coating steel with nanosilica by pulsed direct current electrophoresis for corrosion protection
TRANSCRIPT
Coating Steel with Nanosilica by Pulsed Direct Current Electrophoresis for Corrosion Protection
Ni Made Intan Putri. S, Heru Setyawana
Department of Chemical Engineering, Sepuluh Nopember Institute of Technology, Surabaya, Indonesia
Keywords: electrophoresis, pulsed direct current, silica sol, electrochemical impedance spectroscopy.
Abstract. The purpose of this paper is to investigate the electrophoretic deposited nanosilica on
stainless steel for corrosion protection. The electrophoretic deposition (EPD) was carried out by
pulsed direct current (PDC) of silica sol made of sodium silicate. The amplitude and frequency of
the PDC were varied in the range of 0.1-0.6 V and 30-80 Hz, respectively. The corrosion protection
properties of the silica films were analyzed by Electrochemical Impedance Spectroscopy (EIS) in 2
wt% NaCl solution. The experimental results showed that the silica films exhibit good
characteristics as indicated by their high pore resistance and low admittance. The silica film
corrosion protection characteristics were influenced by the frequency and amplitude of PDC during
preparation of electrophoretic deposition.
Introduction
Metals have many applications in our daily life such as in automotive, factory and in orthopedic.
However they are vulnerable to corrosion attack at fluid conditions or aggressive environment
resulting destruction on the structural materials. So, effort must be done to improve the corrosion
resistance of metal.
Chromate coating has been used widely for many years to prevent steel from corrosion.
However this anticorrosive material is hazardous because of the heavy metal which can pollute the
environment. Recently, coating with chromate was banned. Consequently, many works have been
conducted to look for an alternative coating to substitute chromate as a protective coating which not
only anticorrosion but also has a strong adhesive. One of the alternatives is silica. The properties of
silica which support their use as the alternative coating are strong adhesive, good barrier properties
of water, ion-ion and water vapor diffusion to metal surface, so it can protect metals from corrosion.
Dip coating method was commonly used as a method for metal coating. Coating of stainless
steel with silica from TEOS, MTES and sodium hydroxide by dip coating and EPD (electrophoresis
deposition) has been investigated [1]. However, TEOS and MTES are expensive and toxic that
damages their application industry. Electrophoresis deposition has been propose as an alternative
for obtaining thicker and denser coating with good protective properties than dip coating [1]. The
advantages of EPD method are low cost, less particle wastage and high deposition rate.
It has been shown that electrophoretic deposition of TiO2 nanoparticles on stainless steel by
PDC produced more uniform particle layers compared to those of the conventional DC. By using
PDC, a relatively high volume density of the deposited structure can be obtained [2].
In this paper, electrophoretic deposition of nanosilica by PDC on steel for corrosion protection
is presented. The effect of pulsed parameter on the characteristics of silica film was studied. The
corrosion protective characteristics of the silica films were evaluated by the method of
Electrochemical Impedance Spectroscopy (EIS).
Advanced Materials Research Vol. 896 (2014) pp 578-581Online available since 2014/Feb/19 at www.scientific.net© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.896.578
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Experimental
The starting sol was prepared from sodium silicate solution following the method proposed by
Tsai [3]. One hundred and forty grams industrial grade sodium silicate solution (water glass; 28%
SiO2, SiO2 : Na2O = 3.3) provided by PT PQ Silica Indonesia was diluted with de-ionized water to
1000 ml, that corresponds to a final concentration of 3.6 wt.%. The diluted sodium silicate solution
was then mixed with H+ ion-exchange resin (1 : 1 volume ratio) for 30 min under mild stirring to
form a silicic acid solution of pH 2 after the ion exchange. The silicic acid solution was titrated to 1
wt% KOH solution at a temperature of 60 ºC with a constant flow rate of about 10 ml/min by a
peristaltic pump.
Stainless steel plate with a size of (2 × 6) cm was used as the substrate. It was installed as
anode. Prior to particle deposition, the substrate was pretreated with sulphuric acid solution (0.1 M)
for 10 min, rinsed with de-ionized water and aceton, polished and dried. A grafit was used as the
counter electrode. Both electrodes were submerged into the prepared silica sol with a distance of 3
cm. Function generator was used as pulsed current source. Frequency and amplitude were varied in
a range of 30 Hz-80 Hz and 0.1 V-0.6 V, respectively. All experiments were conducted at room
temperature and the deposition time was fixed at 9 min. The deposited substrate was dried at 120°C
in an oven for 2 h.
The protective behavior of the deposited substrate against corrosion was studied by
Electrochemical Impedance Spectroscopy in 2 wt.% NaCl solution.The tests were carried using a
potensiostat/galvanostat equipment (Autolab PGSTAT 302N, Metrohm) which was fully controlled
by a computer using NOVA software. In the measurements, the conventional three-electrode system
was used where the deposited substrate acted as the working electrode, platinum plate as the counter
electrode and Ag/AgCl as the reference electrode. The sinewave amplitude was 10 mV and the
frequency range was 0.01 Hz-1000 Hz. The data obtained after the measurements were analyzed
using NOVA software.
Results and Discussion
The effect of frequency on the characteristics of silica film. Figure 1 shows the
representative impedance spectra of the silica film deposited using PDC. It seems that the frequency
during EPD influences the corrosion protection characteristics. As shown by the impedance spectra
in Fig. 1, the silica film obtained at various frequency exhibit good coating for corrosion protection.
The impedance spectra in Fig. 1 were modeled by an equivalent circuit shown in Fig. 2. The
impedance spectra at frequency of 30 Hz were modeled by equivalent circuit model A (Fig. 2(a)).
Rpore is used to determining the area of the defects through the coatings, the charge transfer
resistance (Rct) is used to show the electrochemical behavior and the corrosion processes at the
metal surface. The charges transfer resistance is inversely proportional to the corrosion rate and to
the surface area under corrosion. Y0 is the admittance of an ideal capacitance, used to show the
easiness of charge to flow through the breaks or pores of coating, N is an empirical constant to
show the characteristics of coating as a capacitor or resistor and from the double layer capacitance
(Cdl) value it is possible to obtain the wet area [4]. Model A showed that water and oxygen
molecules reached the substrate surface and the electrochemical reactions at the metal/coating
interface may take place [5].
The increasing of frequency (40 Hz) produced different impedance spectra showed in Fig. 1.
Model B (Fig. 2(b)) was introduced to fit the spectra. Same with model A, model B showed that
water and oxygen molecules reached the substrate surface and the electrochemical reactions at the
metal/coating interface may take place. With the other frequency, 50 Hz, 60 Hz and 70 Hz, model
A, model B, and model A was used to fit the spectra, respectively. The increase of frequency (80
Hz) produces different spectra than the others. The coating was equivalent to a barrier layer with a
high value coating resistance in parallel with a low value coating capacitance, which is presented by
electrical equivalent circuit model C (Fig. 2(c)). From another research by Naim et al., by using
higher frequency on PDC deposition could narrow the particle size distribution or dispersity of
Advanced Materials Research Vol. 896 579
0 500 1000 1500 2000 2500 3000 3500 4000 45000
2000
4000
6000
8000
10000
-Z''(
oh
m)
Z'(ohm)
30 Hz
40 Hz
50 Hz
60 Hz
70 Hz
80 Hz
particles depositing on the surface of a stainless steel electrode. So it also affects the corrosion
protection characteristics of the silica film obtain in this research.
Figure 1. Impedance spectra and fitting results of silica coating electrophorized at a constant duty
cycle and amplitude of 50% and 40 Hz, respectively by varying the frequency.
Figure 2. Electrical equivalent circuit used to fit the impedance spectra.
The fitting parameters of equivalent circuit of impedance spectra are listed in Table 1. It can be
seen from Table 1 that the higher pore resistance was obtained in frequency of 80 Hz. The
increasing values of admittance could be associated with an increase in the expose area of the metal
and electrolyte penetration in the coating through the breaks and pores. On the other hand, the
reduction of the Rpore value could be related to an increasing in pore area offering a low resistance
to the electron transfer in the base of the pore [6]. From the range of frequency which was used, the
higher pore resistance and the lower admittance value was obtained at frequency of 80 Hz. It
showed that by electrophoresis at frequency of 80 Hz could be obtained silica coating with a high
resistance to the electron transfer and small expose area of the metal so the electrolyte penetration in
the coating was low. As corrosion is an electrochemical process that involves electron transfer at
solid/solution interface, stopping current means stopping corrosion process.
Table 1. The parameters of circuit model that fitted the data in Fig. 1
30 Hz 40 Hz 50 Hz 60 Hz 70 Hz 80 Hz
Rs R (Ω) 2.5764 1.905 2.5859 2.8354 2.3704 2.5413
Y0 (Mho) 0.0015494 0.0015275 0.00095778 0.0028636 0.00091357 0.00091966
N 0.84156 0.95579 0.8621 0.99836 0.85716 0.81892
Rpore R (Ω) 3505.4 841.46 12364 549.33 3416.4 81758
Cdl C (F) 9.00x10^-13 9.00x10^-13 9.00x10^-13
Rct R (Ω) 245.7 10387 700 767.96 2137.2
Rpore R (Ω)
Y0 (Mho) 0.0092008 0.0019758
N 0.53511 0.78836
Elemen ParameterNilai
CPE
CPE
(a) Model A (b) Model B (c) Model C
580 Advanced Materials Science and Technology
The effect of amplitude on the characteristics of silica film. The fitting parameters of
equivalent circuit of impedance spectra (not shown) as a function of amplitude is shown in Table 2.
It can be seen from Table 2 that by increasing the amplitude, the pore resistance values were
increase (at amplitude of 0.2 V-0.5 V). The pore resistance values decreased at the amplitude higher
than 0.5 V. The increasing of the pore resistance value could be related to an increase in pore area
offering a low resistance to the electron transfer in the base of the pore. The highest pore resistance
was obtained at amplitude of 0.5 V. It showed that the amplitude of 0.5 V was an optimum
amplitude to obtained silica coating serve as a good barrier to protect steel from corrosion. The
admittance value at this amplitude was also low. It showed that only a small amount of electrolyte
penetrates in the coating through the pores.
Table 2. The parameters of electrical equivalent circuit model
0,1 V 0,2 V 0,3 V 0,4 V 0,5 V 0,6 V
Rs R (Ω) 12.092 2.1261 9.7597 2.5413 11.912 4.4001
Y0 (Mho) 0.001458 0.001328 0.00091565 0.0009197 0.0011973 0.00088213
N 0.85473 0.81565 0.87079 0.81892 0.85843 0.86682
Rpore R (Ω) 85737 337.55 51603 81758 107540 1542.3
Cdl C (F) 110000
Rct R (Ω) 500 9740.5
Rpore R (Ω)
Y0 (Mho) 110000
N 0.44391
CPE
CPE
Element ParameterValue
Conclusion
Good barrier properties for corrosion protection of silica film in steel surface could be obtained
by pulsed direct current electrophoresis. The silica coating characteristics were influence by
frequency and amplitude of electrophoresis. A silica coating with a high pore resistance value and a
small amount of electrolyte penetrates in the coating through the pores was obtained at the
frequency of 80 Hz and amplitude of 0.5 V.
References
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Advanced Materials Research Vol. 896 581
Advanced Materials Science and Technology 10.4028/www.scientific.net/AMR.896 Coating Steel with Nanosilica by Pulsed Direct Current Electrophoresis for Corrosion Protection 10.4028/www.scientific.net/AMR.896.578
DOI References
[1] Y. Castro, A. Duran, J.J. Damborenea, A. Conde, Electrochemical behavior of silica basic hybrid coatings
deposited on stainless steel by dip coating and EPD, Electrochim. Acta. 53 (2008) 6008-6017.
http://dx.doi.org/10.1016/j.electacta.2008.03.042 [4] P.L. Bonora, F. Deflorian, L. Fedrizzi, Electrochemical impedance spectroscopy as a tool for investigating
underpaint corrosion, Electrochim. Acta. 41 (1996) 1073-1082.
http://dx.doi.org/10.1016/0013-4686(95)00440-8 [5] C. Zhu, R. Xie, J. Xue, L. Song, Studies of impedance model and water transport behaviors of
cathodically polarized coating, Electrochim. Acta. 56 (2011) 5828-5835.
http://dx.doi.org/10.1016/j.electacta.2011.04.068 [6] A. Pepe, P. Galliano, M. Aparicio, A. Duran, S. Cere, Sol-gel coatings on carbon steel: electrochemical
evaluation, Surf. Coat. Technol. 200 (2006) 3486-3491.
http://dx.doi.org/10.1016/j.surfcoat.2005.07.102