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16. ASTM, ASTM G85 - Standard Practice for Modified Salt Spray (Fog) Testing, in Annual Book of ASTM Standards. 2009, ASTM: Philadelphia, PA. 17. Yang, X. F., Vang, C., Tallman, D. E., et al., Weathering degradation of a polyurethane coating. Polymer Degradation and Stability, 2001. 74(2): p. 341-351. 18. Yang, X. F., Tallman, D. E., Bierwagen, G. P., et al., Blistering and degradation of polyurethane coatings under different accelerated weathering tests. Polymer Degradation and Stability, 2002. 77(1): p. 103-109. 19. Kendig, M. and Scully, J., Basic Aspects of Electrochemical Impedance Application for the Life Prediction of Organic Coatings on Metals. Corrosion, 1990. 46(1): p. 22-29. 20. Mansfeld, F., Use of Electrochemical Impedance Spectroscopy for the Study of Corrosion Protection by Polymer Coatings. Journal of Applied Electrochemistry, 1995. 25: p. 187- 202. 21. Deflorian, F. and Fedrizzi, L., Adhesion characterization of protective organic coatings by electrochemical impedance spectroscopy. J. Adhesion Sci. Technol., 1999. 13(5): p. 629-645. 22. Mansfeld, F., Kendig, M.W., and Tsai, S., Evaluation of Corrosion Behavior of Coated Metals With AC Impedance Measurements. Corrosion, 1982. 38(9): p. 478-485. 23. Kumar, G. and Buchheit, R.G., Use of Artificial Neural Network Models to Prodict Coated Component Life from Short-Term Electrochemical Impedance Spectroscopy Measurements. Corrosion, 2008. 64(3): p. 241-254. 24. Brug, G. J., Vandeneeden, A. L. G., Sluytersrehbach, M., et al., The Analysis of Electrode Impedance Complicated by the Presence of a Constant Phase Element. Journal of Electroanalytical Chemistry, 1984. 176(1-2): p. 275-295. 25. Macdonald, D.D., Sikora, E., and Engelhardt, G., Characterizing electrochemical systems in the frequency domain - A review. Electrochimical Acta, 1997. 43(1-2): p. 87-107. 26. Esteban, J. M. and Ozarem, M.E., On the Application of the Kramers-Kronig Relations to Evaluate the Consistency of Electrochemical Impedance Data. J. Electrochem. Soc., 1991. 138(1): p. 67-76. 27. Orazem, Mark E. and Tribollet, Bernard, Electrochemical Impedance Spectroscopy - Chapter 22 (p. 443). The Electrochemical Society Series, ed. ECS. 2008. 28. USAF, Technical Manual: Application and Removal of Organic Coatings, Aerospace and Non-Aerospace Equipment (Chapter 3 - p.13-14). USAF T0 1-1-8. 2008. 276
5.6.2 Electrochemical Impedance Spectroscopy (EIS) Study to Predict Long-term Performance of Cr-Free Coatings on Aluminum Alloys Using Artificial Neural Networks (ANNs) 5.6.2.1 Introduction Chromate-bearing coating systems provide excellent corrosion protection to high strength aluminum alloys used in condensing atmospheric exposure conditions. However, the toxic hazard associated with corrosion-inhibiting chromates is unacceptably high, which has prompted the development of alternate coating formulations for corrosion resistant coatings that do not use toxic forms of chromate [1, 2]. Accelerated exposure testing is the most widely used method for evaluating the protectiveness of coating systems. Among these, the salt spray exposure test described in ASTM B117 is common for testing the corrosion resistance of coated aluminum alloys [3]. Development of corrosion damage requires long exposure times ranging up to thousands of hours for some of the very best coating systems. Long test times delay coating development and qualification activities and there is a desire across the coatings community for shorter length tests that determine coating performance. There is also a desire for a shorter test that allows an estimation of useful coating life in service. Electrochemical impedance spectroscopy (EIS), combined with equivalent circuit (EC) modeling of the EIS response, has been shown to be a powerful approach for characterizing the extent and nature of the corrosion protection provided by coating systems [4, 5]. Recently, efforts were made to correlate results from long-term exposure testing to results from much shorter exposures combined with EIS characterization. Buchheit [6] and later Leggat [7] related EIS data collected on ranges of different coating systems after 24 hours immersion in 0.5M NaCl to the salt spray performance after 168 hours. Although the interpretations were debated [8], the authors found that a general relationship existed between coating system performance in salt spray exposure and the total impedance value extracted from EC modeling of the EIS data. In similar fashion, Bierwagen et al. used an accelerated thermal cycling corrosion test together with EIS data to characterize the performance of a pigmented (SrCrO 4 ) water-borne coating in AA2024-T3 and AA7075-T6 [9]. In this study it was found that the less the change in any EC modeling parameter (pore resistance, metal-coating interface capacitance and coating capacitance) upon cyclic exposure, the better the corrosion resistance. Although the ECs used in these studies were closely related to generally accepted physical interpretations of the corrosion mechanisms for coated metals, there are implicit and unverified assumptions about the nature of the physical and chemical changes in the coating and the damage occurring that go along with use of these models. One central assumption is that the total measured impedance of a coated metal sample is inversely related to the overall corrosion rate of the system. This assumption is questionable for coating systems that do not exhibit a clearly resolved faradaic resistance-dominated impedance at low frequencies. This situation arises when chromate primers are applied to aluminum alloys. To avoid the assumptions associated with the application of EC models to EIS data, Kumar introduced a fresh approach in relating EIS results to long-term exposure test results [10]. In this work, artificial neural networks (ANN) approaches were used to find relationships between impedance magnitude or phase angle EIS data and the salt spray results for a range of conversion coated aluminum alloys. The impedance magnitude and phase angle information were 277
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FINAL REPORT Scientific Understandi
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This report was prepared under cont
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List of Acronyms AES Atomic Emissio
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List of Figures Figure 1.1. Figure
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Figure 1.21. Figure 1.22. Figure 1.
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Figure 3.11. Cathodic polarization
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Figure 4.12. Average Roughness of R
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Figure 5.4. Figures 5.5. Apparatus
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Figure 5.36. Figure 5.37. R paramet
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Figure 6.23. Two commercial samples
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Figure 7.1. a) instrumental configu
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List of Tables Table 1.1. Table 1.2
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Table 6.4. Processing parameters fo
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Keywords 1. Al alloys 2. Non-chroma
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1. Executive Summary This report su
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the role of electrophoresis in inhi
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occurring at low pHs and release at
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were obtained by a post treatment w
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4. G.O. Ilevbare, J.R. Scully, J. Y
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3. Objective The primary objective
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5. Results and Accomplishments In t
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powder, slurried with ultrapure wat
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TCP-coated AA2024-T3. A Kratos AXIS
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X-ray Photoelectron Spectroscopy (X
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Potential (V vs. Ag/AgCl) -0.2 -0.3
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Signal Intensity (counts/s) assessi
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Al (including both Al 0 and Al 3+ c
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TEM or during sample preparation, s
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Potential (V vs. Ag/AgCl) and uncoa
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5.1.4.8 Effects of Aging on the Fil
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Intensity (counts/s) Concentration
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|Z| 0.01Hz (ohm cm 2 ) |Z| 0.01Hz (
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The artificial scratch cell was als
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Raman intensity, a.u. 4000 880 3500
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Figure 1.24. Raman spectra for the
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peak at 520 cm -1 and an intense Cr
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Figure 1.28. Plots of the intensity
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Figure 1.30. (A) Video micrograph o
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The Zr and O signals arise from the
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Figure 1.35. (A) Corrosion potentia
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Table 1.1. Corrosion current (i cor
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additional pitting. The TCP coating
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Figure 1.41. Cr(VI) peak intensity
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Work is ongoing to understand how t
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9. L. Li, D-Y. Kim and G. M. Swain,
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carefully rinsed with DI water, air
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decrease to a net anodic current in
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Potential (mV vs. SCE) Potential (m
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i (A/cm 2 ) Immediately after silic
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Potential (mV vs. SCE) Rp (ohm.cm 2
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2.4.4 In situ AFM Scratching Result
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Figure 2.31. In situ AFM scratching
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(2.3) Figure 2.35. Specie diagram f
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concentration and the silicon to ca
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analysis coupled with XPS revealed
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5.2.4.4 In Situ AFM Scratching Befo
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esults in the formation of silicate
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26. P. Schmutz and G.S. Frankel, J.
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Pr 3+ , Y 3+ showed [12] an order o
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0.1M NaCl solution with varying con
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8.7 through pH 12.6 due to the lowe
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(b) (c) 99
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immersed in Ce 3+ remained bright w
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S phase and dissolution of Al matri
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Corrosion rate, i corr (A/cm 2 ) 6x
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I L (microA) 600 500 400 300 NC (-8
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than that of chromate[35]. Historic
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coupon was immersed with the polish
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5.3.2.4 Results 5.3.2.4.1 Speciatio
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(c) Figure 3.8. Speciation diagram
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E vs. SCE (V) -0.70 -0.75 -0.80 -0.
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E vs. SCE (V) 1000 rpm E vs. SCE (V
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Chemical quantification showed a me
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(a) (b) Figure 3.15. (a) (top) SEM
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E vs. SCE (V) E vs. SCE (V) E vs. S
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-Z" (ohm) -Z" (ohm) -Z" (ohm) -Z" (
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(Figure 3.8b). However, no effect o
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CPS CPS CPS x 2 14 10 12 10 8 6 4 2
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CPS CPS 100 95 90 85 80 75 70 x 10
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I k L 0. 2 1 2 AnFC B D 2 3 O 1
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i -800 (A/cm 2 ) 10 -4 NaCl NaCl+5
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Corrosion rate ( 1/R p ) ohm -1 cm
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particles compared to zinc-free sol
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and Zn bentonite compounds have red
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2) Deoxidizing for 3 minutes in an
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Scintag (now ThermoARL) Pad-V TM an
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Table 3.5. Characterization of bent
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Zn 2+ cation release (meq/100g) Pr
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(a) (b) (c) Figure 3.33. (a) An exp
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|Z| (ohm) Phase angle (degrees) 5.3
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|Z| at 0.01 Hz (ohm.cm 2 ) Pore Res
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|Z| at 0.01 Hz (ohm.cm 2 ) |Z| at 0
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pigmented coatings exhibited partia
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5.3.3.6 Conclusions 1. Exchange ben
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39. M. Mahdavian and M. M. Attar, P
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100. F.Liebau, Structural Chemistry
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of the coated sample, which is tigh
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Lubricant Blue (Struers) was used f
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good grip on the dolly, the equipme
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Pressure (kPa) r (mm) Pressure x Ra
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Pressure x Radius (kN/m) plateau bu
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Pressure x Radius (kN/m) Pxr (KN/m)
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Average Roughness (m) In contrast,
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Adhesion Strength (J/m 2 ) PVB PVB
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Pressure (kPa) Constant Infusion up
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(a) (b) (c) (d) Figure 4.19. Coatin
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Min. Potential (V vs SHE) Min. Pote
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Pressure (kPa) exposure in hot wate
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Engineering Stress (MPa) slope of t
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Adhesion Strength (J/m 2 ) ASTM D33
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Pressure (kPa) Pressure (kPa) Radiu
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Adhesion Strength (J/m 2 ) Pressure
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Table 4.7. Adhesion Strength values
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Non-Cl./Deox. No CC Cleaned/Deox. N
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5.4.5 Conclusions and Implications
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5.5 Task 5: Inhibitor Activation an
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solution for equilibration at contr
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Table 5.2. Techniques applied to sp
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The capacitance was determined by E
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combination with zinc molybdate, a
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Concentration, mmol / L Final pH te
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Alkaline affects praseodymium solub
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MoO 4 2- ) inhibition to the system
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Zinc molybdate is reported to be si
Page 259 and 260: The presence of a salt that has no
Page 261 and 262: This approach yields two figures of
Page 263 and 264: Inhibitor mapping of the Hentzen 16
Page 265 and 266: The molybdate loss in the strontium
Page 267 and 268: The capacitance dC is given by 0 (
Page 269 and 270: 2 C( r, t) C( r )[1 r 2 exp( D nt
Page 271 and 272: -thea (degree) logIZI (Ohm-Cm 2 ) P
Page 273 and 274: Capacitance (F) respectively. The c
Page 275 and 276: Capacitance (F) Weight gain (g) For
Page 277 and 278: Normalized Capacitance Change Norma
Page 279 and 280: Potential V (Ag/AgCl) Corrosion rat
Page 281 and 282: 5.5.4.7 Nanopore structure characte
Page 283 and 284: Normaalized Transport Rate (g/m^2_d
Page 285 and 286: S-Parameter S-Parameter Penetration
Page 287 and 288: S-Parameter S-Parameter Penetration
Page 289 and 290: R-parameter R-parameter Penetration
Page 291 and 292: 5. T. M. Letcher, “Thermodynamics
Page 293 and 294: pigment of CaSiO 3 with initial pH
Page 295 and 296: allowed a comparison of the differe
Page 297 and 298: The solution resistance (R sol ) va
Page 299 and 300: Theta [degrees] theta |Z| [ohm] 10
Page 301 and 302: C [F/cm2] Rcorr [ohm*cm2] 7075-AHN
Page 303 and 304: C [F/cm 2 ] Rcorr [ohm*cm 2 ] Rcorr
Page 305 and 306: Visual TTF [hours] Table 6.2. Param
Page 307 and 308: of Metallast pre-treatment, which h
Page 309: Prediction of the TTF obtained by A
Page 313 and 314: 5.6.2.2.1 Coating system descriptio
Page 315 and 316: Table 6.4. Processing parameters fo
Page 317 and 318: population of total TTF vectors th
Page 319 and 320: components of the impedance and the
Page 321 and 322: Figure 6.17. EIS spectra for sample
Page 323 and 324: Figure 6.18. Kaplan-Meier survival
Page 325 and 326: Maximum c i range Maximum ci range
Page 327 and 328: The type and number of input neuron
Page 329 and 330: Predicted TTF The BFM method, intro
Page 331 and 332: The most significant variables to i
Page 333 and 334: 5.6.3 Characterization of Pigment D
Page 335 and 336: of sputtering gold and carbon paint
Page 337 and 338: Figure 6.26. Cross-sectional view o
Page 339 and 340: Figure 6.28. EDX maps of primer cro
Page 341 and 342: Figure 6.31. EDX maps of primer cro
Page 343 and 344: In Figure 6.34, Ca and Si existed a
Page 345 and 346: Table 6.8. Average percentage resid
Page 347 and 348: strictly limited due to the barrier
Page 349 and 350: Figure 6.37. Coating systems in det
Page 351 and 352: Each corrosion volume of scribed ar
Page 353 and 354: Corrosion Area (mm 2 ) 1200 1000 80
Page 355 and 356: Corrosion Area (mm 2 ) Corrosion Ra
Page 357 and 358: Corrosion Rate (mm/yr) Corrosion Vo
Page 359 and 360: Corrosion Area (mm 2 ) corrosion ra
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corrosion rate (mm/yr) Corrosion Vo
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Corrosion Volume (mm/yr) Corrosion
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ate, PPG CA7233 coated samples had
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Appendix 6B Table 6B.1. Corrosion v
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Table 6B.3. Corrosion rate of sampl
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Table 6B.5. Corrosion area of sampl
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5.7. Task 7: Characterization of Lo
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at 65C. After using DI water to rin
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Transmission Mode Conduct EIS measu
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Cdl(F/cm 2 ) Rp(.cm 2 ) relatively
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pit bottom area (cm 2 ) pit bottom
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2days 2days 1mm 1mm 7days 7days Pit
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(a) (b) Si Si O Al Na Ca K Si Al-Cu
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Pit 1 and pit 2 as shown in Figure
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In these experiments, Deft primers
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For the case of as-deposited thin f
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3. L. Balazs, Physica E, 54, 1183-1
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and subsequently re-oxidized in two
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not represent true adhesion strengt
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• The pit morphology in 0.5 M NaC
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Appendix 2. List of Scientific/Tech
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“The Secret Life of Chromate Free
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