Materials Transactions, Vol. 55, No. 11 (2014) pp. 1762 to 1764
© 2014 The Japan Institute of Metals and Materials
EXPRESS REGULAR ARTICLE
Rust Preventive Properties by Using Polarization Curve Measurement
on the Metal Coated with the Rust Preventive Oil
Daisuke Iwashima1, Sayaka Hirata2, Naoki Nagase2, Masahiko Hatakeyama3 and Satoshi Sunada3,+
1
Graduate School of Materials Science and Engineering for Education, University of Toyama, Toyama 930-8555, Japan
Idemitsu Kosan Co., Ltd., Ichihara 299-0107, Japan
3
Department of Materials Science and Engineering for Research, University of Toyama, Toyama 930-8555, Japan
2
Fe-Cu-C sintered steels are widely used as powder materials, because of its small volumetric shrinkage. However, Cu, which acts as
cathode enhance formation of rust (Fe2O3·xH2O) during fabrication. To prevent formation of Fe2O3·xH2O rust preventive oils are genially used.
Therefore, it is necessary to develop new rust preventive oils with contradictory properties of low viscosity and superior rust prevention. In this
study, we developed technique to quantitatively evaluate rust prevention ability by measuring polarization curve through thin corrosive solution
on Fe-Cu-C sintered steels coated with rust preventive oils. Polarization curves were registered after 30 min of exposure to test solution in order
to allow corrosion potential (Ecorr) stabilization. From the experimental, it is possible to evaluate the corrosion rate quantitatively in the surface of
specimen, which was coated with rust preventive oil through thin corrosive solution. The measurement results suggest the anodic reaction is
decreased with oils. [doi:10.2320/matertrans.MAW201417]
(Received April 24, 2014; Accepted August 21, 2014; Published October 18, 2014)
Keywords: sintered material, electrochemical measurement, polarization curve, rust preventive performance
1.
Introduction
Fe-Cu-C sintered steel can easily control the volumetric
change by sintering, and it has about 80% of quantity of
production in the field of powder metallurgy.1­8) However,
it is easily rusted, because there is many Cu and C acting
as the cathode site on their surfaces. Especially, when high
temperature and humid climate continue during their
manufacturing process, the rust of Fe2O3·xH2O will generate
on their surfaces. Though they are coated with rust preventive
oils (RPOs) in order to prevent the rust formation, there exists
a problem. That is, high viscosity of those RPOs decreases
workability, and low viscosity deteriorates rust preventive
performance. Therefore, it is necessary to develop new RPOs
with contradictory properties of low viscosity and superior
rust prevention. However, precise methodology to evaluate
rust prevention ability has not been established. In this study,
we developed new technique to quantitatively evaluate
rust prevention ability by polarization curves measurement
through thin corrosive solution on Fe-Cu-C sintered steels
coated with rust preventive oils. As a result, the ability for
rust prevention can be measured quantitatively. The aim of
this study, therefore, is to evaluate the rust prevention ability
of three kinds of representative rust prevention oils by using
this newly-developed measuring method.9)
2.
Experimental Procedure
Fe-Cu-C sintered steel (Fe, 2.0 mass% Cu and 0.8 mass%
C) was used as a specimen in this experiment. Dimensions of
the specimens were 3.4 © 4.9 © 5 mm2. The wire lead was
attached to this specimen and it was resin-mounted to make
an electrode for specimen. Dry type polishing was carried out
on the electrode surface to No. 2000 of emery paper, and it
was dried after degreasing with acetone. Thus fabricated
electrode for specimen was dipped in the beaker containing
+
Corresponding author, E-mail: [email protected]
Fig. 1 Schematic diagram of apparatus for the polarization curve
measured.
RPO, and it was held for 15 min in the vacuum desiccator to
remove bubbles from the surface of this specimen electrode.
We employed three kinds of test oil named oil A, B and C.
(oil A: conventional rust preventeve oil, oil B: without the
rust inhibitor and without two types of oil film modifier from
the oil A, oil C: containing differ oil film modifiers from the
oil A). The 0.35 mass% NaCl aqueous solution whose pH is
5.76 was used for the test evaluating rust prevention ability
by polarization curve measurement through thin corrosive
solution (newly developed testing method).10) The schematic
diagram of the newly developed testing method used is
shown in Fig. 1. Using a double capillary was added
dropwise to the specimen. The polarization curve measurement through thin corrosive solution on the specimen was
used, Ag/AgCl(3.33 kmol/m3 KCl) as a reference electrode,
platinum wire as the counter electrode, respectively. To
measure the low corrosion rate (Icorr), we employed the
potentiostat (HA-301: Hokuto Denko Ltd., Japan), which has
high ability for detection of the low electric current less than
order of 10¹8 A. Polarization curves were registered after
Potential , E / V vs. Ag / AgCl (3.33kmol·m-3KCl)
Rust Preventive Properties by Using Polarization Curve Measurement on the Metal Coated with the Rust Preventive Oil
0.3
(b) Thin corrosive solution
(a)
0.2
1763
0.1
Surfactant
0
-0.1
-0.2
-0.3
Rust preventive oil
-0.4
-0.5
-0.6
-0.7
(c)
0
50
100
150
200
250
300
350
400
Time, t / ks
Thin corrosive solution
(d)
Thin corrosive solution
Rust preventive oil
Rust preventive oil
Micelle
Fig. 2 (a) Corrosion potential of sintered Fe-Cu-C alloy measured with oil A in thin corrosive solution10) and schematic diagram of formation micelle: (b) the
first stage, (c) the second stage, (d) the third stage.
Fig. 3 Four kind of polarization curves of Fe-Cu-C coated with each rust preventive oils and without oil measured through thin corrosive solution in
0.35 mass% NaCl solution at 298 K.
1764
D. Iwashima, S. Hirata, N. Nagase, M. Hatakeyama and S. Sunada
30 min of exposure to aqueous solution in order to allow
corrosion potential (Ecorr) stabilization. All the polarization
experiments were carried out, from ¹200 mV vs. Ecorr, to
+200 mV vs. Ecorr at a sweeping rate of 0.5 mV/s.
3.
Results and Discussions
Figure 2 shows the result of corrosion potential measured
in the condition of coated with the oil A. In the period from
0 ks to 140 ks, the vibration behavior of the potential was
recognized in initial stage.10) The vibration behavior of the
potential was reported by K. Arai in water/1-octanol/water
(including surfactant) system.11) According to his experiment
the potential oscillation mechanism was found to be due to
the repetitive formation and destruction of a surfactant layer
adsorbed at the octanol/water interface. The results of our
experiment show good agreement with his model. In this
initial stage, surfactant, included in the RPO was coated to
the specimen surface was gradually aligned to the oil/water
interface, and then thin corrosive solution vibration phenomena of the potential observed. Concentration of surfactant at
the interface crowded with time course. It is thought that
the interface might be gradually wavy at that time and
potential was gradually increased. The phenomena correspond to schematic diagram of Fig. 2(b) and (c). After an
increase of the potential, micelles form on surface of
surfactant, which surrounds water of thin corrosive solution.
Then, concentration of micelles would reach critical level
(Fig. 2(d)). Then, the potential decreases quickly. At the
moment, micelles might to be formed as shown in Fig. 2 (d).
In this model, corrosive solution is soluble in oil by formation
of micelles. Figure 3 shows the results of measurement of the
polarization curves through thin corrosive solution on Fe-CuC sintered steels coated with RPOs and without oil. The
polarization curve measurement, draw a Tafel slope to the
polarization curve the corrosion current density. From the
results, in the case of without oil Icorr showed 2.78 © 10¹4
A/cm2. In case of coated with each RPO, Icorr showed as
follows, the oil A: 4.64 © 10¹7 A/cm2, the oil B: 3.29 © 10¹6
A/cm2 and the oil C: 2.53 © 10¹8 A/cm2, respectively. It
resulted in that Icorr is smallest in the oil C, and largest in the
case of without oil. The oil B shows worst improvement
in corrosion resistance among those coated with RPOs.
However, corrosion resistance was improved by approximately 100 times better than that without oil one. The oil C
improved approximately 10000 times better than that without
oil one. According to the results of the polarization curve,
which obtained in the present experiment, Evans diagram
indicates decrease of Icorr, while increase of Ecorr by coating
with RPO.
The result clearly suggests that the coating with RPO
suppress the anodic reaction on surface of Fe-Cu-C sintered
steel. We developed the method to measure corrosion rate
(Icorr) of Fe-Cu-C sintered steel coated with oils and this
method enabled us to evaluate efficiency of oils for rust
preventive quantitatively.
4.
Conclusion
The results of this study are summarized as follows.
(1) It is possible to evaluate the corrosion rate by using the
high performance potentiostat on the surface of Fe-CuC coated with oils through thin corrosive solution.
(2) Corrosion rate is reduced by oil coating because of the
decrease of anodic reaction.
(3) It is possible to evaluate the efficiency of the RPO by
the measurement of the corrosion rate.
(4) The oil C, which replaced the oil film modifiers with
other ones from the oil A, shows best efficiency for rust
preventive in this experiment.
Acknowledgments
This work was supported by the Cooperation Research
Program of IDEMITSU KOSAN Co., Ltd.
REFERENCES
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
S. J. Jamil and G. A. Chadwick: Powder Metall. 28 (1985) 65­71.
N. Dautzenberg and H. J. Dorweiler: Powder Metall. 17 (1990) 10­15.
J. Takata and N. Kawai: Powder Metall. 38 (1995) 209­213.
G. Anthory and M. Ranadall: Int. J. Powder Metall. 30 (1994) 399­
409.
W. F. Wang: Mater. Sci. Eng. A 402 (2005) 92­97.
T. K. Kandavel, R. Chandramouli and P. Karthikeyan: SASTRA
University, Thanjavur, Tamil Nadu, India.
H. Krawiec, V. Vignal and R. Oltra: Electrochem. Commun. 6 (2004)
655­660.
K. Kanno, S. Sunada, K. Majima, M. Ishida and Y. Takeda: J. Jpn. Soc.
Powder Powder Metall. 53 (2006) 661­666.
S. Sunada, K. Nomura, N. Nunomura, S. Hirata and N. Nagase: Proc.
8th Int. Conf. on the Physical Properties and Application of Advanced
Materials, 13­17 August 2013, Weihai City, Shandon, China, (2014)
pp. 3­5.
S. Sunada, N. Nunomura, S. Hirata and N. Nagase: Mater. Sci. Forum
783­786 (2014) 2537­2540.
K. Arai: Bunseki Kagaku 43 (1994) 729­730 (in Japanese).