Effect of pulse plating on the composition and corrosion properties of Zn-Co and Zn-Fe alloy coatings

chemija. 2008. vol. 19. No. 1. P. 7–13
© lietuvos moksl? akademija, 2008
© lietuvos moksl? akademijos leidykla, 2008
Effect of pulse plating on the composition and corrosion
properties of Zn–Co and Zn–Fe alloy coatings
Rimantas Ramanauskas*,
The influence of pulse plating parameters on the chemical and phase composition, surface to-
pography and corrosion resistance of Zn–Co (<1%) and Zn–Fe (<1%) al oy coatings has been
Laima Gudavi?i?t?,
studied. Pulse plating of low-al oyed Zn coatings resulted in the grain size reduction of deposits,
however, this process was not accompanied by any significant reduction in the corrosion cur-
Remigijus Jušk?nas
rents of these al oys. It was suggested that the dual phase formation was the principal reason
why pulse plated low-al oyed Zn coatings did not exhibit any improvement in their corrosion
Department of Metal
resistance.
Electrochemistry, Institute of
Chemistry, A. Goštauto 9,
Key words: pulse electrodeposition, zinc al oys, phase composition, corrosion
LT-01108 Vilnius, Lithuania
Olga Š?it
Department of Chemistry, Vilnius
Pedagogical University, Student? 39,
LT-08106 Vilnius, Lithuania
INTRODUCTION
al oy phase composition, which may also affect the corrosion
performance of the coating.
The service life of sacrificial zinc electrodeposits can be increased
Acidic or alkaline plating baths can be used for the plating of
by means of al oying with relatively more noble Fe group metals. Zn and Zn al oys. The published data on pulse-plated Zn al oys
The most common al oys exhibiting good protective properties are mostly related to coatings deposited from acidic solutions
contain 10–15% Ni [1–10], while less than 1% is needed when [6, 19–24]. For example, it is known, that d. c. electrodeposition
Co or Fe are added to the Zn matrix to achieve the optimum of a Zn–Ni al oy in an acidic bath results in the formation of a
functional properties [6, 11–18]. Al oy coatings appeared to be dual phase structure [25], which causes a significant reduction
attractive, since under similar electroplating conditions these in the corrosion resistance of the coating. Meanwhile, deposi-
deposits in addition to lower corrosion rates possess better phy-
tion in alkaline solutions, in contrast to the acidic ones, is less
sical properties than those of pure Zn layer. For example, such efficient, but gives a more uniform plating and results in the for-
coatings are able to withstand exposure to high temperatures mation of a single-phase Zn–Ni al oy [25, 27]. In addition, pulse
(~300 °C), maintaining similar corrosion properties and good plating effect on the phase composition of low-al oyed Zn coat-
adhesion to a substrate [3], which improves the ability of paint ings with Fe and Co has not been investigated to date.
to adhere to the surface of steel [14, 16].
The objective of the present investigation was to determine
However, the permanent requirement of the industry (es-
the influence of pulse electrodeposition parameters on the phase
pecial y the automobile industry) to reduce the thickness of the composition and corrosion properties of Zn–Co (<1% Co) and
coatings and to increase corrosion resistance encourages the de-
Zn–Fe (<1% Fe) al oy coatings.
velopment of new surface finishing processes for zinc plating.
Pulse electrodeposition can be used as a means for produc-
EXPERIMENTAL
ing unique structures, i. e. coatings with properties unachievable
by direct current (d. c.) plating. The application of non-station-
Zn–Co and Zn–Fe coatings of ~9 µm thickness were electrode-
ary electrodeposition yields smoother and denser deposits with posited on low carbon steel (C 0.05–0.12%, Mn 0.25–0.5%) sam-
negligible porosity, therefore, pulse plating is one of the methods ples, which were polished mechanical y to a bright mirror. An
to obtain coatings that are more resistant to corrosion. However, alkaline cyanide-free plating solution contained ZnO 10 g l–1,
non-equilibrium crystal ization may result in the changes of the NaOH 100 g l–1 and organic additives. A detailed description of
the plating bath and operating conditions are presented else-
* corresponding author. e-mail: ramanr@ktl.mii.lt
where [26–29].

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8
Rimantas Ramanauskas, Laima Gudavi?i?t?, Remigijus Jušk?nas, Olga Š?it
The Zn al oy coatings were deposited at 25 °C varying the
The influence of pulse plating parameters: cathodic peak
cathodic peak current density (i ) from 0.05 to 1 A cm–2, current current density (i ), current on-time (t ) and current off-time
p
p
on
on-time (t ) – from 0.1 to 2 ms and current off-time (t ) – from (t ) on the amount of the al oying elements is presented in
on
off
off
1 to 10 ms. The electrodeposition experiments were carried out Fig. 1. Electrodeposition conditions affected the composition
by varying one parameter at a time with other parameters being of Zn al oys in the fol owing manner: the increase in i and t
p
off
fixed at standard conditions. The Zn–Fe coatings were deposited caused an increase in the amount of both al oying metals in the
under the fol owing fixed plating parameters: i = 0.1 A cm–2, deposit, while the variation in t affected the composition of
p
on
t = 0.2 ms, t = 2 ms and Zn–Co: i = 0.2 A cm–2, t = 0.2 ms, each al oy in a different mode – an increase in Co amount was
on
off
p
on
t = 2 ms. Current efficiency of the plating process varied be-
observed with the increase in t values, whereas the variation of
off
on
tween 40% and 80%.
this parameter had no significant influence on the amount of the
The d. c. plated Zn–Fe and Zn–Co coatings were obtained deposited Fe in the al oy, as its concentration changed in a nar-
under 0.025 A cm–2 current density.
row range between 0.8 and 0.9%. Meanwhile, i and t variations
p
off
X-ray diffraction measurements were performed with a D8 caused an increase in the Fe amount up to 1.2 and 1.5%, when
diffractometer equipped with a Göbel mirror (primary beam i and t higher than 0.7 A cm–2 and 2 ms were applied, respec-
p
off
monochromator) for Cu radiation. A step-scan mode was used tively, (Fig. 1 a, c). The latter cases were not acceptable, as the
in the 2-theta range from 30° to 75° with a step length of 0.02° limiting concentration of the al oying element (1%) was over-
and a counting time of 5 s per step.
passed. Besides, the quality of the deposits, when t higher than
off
The chemical composition of the electrodeposited coatings of 5 ms was applied, was insufficient. An increase in i , t and t
p on
off
was determined applying electron probe microanalysis with caused an increase in the Co amount in the deposit, however, the
SEM JXA-50A.
concentration of this metal varied in the range between 0.5 and
Surface morphology studies were carried out with an AFM 0.8%. The presented dependences (Fig. 1) validate the optimal
by an Explorer (VEECO-Thermomicroscopes) scanning probe range of pulse plating parameters, which ensured the desirable
microscope at atmospheric pressure and room temperature in composition of Zn al oys.
a contact mode. A Si N cantilever with the force constant of
3 4
0.032 N m–1 was used and the obtained resolution of the images Topography
was 300 × 300 pixels. The grain size dimensions of the electrode-
Surface topography studies were based on AFM measurements
posited coatings were determined by means of SPMLab software with the aim to determine the influence of plating parameters
and from profile line analysis.
on the grain size dimensions, as well as to find out the deposi-
The corrosion behaviour of the coatings was investigated tion conditions, which resulted in the surface macro-structural
in an aerated stagnant 0.6 M NaCl + 0.2 M NaHCO solution defect formation. The images representing the influence of pulse
3
(pH 6.8) using a standard three-electrode system with a Pt plating parameters on the surface structure of Zn–Co and Zn–
counter electrode, a saturated calomel reference electrode and Fe coatings are presented in Figs. 2–4.
a PI-50 potentiostat. The corrosion current densities (i ) were
corr
determined from Tafel plot extrapolation. To begin the mea-
surements, the sample was introduced into the cell immediately
after electroplating and was al owed to equilibrate, which usu-
al y took 15 min. Polarization measurements were performed
under potentiodynamic conditions with a potential scan rate of
0.1 mV s–1.
RESULTS AND DISCUSSION
Chemical composition
The principal requirements for the pulse plated Zn al oys were
the absence of macrostructural defects, such as dendrites or areas
of local dissolution on the surface of the coating, and the stability
of the al oy composition. The latter implied a variation in Co and
Fe concentrations in the al oy between 0.4–1.0%. The concentra-
tions of al oying metals in the deposit lower than 0.4% do not ex-
hibit any beneficial effect on the corrosion properties of coatings Fig. 1. Effect of pulse plating parameters on the amount of alloying metals in the
with respect to that of pure Zn, while a higher amount of Co and deposits
Fe in the al oy results in the dual phase formation [1, 29].
The data on the composition, structure and corrosion be-
The investigations on µm level (20 × 20 µm scanned surface
haviour of Zn–Co and Zn–Fe coatings deposited in an alkaline area) have shown that the morphology of both al oy coatings was
bath by a direct current have been presented in our previous studies very similar; therefore, only the images of Zn–Co of the mentioned
[26–30]. It was established there that the low-al oyed deposits were scanned area are presented. D. c. plated Zn–Co and Zn–Fe coat-
single-phase solid solutions of Co and Fe in Zn with 0.6% and 0.5% ings consisted of micron and sub-micron sized granular crystal ite
concentration of the al oying metals, respectively.
agglomerations (Fig. 2 a). The size of these formations (? ) varied
ag

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Effect of pulse plating on the composition and corrosion properties of Zn–Co and Zn–Fe al oy coatings
9
Fig. 2. AFM images of Zn–Co coat-
ings deposited under: a – d. c.
conditions; b, c, d – pulse-plated
under cathodic peak current
density i (A cm–2): b – 0.2,
p
c – 0.3, d – 1. The scanned area
is 400 µm2
Fig. 3. AFM images of Zn–Co coat-
ings deposited under: a – d. c. con-
ditions; b, c, d – pulse-plated under
cathodic peak current density i p
(A cm–2): b – 0.2, c – 0.3, d – 1. The
scanned area is 0.25 µm2

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10
Rimantas Ramanauskas, Laima Gudavi?i?t?, Remigijus Jušk?nas, Olga Š?it
Fig. 4. AFM images of Zn–Fe
coatings deposited under: a – d.
c. conditions; b, c, d – pulse-
plated under cathodic peak cur-
rent density i (A cm–2): b – 0.1,
p
c – 0.2, d – 1. The scanned area
is 0.25 µm2
are presented in Fig. 5. It has been shown in our previous study
with pulse-plated Zn coatings [36] that the grain size values ob-
tained by this technique coincide well with the results of XRD
measurements. A comparison of crystal ite agglomeration and
grain size dimensions with the data on corrosion behaviour of
pulse-plated Zn coatings implied that corrosion resistance was
related more to ? values than to ? ones [36]. Therefore, the
gr
ag
main attention in this study was paid to ? values of the plated
gr
Zn–Co (Fig. 3) and Zn–Fe (Fig. 4) coatings.
All the pulse-plated samples were obtained with higher ca-
thodic current densities than the d. c. deposits. It is well known
that low overpotential deposition produces films with large sur-
face irregularities, whereas high overpotential deposition yields
films with smooth surfaces [31, 32]. A raise in the overpotential
increases the free energy to form new nuclei, which results in a
higher nucleation rate and a smal er grain size. The influence of
i on the surface morphology of pulse plated Zn–Co and Zn–Fe
p
Fig. 5. Effect of pulse plating parameters on the grain size dimensions (? ) of pulse
coatings can be observed from AFM images presented in Figs. 3
gr
plated Zn–Co and Zn–Fe coatings
and 4, respectively.
The main difference in the topography of Zn–Co and Zn–Fe
in the range from 0.4 to 2.5 µm with the average values of 0.9 and electrodeposits obtained by d. c. and pulse techniques was in
1.31 µm for Zn–Co and Zn–Fe, respectively.
the size of crystal ite agglomerations (Fig. 2) and grains (Figs. 3
The ultrafine-grained structure was determined from a and 4). Pulse-plated coatings were more compact and possessed
scanned area of 500 × 500 nm, and it appeared that the ave-
more homogeneous structures with the minimal values of ?
ag
rage grain size (? ) values for d. c. plated samples were 61 nm 0.67 and 0.69 µm for Zn–Co and Zn–Fe, respectively (Fig. 2).
gr
and 72 nm for Zn–Co (Fig. 3 a) and Zn–Fe (Fig. 4 a) coatings, The increase in the cathodic current of pulse plating from 0.1
respectively. The grain size dimensions of the deposited coatings to 0.3 A cm–2 led to the reduction of the average ? from 50 to
gr
have been determined on the basis of AFM measurements and 36 nm and from 68 to 55 nm for Zn–Co and Zn–Fe, respectively.

---

Effect of pulse plating on the composition and corrosion properties of Zn–Co and Zn–Fe al oy coatings
11
However, a further increase in i (>0.3 A cm–2 and >0.5 A cm–2 chemical y are inconsistent with the atmospheric data mainly
p
for Zn–Co and Zn–Fe, respectively) resulted in the origination because of the presence of corrosion products on the surface. Zn
of discrete large crystal ites, possibly the germs of dendrites corrosion in an unbuffered Cl– solution occurs with the forma-
(Fig. 2 d), which caused both a reduction of the homogeneity of tion of a porous oxide film [34]. However, in a HCO – containing
3
grain distribution and an increase in the grain size of both al oy media, the oxide film is supposed to be more compact, adher-
coatings (Fig. 5 a).
ent and less soluble, thus, exhibiting a passivating character [35].
The nucleation rate is enhanced and the grain size of the de-
Aqueous corrosion data for Zn al oy samples in a HCO – con-
3
posit usual y decreases because of higher i ; however, the effect taining media correlate well with the atmospheric corrosion
p
of t and t on the deposit characteristics for a certain system data [30]. Therefore, this solution was applied.
on
off
cannot be predicted, because the crystal ization is strongly influ-
enced by the composition of the plating bath and, hence adsorp-
tion / desorption phenomena. Therefore, during the electrocrys-
tal ization, each system may react differently yielding a different
surface morphology. The variation in t and t parameters did
on
off
not cause an occurrence of any new morphological features of
Zn–Co and Zn–Fe deposits on the nano-metric scale, therefore,
the corresponding images are not given, while the curves depict-
ing the influence of these parameters on the values of ? are pre-
gr
sented in Fig. 5.
The variation in t from 0.1 to 0.5 ms caused a slight decrease
on
in ? values of Zn–Co coating from 58 to 43 nm with a further in-
gr
crease in ? values up to 60 nm at t 2 ms. Meanwhile, the effect of Fig. 6. Polarization curves of pulse-plated Zn alloy electrodes in 0.6 M NaCl + 0.2 M
gr
on
this parameter on the grain size of Zn–Fe deposits was more sig-
NaHCO solution: 1 – Zn-Co, 2 – Zn–Fe. Potential sweep rate is 0.1 mV s–1
3
nificant (Fig. 5 b). The lowest t values applied (0.1 ms) resulted in
on
deposition of a Zn–Fe coating with the grain size close to 100 nm,
which is higher than that of the d. c. plated sample. The minimal ?gr
values (~54 nm) were obtained at t 0.5 ms, with a further sharp
on
increase in ? at higher t , which was even higher than 100 nm at
gr
on
t 2 ms. The reoccurrence of large crystal ites at the longest t was
on
on
the reason of a significant increase in ? .
gr
In pulse plating, there is no applied current during the t pe-
off
riod, and whether fine-grained deposits are obtained in practice
or not depends upon what happens during this period. Zn al-
loy pulse deposition was carried out in the t range from 1 to
off
10 ms, however, because of insufficient quality of the coatings
deposited at t >5 ms, a precise determination of ? values was
off
gr
inexpedient. The ? values of both deposited al oys increase
gr
when t increases from 1 to 2 ms (from 35 nm to 48 nm and
off
from 50 nm to 60 nm for Zn–Co and Zn–Fe, respectively) with
a further gradual decrease, when t changes from 2 to 10 ms up
off
to the initial ? values (Fig. 5 c). If t is long enough, the areas of
gr
off
local dissolution can be produced on the deposited metal surface Fig. 7. Effect of the pulse plating parameters on the corrosion current (i ) of Zn–Co
corr
[25, 33]. Such an effect was observed for pure Zn coatings [36] at and Zn–Fe alloy coatings in 0.6 M NaCl + 0.2 M NaHCO solution
3
t higher than 20 ms. In the case of pulse-plated low-al oyed Zn
The polarization curves of Zn al oys in a test media are pre-
off
deposits, an application of even t >5 ms caused an undesirable sented in Fig. 6. No significant differences were found in the shape
off
increase in the Fe amount in the al oy (Fig. 1) and led to poor of polarization curves for various investigated coatings, thus there
quality of Zn–Co coating (powder-like).
are only the polarization curves for each al oy sample presented. The
The occurrence of the macrostructural defects on the surface corrosion current densities (i ) were determined from Tafel plot
corr
of pulse-plated Zn al oys and the insufficient quality of the coat-
extrapolation. They were obtained from a computer data fit, and the
ings limited the application of higher values of the parameters i , obtained results are presented in Fig. 7.
p
t and t . General y, the grain size of Zn–Co coatings obtained
The i values of pulse-plated Zn al oy coatings varied in the
on
off
corr
under the pulse plating conditions appeared to be slightly lower range from 1.0·10–5 to 3.0·10–5 A cm–2. The minimal values of icorr
with respect to that of Zn–Fe deposits.
(1.0·10–5 A cm–2) for pulse plated Zn–Fe al oy were obtained at
a single value of ip – 0.2 A cm–2, with a further increase in i
corr
Corrosion behaviour
up to 2.0·10–5 A cm–2 when i values higher than 0.5 A cm–2
p
Corrosion behaviour of the pulse-plated Zn coatings was inves-
were applied (Fig. 7 a). Meanwhile, i values of Zn–Co al oy
corr
tigated in a natural y aerated NaCl + NaHCO solution at pH 6.8. with the variation of i varied in a very narrow range (close to
3
p
It is known, however, that corrosion rates measured electro-
1.5·10–5 A cm–2).

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12
Rimantas Ramanauskas, Laima Gudavi?i?t?, Remigijus Jušk?nas, Olga Š?it
General y, the influence of t on the variation of i values of
on
corr
the deposited coatings was not significant, as i varied between
corr
1.9·10–5 and 1.3·10–5 A cm–2. A slight reduction in i values was
corr
observed for both investigated Zn al oy coatings with the in-
crease in t onlyin the initial range from 0.1 to 0.2 ms for Zn–Co
on

and from 0.1 to 0.5 for Zn–Fe.
Pulse deposition of Zn al oys was carried out with t values
off
varying in the range from 1 to 10 ms. General y, the increase in t of
off
the Zn alloy deposition was not an effective means for the improve-
ment of corrosion behaviour of the coatings obtained. The increase
in this parameter from 1 to 5 or 10 ms caused a nearly threefold in-
crease in i values of the pulse plated Zn–Co al oys, meanwhile, it
corr
did not significantly effect i values of Zn–Fe coatings (Fig. 7 c),
corr
which varied between 1.7·10–5 and 1.9·10–5 A cm–2.
Summarizing the results on corrosion behaviour of the
pulse-plated Zn al oys, it can be stated that Zn–Co and Zn–Fe
coatings, except the t variation, exhibited a similar corrosion
off
behaviour, while in general, the application of pulse plating was
not of great significance for the corrosion resistance enhance-
ment of these al oys, as the i values of d. c. plated al oys were
corr
1.5·10–5 A cm–2 and 1.9·10–5 A cm–2 for Zn–Co and Zn–Fe, re-
spectively, while pulse electrodeposition of Zn coatings resulted
in nearly fourfold reduction in the corrosion currents in com-
parison with the direct current plated samples [36].
Phase composition
The influence of pulse plating parameters on the phase composition
of the deposited al oys can be determined from XRD data. Figure Fig. 8. XRD patterns of pulse-plated Zn–Co and Zn–Fe coatings under cathodic peak
8 a depicts the XRD patterns for the pulse-plated zinc al oy coatings. current density i 0.5 A cm–2
p
Pure Zn and low-al oyed coatings with Co and Fe electro-
indicated that both these al oys possessed almost twice as low cor-
crystal ize with a distorted form of hexagonal close packing. The rosion currents compared to those of Zn coatings [26], and corro-
pulse plated Zn–Co and Zn–Fe coatings exhibited sharp peaks cor- sion performance of Zn–Fe deposits was similar to that of Zn under
responding to Zn and Fe (base metal). However, two different phas-
both conditions. Pulse electrodeposition of Zn coatings appeared
es of Zn can be identified for all the deposited low-al oyed Zn coat-
to be beneficial in the grain size and corrosion rate reduction, (e. g.,
ings. The first one is an ?-phase or the solid solution of Co or Fe in a fourfold reduction in the corrosion current in comparison with
Zn. This statement is reasoned in Figure 8 b, where some fragments d. c. plated samples was observed) [36], while the pulse-plated low-
of XRD patterns for Zn–Co and Zn–Fe coatings are presented. The al oyed Zn coatings did not exhibit any significant improvement in
maxima of XRD peaks Zn 10.0 and Zn 10.1 (dashed vertical lines) their corrosion resistance.
are shifted with respect to the position of these peaks for the pure
Zn (solid vertical lines) (PDF 04-0831), while the peak Zn 00.2 CONCLUSIONS
nearly coincides with that for the latter. However, one more peak
can be seen in the vicinity of this peak at higher diffraction angles. Pulse electroplating of Zn al oys in comparison with direct cur-
The peaks 10.0 and 10.1 are obviously attributed to the ?-phase. rent deposition resulted in the grain size reduction from 61 nm
The lattice parameters a and c of the ?-phase can be calculated to 36 nm and from 72 nm to 50 nm for Zn–Co and Zn–Fe coat-
using ? angle of the maximum of the peaks 10.0 and 10.1, respec-
ings, respectively. However, the correspondent reduction in the
tively. Having determined the lattice parameter c, one can calculate corrosion currents of these al oys was not observed.
2 ? angle of the maxima of the peaks Zn–Co 00.2 and Zn–Fe 00.2,
Non-stationary crystal ization produced two different phas-
which are represented by dashed vertical lines in Figure 8 b. These es of Zn during Zn–Co and Zn–Fe plating. The low-al oyed coat-
lines coincide with the peaks, which are in the vicinity of that for ings obtained by pulse deposition presented a mixture of two
pure Zn 00.2. So, these low intensity peaks on XRD patterns for phases; one of them was the ?-phase and the other was pure Zn
Zn–Co and Zn–Fe are attributable to the ?-phase. Consequently, or the ?-phase with a significantly lower concentration of Co or
the pulse plated coatings of Zn–Co and Zn–Fe are mixtures of two Fe. It could be supposed that one of the principal reasons, why
phases, one of them being the ?-phase and the other – pure zinc or the pulse-plated Zn–Co and Zn–Fe coatings did not exhibit a re-
the ?-phase with a significantly lower proportion of Co or Fe.
duction in their corrosion currents was the formation of a dual
Although during previous corrosion behaviour studies of d. c. phase during the pulse deposition.
plated Zn al oy coatings it was established that Zn–Co exhibited
from two- to three-fold lower atmospheric corrosion rates than
Received 11 December 2007
pure Zn [26, 30], the results of the electrochemical measurements
accepted 19 December 2007

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Effect of pulse plating on the composition and corrosion properties of Zn–Co and Zn–Fe al oy coatings
13
References
25. N. v. mandich, Metal Finishing, 98, 375 (2000).
26. R. Ramanauskas, Appl. Surf. Sci., 153, 53 (1999).
1. D. e. hall, Plating and Surf. Finish., 70, 59 (1983).
27. R. Ramanauskas, R. jušk?nas, a. Kalini?enko, l. F. Garfias-
2. l. Felloni, R. Fratesi, e. Quadrini, G. Roventi, J. Appl.
mesias, J. Solid State Electrochem., 8, 416 (2004).
Electrochem., 17, 574 (1987).
28. m. a. Pech-canul, R. Ramanauskas, l. maldonado,
3. N. Zaki, Metal Finish., 87, 57 (1989).
Electrochim. Acta, 42, 255 (1997).
4. D. a. Wright, N. Gage, Trans. IMF, 72, 130 (1994).
29. R. Ramanauskas, l. Gudavi?i?t?, l. Diaz-Ballote, P. Bartolo-
5. N. R. Short, a. abibsi, j. K. Dennis, Trans. IMF, 67, 73
Perez, P. Quintana, Surf. Coat. Technol, 140, 109 (2001).
(1989).
30. R. Ramanauskas, l. muleshkova, l. maldonado, P. Dob-
6. G. D. Wilcox, D. R. Gabe, Corros. Sci., 35, 1251 (1993).
rovolskis, Corros. Sci., 40, 401 (1998).
7. K. R. Baldwin, c. j. e. Smith, Corrosion, 51, 932 (1995).
31. R. T. c. choo, j. m. Toguri, a. m. el-Sherik, U. erb, J. Appl.
8. K. R. Baldwin, c. j. e. Smith, Trans. IMF, 74, 202 (1996).
Electrochem., 25 348 (1995).
9. a. m. alfantazi, U. erb, Corrosion, 52, 880 (1996).
32. N. ibl, j. cl. Puipe, h. angerer, Surf. Technol., 6, 287
10. l. Fedrizzi, R. Fratesi, G. lunazzi, G. Roventi, Surf. Coat.
(1978).
Technol., 53, 171 (1992).
33. R. Ramanauskas, l. Gudavi?i?t?, a. Kalini?enko, R. juš-
11. a. P. Shears, Trans. IMF, 67, 67 (1989).
k?nas, J. Solid State Electrochem., 9, 900 (2005).
12. a. Stankevi?i?t?, l. leinartas, G. Bikul?ius, D. virbalyt?,
34. T. e. Graedel, J. Electrochem. Soc., 136, 193c (1989).
a. Sudavi?ius, e. juzeli?nas, J. Appl. Electrochem., 28, 89
35. R. Guo, F. Weinberg, D. Tromans, Corrosion, 51, 356
(1998).
(1995).
13. R. Fratesi, G. Roventi, c. Branca, S. Simoncini, Surf. Coat.
36. R. Ramanauskas, l. Gudavi?i?t?, R. jušk?nas, O. Š?it,
Technol., 63, 97 (1994).
Electrochim. Acta, 53, 1801 (2007).
14. j. ch. chang, h. Wei, Corros. Sci., 30, 831 (1990).
15. G. Beck Nielsen, m. Kjaer larsen, K. a. jensen, D. Ulrich,
Rimantas Ramanauskas, Laima Gudavi?i?t?, Remigijus Jušk?nas,
Corros. Sci., 30, 1907 (1990).
Olga Š?it
16. j. Giridhar, W. j. Ooij, Surf. Coat. Technol., 53, 35 (1992).
IMPULSIN?S ELEkTROLIz?S ?TAkA zn–Co IR zn–Fe
17. Z. Zhang, W. h. leng, h. B. Shao, j. Q. Zhang, j. m. Wang,
ELEkTROLITINI? LyDINI? SUD??IAI IR kOROzIN?MS
c. N. cao, J. Electroanal. Chem., 516, 127 (2001).
SAvyb?MS
18. j. l. Ortiz-aparicio, Y. meas, G. Trejo, R. Ortega, T. W. chapman,
e. chainet, P. Ozil, Electrochim. Acta, 52, 4742 (2007).
S a n t r a u k a
19. K. Kondo, m. Yokoyama, K. Shinohara, J. Electrochem. Soc.,
Darbe buvo tiriama impulsin?s elektroliz?s parametr? ?taka Zn–Co
142, 2256 (1995).
ir Zn–Fe elektrolitini? lydini? cheminei ir fazinei sud??iai, paviršiaus
20. F. Y. Ge, S. K. Xu, S. B. Yao, S. m. Zhou, Surf. Coat. Technol.,
topografijai ir dang? korozin?ms savyb?ms. Impulsin?s elektroliz?s tai-
88, 1 (1996).
kymas mažai legiruotiems Zn lydiniams nusodinti ?galino sumažinti
21. Y. Tsuru, h. egawa, Denki Kagaku, 64, 112 (1996).
dang? kristalit? dydžius, ta?iau j? korozinio atsparumo pager?jimo ne-
22. Y. Tsuru, h. egawa, Denki Kagaku, 65, 143 (1997).
pasiekta. Padaryta prielaida, kad dang? korozijos grei?io sumažinti ne-
23. h. ashassi-Sorkhabi, a. hagrah, N. Parvini-ahmadi,
pavyksta d?l dvifazio lydinio susidarymo impulsin?s elektroliz?s metu.
j. manzoori, Surf. Coat. Technol., 140, 278 (2001).
Rentgeno difrakciniais tyrimais nustatyta, kad mažai legiruoti Zn lydi-
24. j-Y. Fei, G. D. Wilcox, Electrochim. Acta, 50, 2693 (2005).
niai sudaryti iš ?-faz?s (kieto Co ar Fe tirpalo Zn) ir gryno Zn faz?s.

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