ac bridge were recalculated to Cs and Rs values
[4]. The equivalence of the circuit was verified using
the procedure described in [5]. The electrode imped-
In [2], the electrodeposition of tin from a sulfate
electrolyte in the presence of syntanol, formalin (37%
solution), and benzyl alcohol was studied. It was
shown that that, with these organic substances present
simultaneously in an electrolyte subjected to stirring,
ance components Rs and 1/ Cs were studied in rela-
1/2
tion to
.
2
shining coatings are formed at ic = 4 12 A dm .
The results obtained in measuring the cathode cur-
rent density and EDL capacitance as functions of the
electrode potential demonstrate that organic additives
inhibit tin electrodeposition (Fig. 1, curves 1 and 2).
It was of interest to study the kinetics of tin electro-
deposition in the presence of these organic substances.
This was done, as in [1], using the Faraday impedance
method. The differential capacitance was measured
during electrolysis with an R-5021 ac bridge at fre-
quencies in the range 200 Hz 20 kHz on an electrode
made of tin-coated platinum wire (S = 0.126 cm2),
placed at the center of a platinum-black-coated plat-
inum cylinder. Electrochemical measurements were
carried out using a P-5878 potentiostat in an electro-
lyte stirred with a magnetic stirrer.
At potentials in the range 0.3
0.4 V the EDL
A tin layer 10 m thick was deposited onto the sur-
face of the working electrode. The electrode surface
was refreshed before making a measurement at each
potential. The discrepancy between the results of
measurements in different series did not exceed 5%.
The potentials are given relative to a standard hydro-
gen electrode. The differential capacitances in electro-
lytes with organic additives are given with account of
the roughness factor f. The procedure for determining
f was described in [3].
Fig. 1. (1) Cathode current density i and (2) differential
c
capacitance of the electrical double layer, C, at 30 kHz vs.
1
the electrode potential E. Electrolyte composition (g l ):
The results obtained in measurements of the dif-
ferential capacitance C at different electrode potentials
SnSO 30, H SO 100, syntanol 2; formalin and benzyl
4
2
4
1
alcohol 6 ml l each; mechanical stirring.
1070-4272/02/7508-1234 $27.00 2002 MAIK Nauka/Interperiodica

A STUDY OF THE KINETICS OF TIN ELECTRODEPOSITION FROM SULFATE ELECTROLYTE 1235
Fig. 3. Electrode impedance components (1) R and (2)
s
1/2
1/ C and (3, 4) phase shift vs.
at different elec-
s
trode potentials. Potential (V): (1, 2) 0.8; (3) 0.3 and
0.6; and (4) 0.4, 0.7, and 0.8.
Fig. 4. Equivalent electric circuits of the process of tin de-
position from a sulfate electrolyte with organic additives
at different potentials. R is the electrolyte resistance;
e
Fig. 2. Electrode impedance components (1, 2; 5, 6) R
C , capacitance of the electrical double layer; R , the transi-
s
d
t
1/2
and (3, 4; 7, 8) 1/ C vs.
at different electrode po-
tion resistance; and C and R , the capacitance and resis-
s
r
r
tentials. Potential (V): (1, 4) 0.3, (2, 3) 0.4, (5, 7) 0.6,
and (6, 8) 0.7.
tance of a heterogeneous chemical reaction. Potential (V):
(a) 0.3, 0.4, and 0.8; (b) 0.7 and 0.8.
2
2, and 5). At a potential of 0.7 V, Rs passes through
a maximum with increasing frequency and then tends
to zero (Fig. 2, curve 6). The capacitive components
of the impedance, 1/ Cs, much exceed Rs. At a fre-
quency of 200 Hz and potentials equal to 0.3, 0.4,
0.6, and 0.7 V, 1/ Cs varies in the interval
16 40 cm2 (Fig. 2, curves 3, 4, 7, and 8). With in-
creasing frequency, 1/ Cs decreases, passes through
a maximum at a certain frequency, and then tends to
capacitance is 5.9 6.1 F cm . At E < 0.54 V the
EDL capacitance and the electrodeposition rate in-
crease. The inhibition of the process in the electrolyte
with organic substances is due to their adsorption and
formation on the electrode surface of a dense adsorp-
tion layer, which starts to disintegrate at E < 0.4
owing to desorption of molecules of the organic sub-
stances [6]. Dull coatings are obtained at potentials in
0.6 V, and shining coatings, at
0.7 0.83 V. With account of these data, the Far-
aday impedance was measured at potentials of 0.3,
0.4, 0.6, 0.7, and 0.8 V. The dependences of
the range 0.2
zero. The only exception is the potential of 0.8 V at
1/2
which the 1/ Cs
from 4.2 to 2.5
curve 2).
dependence shows a decrease
cm2 after the maximum (Fig. 3,
1/2
Rs and 1/ Cs on
are presented in Figs. 2 and
3, curves 1 and 2, whence it can be seen that Rs at
200 Hz varies within the interval 1 10 cm2 at all
the potentials studied. At 0.3, 0.4, and 0.6 V,
Rs grows gradually with increasing frequency and
passes through a maximum to reach a constant value
after that at a frequency of 20 kHz (Fig. 2, curves 1,
2, and 5). At E = 0.8 V, Rs varies in the range 0.9
Analysis of the results of impedance measurements
suggests that the impedance dependences correspond
to equivalent electric circuits with in-series connec-
tion of the transition resistance Rt, capacitance Ct
and resistance Rr of a heterogeneous chemical re-
action at E = 0.3, 0.4, and 0.8 V (Fig. 4a); and
to in-series connection of the capacitance Cr and re-
sistance Rr of a heterogeneous chemical reaction at
E = 0.7 and 0.8 V (Fig. 4b).
1.2
cm2 with frequency increasing in the interval
200 3000 Hz; at higher frequencies Rs increases to
1.6 cm2 (Fig. 3, curve 1). Extrapolation of Rs val-
ues to higher frequencies yields the ?transition resis-
tance Rt. At E equal to 0.3, 0.4, and 0.6 V, Rt
is, respectively, 8.5, 4, and 3 cm2 (Fig. 2, curves 1,
Thus, it may be concluded that the process kinetics
is governed by a transition reaction and a heteroge-
neous chemical reaction in obtaining dull coatings,
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 8 2002

1236
MEDVEDEV, MAKRUSHIN
and by a heterogeneous chemical reaction in deposit-
ing shining coatings. The transition resistance at E =
0.3, 0.4, and 0.6 V is due to the hindered stage
of discharge of tin ions. The heterogeneous chemical
reaction is of varied nature, depending on the elec-
trode potential.
kinetics of the electrodeposition process is determined
by a heterogeneous chemical reaction, which has var-
ied nature depending on the electrode potential.
CONCLUSIONS
(1) A study of the kinetics of tin electrodeposition
from a sulfate electrolyte in the presence of syntanol
DS-10, formalin (37% solution), and benzyl alcohol
by the method of the Faraday impedance established
that the kinetics of the process in the range of poten-
tials at which dull tin coatings are formed is deter-
mined by a transition reaction and a heterogeneous
chemical reaction.
At the potential of maximum adsorption, E = 0.3
and 0.4 V) the heterogeneous chemical reaction is
determined by the stage of tin ion penetration to the
electrode surface across the adsorption layer. In this
case, the process kinetics is governed by the so-called
penetration overvoltage [7].
At E = 0.6 and 0.7 V, when the adsorption layer
starts to disintegrate because of the desorption of or-
ganic substances from the electrode surface, the het-
erogeneous reaction is the chemical reaction of tin
atoms adsorbed on the electrode surface with organic
substances or products of their reduction. The het-
erogeneous chemical process occurring at E = 0.8 V
is crystallization, with the transition resistance Rt =
(2) In the range of potentials at which shining
coatings are formed, the process rate is determined
by a heterogeneous chemical reaction.
(3) It was shown that the part of the transition re-
action is played by the hindered reaction of discharge
of tin ions, and the heterogeneous reaction has varied
nature, depending on the electrode potential. At po-
tentials of 0.3 and 0.4 V, when a dense adsorption
layer is formed on the electrode surface, the hindered
stage of the process is penetration of tin ions across
the adsorption layer.
Rcr (crystallization resistance), Rcr = 2
cm2.
As already noted, at E = 0.8 V the capacitive
component of the impedance reaches a constant value
after passing through a maximum. Extrapolation of
1/ Cs to higher frequencies yields a value 1/ Ccr,
where Ccr is the crystallization capacitance. Accord-
ing to the data of [5]
(4) At more electronegative potentials (E = 0.6,
0.7 V), when the adsorption layer starts to disinte-
grate as a result of desorption of organic substances
from the electrode surface, the role of the heteroge-
neous reaction is played by the interaction of metal
atoms adsorbed on the electrode surface with organic
substances or products of their reduction, and at E =
0.8 V, by crystallization.
Ccr = z2F2Cad/RT,
where Cad is the concentration of adatoms on the elec-
trode surface, z is the charge of tin cations, and F is
the Faraday number.
The calculations performed demonstrate that Cad
=
REFERENCES
14
2
2.6 10
mol cm for tin. The assumption that
heterogeneous reactions occur depending on the elec-
trode potential is also confirmed by measurements of
the phase shift . The phase shift was calculated in
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2. Medvedev, G.I. and Makrushin, N.A., Zh. Prikl. Khim.,
accordance with [5]. With account of the
found from the dependence 1/ Cs
1/2, the reaction
rate constant k was determined. For a heterogeneous
reaction, = k and tan /k, 90 . The
value
max
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and 4. It can be seen that the phase shift does ap-
proach 90 at potentials of 0.3
0.8 V.
To conclude, it should be noted that the experi-
mental data on the kinetics of tin electrodeposition
from sulfate electrolytes with organic additives, ob-
tained in [1] and in the present study, indicate that,
in depositing dull coatings, the rate of the process is
determined by a transition reaction and a heteroge-
neous and homogeneous chemical reactions. At the
same time, when shining coatings are deposited, the
5. Vetter, K.J., Electrochemische Kinetik, Berlin: Springer,
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 8 2002