Materials Sciences and Applications, 2011, 2, 435-438
doi:10.4236/msa.2011.25057 Published Online May 2011 (http://www.SciRP.org/journal/msa)
435
Electrochemical Behavior of Nanocrystalline
Fe88Si12 Alloy in 3.5 wt% NaCl Solution
Licai Fu1,2,*, Jun Yang1, Qinling Bi1, Weimin Liu1
1State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, China;
2Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Canada.
Received February 9th, 2011; revised April 13th, 2011; accepted April 15th, 2011.
ABSTRACT
Influence of microstructure on electrochemical behavior of nanocrystalline Fe88Si12 alloy has been investigated in 3.5
wt% NaCl solution. The results show that Fe88Si12 alloy with optimal corrosion resistance is composite of ordered Fe3Si
and disordered Fe(Si) phases and grain size of 40 nm. Because the ordered Fe3Si structure is beneficial to form SiO2
film, which possesses good corrosion resistance compared with the Fe2O3 film from disordered Fe(Si). Moreover, al-
though the decreased grain size is conducive to form preservative, as the grain size decreases to 10 nm, the grain
boundary increases to above 30 vol%, which is the active sites for corrosion attack.
Keywords: Fe88Si12 Alloy, Nanocrystalline, Microstructure, Electrochemical Behavior
1. Introduction
Corrosion resistance is of great importance in assessing
many future applications of the nanocrystalline materials.
The corrosion behavior of the nanocrystalline materials
has been investigated over the last two decades for a va-
riety of materials (pure metals, alloys, and composites)
[1-5]. Mishra [6] indicated that the high micro-strain in
the electrodeposition Ni with grain size of 8 nm can be
related to the lower corrosion rate in the 1 mol/l H2SO4
solution. Owing to the higher grain boundary density, the
nanocrystalline Co coating exhibited good corrosion re-
sistance comparing with coarse grained Co coating in the
NaOH or NaCl solutions [7]. Xu et al. [8] reported that
the corrosion resistance of a nanocrystalline Ti5Si3C0.8
film and a nanocrystalline Ti5Si3 film with an average
grain size of 15 nm was superior to that of Ti-6Al-4V
alloy. However, Vinogradov investigated [9] that the co-
rrosion behavior of the nanocrystalline Cu changed
slightly compared with the coarse grained Cu. These re-
searches indicate that the corrosion resistance of the nano-
crystalline materials depends on their unique microstruc-
ture.
Fe88Si12 (atom ratio) alloy has been extensively inves-
tigated due to their excellent soft magnetic properties [10,
11]. However, the corrosion resistance of the Fe88Si12
alloy, especially about the nanocrystalline Fe88Si12 alloy,
has not received much attention. In this paper, the elec-
trochemical behavior of the nanocrystalline Fe88Si12 alloy
has been studied by the electrochemical tests, to research
influence of the grain size and phase structure on the
electrochemical behavior.
2. Experimental
The different microstructures of Fe88Si12 alloys has been
fabricated by a self propagating high temperature synthe-
sis technique (SHS) [12], and annealed treat at 900˚C and
1000˚C for 1 h with air atmosphere, respectively. The
grain size and phase structured of the different Fe88Si12
alloys are shown Table 1.
Potentiodynamic polarization curves of the different
Fe88Si12 alloys were performed with 3.5 wt% NaCl solu-
tion at 25˚C. A three-electrode cell system was employed.
All the results are referred to standard hydrogen elec-
trode (SHE). The ribbons measuring 40 mm × 8 mm
were cut from the samples. They were mechanically po-
lished with 600 emery paper and rinsed with ethanol and
distilled water prior to the electrochemical test. Linear
polarization curves were obtained at a scan rate of 0.01
mV/s. The sample was allowed to reach a stationary open
circuit potential (90 min). Then, a potential value 200
mV lower than the corrosion potential was applied for 5
minutes and the potentiodynamic scan was initiated. The
specimens were examined by X-ray diffract-meter (XRD)

Electrochemical Behavior of Nanocrystalline Fe88Si12 Alloy in 3.5 wt% NaCl Solution 436
Table 1. Grain size and phase structure of the different
Fe88Si12 alloys.
Sample Grain size Phase structured
NC10 10 nm B2 + D03
NC40 40 nm B2 + D03
CG >1 μm B2
and transmission electron microscope (TEM). Specimens
after the polarization tests were examined by the corro-
sive surfaces were characterized by a scanning electron
microscope (SEM) and a PHI-5702 multifunctional X-
ray photoelectron spectroscope (XPS), respectively.
3. Results and Discussion
Typical anodic potentiodynamic polarization curves of
the Fe88Si12 alloys in 3.5 wt% NaCl solution are given in
Figure 1(a), a typical active-passive-transpassive-active
behavior can be clearly observed. Normally, these pas-
sive films cover the surface of the corroded samples and
increase the difficulty of Fe or Si ions migrating to sur-
face to participate in electrochemical reaction, and thus
create the passivation region where the current density is
almost independent of potential.
Corrosion rate of the Fe88Si12 alloys are determined
using the Stern-Geary equation from the polarization
measurement [13].

corr 2.303 acP ac
iR  



(1)
where icorr is the corrosion current density, Rp the polari-
zation resistance, βa and βc the anodic and cathodic tafel
slopes, respectively. The Rp is determined from the
slopes of the potential-current plots measured by the li-
near polarization curve in the range of ±10 mV about the
open-circuit potential (Eocp) (Figure 1(b)). The corrosion
potential (Ecorr) and corrosion current density (icorr) are
summarized in Table 2.
Generally, corrosion potential and corrosion current
density are used to characterize the active dissolution
ability of materials, while passivation current density and
passivation potential are used to characterize the passiva-
tion ability of materials [14]. Corrosion potential of the
NC40 significantly decreases and polarization resistance
largely increases. Thus potentially much improve corro-
sion resistance comparing with NC10 and CG. Moreover,
NC40 possesses lower passive current density (12.3
μA·cm−2) than that of NC10 (74.1 μA·cm−2) and CG (51.3
μA·cm−2), which indicates that the NC40 is easier to pas-
sivate than the NC10 and CG.
Figure 2 shows the SEM morphologies of the surface
of the Fe88Si12 alloys after running the polarization
curves. Comparing with the CG, only some slight and
(a)
(b)
Figure 1. Potentiodynamic polarization (a) and linear pola-
rization (b) curves of the Fe88Si12 alloys in 3.5 wt% NaCl
solution.
Table 2. The fitting results of the LSV and potentiodynamic
polarization tests.
Sample Ecorr (mV)icorr (μA/cm2) Rp (Ω/cm2) Ipass (μA/cm2)
10 nm 997 70.9 3890 74.1
40 nm 932 18.2 4720 12.3
CG 1046 42.8 3500 51.3
discrete corrosion pits are observed on the surface of
NC40 and NC10. It can be associated with more protective
passive film formation on NC40 and NC10 than that of CG.
It is conclude that the lower corrosion rate of nanocrys-
talline Fe88Si12 alloys can attribute to its more protective
passive film. However, some micro-crack and large cor-
rosion hole are observed on the surface of the NC10
(Figure 2(a)), which shows the corrosion resistance de-
creases as the grain size decreases to 10 nm.

Electrochemical Behavior of Nanocrystalline Fe88Si12 Alloy in 3.5 wt% NaCl Solution 437
(a) (b) (c)
Figure 2. SEM morphologies of the Fe88Si15 alloys after electrochemical corrosion test.
Palumbo [15] has shown that the passivity of the 14
at% to 20 at% Si-Fe alloy, which consist of ordered Fe3Si
and few disordered Fe(Si) phases, is controlled by the
formation of a silicon dioxide (SiO2) film in 1 mol/l sul-
furic acid. The research [15] indicated that the phase
composition of the Fe-Si alloy influences the formation
mechanisms, growth kinetics, thickness, and composition
of passive layers. It also showed that high-Si content can
improve the passivation behavior. Although the Si con-
tent of the Fe-Si alloy is only 12 at%, the NC10 and NC40
consist of ordered D03 Fe3Si and disordered Fe(Si) phas-
es. So, the SiO2 film was observed on the surface of the
NC10 and NC40 (Figure 3), but only Fe2O3 film was ex-
amined on the surface of the CG, which suggests that the
corrosion resistance of the NC10 and NC40 is better than
the CG.
On the other hand, with the grain size decreases to 10
nm, the grain boundaries and triple junctions increase to
above 30 vol% [16], which are the active sites for corro-
sion attack when exposed to a corrosion environment. As
a result, preferential corrosion at grain boundaries and
triple junctions significantly accelerates the corrosion
rate of NC10. It is note that the NC10 possesses large
numbers of micro-strain, which also makes for easier
corrosion. However, the grain boundaries and triple junc-
tions are decrease to below 5 vol% sharply as the grain
size increases to 40 nm, and the micro-strain decreases as
the annealing. Thus, although some ordered Fe3Si struc-
ture transformed to the disordered Fe(Si) structure, the
corrosion resistance improve as the grain size increases
to 40 nm. Because the CG only composed of disordered
Fe(Si) solid solution. There only Fe2O3 film is examined
on the CG (Figure 3). The Fe2O3 film is unstable com-
pared with the SiO2 film [17]. So the corrosion resistance
of the CG is worse than the NC40.
4. Conclusion
The electrochemical behavior of different microstruc-
tures of the Fe88Si12 alloys in 3.5% NaCl solution has
been investigated. Both the Fe88Si12 alloys with grain size
Figure 3. XPS expectra of O2p in the Fe88Si15 alloys after
electrochemical corrosion test.
of 10 and 40 nm consist of ordered Fe3Si and disorder
Fe(Si) phases. But the CG is only composed of disor-
dered Fe(Si) phase. The order Fe3Si structure is favor to
form SiO2 film. It possesses excellent corrosion resis-
tance comparing with the Fe2O3 film which forms from
disordered Fe(Si). On the other hand, as the grain size
decreases to 10 nm, the grain boundaries and triple
boundaries increase to above 30 vol%, which are the
active sites for corrosion. Based on the above two sides,
the corrosion resistance of the Fe88Si12 alloy with grain
size of 40 nm is optimal.
5. Acknowledgements
This work was supported by the National Natural
Science Foundation of China (50801064) and the Na-
tional 973 Project of China (2007CB607601)
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