Transcript Slide 1

Advanced sol-gel coating for
corrosion protective of
aerospace aluminium alloys
John Colreavy, Brendan Duffy, Rajath Varma
CREST, Dublin Institute of Technology
Summary
• Sol-Gel: History, Chemistry, Properties
• Common Silane Precursors
• Current Research in Protective Coatings
• CREST Research
–Incorporating Organometallic Precursors
–Incorporating Amine Chemistry
–Novel Inhibitor Incorporation
Sol-Gel: History
1846
1864
1939
1951
1959
1964
1965
1974
1981
1984
1984
1989
1989
1992
1996
1996
2000
Silica glass via silica acid esters
Coined the term “sol gel”
First patent for coatings (SiO2 and TiO2)
Silica sols patented
Car rearview mirror (TiO2-SiO2-TiO2).
Antireflection coatings (Mirogard)
Ormosil clad UV-fiber optics
ZrO2-SiO2 refractory fiber
Introduction of Regal coated-abrasive product
Inorganic/organic hybrids (Ormosils)
Organic-inorganic hybrids
Window-glass antireflection coatings (Amiran) and
coatings for computer monitors (Conturan)
Protective coatings for steel
Automotive water-repellent coatings
UV-shielding automotive coatings
Inorganic/organic hybrids (ZrO2-SiO2) for metal
alloys
Glass encapsulated UV absorbers for sunscreen
lotions
Ebelmen
Graham
Schott Glaswerke
Dupont
Deutsche Spezialglas AG
Deutsche Spezialglas AG
Schott Glaswerke
3M
3M
Schmidt
Hebrew University
Schott Glaswerke
Nisshin Steel
Central Glass
Asahi Glass
Boeing
Sol Gel Technologies Ltd.
(Israel)
Sol-Gel: Chemistry
Sol-Gel: Chemistry
• Main reactions of hydrolysis-polycondensation which take place
with organically modified alkoxides are the following:
R'
Si (OR)3
(RO)2
(RO)2
R'
Si OH
R'
Si OH
[H+]/[OH-]
H2O
R'
RO Si (OR)2
R'
HO Si (OR)2
(RO)2
[H+]/[OH-]
R'
Si OH
ROH
(1)
(RO)2
R'
R'
Si O Si (OR)2
ROH
(2)
(RO)2
R'
R'
Si O Si (OR)2
H2O
(3)
[H+]/[OH-]
Sol-Gel: Properties
Sol-Gel: Properties
P. Judenstein and C. Sanchez, J. Mater. Chem., 1996, 6, 511
Common Silane Precursors
C. Sanchez et al., J. Mater. Chem., 2005, 15, 3559–3592
Current Research in Protective Coatings
• Within the aerospace industry, sol-gel chemistry has attracted
considerable attention:
– Boeing has developed an environmentally compliant sol-gel product
called Boegel® based on epoxysilane and zirconium chemistry, to
replace carcinogenic chromium conversion coatings as an adhesion
promoter on aluminium alloys.
– EADS (Airbus (Fr)), in 2007, was granted a patent for a sol-gel coating
based on epoxysilane and zirconium chemistry for corrosion protection
of Aluminium.
– EADS (Munich) has used this patented chemistry to study the
performance of sol-gel coatings on leading edges against rain erosion,
as part of the FP6 Project “NAPOLYDE”
– EADS (Munich) is a leading partner in an FP6 Project
“MULTIPROTECT”, which is investigating sol-gels as alternatives to
heavy metal coatings.
Protective Coating Technology
• ORMOCERS® developed by FhG ISC
Zheludkevich et al. J. Mater. Chem., 2005, 15, 5099–5111
Aerospace Coatings: Boe-Gel System
OCH3
O
H2C
CH
CH2 O
CH2 CH2 CH2 Si
Zirconium Alkoxide
OCH3
US Patents:
OCH3
5,869,141
Organic
Resin
NH2
O
Si
Sol-Gel
Film
30-200nm
Si
O
Si
O
O
Zr
O
O
O
O
O
Zr
Zr
Si
O
O
Si
Zr
Si
Zr
Si
Zr
O
O
6,077,885
O
O
O
5,939,197
Zr
O
Condensation
O
Zr
Zr
O
HO
Si
O
O
Zr
Si
Zr
Si
O
Si
O
Si
O
O
Si
Metal
Substrate
Si
O
O
NH2
O
Zr
Zr
NH2
O
O
O
NH2
Hydrolysis
NH2
• Issue: Protective coating but no corrosion inhibition
Incorporating Organometallic Precursors
Methacrylic Acid (MAAH)
Acetic Acid (AcOH)
2,2’ Bipyridyl (BP)
Acetylacetone (Acac)
PrO
Zr
PrO
HO
OPr
OPr
Zr (OPr)4
O
PrO
C
+
Isobutyric Acid (IBA)
=O
=C
=H
= Zr
=N
R
+
PrO
O
Acid ligand
R
Zr
O
Hydrolysable
Protected
Zr(OPr)2(ligand)
Neutral Salt Spray Study ( 1 week)
MAPTMS/Zr (MAAH)
MAPTMS/Zr (Acac)
MAPTMS/Zr (AcOH)
MAPTMS/Zr (BP)
Corrosion protection:
MAPTMS/Zr (IBA)
MAPTMS ( 48 Hrs)
MAAH=AcOH>IBA>Acac > BP > no Zr
Incorporating Amine Chemistry
PrO
O
OPr
Zr
+
OPr
PrO
O
PrO
Zr
PrO
O
O
b-Diketone (acac)
NH2
NH2
Zr
PrO
HO
OPr
PrO
C
+
OPr
O
PrO
NH2
Zr
PrO
O
Amine rich carboxylic acid
O
NH2
Surface Topography
1m
1m
MAPTMS
MAPTMS/Zr/acac
MAPTMS/Zr/DABA
Thermal Stability
30
Heatflow (mW)
25
20
15
10
0
-5
195
130
5
230
MAPTMS /Zr/DABA
MAPTMS /Zr/acac
MAPTMS
-10
50
100
150
200
Temperature(deg cel)
250
300
EIS Data
8
7
6
2
Log|Z| (Ohm cm )
2
Log|Z| (Ohm )cm
MAPTMS
MAPTMS/Zr/acac
MAPTMS/Zr/DABA
7
Non-Porous
6
5
4
Porous
3
5
4
3
2
2
1
1
0
0
-100
-100
-90
-90
-80
-80
-70
-70
Phase angle(deg)
Phase angle(deg)
8
MAPTMS
MAPTMS/Zr/acac
MAPTMS/Zr/DABA
-60
-50
-40
-30
-60
-50
-40
-30
-20
-20
-10
-10
0
0
-2
-1
0
1
2
3
Log Frequency (Hz)
4
5
-2
-1
0
1
2
3
Log Frequency (Hz)
4
5
29Si-NMR
Species
Notation
T
0
T
1
R-Si-(OMe)OH2
T
2
R-Si-(OH)3
T
3
R-Si-(OMe)3
R-Si-(OMe)2OH
Notation
Chemical
shift
(ppm,
±0.1)
No. of OH groups
-42.3
0
-41.3
0
-40.6
0
T
0
0
-40.1
0
R-Si-(OMe)2-OSi
T10
-49.9
R-Si-(OMe)OH-OSi
T11
-50.5
R-Si-(OH)2-OSi
T12
-49.3
R-Si-(OMe)-(OSi)2
-59.1
R-Si-(OH)-(OSi)2
T21
-58.5
R-Si(OSi)3
T30
-67.4
No. of Si–O-Si linkages
R'
MeO Si OMe
OMe
=
T
0
0
Following Sol-Gel formation with 29Si-NMR
•
The products of condensation are found at values more
negative than those of the alkoxides.
T
0
0
R'
MeO Si OMe
OMe
T12
R'
HO Si O Si
OH
1
2
T
R'
HO Si O Si
O
Si
T30
R'
Si O Si O Si
O
Si
ppm
-40
-50
Condensation
-60
-70
Following Sol-Gel formation with 29Si-NMR
•
Example:
MAPTMS/Zr/acac
T1
T1
MAPTMS+Zr-acac
pre-hydrolysed MAPTMS T0
0
-20
2
0
T2 T3
1
T2
0
1
0
-40
-60
-80
-100
ppm
•
The presence of the Zr speeds up the condensation process
29Si
NMR Analysis
1
T2 T2
T0
sol gel-MAPTMS
T0
0
1
T3
3-D Structure poorly forms
0
0
precursor-MAPTMS
0
-20
3-D Structure strongly forms
-40
-60
-80
-100
ppm
0
MAPTMS/Zr/acac
T1
2
T1 T2
MAPTMS+Zr-acac
pre-hydrolysed MAPTMS T0
0
-20
0
T2 T3
1
0
MAPTMS/Zr/DABA
1
T1
MAPTMS+Zr-DABA
T1
0
pre-hydrolysed MAPTMS
-40
-60
ppm
-80
-100
0
-20
T0
1
T2 T 0
3
2
0
-40
-60
ppm
-80
-100
Salt Spray Exposure
Salt spray results plots for various sol
gel coatings:
(A) Bare AA2024 after 24 Hours
(B) MAPTMS for 48 hrs and
(C) MAPTMS/Zr/acac
(D) MAPTMS/Zr/DABA for 1 week
Current Strategy in CREST
• Sol-gel coatings showing most promise involve Zirconium
• Improved pH resistance
• Functionalised surface improving topcoat adhesion
• Inhibitors work best at lower concentrations
• Novelty: Incorporation Route – Patent Filed Nov 2007
• Inhibitors are bound in the network and dispersed
O
uniformly
Zirconia
nanoparticles
-O-Si-OR
Novel Inhibitor Incorporation (Patent Filed)
1.0
Silane + Zirconium Coating
+ Inhibitor
0.5
E (Volts)
Silane + Zirconium Coating
0
Blank Al 2024
-0.5
Silane Coating
-1.0
-1.5
-12
10
-11
10
-10
10
-9
10
-8
10
-7
10
-6
10
I (Amps/cm2)
-5
10
-4
10
-3
10
-2
10
-1
10
Comparison of Organic Inhibitors (0.3% w/w)
EIS (Bode Plots)
1,2,4-Triazole
Novel Inhibitor
107
0 hr
24 hrs
48 hrs
72 hrs
105
104
103
|Z|
|Z|
106
102
101
10-2
10-1
100
101
102
103
104
105
106
108
107
106
105
104
103
102
101
10-2
0 hr, 24 hrs, 48 hrs,72 hrs
10-1
100
Frequency (Hz)
1
10
0 -2
10-2
10-1-1
0
10
100
1
10
101
0 hr
24 hrs
48 hrs
72 hrs
2
10
102
3
10
103
4
10
104
107
-200
106
-150
105
-100
104
-50
103
2
10
0
1
10
50 -2
10
10-2
5
10
105
6
10
106
104
105
106
4
10
104
5
10
105
6
10
106
0 hr
24 hrs
0 48
hr,hrs
24 hrs, 48 hrs,72 hrs
72 hrs
-1
10
10-1
0
10
100
1
10
101
2
10
102
3
10
103
Frequency (Hz)
Frequency
Frequency (Hz)
(Hz)
-100
-100
0 hr
a
-75
103
Imidazole
|Z|
theta
|Z|
theta
0 hr
24 hrs
48 hrs
72 hrs
102
Frequency (Hz)
Benzotriazole
-100
107
106
-755
10
104
-50
103
-252
10
101
-75
0 hr
24 hrs
Novel Inhibitor Route
• Novel organic corrosion inhibitor for aluminium
• Highly reducible species, based on Nitrogen chemistry
–Eo = -1.2V
• Compatible with sol-gel chemistry and can be bound at
specific sites
• pH triggered release with selective binding at copper
rich intermetallics
• Inhibition of the electrochemical cell and corrosion
process
Sample Testing
Surface Treatment
Primer Coat
Topcoat
None – just Al
None
Aerospace
Alodine 1200
Cr Primer
BSAA
Cr-Free Primer
CAAA
Dualion
Dualion
Dualion (UV Active)
Dualion (UV Active)
Total:
6
5
1
Typical Thickness (<5 m)
25 m Top Coat
20 m Cr-Free Primer
3 m Dualion
Aluminium
x 350
100 m
Salt Spray Data
1st Treatment
2nd Treatment
Failure (Hrs)
1st Treatment
2nd Treatment
Failure (Hrs)
Alodine
None
300
Sol-Gels
None
800
Alodine
Sol-Gels
800
Sol-Gels
Cr-free primer
800
Alodine
Cr-free primer
1800
Sol-Gels
Cr-free primer*
1500
Alodine
Cr primer
2000
Sol-Gels
Cr primer
2000
1st Treatment
2nd Treatment
Failure (Hrs)
1st Treatment
2nd Treatment
Failure (Hrs)
BSAA
None
800
CAA
None
1800
BSAA
Sol-Gels
1500
CAA
Sol-Gels
1300
BSAA
Cr-free primer
2000
CAA
Cr-free primer
2000
BSAA
Cr primer
2000
CAA
Cr primer
2000
1st Treatment
2nd Treatment
Failure (Hrs)
None
None
300
None
Sol-Gels
800
None
Cr-free primer
300
None
Cr primer
500
* - Precommercial Product
Comparative Thicknesses of Coatings
Topcoat
Topcoat
Topcoat
Topcoat
Topcoat
Cr(VI) Primer
Cr(VI) Primer
Cr(VI) Free Primer
Dualion
Akzo Cr(VI) Free
Cr(VI) Alodine 1200
Dualion
AA 2024-T3
AA 2024-T3
2,000 Hrs
500 Hrs
AA 2024-T3
300 Hrs
AA 2024-T3
800 Hrs
AA 2024-T3
1,500 Hrs
Conclusion
• Sol-Gel chemistry is a viable option for protecting
aerospace aluminium alloys
• Sol-gels can be designed to combine the properties
of both a conversion coating and a primer
• Novel organic inhibitors can be engineered into such
coatings thereby avoided heavy metal alternatives
Thank you for your attention!