ted steel under ultraviolet radiationb

dakyam

stespgraandlic wnateot o, bue co

usedres. Thstrateine (Urne salcan og oxygnt (cath

tect corrosion of the underlying steel, simply from appearance,especially for thick, heavy-duty polymer coatings. In laboratorytests, many methods are employed to evaluate polymer degrada-tion. Surface coatings have been examined in detail by opticalmicroscope, scanning electron microscopy (SEM) and atomic forcemicroscopy (AFM) [15]. Changes in thickness, mass and colourhave been evaluated quantitatively [2,610]. Surface roughness

2. Experiments

2.1. Polymer coatings

Carbon steel plate (SS400, Nippon Test Panel, JIS G3101,67 mmW 150 mmH 1.5 mmT) was used as the substrate. Epoxyand polyester-urethane, which have different UV performance,were employed as the polymer coating. Epoxy contains benzenerings, and is well known to have short service life because the ben-zene rings are easily decomposed by UV radiation. In contrast,polyester-urethane does not contain benzene rings and has long

* Corresponding author. Tel.: +81 50 7772 2928; fax: +81 52 624 9207.

Corrosion Science 52 (2010) 20802087

Contents lists availab

n

.e lE-mail address: Hattori.Masanori3@chuden.co.jp (M. Hattori).tion of the paint is induced due to formation of OH. Degradationof the paint itself by environmental factors such as sunshine andwetdry cycles may enhance the formation of defect sites and thusthe onset of corrosion of the underlying steel. Thus it is importantto investigate the degradation of paints due to environmental fac-tors as the rst stage of corrosion of the underlying steel.

In actual steel structures, degradation of the polymer coating isoften evaluated by visual examination with the naked eye. How-ever, it is not easy to evaluate the extent of degradation, or to de-

useful tool for detecting the onset of corrosion of underlying steel[3,5,7,13,14]. However, it is not yet known whether this techniquecan detect deterioration of the polymer itself, which precedes cor-rosion of the underlying steel in actual atmospheric environments.In this study, we have investigated the EIS characteristics of poly-mer coating exposed to UV radiation, which enhances degradationof polymer itself.1. Introduction

Polymer-coated steels are oftenbuildings, bridges and similar structuing acts as a barrier to protect the subenvironmental factors such as sunshof temperature and humidity, airbo(SOx, NOx). Dissolution of the steelthe paint (anode); the compensatinthe other steel surface under the pai0010-938X/$ - see front matter 2010 Elsevier Ltd. Adoi:10.1016/j.corsci.2010.01.038in the construction ofe polymer (paint) coat-steel from corrosion byV), rainfall, daily cyclests and aggressive gasesccur at defect sites onen reduction occurs atode), where delamina-

of polymer coatings has been measured by laser displacement sen-sor and AFM [1,2,4,8,1114]. Chemical changes to the polymer sur-face due to chemical-bond scission have been analysed by Fouriertransform infrared spectroscopy (FT-IR) and X-ray photoelectronspectroscopy (XPS) [1,15,16]. Polymer cross-sections have beeninvestigated by combined FT-IR and dielectric sorption analysis(DSA) [4,1619]. In addition, coatings have been evaluated in termsof their glass transition point, which is related to chemical bonding[1,10,1416,18,19].

Electrochemical impedance spectroscopy (EIS) is a particularlyB. SEMC. Polymer coating

2010 Elsevier Ltd. All rights reserved.EIS study on degradation of polymer-coa

Masanori Hattori a,*, Atsushi Nishikata b, Tooru Tsurua Energy Applications R&D Center, Chubu Electric Power Co., Inc., 20-1 Kitasekiyama, OhbGraduate School of Science & Engineering, Tokyo Institute of Technology, 2-12-1 Ooka

a r t i c l e i n f o

Article history:Received 6 November 2009Accepted 28 January 2010Available online 2 February 2010

Keywords:A. SteelA. Organic coatingB. EISB. IR spectroscopy

a b s t r a c t

Degradation of heavy-dutyelectrochemical impedanceof evaluation of the UV deplus epoxy primer (PU/E)strate and exposed to cyccracks but did not delamithe underlying steel was nance, exposing the primerand chemical changes wer

Corrosio

journal homepage: wwwll rights reserved.a-cho, Midori-ku, Nagoya 459-8522, Japana, Meguro-ku, Tokyo, Japan

el coatings when exposed to ultraviolet (UV) radiation was investigated byectroscopy (EIS) and additional techniques in order to clarify the feasibilitydation by EIS. Two coatings were considered: polyester-urethane topcoatepoxy topcoat plus epoxy primer (E/E). Each was applied to a steel sub-ettingdrying under UV radiation. The PU/E coating developed topcoatfrom the substrate; capacitive behaviour was evident, and corrosion ofbserved. The E/E coating showed topcoat chalking and partial disappear-t corrosion of the underlying steel was not observed. The morphologympared with the results of EIS.le at ScienceDirect

Science

sevier .com/locate /corsc i

service lives. To each substrate, primer and topcoat polymer coat-

was then exposed directly to the corrosion environment. Fig. 6

Table 1Coating specications.

Kind

No. 1 Topcoat Polyester-urethanePrimer Epoxy

No. 2 Topcoat EpoxyPrimer Epoxy

M. Hattori et al. / Corrosion Science 52 (2010) 20802087 2081ing were applied in sequence. The primer in each case was 125-lm-thick epoxy with red pigment (Fe2O3). Two types of topcoatpolymer coating (Dai Nippon Paint Co., Ltd.) were used: polyes-ter-urethane with white pigment (TiO2, Al2O3) and epoxy withwhite pigment (TiO2, Al2O3). Primer and topcoat specicationsare shown in Table 1. Each substrate was ground with #400 abra-sive paper, dried, spray-painted on one side with primer and top-coat, and sealed on the other side. Total thicknesses were asfollows: for the polyester-urethane/epoxy (PU/E) coating,190 lm; for the epoxy/epoxy (E/E) coating, 174 lm. Both valuesare slightly larger than the expected value of 170 lm.

2.2. Accelerated corrosion test

Accelerated corrosion tests were performed using a sunshineweather meter (Suga Test Instruments Co., Ltd. S80). Test speci-mens were exposed to repeated wetdry cycles under continuousUV radiation provided by a sunshine carbon arc (255W/m2 10%, 300700 nm). Each cycle consisted of wetting by tap-water spray (12 min) followed by drying at 63 C (48 min). The to-tal test time was 4553 h. Specimens were removed from the testchamber at 1006, 1468, 2459, 3540 and 4553 h, and coating degra-dation was evaluated by various methods as described below.

2.3. Evaluation of coating degradation

Coating surfaces were observed by optical microscope and ana-lysed by SEM/EDX. Changes in chemical bonding were analysed byFT-IR. Coating thickness was measured with an electromagneticlm thickness tester (Kett Electric Laboratory LE300J) at nine ran-dom points on the surface and the values averaged. Colour changewas quantitatively evaluated with a colour difference meter atthree points on the surface. For cross-sectional observation, poly-mer-coated steel samples were cut into small pieces, immersedin liquid nitrogen for several minutes, covered with a ller clothto prevent damage to the coating surface, and then crushed witha hammer. Cross-sections were analysed by SEM/EDX.

Fig. 1 shows the three-electrode cell in which electrochemicalimpedance was measured by EIS during the corrosion test. A KCl-Pt counter ElectrodeReference Electrode (SSE)

3%NaCl solution3%NaCl

Polymer-coated steel

Fig. 1. Cell for EIS measurements.shows SEM images of the E/E coating after exposure. At 1006 h,many microcracks are evident on the surface, much earlier thanfor the PU/E coating. At 4553 h, the surfaces of both the topcoat(Fig. 6b, showing the white part of Fig. 5c) and the primer(Fig. 6c, showing the red part of Fig. 5c1) show many microcracks.

Fig. 7 shows FT-IR spectra of the PU/E coating before and afterexposure. Before exposure, a typical pattern for polyester-urethaneis observed, with the following absorption peaks: 30002900 cm1, ACH2 bonding; 1700 cm1, AC@O ester bonding;16001400 cm1, ACOO bonding; 1300 cm1, ANH group. Atsaturated Ag/AgCl electrode was used as a reference electrode; aplatinum electrode was used as a counter electrode. EIS measure-ments were performed in 3 mass% NaCl solution with a potentio-stat (Solatron SI1260) and impedance/gain-phase analyser(Solatron SI1287). The exposed area was approximately 35 cm2.Since the high-impedance limit of the employed instrument wasapproximately 1 109X (3 1010X cm2) in the low-frequencylimit, the impedance up to 1 1010X cm2 was used for the coatingevaluation.

3. Results and discussion

3.1. Characterization of the coating surface

Fig. 2 shows photographs of the PU/E coating before exposureand after exposure. At 2459 and 4553 h, the surface colour haschanged slightly with exposure, as conrmed with the colour dif-ference meter. SEM images of the PU/E coating before and afterexposure are shown in Fig. 3. At 2459 h, microcracks are evidenton the surface. At 4553 h, however, the cracks are difcult to ob-serve because the surface is covered with deposits, mainly SiO2,probably originating from the tap-water used for surface wettingin the corrosion test, as described in a later section.

Fig. 4 shows photographs of the E/E coating before and afterexposure. At 2459 h, the surface colour has changed to yellowishand to reddish at 4553 h, as conrmed with the colour differencemeter. In Fig. 5, magnied photographs of the E/E coating beforeand after exposure are shown. Before exposure, the surface is rela-tively smooth. At 2459 h, it has become rougher, with the roughen-ing surface and white topcoat distributed in island-like forms onthe primer surface. Between 3500 and 4553 h, the primer surface

Thickness (lm) Colour

Target value Final value

45 187.1 White125 Red

45 174 White125 Red2459 and 4553 h, these peaks have almost disappeared, indicatingthat the coating surface has deteriorated due to UV radiation. Theresults of elemental analysis of the coating surfaces by EDX areshown in Table 2. Silicon content increases with exposure timeand therefore peaks in the 13001000 cm1 IR region may beattributable to silicon as follows: 11001050 cm1, SiAO bonding;1300 cm1, SiACH3 bonding. The silicon is thought to originatefrom the spray water of the sunshine weather meter. In contrastboth Al and Ti, which are additives of the coatings, decrease withexposure time. Fig. 8 shows FT-IR spectra of the E/E coating before

1 For interpretation of color mentioned in this gure the reader is referred to theweb version of the article.,

,

e; (b

ScieFig. 2. Photographs of the PU/E coating: (a) before exposur

2082 M. Hattori et al. / Corrosionand after exposure. The chemical bonding on the surface changeswith exposure. Before exposure, absorption peaks are as follows:30002900 cm1, ACH2 bonding; 1500 cm1, benzene ring;13001200 and 950800 cm1, peroxide. At 2459 and 4553 h,these peaks have almost disappeared.

3.2. Characterization of the coating cross-section

Figs. 9 and 10 show SEM images of cross-sections of the PU/Eand E/E coatings, respectively. For both coatings, the microstruc-ture of the primer is coarser than that of the topcoat, perhapsdue to the pigment. The PU/E coating changes little in thicknesswith exposure, as conrmed with the electromagnetic lm thick-

Fig. 3. SEM images of the PU/E coating: (a) before exposure; (b

Fig. 4. Photographs of the E/E coating: (a) before exposure; (b

Fig. 5. Magnied photographs of the E/E coating: (a) before exposu

Fig. 6. SEM images of the E/E coating: (a) after exposure for 1006 h; (b) pr) after exposure for 2459 h; (c) after exposure for 4553 h.

nce 52 (2010) 20802087ness tester. The E/E coating topcoat is roughened by chalking,and seems thicker at the island parts (white areas in Fig. 5c) onthe primer surface. The primer itself changes little in thicknesseven after 4554 h. Figs. 11 and 12 show magnied SEM images ofcross-sections of the PU/E and E/E coatings, respectively. For thePU/E coating, the topcoat microstructure is slightly coarse after4553 h, while the primer microstructure seems less changed, per-haps because the topcoat is slightly damaged by UV radiation butthe primer is not. For the E/E coating, the topcoat is severely dam-aged and the primer is only little damaged. These changes suggestthat UV radiation causes only little deterioration for the polyester-urethane topcoat but signicant damage for the epoxy topcoat asexpected.

) after exposure for 2459 h; (c) after exposure for 4553 h.

) after exposure for 2459 h; (c) after exposure for 4553 h.

re; (b) after exposure for 2459 h; (c) after exposure for 4553 h.

imer after exposure for 4553 h; (c) topcoat after exposure for 4553 h.

it of a standard EIS instrument is approximately 1 109X(3 1010X cm2) in the low-frequency limit. Since the lm resis-tance Rf of the heavy-duty coating used in this study is much high-er than the limit, it should be difcult to determine the lmresistance of non-deteriorated heavy-duty coatings. Fig. 13 showsequivalent circuits for the various EIS results achieved in this studyand described below. The equivalent circuit for non-deterioratedheavy-duty coated steel is shown in Fig. 13a.

Fig. 14 shows Bode impedance and change plots for the PU/Ecoating. As expected from the previous results, the plot shows typ-

O

C NHC NH

O

CH 2C O

CH 2

Inte

nsity

(b)

(a)

M. Hattori et al. / Corrosion Science 52 (2010) 20802087 2083(c)

70013001900250031003700 70013001900250031003700Wave number / cm-13.3. EIS characteristics

3.3.1. PU/E coatingEIS of non-deteriorated coatings on steel substrate should show

capacitive behaviour (where Cf is the capacitance of polymer lm)over the entire frequency region, because the high-impedance lim-

Fig. 7. FT-IR spectra of the PU/E coating: (a) before exposure; (b) after exposure for2459 h; (c) after exposure for 4553 h.

Table 2Elemental analysis, determined by EDX analysis (except for carbon and oxygen).

Exposure time (h)

0 (%) 1006 (%) 1468 (%) 2459 (%) 3540 (%) 4553 (%)

Al 11.9 9.56 10.2 7.94 6.69 5.53Si 8.70 7.77 9.89 18.2 23.1Ti 88.1 81.7 82.1 82.2 75.1 71.4

O

C C

CHCH 2

Inte

nsity

(a)

(b)(b)

(c)70013001900250031003700 70013001900250031003700

Wave number cm -1/

Fig. 8. FT-IR spectra of the E/E coating: (a) before exposure; (b) after exposure for2459 h; (c) after exposure for 4553 h.

Fig. 9. SEM images of cross-sections of the PU/E coating: (a) before expical capacitive behaviour, characterized by a straight line with aslope of (o log |Z|/o log f) of 1 and a phase shift of about 90.There are no EIS changes in the employed frequency range duringthe corrosion test, even at 5568 h. The EIS can be explained by theequivalent circuit in Fig. 13a, and indicates that the PU topcoat hashigh resistance to UV radiation. The change in coating capacitanceCf with exposure time for the PU/E coating, measured from the EISdata of Fig. 14, is shown in Fig. 15, together with coating resistanceRf. Rf was beyond the limit (>1010X cm2) of the employed EIS, evenat 5568 h. If the coating deteriorates and absorbs large amounts ofwater, Cf should increase [13,14]. In fact, Cf initially decreasesslightly and, after 1488 h, remains constant at 35 pFcm2. The con-stant nature of Cf indicates that the PU topcoat suffers no fataldamage by UV radiation.

3.3.2. E/E coatingFig. 16 shows Bode impedance and change plots for the E/E

coating. Until 3540 h, impedance for E/E behaves in a manner sim-ilar to that for PU/E, indicating simple capacitive behaviour. How-ever, at 4553 h, impedance in the frequency range

Scie2084 M. Hattori et al. / Corrosioning steel corrosion, is also evident. During immersion, Rf drops to4 107X cm2 at the onset of delamination and corrosion of theunderlying steel. The EIS can be expressed by the equivalent circuitof Fig. 13b. In further lower frequency region (

4-40

/,

t

Scie10100e

0

ree

-20eg

40

/ d

-40

,

t

1010 2459h10

m2

1006h2459h3540h

109cm 1006h 3540h

4553h

108

/ 5568h108ZI

/

107e,

IZ

10

nce

106dan

105

ped

105Im

1006100624592459354045535568

ExposureExposuretime (h)( )

M. Hattori et al. / Corrosionthe anode and cathode on the coating surface, as described in thenext section. It can be concluded that degradation of the polymercoating itself decreases Rf to a measurable value in the sunshineweather meter test, while delamination of the coating reduces itin the immersion test.

3.4. Mechanism of degradation

Polymer-coated steels are used mostly in atmospheric environ-ments. The degradation process in a general atmosphere can be di-vided into two stages: Stage I, degradation of the polymer coating;and Stage II, corrosion of the underlying steel.

During Stage I, degradation of the coating occurs mainly by sun-light (UV and heat) in atmosphere. Wet/dry cycles may enhancedegradation by causing cyclic swelling/shrinking due to waterabsorption/desorption. Degradation of the polymer creates diffu-sion paths for molecules of water and oxygen, and diffusion ratesincrease gradually with exposure time. During wet conditions, lo-cal cells form as water pass through coating defects between the

-60hif

2459h80e

sh

1006h2459h3540h

-80

ase 4553h

h-100Ph

a

5568h

10-2 10-1 100 101 102 103 104 105

P

10 10 10 10 10 10 10 10F f /HFrequency, f /Hz

Fig. 14. Bode impedance and phase plots for the PU/E coating, measured by EIS.

10010

m-2

m2

cmcm

808 pFG

/p/

606

C fR f

ce,

ce,

anc

anc

404 acitista

apares

202 g ca

ng

r

2

ing

atin

oat

Coa

00 CoC

0 1500 3000 4500 6000Exposure time t / h,

Fig. 15. Plot of change in coating capacitance Cf with exposure time for the PU/Ecoating, measured by EIS.10102

109

cm

10c

108

/

10IZI

107ce,

106

anc

10eda

105mpe

10Im

104

0e

20

ree

-20deg

d

time (h)1006

35404553

14682459

Exposure

nce 52 (2010) 20802087 2085anode and cathode on the surface of the substrate steel. Local cellcurrent, however, should be negligible during this stage and mayincrease very slowly as coating degradation progresses.

During Stage II, further degradation of the polymer coating, hav-ing increased the local cell current, now nally induces delamina-tion of the coating. During wet conditions, iron at the anode maydissolve at a considerable rate into water under the deterioratedcoating, and iron hydroxide (FeOOH) and magnetite (Fe3O4) mayform:

Fe! Fe2 2e 12Fe2 O2 2H2O! 2FeOOH 2H 23Fe2 1=2O2 3H2O! Fe3O4 6H 3At the cathode, oxygen is reduced on the surface of the substratesteel:

O2 2H2O 4e ! 4OH 4

60-60hif

-80e s

h

100

ase

2 1-100Ph

a

10-2 10-1 100 101 102 103 104 105

P

Frequency f /Hz, Fig. 16. Bode impedance and phase plots for the E/E coating, measured by EIS.

10010

-22

cm-

cm2

808 Fc

c

808

/ pG

606 Cf

R f/

606

ce,

e,

R

anc

nce

404 cita

sta

pac

esi

s

202 ca

g re

202

ng ting

oati

oat

00 CoC 0 1000 2000 3000 4000 5000

Exposure time t /h,

Fig. 17. Plot of changes in lm (coating) capacitance Cf (circles) and lm (coating)resistance Rf (squares) with exposure time for the E/E coating, determined by curve-tting the EIS data in Fig. 16.

10m

2cm 9

ZI

/

8

, IZ

7

nce

dan

6

ped

Imp

5I

4

ree

20egr

-20/ de

/

0

10

1010

1010

10

1010

10

10 m-2

50cm

absorption desorption absorption desorptionpF

40C f/

40

e,

Cn

ce

30itan

paci

20cap 20

g c

10atin

100 4 8 12 16Coa

0 4 8 12 16C

Time, t/h

Fig. 21. Plot of change in lm (coating) capacitance Cf with exposure time, startingjust after immersion in 0.5% NaCl solution, measured by EIS.

2086 M. Hattori et al. / Corrosion Science 52 (2010) 20802087-4040

60hift

,

-60

sh

-80ase

80

100Pha

-100P

10-2 10-1 100 101 102 103 104 10510The cathode surface thus alkalizes, inducing delamination of thecoating from the substrate steel [20,21]. During Stage II, as de-scribed above, formation of local cells enhances delamination ofthe coating at the cathode and corrosion of the underlying steelat the anode. During this stage, adhesiveness of the polymer coat-ing to the substrate steel may be an important factor.

Frequency, f /HzFig. 18. Bode impedance and phase plots for a PU/E coating without UV radiation,measured by EIS.

Fig. 19. Photograph of a PU/E coating after the immersion test.

Fig. 20. Schematic cross-sections of a coating after both types of corrThis study employed wetdry conditions of 12-min wetting fol-lowed by 48-min drying, and the time of wetness (TOW) was thus20% of the total exposure time. TOW is well known to be an impor-tant factor in the atmospheric corrosion of metallic materials, and avalue of 20% is not extremely short compared to general atmo-spheric conditions. As described previously, however, after UVexposure in the sunshine weather meter test for even 4533 h,delamination and corrosion of the underlying steel are not evident,even though the E/E topcoat has deteriorated signicantly. Appar-ently, for polymer-coated steel, the length of the wet period in awetdry cycle is more important for the onset of delaminationand underlying steel corrosion than the TOW. TOW is often denedas the period of time during which relative humidity (RH) exceeds80% [22], and corrosion of uncoated metallic materials is assumedto start when RH exceeds 80% RH. For polymer-coated steels, how-ever, it takes a certain amount of time for water to reach the steel-coating boundary, establish local cells between the anode andcathode, and thus enhance delamination and corrosion. If the dry-ing stage of a cycle starts before water can penetrate the boundary,delamination and corrosion do not occur. The wetting period of12 min per cycle may thus be too short for the onset of delamina-tion and corrosion.

To conrm the time period of water absorption, a cycle test ofwater absorption/desorption using the PU(100 lm)/E(100 lm)coating was performed by alternate exposure to 0.01 M LiCl solu-tion (4 h) and 10 M LiCl solution (4 h) at 60 C. A LiCl-saturated-solution was selected for water desorption because it has the low-est activity of H2O among chloride-saturated solutions. Fig. 21shows the change in coating capacitance. The coating capacitance

was monitored by continuous measurements of impedance at

osion test: (a) sunshine weather meter test; (b) immersion test.

1 kHz [23]. The increase in capacitance in the dilute solution (activ-ity of water, aH2O 1) is attributed to water absorption into thepolymer coating, while the decrease in capacitance in the concen-trated solution (aH2O 0.15) is due to water desorption. From themonitoring result, it is found that it takes about 4 h for water tosaturate the coating, conrming that the wetting time of 12 mineach cycle is too short for the onset of lm delamination and cor-rosion of the underlying steel.

4. Conclusions

Accelerated corrosion tests of PU/E- and E/E-coated steels wereperformed under exposure to UV radiation for about 4500 h, anddegradation was evaluated by SEM, FT-IR, EDX and EIS. The follow-ing conclusions were drawn:

(1) The PU/E coating deteriorates only a very little. In contrast,the E/E topcoat deteriorates signicantly due to chalking,and partially exposes the primer.

(2) The PU/E coating shows only capacitive behaviour, whichdoes not change with exposure time. In contrast, the E/Ecoating shows resistance Rf in the low-frequency range ofthe Bode plot, indicating topcoat degradation, in good agree-ment with SEM observations.

(3) The E/E coating, despite signicant topcoat deterioration andcorresponding decrease in Rf, does not delaminate from thesubstrate steel, and corrosion of the steel does not occur.The decrease in Rf is due to deterioration of the polymercoating.

(4) EIS is an effective technique for evaluating polymer coating

References

[1] X.F. Yang, C. Vang, D.E. Tallman, G.P. Bierwagen, S.G. Croll, S. Rohlik, PolymerDegradation and Stability 74 (2001) 341.

[2] X.F. Yang, D.E. Tallman, G.P. Bierwagen, S.G. Croll, S. Rohlik, PolymerDegradation and Stability 77 (2002) 103.

[3] R.D. Armstrong, A.T.A. Jenkins, B.W. Johnson, Corrosion Science 37 (1995)1615.

[4] X.F. Yang, J. Li, S.G. Croll, D.E. Tallmana, G.P. Bierwagen, Polymer Degradationand Stability 80 (2003) 51.

[5] J.M. Sanchez-Amaya, R.M. Osuna, M. Bethencourt, F.J. Botana, Progress inOrganic Coatings 60 (2007) 248.

[6] J.E. Pickett, Polymer Degradation and Stability 85 (2004) 681.[7] F. Deorian, S. Rossi, M. Fedel, Corrosion Science 50 (2008) 2360.[8] V.C. Malshe, G. Waghoo, Progress in Organic Coatings 56 (2006) 131.[9] B.S. Lee, D.C. Lee, IEEE Transactions on Dielectrics and Electrical Insulation 6

(1999) 907.[10] S.G. Croll, A.D. Skaja, Journal of Materials Science 37 (2002) 4889.[11] V.C. Malshe, G. Waghoo, Progress in Organic Coatings 51 (2004) 172.[12] V.C. Malshe, G. Waghoo, Progress in Organic Coatings 51 (2004) 267.[13] Y. Gonzalez-Garca, S. Gonzalez, R.M. Souto, Corrosion Science 49 (2007) 3514.[14] J. Mallegol, M. Poelman, M.-G. Olivier, Progress in Organic Coatings 61 (2008)

126.[15] R. Narayan, D.K. Chattopadhyay, B. Sreedhar, K.V.S.N. Raja, N.N. Mallikarjuna,

T.M. Aminabhavi, Journal of Applied Polymer Science 97 (2005) 1069.[16] S. Hong, Polymer Degradation and Stability 48 (1995) 211.[17] M.G. Penon, S.J. Picken, M. Wubbenhorst, J. van Turnhout, Polymer

Degradation and Stability 92 (2007) 1247.[18] D.R. Bauer, J.L. Gerlock, D.F. Mielewski, M.C.P. Peck, R.O. Carter III, Industrial

and Engineering Chemistry Research 30 (1991) 2482.[19] F.X. Perrin, M. Irigoyen, E. Aragon, J.L. Vernet, Polymer Degradation and

Stability 70 (2000) 469.[20] Japan Paint Manufacturers Association, Handbooks of heavy anticorrosion

paint, 1995/12.[21] H. Kiryu, H. Kasamatu, Foundation and Physical Properties of High Efcient

Paint, CMC Publish Co., Ltd., 1985/8.[22] ISO9223-1992, Corrosion of metals and alloys corrosivity of atomspheres

classication.[23] J.H. Park, G.D. Lee, H. Ooshige, A. Nishikata, T. Tsuru, Corrosion Science 45

(2003) 881.

M. Hattori et al. / Corrosion Science 52 (2010) 20802087 2087degradation as well as for detecting the onset of corrosionof underlying steel.

EIS study on degradation of polymer-coated steel under ultraviolet radiationIntroductionExperimentsPolymer coatingsAccelerated corrosion testEvaluation of coating degradation

Results and discussionCharacterization of the coating surfaceCharacterization of the coating cross-sectionEIS characteristicsPU/E coatingE/E coatingDifference between EIS in sunshine weather meter test and immersion test

Mechanism of degradation

ConclusionsReferences