Electrocrystallization of Pb and Pb assisted Al on aluminum electrode from molten salt (AlCl3-NaCl-KCl)

Article abstract of DOI:10.1016/j.jallcom.2008.12.001

Electrochemical deposition of aluminum and lead from basic molten AlCl₃-NaCl-KCl mixture on an aluminum electrode at 180 °C was studied by the methods of voltammetry, potential and current transient and constant current deposition. The depositi

Full text of DOI:10.1016/j.jallcom.2008.12.001

Journal of Alloys and Compounds 478 (2009) 83–88
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Electrocrystallization of Pb and Pb assisted Al on aluminum electrode
from molten salt (AlCl –NaCl–KCl)
3
a,∗
a
a
b
a
M. Jafarian , I. Danaee , A. Maleki , F. Gobal , M.G. Mahjani
a
Department of Chemistry, K.N. Toosi University of Technology, P.O. Box 15875-4416, Tehran, Iran
Department of Chemistry, Sharif University of Technology, P.O. Box 11365-9516, Tehran, Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 September 2008
Received in revised form
Electrochemical deposition of aluminum and lead from basic molten AlCl –NaCl–KCl mixture on an
aluminum electrode at 180 C was studied by the methods of voltammetry, potential and current
3
◦
transient and constant current deposition. The deposition of aluminum was found to proceed via a nucle-
ation/growth mechanism, while the deposition of lead was found to be diffusion controlled. The diffusion
2
5 November 2008
Accepted 1 December 2008
2
+
coefficient calculated for Pb ions in basic melt by voltammetry was in agreement with the deductions of
transient method. The analysis of the chronoamperograms indicates that the deposition process of lead
on Al substrates was controlled by 3D diffusion control, nucleation and growth. The processes are man-
ifested as peaks on a decaying chronoamperogram. Non-linear fitting methods were applied to obtain
the kinetic parameters from the theoretical model proposed for this system. It is found that under more
cathodic potential, the saturation number density of the formed lead nuclei and also the efficiency of the
use of the available surface nucleation sites increased. The morphology of the aluminum deposits in both
the presence and absence of PbCl2 was examined by SEM.
Available online 6 December 2008
Keywords:
Electrocrystallization
Nucleation
Growth
Aluminum
Lead
©
2008 Elsevier B.V. All rights reserved.
1
. Introduction
In view of their interesting acid–base properties chloroalumi-
nate melts (alkali metal chloride–AlCl3 mixtures) have received
considerable attention by molten salt chemists and a number of
reports on the electrochemical and spectroscopic studies of both
organic and inorganic species in this media have appeared in the
literature [16].
The electrocrystallization of metal on foreign substrates contin-
ues to attract a great deal of interest in modern electrochemistry
due to its technological importance [1]. Nucleation and the growth
of the first metallic nuclei formed on a substrate are critical steps
that determine the physicochemical properties of electrodeposits
and their studies are crucial in the understanding and control of
the process. The first stage, the nucleation on a substrate surface, is
in fact the important step in all metal deposition processes [2–7].
This early stage of electrochemical phase transformation is usually
associated with a one, two- or three-dimensional nucleation pro-
cess and the analysis of transients by means of different theoretical
formalisms allows us to identify the different growth types or dif-
ferent steps which control or determine the nucleation processes
The AlCl –NaCl melts have been employed as electrolytes for
3
electrodeposition of metals and rechargeable batteries. During the
charging of a rechargeable battery based on aluminum anodes, it
has been found that [17,18] both aluminum dendrites and spongy
deposits form under certain circumstances. As previously demon-
strated [19], spongy deposits of aluminum could be prevented with
the addition of MnCl2 and codeposition of Al and Mn.
Amorphous alloys have received widespread attention because
of their promising chemical, electrical, corrosion resistance and
mechanical properties [20]. The effect of many inorganic additives
in electrodeposition of aluminum from molten salts has been inves-
tigated. Among them PbCl2 [20] and SnCl2 [20,21] were found to
have some beneficial effects on aluminum deposition.
[
8–12]. The formation and growth of an electrodeposit involve com-
plex nucleation processes and several models have been proposed
to describe the cathodic deposition of metals especially when the
substrate and the electrodeposit are the same [13,14]. It has also
been shown that in many cases the electrolysis is mass transfer
controlled and experiments have been devised to determine the
diffusion coefficients of electroactive species [15].
Little work has been reported on voltammetry, chronopo-
tentiometry and chronoamperometry studies in AlCl –NaCl–KCl
3
melts. In our earlier work electrocrystallization of aluminum onto
graphite from a molten electrolyte containing AlCl –NaCl–KCl was
3
studied by the method of current transient and impedance spec-
troscopy [22,23]. In the early stage of the deposition and at low
cathodic potentials, two-dimensional (2D) nucleation and layer-
by-layer growth with some overlapping followed the initial double
∗ Corresponding author. Tel.: +98 21 22853551; fax: +98 21 22853650.
E-mail address: mjafarian@kntu.ac.ir (M. Jafarian).
0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2008.12.001

8
4
M. Jafarian et al. / Journal of Alloys and Compounds 478 (2009) 83–88
energy required to initiate nucleation while the negative on-set of
stripping is traced to unstable structure of the deposit compared
to more compact bulk Al. It was found that the cross-over poten-
tial is independent of the negative reverse potential. From these
and the Fletcher [25,26] theory it is concluded that the growth
rate is independent of the nucleation time (the experimental range
of time selected for examining the growth of the nuclei). There-
fore, the nuclei’s growth rate is controlled by charge transfer and is
determined only by the imposed potential.
The current step method is also a useful mean of detecting the
presence of nucleation. Potential maxima at the beginning of the
transition time can be attributed to the nucleation process [27].
Experimental chronopotentiograms exhibit a characteristic maxi-
mum in the early stages of deposition as shown in Fig. 2a. At the
very beginning of the chronopotentiogram, the steep falling poten-
tial has contributions of both double layer as well as adsorptive
pseudo capacitance charging [28] followed by monolayer deposi-
tion of the electroactive constituents. As the potential increases
nucleation takes place [29] and overpotential is required to meet the
galvanostatic conditions. As soon as nuclei are growing, the over-
potential for reduction decreases. The product Ioꢀ1 was found to
decrease with increasing applied current density, Fig. 2b, showing
that the deposition of aluminum in basic melts is not controlled
by diffusion and the reaction appears to be confined to the surface
or near surface domains [30]. The decreasing trend suggests that a
preceding chemical reaction mechanism similar to that observed
◦
Fig. 1. Cyclic voltammogram of the aluminum electrode in basic molten salt (180 C)
−
1
without PbCl2. The scan began at 0.2 V/Al with a scan rate of 60 mV s and electrode
2
area 0.5 cm .
layer charging. The processes manifested themselves as peaks on
decaying chronoamperograms. In impedance spectroscopy investi-
gations a model based on random birth and deterministic growth
of monolayers was proposed, in which the edges were assumed to
follow a propagation law. Parameters of impedance model in this
system could be calculated from the fitting of experimental data to
the faradaic impedance function derived theoretically.
It is the purpose of this study to investigate the electrochemical
deposition of Al, Pb and Pb assisted Al on aluminum electrode from
basic NaCl–KCl–AlCl3 molten salt. This system can be of great sig-
nificance from technological point of view because of its low vapor
/2
in the AlCl –(Bupy)Cl electrolyte prevails [31].
3
A
typical cyclic voltammogram of
a
PbCl2 containing
◦
melt/aluminum electrode of a slightly basic nature at 180 C
is shown in Fig. 3. The scan rate was 60 mV s
−
1
in the potential
◦
range 0.1 to −0.9 V/Al. In the cathodic half cycle the on-set of the
reduction peak at −0.5 V is clearly observed. Peak that appears at
a −0.65 V is attributed to the reduction of Pb species. The peak
pressure and its low melting point of 115 C. The kinetics of nucle-
ation and growth of Pb on aluminum electrode is also studied by
current transient.
current increases with scan rate and with PbCl concentration. This
2
−
2.
Experimental
peak is followed by the reduction of AlCl4 . No overcrossing was
observed in the direct and reverse scans and the dissolution peak
of deposited lead is observed at −0.12 V/Al. The relative locations of
the deposition and stripping signals suggest complex irreversible
type mechanism identified by Fletcher [25,26]. The ratio of the
anodic peak current to the cathodic peak current obtained from
this figure is nearly equal to one and also the columbic charge
associated with the deposition process is nearly equal to that of
the stripping process. This indicates that the deposited lead is an
insoluble product with constant activity during the deposition and
Materials used in this work were analytical grade of Merck origin. AlCl3
◦
was redistilled while NaCl and KCl were dried for 4 h at 400 C prior to use.
Fused electrolytes having the composition of 66–20–14 wt% (AlCl3–NaCl–KCl) with
the addition of 0.6% anhydrous PbCl2 were employed. Handling of the materi-
als and the procedures concerning the preparation of the fused electrolyte were
much the same as reported previously [22]. The experiments were carried out at
◦
1
80 C.
The experiments were carried out in a conventional three-electrode cell with a
2
hand polished aluminum rod with the surface area of 0.50 cm forming the working
electrode. Its potential was monitored against an aluminum (99.999% purity) refer-
ence electrode directly immersed in the melt [16]. A large graphite rod was used as
the counter electrode.
stripping process. A plot of peak current (i ) vs. the square root
p
The electrochemical cell was powered by an EG&G model 273A potentio-
stat/galvanostat run by a PC through M270 commercial software where the methods
of cyclic voltammetry (CV), chronopotentiometry (CP) and chronoamperometry (CA)
were employed. The data were analyzed through Statistica Stat Soft software. The
surface morphology of the deposit was evaluated by scanning electron microscopy
(
SEM, Philips XL30).
3
. Result and discussion
Cyclic voltammogram obtained in the potential range of 0.2 to
◦ −1
0.9 V/Al at 180 C with the scan rate of 60 mV s is presented in
−
Fig. 1. In the cathodic half cycle, a significant crystallization overpo-
tential is witnessed before aluminum electrodeposition begins. The
−
electroactive entity, probably AlCl4 , starts to reduce at −0.73 V/Al.
On reversing the potential sweep direction, nuclei already formed
on the electrode surface continue to grow as a result of the
−
−
AlCl4 + 3e ↔ Al + 4Cl reaction remaining thermodynamically and
kinetically favorable. The cross-over loop observed in reverse scan
signifying nucleation/growth in the course of a cathodic scan [24]
is accompanied by the anodic dissolution peak of Al at −0.3 V/Al.
The high negative overpotential for deposition is largely due to the
Fig. 2. (a) Chronopotentiogram of the aluminum electrode in basic melt with-
−
2
−2
out PbCl2 in different current densities I1 = 16.5 mA cm
,
I2 = 15.95 mA cm
,
−2
−2
−2
−2
I3 = 15.55 mA cm , I4 = 15.1 mA cm , I5 = 14.6 mA cm , and I6 = 14 mA cm . (b) Plot
1
/2
of Iꢀ
vs. I for chronopotentiograms depicted in panel (a).

M. Jafarian et al. / Journal of Alloys and Compounds 478 (2009) 83–88
85
Fig. 3. Cyclic voltammogram of the aluminum electrode in basic melt in the presence
◦
−1
.
of PbCl2 (180 C). The scan began at 0.1 V/Al with a scan rate of 60 mV s
Fig. 5. (a) Chronopotentiogram of the aluminum electrode in basic melt in the pres-
◦
−2
−2
ence of PbCl2 (180 C) in different current densities I1 = 12 mA cm , I2 = 10 mA cm ,
I3 = 8 mA cm−2, I4 = 6 mA cm , I5 = 4.5 mA cm , and I6 = 3.6 mA cm . (b) Plot of
−2
−2
−2
1
/2
Iꢀ
vs. I for chronopotentiograms depicted in panel (a). (c) Dependence of E on
ln(ꢀ − t ) derived in current density 4.5 mA cm
of scan rate (v) for the deposition processes exhibits a straight
line which passes through the origin within experimental error
1
/2
1/2
−2
.
(
Fig. 4). This feature point to the diffusion-controlled nature of
lead deposition in molten salts and the corresponding dependency
to be 2 in agreement with expectations.
3
/2 3/2
1/2 1/2 1/2
1/2 1/2
is well known (Ip = 0.496n
F
C˛
D
v
/R
T
) [32].
RT
E = Eth +
ln(ꢀ1/2 − t1/2)
(1)
From the slope of the straight line and using a transfer coefficient
n˛F
2+
value of 0.5 [33,34], the diffusion coefficient of Pb was obtained
as DPb2+ = 8 × 10 cm s
−6
2
−1
Fig. 6 presents chronoamperograms (CA) recorded at various
.
applied cathodic potential steps in the range of −0.58 and −0.61 V in
Chronopotentiometric measurements were also conducted with
the aluminum electrode in slightly basic melt and in the presence
of PbCl2 and the results are presented in Fig. 5a where two steps
appear in the chronopotentiograms. The first step is related to the
reduction of ionic Pb species and is at a potential in agreement
with that of the corresponding process in the cyclic voltammo-
gram. The second step which appears at longer times is related to
the presence of PbCl . As it can be seen, all transients are of the same
2
shape with characteristic and well defined current maxima. Consid-
ering the shape of the experimental current transients, Scharifker
et al. theory [35,36] was used for a 3D nucleation and growth mech-
anism limited by diffusion of the electroactive species (3D − DC) to
evaluate further kinetic parameters.
−
In the curves shown in Fig. 6, the fast decaying current corre-
sponding to the charging of the double layer is followed by a rising
current due to the growth of the new phase and/or the increasing
number of nuclei. At later stages the diffusion zones of adjacent
nuclei overlap and the current density reaches a maximum fol-
lowed by a decaying portion converging to a limiting current
corresponding to the linear diffusion of the electroactive ions
towards a planar electrode (Cottrell equation). The model of 3D
nucleation with hemispherical diffusion control of the growing 3D
clusters accounts for the kinetics of electrolytic phase formation in
the early stages when diffusion of the depositing species from the
bulk of the solution to the electrode/solution interface is the slow
step. Eventually overlap of diffusion zones and the development of
AlCl4 reduction in basic melt. At the transition time, the potential
rises sharply as the concentration of electroactive species at the
electrode surface approaches zero. The product Ioꢀ1/2 was found
to be constant with increasing current density, Io, showing that
2+
Pb reduction is controlled by diffusion and Sand’s law is obeyed
Fig. 5b). The diffusion coefficient deduced from Sand’s law is in very
good agreement with that obtained in voltammetry and was found
(
−6
2
−1
to be DPb2+ = 8.5 × 10 cm s . Logarithmic analysis of chronopo-
tentiograms obtained in diffusion controlled region, Eq. (1), gave
good linear fits for the insoluble product model where the plot of E
vs. ln(ꢀ − t ) is linear (Fig. 5c). Assuming the value of ˛ to be 0.5,
from the slopes of these plots the average value of n was calculated
1
/2
1/2
Fig. 4. (a) Cyclic voltammogram of the aluminum electrode in basic melt in limited
Fig. 6. Potentiostatic current transient obtained for deposition of Pb on aluminum
at different potentials: (1) −0.58, (2) −0.585, (3) −0.59, (4) −0.595, (5) −0.6, (6)
−0.605, and (7) −0.61 V/Al.
◦
potential range due to Pb deposition (180 C). (b) The proportionality of cathodic
−
1
peak currents to the square roots of sweep rate (2–500 mV s ).

8
6
M. Jafarian et al. / Journal of Alloys and Compounds 478 (2009) 83–88
Fig. 8. (a) Experimental current transient (—) recorded at −0.595 V and a corre-
sponding theoretical curve (- - -) for 3D nucleation transition. Contributions to the
transient current from the double layer charging phenomenon (IDL) and 3D dif-
o
Fig. 7. Experimental and theoretical (—) current transients compared and presented
in a non-dimensional I2/Im vs. t/tm, plot. Experimental current transients associated
2
with the peak, recorded at −0.58 (×), −0.585 (ꢀ), −0.59 (ꢁ), −0.60 (ꢂ), and −0.605
fusion control nucleation processes (I3D) are also shown. (b) Plot of ln(AN ) vs. E
(ꢃ) V/Al.
derived from theoretical current transient. (c) Dependence of ln(N ) on E derived
s
from theoretical current transient.
nucleation exclusion zones around the already established nuclei
prevail. The time necessary to reach current maximum (tm) depends
on the overpotential and decreases as the potential is made more
cathodic.
limited by diffusion control growth (I3
).
D−DC
ꢊ
ꢋ
ꢀ
ꢂ
ꢃ
ꢄꢅꢁ
nFD1/2
ꢁ1/2t1/2
C
1 − exp(−At)
I3
=
1 − exp −NoꢁkD t −
D−DC
A
As a preliminary step all current transients were presented in
a non-dimensional form, normalized current vs. time [(I/Im)2 vs.
(4)
t/tm] plots. Im and tm are the current and time values corresponding
to the points of maxima used in the normalization processes [35].
According to this methodology a comparison of the theoretical plots
with the experimental data allows the determination of nucleation
process mechanism: instantaneous vs. progressive.
This equation is equally valid for describing instantaneous and
progressive nucleation and does not require distinction of the
nucleation mechanism prior to its use. In this equation zF is the
molar charge transferred during electrodeposition, D is the diffu-
sion coefficient, and C is the bulk concentration of the electroactive
species. Time is t, the number density of active sites is No, the nucle-
ation rate constant is A, and Eq. (5) defines k:
The current–time dependencies of the two types are distinctly
different and follow Eqs. (2) and (3):
ꢀ
ꢀ
ꢁ ꢂ
ꢃ
ꢀ
ꢀ
ꢁꢄꢅ
ꢀ
ꢁ
I2
2
−1
2
1/2
t
t
8ꢁCM
ꢂ
=
=
1.9542
1 − exp −1.2564
(2)
(3)
k =
(5)
I
tm
tm
m
ꢆ
ꢇ
ꢈꢉ
M and ꢂ are the atomic weight and the density of the deposit,
respectively.
ꢁ
ꢁ
2
I2
2
−1
2
t
t
1.2254
1 − exp −2.3367
I
tm
tm
As can be seen below, this expression can be presented in non-
dimensional form which is in agreement with experimental data
observed in Fig. 7.
m
for instantaneous and progressive processes, respectively.
Fig. 7 shows such a non-dimensional plot for typical current
transients recorded at different potentials for lead deposition on
aluminum electrode. As it can be seen very clearly the relationship
between the experimental curves and the theoretical models are
the same in all potential. These curves indicate an instantaneous
type of nucleation. At potentials greater than −0.625 V, nucleation
tends to switch toward the progressive type for t > tm.
In the case when the nucleation mechanism changes with the
applied potential the evaluation of kinetic parameters based on the
non-dimensional plots cannot be used. To estimate typical kinetic
parameters for Pb deposition onto aluminum, we used Scharifker
and Mostany’s [37] general equation (Eq. (4)) for time evolution
of the current density in the course of the 3D nucleation process
I2
2
2
tm {1 − exp[−xt/tm + ˛(1 − exp(−xt/˛tm))]}
=
(6)
2
I
t
{1 − exp[−x + ˛(1 − exp(−x/˛))]}
m
x = NoꢁDktm
NoꢁDk
˛ =
A
The rate of nucleation does not remain constant during the elec-
trocrystallization process but decreases continuously due to the
decline of the number density of active site available for nucleation.
Thus the saturation number density of the formed lead nuclei, Ns,
Table 1
Kinetic parameters obtained from the non-linear fitting of Eq. (4) with addition of double layer effect to the potentiostatic current transients shown in Fig. 6.
D (×10 cm2
6
s
−1
)
No (×10−5 cm−2
)
A (s
−1
)
ANo (×10−5 cm
−2 −1
s
)
Ns (×10−5 cm−2
)
Ns/No
K1(DL) (A cm
−2
)
−1
K2(DL) (s )
E (V vs. Ag/AgCl)
−
−
−
−
−
−
−
0.58
0.585
0.59
0.595
0.6
7.6
8
7.9
8.1
8
0.763
1.186
1.779
2.262
2.866
4.449
6.18
0.2
0.4
0.7
1.2
2
0.152
0.474
1.245
2.715
5.733
15.573
37.083
0.412
0.702
1.138
1.64
2.4
4.024
6.043
0.54
0.007
0.011
0.015
0.0165
0.017
0.2
06
1.2
2.5
2.9
3
0.592
0.639
0.725
0.837
0.904
0.977
0.605
0.61
8
8.2
3.5
6
4.2
4.5
0.033

M. Jafarian et al. / Journal of Alloys and Compounds 478 (2009) 83–88
87
through
ꢀ
ꢁ
kT
d lnA
dE
Nk
=
− ˛
(9)
neo
Eq. (9) indicates that the slope of an experimental curve of ln A
vs. E gives the size of the critical nucleus. The experimental ln A
vs. potential plots for all concentrations studied in this work gave
straight lines throughout the potential range. From their slope at
4
53 K and using a transfer coefficient value of 0.5, Eq. (9) the number
of atoms that form critical nucleus was estimated to be 2.1 atoms.
3.1. Constant current deposition studies
Fig. 10a presents the scanning electron micrographs of Al elec-
trodeposited from basic melt on aluminum electrode in current
Fig. 9. Dependence of the nucleation rate on applied potential for the deposition of
Pb.
−2
◦
density 0.06 A cm . As can be seen, in basic melts at 180 C, it seems
that dull, dark, spongy deposits and weakly adherent to the sub-
strate are always formed on. Fig. 10b presents the scanning electron
micrographs electrodeposited surface from basic melt with addi-
is [35]:
−
2
ꢀ
ꢁ
1/2
tion of PbCl on aluminum electrode in current density 0.06 A cm
.
2
ANo
kD
Ns =
(7)
In the presence of PbCl2 the Al layer was silver bright, partly com-
pact, and smoother. When PbCl2 is present, codeposition of Al and
Pb apparently promotes the nucleation [19] and therefore the for-
mations of spongy deposits are avoided.
2
Taking into account the contribution of double layer charging
in current–time transient, IDL = k exp(−k t), theoretical equations
1
2
were fitted to the experimental current transient (Fig. 8a) and dif-
fusion coefficient for ionic Pb species and characteristic kinetic
parameters, the nucleation rate constant (A), number density of
active sites (No), the ANo product and the ratio Ns/No were obtained
and are presented in Table 1.
As it was expected in accordance with the theory we found
that A, No and Ns increase with the application of more cathodic
electrode potential. The product ANo which gives the stationary
nucleation rate increased with increasing applied cathodic poten-
tial, Fig. 8b. The Ns/No ratio, which can also be defined as the
efficiency of the use of the available surface nucleation sites,
increases at more cathodic electrode potentials indicating that in
more negative potentials higher number of surface sites are occu-
pied by lead nuclei.
The potential dependence of ln(Ns) is linear pointing to the expo-
nential relationship between Ns and the electrode potential, Fig. 8c.
The potential dependence of No is due to distributed energies of
nucleation on different sites. At low overpotentials, nucleation is
restricted to very few active sites on the surface which become
exhausted at an early stage in the process and nucleation thus
approaches the instantaneous limit at low supersaturation. At very
high cathodic overpotential the nucleation approaches progressive
limit (Fig. 9).
Within the framework of the atomistic theory of nucleation [38],
the number of atoms necessary to form the critical nucleus can be
estimated directly from the potential dependence of the nucleation
rate. The largest cluster for which the probability for attachment of
one atom is less than one-half is defined as critical. The attachment
of a new atom converts this cluster into a stable one for which the
probability for attachment of the next atom is already higher than
one-half and henceforth able to grow spontaneously. According to
the atomistic theory, the nucleation rate can then be expressed as
ꢀ−
ꢁ
ꢀ
ꢁ
Wk
˛neoE
kT
A = K1 exp
exp
(8)
kT
where K is the pre-exponential factor, eo is the elementary electric
1
charge, ˛ is the cathodic transfer coefficient, E is the overpotential,
and W is the reversible work for the formation of a critical nucleus
k
Fig. 10. (a) Surface of aluminum deposited in basic melt by SEM micrograph. (b)
consisting of N atoms. It has been shown [39] that, regardless of the
k
Surface of aluminum deposited in basic melt in the presence of 0.6% PbCl2 by SEM
nucleation model and for the case when the excess Gibbs energy of
−2
◦
micrograph. Current density 0.06 A cm , deposition time 8 h, temperature 180 C,
and melt composition 66–20–14 wt%.
nucleus formation is potential dependent, N , A, and E are related
k

8
8
M. Jafarian et al. / Journal of Alloys and Compounds 478 (2009) 83–88
4
. Conclusion
[7] G. Gunawardena, G. Hills, I. Montenegro, B. Scharifker, J. Electrochem. Soc. 138
1982) 225–231.
8] D.J. Astely, J.A. Harrison, H.R. Thirsk, Trans. Faraday Soc. 64 (1968) 192–201.
9] M. Fleischmann, H.R. Thirsk, Electrochim. Acta 2 (1960) 22–49.
(
[
[
Electrodeposition of aluminum and lead onto an aluminum
electrode from molten (AlCl –NaCl–KCl) salts were studied by
[10] G.A. Gunawardena, G.J. Hills, I. Montenegro, Electrochim. Acta 23 (1978)
93–697.
3
6
the methods of cyclic voltammetry, chronopotentiometry and
chronoamperometry. Electrochemical deposition of aluminum
onto aluminum electrode in basic melt was found to proceed via
a nucleation/growth mechanism, while deposition of lead from
basic melts showed that ionic Pb species reduction was con-
trolled by diffusion. The diffusion coefficient of such species was
obtained by voltammetry, chronopotentiometry and is in agree-
ment with the chronoamperometric measurements and was found
[
11] M. Fleischmann, H.R. Thirsk, in: P. Delahay (Ed.), Advanced Electrochemistry
and Electrochemical Engineering, vol. 3, Academic Press, New York, 1963, p.
123.
[12] I.N. Stranski, R. Kaishev, Z. Physik 36 (1935) 393–398.
[
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7
−
6
2
−1
.
to be 8 × 1 cm s
[
The analyses of the chronoamerograms indicate that the depo-
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2
[
[
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[
5
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1