22 February 2005 JCT CoatingsTech

EXPOSURE TESTSFor the purposes of this discussion,

an “exposure test” implies a testing pe-riod equivalent to a typical standardizedcabinet or atmospheric test. This maybe as short as 15–30 days or as long asseveral years.

*734 Louis Dr., Warminster, PA 18974; Voice: 215.682.9330; Fax: 215.682.9331; Email: brodgers@gamry.com.

David Loveday, Pete Peterson, and Bob Rodgers—Gamry Instruments*

Evaluation of Organic Coatings withElectrochemical Impedance Spectroscopy

Part 3: Protocols for Testing Coatings with EIS

EIS and Atmospheric Exposure Tests

For the ultimate in coatings evalua-tion, atmospheric exposure is still the“gold standard.” Every other test is anattempt to simulate the results of at-mospheric tests. The problem with at-

mospheric tests, of course, is that theyrequire a long, long time. Nothing canaccelerate the deleterious effects of at-mospheric exposure, but EIS can ob-serve the deterioration of the coatinglong before visual defects appear.

Measure the EIS curve periodicallyduring the exposure period. Place thesample in contact with the electrolyte inan electrochemical cell and measure theopen-circuit potential (Eoc) as a func-tion of time. The electrolyte can be cho-sen to simulate the particular atmos-pheric conditions of the exposure test.Run the EIS experiment when the sam-ple has reached a steady state, signaledby a stable value of Eoc. Most comput-erized EIS instruments can measure thestability of Eoc. You can run the experi-ment when the stability is better than0.1 mV/sec.

Immersion and Measurement ofImpedance Magnitude at 0.1 Hz

The most straightforward use of EISto characterize coatings is to immersethe sample in an electrolyte and period-ically measure the impedance spectrum.This approach is exemplified by Grayand Appleman,5 who developed amethod to determine the barrier protec-tion properties of coatings. Sampleswere immersed in 5% NaCl solution,sealed, and placed in an oven at 65°Cto accelerate attack. The panels were re-moved from the oven at 1, 4, 7, 14, and28 days and the EIS curve was run. (SeeFigure 1.)

The limiting impedance at low fre-quency is equal to the sum of PoreResistance (Rpore), the PolarizationResistance (Rp), and the SolutionResistance (Rs). Rp and Rpore are ini-

In Parts 11 and 22 of this Series, we discussed the technology of applying electrochemicalimpedance spectroscopy (EIS) to organic coatings on a metallic substrate such as aircraft,marine, or industrial maintenance coatings. This article describes several experimental proto-cols to evaluate these coatings with EIS. These experimental protocols differ primarily in theprocess used to stress the coating and accelerate the degradation of the coating.

There is no standard recipe for an EIS-based evaluation program that is guaranteed towork for every coating in every environment. This may come in time and, indeed, a standardfor EIS evaluation of coatings is under development at ASTM and ISO.3 However, EIS canbe employed in a variety of ways to evaluate virtually any coating.

It may be useful to think of EIS as a very sensitive detector that provides a snapshot ofcoating status. However, a single EIS measurement of an organic coating tells you nothing.To measure coating lifetime or performance, the coating must be stressed to bring about itsfailure. By making periodic EIS measurements during the stress process, a rate of coatingfailure can be estimated and a series of coatings may be ranked.

Even though some publications discuss the determination of the time-to-failure of a coat-ing, this may be an unrealistic goal. There are too many variables that separate us from this“Holy Grail,” most of which are not related to EIS. A more achievable objective is to use EISin an experimental program that results in a performance ranking of a series of coatings foruse in a specific environment.

The nature of the stress applied to the coating is, of course, very important in several as-pects. The experimental design to prompt the failure of the coating must (1) simulate theservice environment the coating will encounter and (2) it must not change the failure mech-anism.4

To use EIS to evaluate a specific coating system, (1) place the coated sample in an envi-ronment designed to accelerate the degradation of the coating, (2) measure the EIS curvesover time, and (3) identify an “index” that tracks coating quality. The index could be theCoatings Capacitance or the Pore Resistance, for example. The index can be very simple ormore complex and we will look at several examples in this article. Unfortunately, all coatingsdo not fail in the same way, so there is no universal index for assessing coating quality withEIS.

This complex nature of coatings is no surprise to coatings scientists. A coating system mayconsist of the metal substrate, surface pretreatment, a primer, and one or more topcoats.Results can vary depending on types of coatings, thickness, number of layers, surface treat-ment, and the nature of the metal substrate.

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tially quite high and usually decreasewith time as a result of the attack onthe coating and initiation of under-filmcorrosion. Rs is usually very low andcan be ignored. The log of the imped-ance modulus at 0.1 Hz was plotted asa function of immersion time. The datasuggests that if the log of the imped-ance modulus is above 7 (impedance >107 ohm-cm2), then the coating was af-fording adequate corrosion protectionto the surface. Below this impedance,the protection was poor. Above a valueof 9 (impedance > 109 ohm-cm2), theprotection is good to excellent. Thesetests were conducted on both labora-tory and field samples.

Long-Term Shelf-Life Tests In an early publication,6 Tait de-

tailed the results of extended shelf-lifetests. A large population of internallycoated metal containers was aged in“typical” proprietary electrolytes at nor-mal storage temperatures (21°C or70°F) for longer than two years.Impedance measurements were made atperiodic intervals. The coatings fell intothree classes.

In the first class, the EIS responsewas essentially that of a capacitor (seeFigure 3A of Part 2 of this series1). Aftersix months, the capacitance values werevirtually the same as when the exposuretest was started. After 24 months, nocorrosion or coating delamination wasobserved upon physical examination ofthe samples. The constancy of the coat-ing capacitance indicates little or no wa-ter uptake in the first six months.

In the second class of coatings, theEIS response closely followed the “coat-

ing model” (Figure3 in Part 2 of thisseries). Tait foundthat the time-to-failure tracked therate at which thepolarization resist-ance value in themodel droppedwith time. If theRp changed rap-idly in the firstdays of exposure,the containerfailed after threemonths. Thosecontainers with aslowly changingRp lasted morethan two years.

In the third class of coatings, the EISresponse was also similar to that of the“coating model.” However, another cir-cuit element, the Warburg Impedancethat models diffusion, was required tofit the data. In this class, the fraction ofdelaminated coating was found to trackthe rate at which the coating capaci-tance, Ccoating, changed over the four-month test period.

EIS and Cabinet TestsThe most common testing technique

for coatings is exposure to a series ofcontrolled aggressive conditions in acabinet constructed for this purpose.The conditions include a variety ofchemistries as well as exposure to UVradiation and cycles of wetness/drynessand heat/cold. These cabinets have beenin common use for decades and at-tempt to simulate atmospheric or in-dustrial conditionsthat can be used todegrade the coatingin a realistic fashion.The goal is to corre-late cabinet testswith actual exposuretests to predict time-to-failure. It is gener-ally accepted thatcabinet tests providecomparative resultsand not absolute re-sults.

When used withcabinet tests, EIS actsas a quantitative de-tector of coatingsquality. The EIS re-sponse of a sample

undergoing cabinet tests will follow thegeneral trend described in Figure 3 ofPart 2 in this series.2 An EIS experimentis conducted on the specimens in thecabinet on a regular basis. If the sam-ples are deteriorating rapidly, the EIScurves should be run daily. For moredurable paints, a weekly EIS evaluationmay be sufficient.

Some of the more popular cabinettests are ASTM B 117 Salt Spray, ASTMD 5894 Cyclic Salt Fog/UV Exposure,and SAE J2234 Laboratory CyclicCorrosion Test. The cabinet test stan-dards specify the conditions for expo-sure in the cabinet, but do not providetesting methods or pass-fail criteria.This is addressed in ASTM D 1654,“Evaluation of Painted or CoatedSpecimens Subjected to CorrosiveEnvironments.” All of these testing pro-tocols are qualitative in nature.Coupling EIS with these standard cabi-net tests can provide a quantitativemeasure of coating deterioration.

ASTM D 1654 discusses both scribedand unscribed panels. A scribed panel isgenerally used to simulate major dam-age to the coating that exposes the sub-strate-coating interface. The loss of ad-hesion is quantitated by measuring thelength of “creepage” of the paint filmfrom the scribe after air blow-off orscraping. Adhesion may also be meas-ured with a tape pull-off test (ASTM D3359). Tests on a scribed panel do notmeasure the barrier properties of thecoating; they measure the ability of thecoating-substrate to self-repair when thesubstrate is exposed.

The Knife Adhesion Test in ASTM D6677 tests the adhesion of the coatingon an unscribed sample, usually after a

Figure 1—EIS response of a pipeline coating in 5% NaCl at 65°C.(Figure 8 from reference 5.)

Figure 2—Reversible behavior of a coating during thermal cycling.Open circles indicate heating, closed circles indicate cooling. (Figure6 from reference 9.)

24 February 2005 JCT CoatingsTech

controlled exposure of some sort. Thereis a fundamental difference betweenpulling the coating off with tape andlifting the coating with a knife, andsome workers prefer the latter.

An unscribed panel is used to test forrusting (ASTM D 610), blistering (ASTMD 714), or adhesion (ASTM D 3359)through the coating. Both D 610 and D714 provide a semi-quantitative rankingtechnique involving the comparison ofthe tested panel to a series of photo-graphs. The quantitative numerical re-sults from EIS are seen as a major tech-nical advancement in this area.

Since one of the key advantages ofEIS is the ability to simultaneouslymeasure the barrier properties and thecorrosion properties, scribed panels arerarely used with EIS. The scribe inflictsphysical damage to the paint film andunderlying substrate and contributes topoor reproducibility.7

ASTM B 117 Salt Spray is the oldeststandard cabinet test and, therefore, thetest with the most history. B 117 is usedto test bare metals and painted metals.With regard to painted metals, historyhas not been kind to ASTM B 117 andmost users accept that B 117 does notcorrelate well with actual exposure.Nevertheless, it is still in common use,particularly for quality control applica-tions or comparing different materials.ASTM B 117 uses a salt fog of 5% NaClto accelerate the natural corrosionprocess.

Based on comments from within theindustry, ASTM B 117 is not consideredto be a useful technique for evaluatingcoatings and its use with EIS is not rec-ommended.

ASTM D 5894Cyclic Salt Fog/UVExposure of PaintedMetal differs fromB 117 in three keyfactors: UV expo-sure, more dilutesalt solution, andwet/dry cycles. Theintense UV radia-tion at 340 nmphotochemicallydegrades the coat-ing and is a key fac-tor in simulatingexposure in exteriorconditions. The wetand dry cycles pro-vide realistic condi-tions for corrosion.The test involves:

• A one-week (168 hr) exposure cy-cle of 4-hr UV at 60°C and 4-hrcondensation at 50°C followedby:

• A one-week (168 hr) fog/dry cycleof 1-hr fog (0.05% NaCl and0.35% NH4SO4) at ambient tem-perature and 1-hr dry-off at 35°C.

• The cycles may be repeated ifagreed by the parties involved.

ASTM D 5894, unlike B 117, was de-veloped specifically for coatings and isgenerally agreed to give more realisticresults. These results, however, are com-parative and not absolute. ASTM D5894 is also referred to as a ProhesionTest, from “Protection by Adhesion.”

ASTM D 5894 has enjoyed wide ac-ceptance by the coatings community.Bierwagen4 recommends the use of D5894 with weekly EIS analysis to trackthe status of the coating.

To employ EIS as a quantitative sen-sor of coating degradation during D5894, remove the panel from the fog cy-cle, immerse the panel in an electrolyteof 0.05% NaCl and 0.35% NH4SO4, al-low the sample to equilibrate for30 min, then run the EIS curve. Toobtain the most consistent results,the samples should be removedfrom the cabinet at the samepoint in the cycle. If possible, co-ordinate multiple panels so theyare outside of the cabinet for thesame amount of time.

SAE J2334 Laboratory CyclicCorrosion Test8 was developed bythe automotive and steel industryspecifically for automotive coat-ings and is widely used by both

the automobile manufacturers and theirvendors. The development involvedcomparing several different test condi-tions on standard panels that had beenexposed to an urban industrial environ-ment for five years. The test conditionsthat gave the best correlation to the ex-posure tests were selected. The condi-tions of J2334 were selected primarilyto simulate the effects of road salts. It isinteresting that J2334 does not employUV exposure.

One 24-hr cycle of SAE J2334 con-sists of three stages:

• Humid Stage—50°C and 100%relative humidity for 6 hr.

• Salt Application Stage—Dip, fog,or spray a salt solution (0.5%NaCl, 0.1% CaCl2, 0.075%NaHCO3) for 15 min.

• Dry Stage—60°C and 50% rela-tive humidity for 17 hr, 45 min.

The typical SAE J2334 test is con-ducted for 60 cycles for coated samples.The test allows for either manual or au-tomatic operation. Because SAE J2334was developed for a relatively specificsample, there is a correlation to actualexposure time: 80 cycles of SAE J2334corresponds to about five years of expo-sure.

ACCELERATED TESTSEven though a cabinet test is faster

than real-world exposure, it still takes along time. One cycle of ASTM D 5894requires two weeks. One cycle of SAEJ2334 takes 24 hours and the normaltest requires 60 cycles, or two months!Since nothing is ever fast enough, sev-eral attempts have been made to de-velop quicker tests for paints. Theseshort-term tests introduce more aggres-sive stress conditions to induce failurein a shorter time. The user of the accel-erated tests must be concerned that (1)

Figure 3—Irreversible behavior of a coating during thermal cycling.Open circles indicate heating, closed circles are cooling. (Figure 8from reference 9.)

Figure 4—Equivalent circuit used in the REAP proce-dure. The Constant Phase Element is indicated by .O

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the stress method does not change themechanism of failure and (2) the stressmethod is sufficiently analogous to theservice conditions to be relevant. Theultimate goal is a short test that pro-duces a predictive result.

Thermal Cycling Bierwagen9 has investigated the ac-

celeration of coatings failure by hightemperature. An increase in temperaturewill increase the rate of diffusion of theelectrolyte into the coating, reducingthe barrier properties of the coating andpossibly enhancing the chemical andphysical “aging effects” from attack bythe electrolyte.

The sample is immersed in the elec-trolyte (0.05% NaCl and 0.35%NH4SO4) from ASTM D 5894. An EIScurve is obtained at room temperature,35º, 55º, 75º, and 85ºC, then in thesame sequence back to room tempera-ture. The EIS data is obtained at eachtemperature after equilibrating for 20min. A complete test procedure consistsof three temperature cycles, followed bya three-day immersion, and a final EISscan. A complete test period requiresabout one week. To obtain similar re-sults with a Prohesion Test may require4–12 weeks.

The behavior of the EIS curves dur-ing the thermal excursions provides anindication of coating quality and corro-sion resistance. As the temperature is in-creased, the total impedance at low fre-quencies is reduced. When the sampleis cooled, the low frequency impedancemay (Figure 2), or may not (Figure 3),return to its original value. The return ofthe impedance at low frequency to itsinitial value is an indication of good cor-rosion resistance of the coated sample.

If the temperature range of the ther-mal cycling test includes the glass tran-sition temperature (Tg), it might be wiseto run two tests: one that remains be-low Tg and another that incorporatesthe normal temperature limits.

Rapid Electrochemical Assessment of Paint (REAP)In 1996, Kendig and coworkers pub-

lished an electrochemical approach to a24-hour determination of the time-to-failure of an automotive coating onmild steel.10 The Rapid ElectrochemicalAssessment of Paint (REAP) protocol in-corporates an impedance measurement

to determine thebarrier propertiesof the coating anda cathodic dis-bonding procedureto determine thedamage caused bycorrosion at themetal-paint inter-face. To our knowl-edge, the REAP testis the only pub-lished procedure tocombine an EISmeasurement witha physical test forpaint adhesion.

The EIS meas-urements were per-formed in 0.5 MNaCl. The imped-ance was measuredimmediately afterimmersion andagain after 24 hr.Although a fre-quency sweep from104 to 0.1 Hz issufficient to charac-terize the sampleinitially, a lowerfrequency of 0.01Hz is needed forthe later scan. Thelower frequency isnecessary to definethe EIS curve afterthe development ofa Pore Resistanceand a Polarization Resistance.

The equivalent circuit shown inFigure 4 was used to model the system.Notice that the authors chose to use aConstant Phase Element (CPE) insteadof a capacitor to model the coating-metal interface. A CPE has been de-scribed as an “imperfect capacitor” andis mathematically expressed as:

Zcpe = (1/Y0)/ (jω)α

Y0 is a constant, j = (–1)½, ω = 2πf, andα is a constant between 0 and 1. If α =1, Y0 is the capacitance. The use of theCPE as an element in the equivalent cir-cuit is left to the discretion of the user.Use of a CPE can sometimes give a bet-ter fit with a model. Even though theCPE does not have a simple explana-tion, it is relatively popular in the elec-trochemical literature.

The cathodic disbonding experimentis performed on a second identical sam-ple. The sample is scribed through the

paint to expose the underlying metal.The scribed sample is immersed in 0.5M NaCl and a potential of -1050 mV isapplied for 24 hr. The primary reactionis the reduction of oxygen.

O2 + 4e– + 2H2O → 4OH–

The alkaline environment producedby the cathodic reaction is particularlydetrimental to the adhesion of the coat-ing to the metal. The coating is furtherstressed by the oxidation of the metal(usually iron) to the oxides, which havea higher volume than the base metal.

After completion of the cathodic po-larization, delamination of the coatingis measured by placing tape across thescribe and pulling to remove the por-tion of the coating that has disbonded.

The goal of the REAP technique isambitious, since the authors not onlyhad to define the parameters to predicttime-to-failure, they also had to definetime-to-failure itself, a not insignificant

Figure 5a—Impedance response of an epoxy coating on steel to theAC-DC-AC procedure. (Figure 3 from reference 12.)

Figure 5b—Phase response of an epoxy coating on steel to the AC-DC-AC procedure. (Figure 3 from reference 12.)

26 February 2005 JCT CoatingsTech

task that, regardless of the definition, iscertain to attract critics. ASTM B 117 saltfog was chosen as the accelerated test,not so much for its successful predic-tion of lifetimes, but because of itswidespread use in the coatings industry.

The best correlation was obtained byusing Rcor, % water uptake, and pull-back (dx/dt) to estimate time-to-failure.Note that Rcor and Rp are identical.

TTF = –830.1 + 118 log Rcor – 169.2 logdx/dt – 48.03 (%water)

The water uptake was calculated bymeasuring the initial EIS spectrum andagain after 24 hr. Coating capacitances(C) were evaluated from the EIS meas-urements.

Volume fraction of water = Log (Ct/Co)Log 80

The concept of combining EIS tomeasure the barrier properties andmore conventional physical techniquesto evaluate adhesion is attractive tomany researchers. The consensus seemsto be that barrier properties and adhe-sion are both important, but very dif-ferent. Since adhesion is a function ofchemical, electrochemical, and physi-cal properties, EIS may not alwaysserve to evaluate adhesion. In additionto the tape pull-back test, adhesion canbe tested with ASTM D 6677 (KnifeAdhesion Test). It can also be useful tocombine cathodic disbonding withtests such as D 6677. In the case of D6677, cut the coating with the knife,then apply a potential of about –1 voltvs. SCE to encourage cathodic disbond-

ing. Assess the dis-bonding as de-scribed in D 6677.

AC-DC-ACThe AC-DC-AC

test employs EIS toobserve the condi-tion of the coatingbefore and after anelectrochemical dis-bonding step.11,12

The test consists ofthree steps: (1) anEIS curve is run toestablish the initialcondition of thecoating; (2) thesample is cathodi-

cally polarized to generate an alkalineenvironment and stimulate delamina-tion; and (3) an EIS curve is run to as-sess the condition of the coating afterdelamination. Steps 2 and 3 may be re-peated to apply additional stress to thesample if desired (Figure 5).

The cathodic potential (a negativepotential is termed “cathodic” becauseit prompts a reduction reaction) gener-ates hydrogen and hydroxide ions at thesurface of the metal beneath the coat-ing.

H2O + e– → H2 + OH–

The adhesion of the coating is com-promised by the alkaline environmentand delamination is further encouragedby the pressure of the hydrogen beneaththe coating.

For fresh, intact coatings, it is neces-sary to apply a pronounced negativepotential (from –2 to –3 volts) to in-duce a stress. Based on the interpreta-tion of the structure of a paint film ona metallic substrate, the cathodic polar-ization step must attack the coating byopening pores, allowing access to themetal surface. From the EIS response tothis applied stress, that is exactly whatis happening as noted by the reductionin the limiting impedance at low fre-quency.

The AC-DC-AC test can be con-ducted on a paint panel in a typicalthree-electrode electrochemical cell. Ithas also been successfully employed onroutine samples or on samples outsideof the laboratory by using the EIS in-strument in “two-electrode mode” and

contacting the sample using a copperdisk and filter paper moistened with theappropriate electrolyte.

STUDIES OF FREE PAINT FILMS

The effect of the paint film can beseparated from effects of the metal sub-strate or the metal-paint interface bystudying the free paint films. The freefilms can be produced by applying toglass, plastic, or smooth metal and care-fully removing. The free films aremounted in an electrochemical cell thatallows an electrolyte to be placed on ei-ther side of the film. The EIS curve isgenerated using a “four-terminal” or“four-electrode” measurement, in whicha reference electrode and an inert elec-trode (usually platinum) are placed oneither side of the membrane.

Permeation of the coating with ionsor water can be precisely studied withfree films.13,14 The changes in imped-ance of a free film after immersion aresimilar to the changes observed in coat-ings applied to substrates, but they oc-cur faster. The EIS response typicallydisplays a decrease in impedance andan increase in capacitance as water pen-etrates the film (see Figure 6).

PRACTICAL ISSUES

EIS and Coating Thickness A newcomer to EIS may have con-

cerns regarding the maximum coatingthickness that can be measured. Thethickness of the coating is not the issue;the impedance of the coating is the fig-ure of merit. Thickness is immaterial.For example, a two-inch filled poly-meric coating on the high-strength steelhull of an ocean-going vessel can beevaluated using EIS. The impedance isabout 1013 ohms-cm2, which is veryhigh. The EIS measurement was assistedby using a 12 in.2 sample.

Precision of EIS MeasurementsTo have confidence in a scientific

measurement, it is important to under-stand the accuracy and precision of themeasurement. The accuracy and preci-sion of modern EIS instrumentation is

Figure 6—EIS response of a free PVC plastisol film during immersionin 3% NaCl. (Figure 2 from reference 13.)

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typically ±1% for impedances between1 and 10 megaohms at frequencies be-tween 10 µHz and 100 kHz. For organiccoatings with impedances higher than10 Mohms (107 ohms), the user shouldconfirm that the EIS instrument is capa-ble of proper operation in this imped-ance region by running an Open LeadCurve. (See Part 1 of this Series.)

The greatest source of error is thevariation in coating thickness. This vari-ation can occur on the surface of an in-dividual sample and from sample-to-sample and can be remarkably high.These issues are discussed for coatedaerosol containers by Tait.15 When deal-ing with sample variability, it is best toincrease the number of sample replica-tions. Tait recommends eight replicatesfor coated samples.

Cable Length In the field, the sample can be a long

distance from the EIS instrument. Thisis particularly true for towers, aircraft, orwatercraft. This requires the use of longcables that, because of the additionalcapacitance they add to the system, cancause serious problems with noise pick-up. Cable length should be kept asshort as possible. In the event that ex-tended cables are required, seek the ad-vice of the manufacturer and, if possi-ble, purchase the cables from themanufacturer. In spite of this potentialproblem, EIS measurements have beensuccessfully performed on an aircraft inan operating hangar with 80-ft (25 m)cables on aircraft coatings with imped-ances as high as 1011 ohms.

FUTURE DIRECTIONSEIS is a unique measurement tool in

that it provides a quantitative test onthe complete coating system (metal sub-strate and coating). We expect that thesteady proliferation of EIS into the coat-

ings community will lead to a greaterunderstanding of the breadth of appli-cations to various coatings. Within gen-eral classes of coatings, it is likely thatfailure mechanisms will be classifiedand routinized.

The need for more rapid results willdrive the continued development of ac-celerated tests. To incorporate delamina-tion into testing procedures, the combi-nation of EIS and adhesion testing willprobably be exploited. As EIS gains ac-ceptability by coatings researchers, therewill be a need for multichannel instru-ments for greater sample throughput atlower cost. If cabinet tests remain popu-lar, there will be a demand for auto-mated EIS measurements during the ex-posure period.

ACKNOWLEDGMENTSThe authors thank the following col-

leagues for their input and discussion:Gordon Bierwagen and Vicki Gelling(North Dakota State University),Richard Granata (Florida AtlanticUniversity), Linda Gray (KTA-Tator),Lingyun He (General Electric Corp.),Jochen Hollaender (FraunhoferInstitute), Yuly Korobov (Carboline),Larry Laliberte (ConcurrentTechnologies), Martin Kendig (RockwellScientific), Oscar Mattos (FederalUniversity of Rio de Janeiro), AldaSimoes (Instituto Superior Tecnico),Brian Skerry (Sherwin-Williams), JulioSuay (Castellon University), and MarcWirtz (PPG Industries).

References(1) Loveday, D., Peterson, P., and Rodgers, B.,

“Evaluation of Organic Coatings withElectrochemical Impedance Spectroscopy:Fundamentals of ElectrochemicalImpedance Spectroscopy,” JCTCOATINGSTECH, 1, No. 8, p. 46 (August2004).

(2) Loveday, D., Peterson, P., and Rodgers, B.,“Evaluation of Organic Coatings withElectrochemical Impedance Spectroscopy:

Application of EIS to Coatings,” JCTCOATINGSTECH, 1, No. 10, p. 88 (October2004).

(3) ISO TC 35 SC9 WG 29/ASTM D01.27.32.Standard Practice for PerformingElectrochemical Impedance Spectroscopy(EIS) on High Impedance CoatedSamples. Expected publication in Spring2005.

(4) Bierwagen, G., Tallman, D., Li, J., and He,L., “EIS Studies of Coated Metals inAccelerated Exposure,” Prog. Org. Coat., 46,148 (2003).

(5) Gray, L. and Appleman, B., “Electrochemi-cal Impedance Spectroscopy: A Tool toPredict Remaining Coating Life,” J. Prot.Coat. Linings, p. 66, February 2003.

(6) Tait, W.S., “Using ElectrochemicalImpedance Spectroscopy to StudyCorrosion Behavior of Internally CoatedMetal Containers,” JOURNAL OF COATINGS

TECHNOLOGY, 61, No. 768, 57 (1989).(7) Yasuka, H.K. et al., “Effect of Scribing

Mode on Corrosion Test Results,”Corrosion, 57, 29 (2001).

(8) Society of Automotive Engineers, 400Commonwealth Dr., Warrendale, PA15096-0001 USA; web: www.sae.org;phone: 724-776-4970.

(9) Bierwagen, G.P., He, L., Li, J., Ellingston,L., and Tallman, D.E., “Studies of NewAccelerated Evaluation Method forCoating Corrosion Resistance—ThermalCycling Testing,” Prog. Org. Coat., 39, 67(2000).

(10) Kendig, M., Jeanjaquet, S., Brown, R., andThomas, F., “Rapid ElectrochemicalAssessment of Paint,” JOURNAL OF COATINGS

TECHNOLOGY, 68, No. 863, 39 (1996).(11) Hollaender, J., Food Additives and

Contaminants, 14, 617 (1997).(12) Suay, J.J. et al., “Rapid Assessment of

Automotive Epoxy Primers byElectrochemical Techniques,” JOURNAL OF

COATINGS TECHNOLOGY, 75, No. 946, 103(2003).

(13) Castela, A.A. and Simoes, A.M., “WaterSorption in Freestanding PVC Films byCapacitance Measurements,” Prog. Org.Coat., 46, 130 (2003).

(14) Mattos, O.R. and Margarit, I.C.P., “AboutCoatings and Cathodic Protection:Properties of the Coatings InfluencingDelamination and Cathodic ProtectionCriteria,” Electrochimica Acta, 44, 84(2003).

(15) Tait, W.S., “Using ElectrochemicalMeasurements to Estimate Coatings andPolymer Film Durability,” JOURNAL OF

COATINGS TECHNOLOGY, 75, No. 942, 45(2003).

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