EMPLOYING ELECTROCHEMICAL IMPEDANCE IN … EIS in Corrosion (New).pdfEMPLOYING ELECTROCHEMICAL...
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Strictly confidential - proprietary information of HALOX www.halox.com EMPLOYING ELECTROCHEMICAL IMPEDANCE IN PREDICTING CORROSION EVENTS Dr. Tony Gichuhi
Transcript of EMPLOYING ELECTROCHEMICAL IMPEDANCE IN … EIS in Corrosion (New).pdfEMPLOYING ELECTROCHEMICAL...
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EMPLOYING ELECTROCHEMICAL IMPEDANCE IN PREDICTING
CORROSION EVENTSDr. Tony Gichuhi
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HALOX Overview
Objectives Challenges Corrosion Correlations EIS Background
» Principles – Equipment – Modeling» Interpretation – Why EIS?
Direct-to-Metal Coating Screening Study Data Comparison EIS Prediction Conclusion
Substrate
Coating
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Objectives
EIS Test Can we use EIS to predict
coating performance? Find correlation between EIS
response and Salt Spray and Prohesion resultsDoes coating deterioration via
EIS mimic cabinet test results? Can we shorten screening
time?
Cabinet Tests Salt Spray
»Static test» 5% NaCl»Constant 35°C, 100% RH
Prohesion»Cyclic test»1 hr salt mist at ambient &
1 hr drying at 35°C» 0.05% NaCl, 0.35%
(NH4)2SO4
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Challenges
Cd plating vs. Zn plating on
automotive parts
Painted CRS vs. Electro-galvanized
steel
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Challenges
- Cabinet tests- Neutral salt spray considered industry standard for
over 50 years- Neutral salt spray has been the achilles heel for W/B
coatings breakthroughs- Can sometimes take too much time- Many use neutral salt spray as quality control to
qualify DTM coatings designed to provide barrier properties, good adhesion, hardness, toughness, chemical resistance, etc
- Do not always tell us why a coating failed or passed
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Challenges
- ASTM B-117 Salt Fog- How many hours of salt spray is equivalent to 1 or 10
yrs real world corrosion?
Cyclic Prohesion Xenon Arc
Cyclic Salt Spray Condensation
Humidity QUV
Prohesion Volvo outdoor SCAB test(Simulated Corrosion Atmospheric Breakdown)
Salt Spray SAE J2334 Cosmetic Corrosion Lab Test(80 cycles = 5 yrs on vehicle testing)
Resistance to SO2(Kesternich)
GMW14872 Cyclic Accelerated Corrosion Testing(Formerly GM9540P 60 cycles = 10 years)
Immersion CASS (Copper Accelerated Acetic Acid Salt Spray)
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Corrosion Correlation
Reference: John Repp – Corrpro Companies, Inc - US Army Corrosion Summit 2002
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EIS Background
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EIS Principles
- Rapidly provides info on physical and electro chemical behavior of coatings
- Monitors permeability of electrolyte through ionic conduction
- Good wet adhesion is paramount for good protection
- Changes in coating resistance correlate to penetration of ionic species
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EIS Equipment
Gamry PC3 with Multiplexer for 8 channel SCE Reference Electrode
Flat cell with exposed area about 22.56 cm2 Graphite Counter Electrode
Electrolyte: 5% NaCl or 0.05% NaCl/0.35% (NH4)2SO4 Cold Rolled Steel Working Electrode
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Equivalent Circuit Modeling
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EIS Interpretation
Reference: David Dubowik & Greg Ross – Air Products
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EIS Response (Defects vs. No Defects)
Reference: Electrochemical Impedance Spectroscopy as a Method for Quality Control of Mirror Coatings in Applications
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Why EIS?
For paints/coatings on a metal substrate, EIS acts as a very sensitive quantitative detector of changes in both the coating and the metal substrate during long-term exposure to an electrolyte.
Changes in the coating will be apparent in EIS long before any visible damage occurs.
Apply stress to the sample to cause it to fail. The stress should simulate the service environment, which could be weathering or a specific chemical attack, e.g., seawater.
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Why EIS?
Measure an EIS curve immediately upon exposure and periodically thereafter until the test is complete. Changes in the EIS curve with time reflect changes in the
paint or the metal substrate. These changes are accelerated by the artificial stress. Fit an equivalent circuit to the data to determine the value
of the circuit elements. Evaluate the data to select an “indicator” of coating
deterioration. The indicator may be Ztotal, capacitance, pore resistance, etc. In many cases, Z at low frequency is satisfactory.
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DTM SCREENING STUDY
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Screening Protocol
Salt Spray(ASTM B-117)
Prohesion(ASTM G85)
EIS(ASTM G106)
24, 48, 72, 168 and 504 hrs
504 hrs Initial, 24, 48, 72 and 168 hrs
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Screening Parameters
All coating DFTs were between 2.5-3.0 mils All coatings were air dried for 7 days before testing Substrate: Cold rolled steel (ACT matte finish) Panels were tested in duplicate No corrosion inhibitors were incorporated Recommended flash rust inhibitors were added
CRS
DTM coating 2.5-3.0 mils
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DTM FORMULATION MATRIX
Sys Description Type pH KU ICI Wt. Solids
Vol. Solids VOC
A Maincote HG-86 Acrylic Gloss DTM 9.22 59.4 0.3 46.28 34.82 222.38
B NeoCryl XK-87 High Solids Styrene Acrylic 7.46 63.1 0.9 56.50 43.08 158.07
C Maincote HG-54D Acrylic Dispersion 9.26 93.0 0.7 41.12 28.02 356.44
D HexionAquamac 705 Acrylic DTM 8.79 68.6 0.6 47.17 36.69 117.67
E Hexion Aquamac 580 Vinyl Acrylic DTM 7.83 64.3 0.8 TBD TBD TBD
F EPS 2540 High Gloss Acrylic 8.87 67.9 0.8 44.69 33.71 211.79
G NeoCryl A-6099 High Gloss DTM 9.46 57.6 1.4 40.64 28.90 257.86
H NeoCryl XK-98 Acrylic DTM Enamel 8.12 79.3 1.4 43.93 41.92 29.82
I BASFJoncryl 1522 Acrylic Latex SEH-0183D 8.43 51.5 0.5 45.57 37.36 <240
J Avanse MV-100 High Gloss Acrylic DTM 9.38 80.4 0.3 46.30 34.94 103
K Sher-Cryl HPA High Performance Acrylic Gloss 9.25 88.9 1.4 ~51 ~38.5 <200
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Bode Plots for DTM PaintsInitial scan
Rank Sys
1 F2 I3 G4 J5 K6 E7 A8 B9 D10 C11 H
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Bode Plots for DTM PaintsAfter 24 hrs
Rank Sys
1 I2 F3 G4 J5 K6 A7 E8 B9 D10 C11 H
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Bode Plots for DTM PaintsAfter 48 hrs
Rank Sys
1 I2 F3 G4 J5 A6 E7 K8 B9 D10 C11 H
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Bode Plots for DTM PaintsAfter 168 hrs
Rank Sys
1 F2 A3 K4 I5 E6 B7 J8 G9 C10 D11 H
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Bode Plots for DTM PaintsBest Systems Initially and after 168 hrs
INITIAL SCAN
AFTER 168 hrs
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Bode plots for overall best system:Initial - 24 – 48 – 168 hrs
Best System
F
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Nyquist plots for overall best system:Initial – 24 – 48 – 168 hrs
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Cabinet Test ResultsNSS 504 hrs
F A K I
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Cabinet Test ResultsProhesion 504 hrs
F A K I
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Corrosion ProgressionSalt Spray: 72, 168, 504 hrs
F F F
72 hrs 168 hrs 504 hrs
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Correlation
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Total Impedance [Z]
1 10 100 1000 10000 100000 1000000 10000000 100000000 1E+09
HPA
EPS
AQ 705
MV 100
HG 86
XK 87
JC 1522
NC 6099
HG 54-D
AQ 580
XK 98
Ohms
DTM Paint System
Total Impedance Z
168 hrs
24 hrs
Initial
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Total Impedance [Z]
1
10
100
1000
10000
100000
1000000
10000000
100000000
1E+09
HPA EPS AQ 705 MV 100 HG 86 XK 87 JC 1522 NC 6099 HG 54-D AQ 580 XK 98
Ohm
s
DTM Paint System
Total Impedance ZInitial
24 hrs
168 hrs
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Best DTM Coatings
1
10
100
1000
10000
100000
1000000
10000000
100000000
1E+09
HPA EPS HG 86 JC 1522
Initial
24 hrs
168 hrs
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Summary
EIS RESULTS(ZTOT)
CABINET RESULTS(504 hrs)
Rank Initial 24 hrs 48 hrs 168 hrs NSS Prohesion
Best F I I F F F
2 I F F A A A
3 G G G K K K
4 J J J I I I
Worst H H H H H H
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Conclusion
- EIS predicted the leadingand worst coatings in salt spray within the first 24-168 hrs
- EIS response also tracked well with Prohesion
- EIS accurately predicted which coatings would perform the best long-term
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THANK YOU FOR YOUR ATTENTION
