Final Report - Strategic Environmental Research and Development ...

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La and Zn bentonites showed better performance compared to the other exchange bentonites when incorporated into epoxy coatings with total impedance magnitude in the same order as the SrCrO 4 standard. The presence of TiO 2 solids increased the permeability of the epoxy resin and impedance suggested strong water uptake by the epoxy coatings, enabling La 3+ and Zn 2+ cation release and promoting interfacial passivity. EIS measurements showed that PVA behaved like a gel and exhibited very low barrier properties. Bentonites did not passivate the interface suggesting that not enough inhibitor cation was released to completely passivate the surface. EIS on the PVB coatings on the other hand suggested no water uptake due to which the inhibitor cation was not released. Bentonites degraded the barrier properties of PVB and provided no inhibition. Salt spray exposures showed that Zn bentonite incorporated into PVB performed relatively better compared to the neat PVB and other pigmented bentonites with very few blisters. La bentonite incorporated in epoxy coatings showed no attack around the scribe compared to other pigmented epoxy coatings. However, all the pigmented epoxy coatings showed partial scribe protection. Task 4. Paint adhesion strength and mechanism. The blister test (BT) was developed in this work to study the adhesion of paint to metal surfaces. The BT is a very versatile technique that allows calculation of stress at fracture and adhesion strength. The adhesion strength results from the BT are reproducible and help to discern regarding different surface treatments. Roughness degree and surface topography are very important factors for adhesion strength of PVB to AA2024-T3. Adhesion strength increases with roughness and surface area due to a larger interaction in the primer/substrate interface. Randomly abraded samples have higher adhesion strength than random abraded samples. Numerous approaches were tested to sample adhesion strength using the BT after adhesion degradation of the interface. However, no adhesion strength degradation was found. Galvanic coupling of SS316 fasteners to AA2024-T3 activates the underlying metal due to the high cathodic current on the fastener. The minimum potential along the scribe tends to decrease with increased galvanic coupling owing to activation of the aluminum alloy. This contradicts the typical assumptions of galvanic coupling. The galvanic interaction and coating degradation varies with different fastener materials according to SS316 > Ti 6-4 > AA2024-T3 No fastener. Other adhesion test techniques were investigated and found to be inferior to the BT. The pull-off test does not produce adhesive failure across the whole interface so the results do 362
not represent true adhesion strength. The tape test is very qualitative and does not discern the performance of different coating systems. In contrast, the BT produces adhesive failure of the primer studied, is very reproducible and is able to show adhesion strength difference between different coating systems. Conversion coating treatment improves adhesion strength of acetoacetate and epoxy coatings to AA2024-T3. Cleaning and deoxidizing improves adhesion of acetoacetate samples for all conversion coatings except for chromate conversion coating. For epoxy coatings the addition of the cleaning/deoxidizing step improves the adhesion strength of the chromate conversion coating samples, but no effect is noticeable for titania-based conversion coating and TCP. Si contamination seems to affect deleteriously the adhesion strength and resistance of coating systems to osmotic blistering. Task 5. Inhibitor activation and transport in the primer layer. Corrosion inhibitive pigments have substantially increased solubilities in strong electrolytes such as salt water. The magnitude of the solubility enhancement increases with increasing charge of the soluble inhibitor complex. Exposure to air can increase the solubility of inhibitive pigments both through acidification and carbonation reactions. Some existing chromate free inhibitive pigments are formulated with reactive copigments or complexing agents to form and stabilize soluble species in response to hydration. In one instance, a praseodymium hydroxide inhibitor was determined to form both anionic and cationic sulfate complexes through reaction with a calcium sulfate additive. Corrosion inhibitor complexes can be transported through primer films in response to electric fields. The state of charge on the soluble complex (anionic or cationic) is expected to determine its electromigration to either anodic or cathodic corrosion sites. Based on several experiments, the transport and release rates of corrosion inhibitors through and from primer samples are low. Attempts to detect a passivation response by AA2024-T6 immersed in a bulk primer chip slurry were unsuccessful. Aerospace primers are relatively permeable to water vapor. A water – reducible primer was found to transmit water vapor at high rates for an extended cure interval compared to solvent base primers. The rate of water vapor transmission is isotropic, with in-plane diffusivity values approximately 3x greater than through-plane values. Aerospace primers were found to have a fine structure characterized by a dense layer at the air and substrate interface, encapsulating a central nanoporous layer. This fine structure is believed to account for the isotropic transmission of water vapor and the sluggish transport and release of inhibitors from primer surfaces. 363
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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
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The presence of a salt that has no
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This approach yields two figures of
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Inhibitor mapping of the Hentzen 16
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The molybdate loss in the strontium
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The capacitance dC is given by 0 (
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2 C( r, t) C( r )[1 r 2 exp( D nt
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-thea (degree) logIZI (Ohm-Cm 2 ) P
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Capacitance (F) respectively. The c
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Capacitance (F) Weight gain (g) For
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Normalized Capacitance Change Norma
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Potential V (Ag/AgCl) Corrosion rat
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5.5.4.7 Nanopore structure characte
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Normaalized Transport Rate (g/m^2_d
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S-Parameter S-Parameter Penetration
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S-Parameter S-Parameter Penetration
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R-parameter R-parameter Penetration
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5. T. M. Letcher, “Thermodynamics
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pigment of CaSiO 3 with initial pH
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allowed a comparison of the differe
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The solution resistance (R sol ) va
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Theta [degrees] theta |Z| [ohm] 10
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C [F/cm2] Rcorr [ohm*cm2] 7075-AHN
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C [F/cm 2 ] Rcorr [ohm*cm 2 ] Rcorr
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Visual TTF [hours] Table 6.2. Param
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of Metallast pre-treatment, which h
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Prediction of the TTF obtained by A
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5.6.2 Electrochemical Impedance Spe
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5.6.2.2.1 Coating system descriptio
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Table 6.4. Processing parameters fo
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population of total TTF vectors th
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components of the impedance and the
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Figure 6.17. EIS spectra for sample
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Figure 6.18. Kaplan-Meier survival
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Maximum c i range Maximum ci range
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The type and number of input neuron
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Predicted TTF The BFM method, intro
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The most significant variables to i
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5.6.3 Characterization of Pigment D
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of sputtering gold and carbon paint
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Figure 6.26. Cross-sectional view o
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Figure 6.28. EDX maps of primer cro
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Figure 6.31. EDX maps of primer cro
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In Figure 6.34, Ca and Si existed a
Page 345 and 346: Table 6.8. Average percentage resid
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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
Page 361 and 362: corrosion rate (mm/yr) Corrosion Vo
Page 363 and 364: Corrosion Volume (mm/yr) Corrosion
Page 365 and 366: ate, PPG CA7233 coated samples had
Page 367 and 368: Appendix 6B Table 6B.1. Corrosion v
Page 369 and 370: Table 6B.3. Corrosion rate of sampl
Page 371 and 372: Table 6B.5. Corrosion area of sampl
Page 373 and 374: 5.7. Task 7: Characterization of Lo
Page 375 and 376: at 65C. After using DI water to rin
Page 377 and 378: Transmission Mode Conduct EIS measu
Page 379 and 380: Cdl(F/cm 2 ) Rp(.cm 2 ) relatively
Page 381 and 382: pit bottom area (cm 2 ) pit bottom
Page 383 and 384: 2days 2days 1mm 1mm 7days 7days Pit
Page 385 and 386: (a) (b) Si Si O Al Na Ca K Si Al-Cu
Page 387 and 388: Pit 1 and pit 2 as shown in Figure
Page 389 and 390: In these experiments, Deft primers
Page 391 and 392: For the case of as-deposited thin f
Page 393 and 394: 3. L. Balazs, Physica E, 54, 1183-1
Page 395: and subsequently re-oxidized in two
Page 399 and 400: • The pit morphology in 0.5 M NaC
Page 401 and 402: Appendix 2. List of Scientific/Tech
Page 403 and 404: “The Secret Life of Chromate Free
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