Employing Electrochemical Impedance in Predicting ... - Halox

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EMPLOYING ELECTROCHEMICAL
IMPEDANCE IN PREDICTING
CORROSION EVENTS
Dr. Tony Gichuhi
Strictly confidential - proprietary information of HALOX

HALOX Overview
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• Objectives
• Challenges
• Corrosion Correlations
• EIS Background
» Principles – Equipment – Modeling
» Interpretation – Why EIS?
• Direct-to-Metal Coating Screening Study
• Data Comparison
• EIS Prediction
• Conclusion
Coating
Substrate
2

Objectives
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EIS Test
• Can we use EIS to predict
coating performance?
• Find correlation between EIS
response and Salt Spray and
Prohesion results
•Does 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%
(NH 4 ) 2 SO 4
3

Challenges
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Cd plating vs. Zn
plating on
automotive parts
Painted CRS vs.
Electro-galvanized
steel
4

Challenges
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- 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
5

Challenges
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- ASTM B-117 Salt Fog
- How many hours of salt spray is equivalent to 1 or 10
yrs real world corrosion?
Cyclic Prohesion
Cyclic Salt Spray
Humidity
Prohesion
Salt Spray
Resistance to SO 2
(Kesternich)
Immersion
Xenon Arc
Condensation
QUV
Volvo outdoor SCAB test
(Simulated Corrosion Atmospheric Breakdown)
SAE J2334 Cosmetic Corrosion Lab Test
(80 cycles = 5 yrs on vehicle testing)
GMW14872 Cyclic Accelerated Corrosion Testing
(Formerly GM9540P 60 cycles = 10 years)
CASS (Copper Accelerated Acetic Acid Salt Spray)
6

Corrosion Correlation
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Reference: John Repp – Corrpro Companies, Inc - US Army Corrosion Summit 2002
7

EIS Background
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8

EIS Principles
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- 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
9

EIS Equipment
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Gamry PC3 with Multiplexer for 8 channel
Flat cell with exposed area about 22.56 cm 2
Electrolyte: 5% NaCl or 0.05% NaCl/0.35% (NH 4 ) 2 SO 4
SCE Reference Electrode
Graphite Counter Electrode
Cold Rolled Steel Working Electrode
10

Equivalent Circuit Modeling
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11

EIS Interpretation
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Reference: David Dubowik & Greg Ross – Air Products
12

EIS Response (Defects vs. No Defects)
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13
Reference: Electrochemical Impedance Spectroscopy as a Method for Quality Control of Mirror Coatings in Applications

Why EIS?
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• 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.
14

Why EIS?
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• 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 Z total , capacitance,
pore resistance, etc.
• In many cases, Z at low frequency is satisfactory.
15

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DTM SCREENING STUDY
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Screening Protocol
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Salt Spray
(ASTM B-117)
24, 48, 72, 168
and 504 hrs
Prohesion
(ASTM G85)
EIS
(ASTM G106)
504 hrs Initial, 24, 48, 72
and 168 hrs
17

Screening Parameters
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• 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
DTM coating 2.5-3.0 mils
CRS
18

DTM FORMULATION MATRIX
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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
Hexion
Aquamac 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
I BASFJoncryl 1522
J
K
Avanse MV-100
Sher-Cryl HPA
Acrylic DTM
Enamel
Acrylic Latex
SEH-0183D
High Gloss Acrylic
DTM
High Performance
Acrylic Gloss
8.12 79.3 1.4 43.93 41.92 29.82
8.43 51.5 0.5 45.57 37.36

Bode Plots for DTM Paints
Initial scan
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Rank
Sys
1 F
2 I
3 G
4 J
5 K
6 E
7 A
8 B
9 D
10 C
11 H
20

Bode Plots for DTM Paints
After 24 hrs
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Rank
Sys
1 I
2 F
3 G
4 J
5 K
6 A
7 E
8 B
9 D
10 C
11 H
21

Bode Plots for DTM Paints
After 48 hrs
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Rank
Sys
1 I
2 F
3 G
4 J
5 A
6 E
7 K
8 B
9 D
10 C
11 H
22

Bode Plots for DTM Paints
After 168 hrs
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Rank
Sys
1 F
2 A
3 K
4 I
5 E
6 B
7 J
8 G
9 C
10 D
11 H
23

Bode Plots for DTM Paints
Best Systems Initially and after 168 hrs
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AFTER 168 hrs
INITIAL SCAN
24

Bode plots for overall best system:
Initial - 24 – 48 – 168 hrs
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Best
System
F
25

Nyquist plots for overall best system:
Initial – 24 – 48 – 168 hrs
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26

Cabinet Test Results
NSS 504 hrs
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F A K I
27

Cabinet Test Results
Prohesion 504 hrs
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F A K I
28

Corrosion Progression
Salt Spray: 72, 168, 504 hrs
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F F F
29
72 hrs 168 hrs 504 hrs

Correlation
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30

Total Impedance [Z]
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Total Impedance Z
XK 98
AQ 580
168 hrs
24 hrs
Initial
HG 54-D
NC 6099
JC 1522
DTM Paint System
XK 87
HG 86
MV 100
AQ 705
EPS
HPA
1 10 100 1000 10000 100000 1000000 10000000 100000000 1E+09
Ohms
31

Total Impedance [Z]
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Total Impedance Z
Initial
24 hrs
168 hrs
Ohms
1E+09
100000000
10000000
1000000
100000
10000
1000
100
10
1
HPA EPS AQ 705 MV 100 HG 86 XK 87 JC 1522 NC 6099 HG 54-D AQ 580 XK 98
DTM Paint System
32

Best DTM Coatings
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1E+09
100000000
10000000
1000000
100000
10000
Initial
24 hrs
168 hrs
1000
100
10
1
HPA EPS HG 86 JC 1522
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Summary
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EIS RESULTS
(Z TOT )
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
34

Conclusion
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- EIS predicted the leading
and 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
35

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THANK YOU FOR YOUR ATTENTION
Strictly confidential - proprietary information of HALOX