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Laboratory for Surface Analysis and Corrosion Science
Applications of Synchrotron Infrared Microspectroscopy (SIRMS) to Corrosion,
Contamination and Coatings
Gary P. Halada and Clive R. Clayton
F1 - State-of-the-Art Application of Surface and Interface Analysis Methods to Environmental Material Interactions: In Honor of James E. Castle's 65th Year
Tuesday, March 27, 2001
199th Meeting of the Electrochemical Society
Laboratory for Surface Analysis and Corrosion Science
Interaction of Electromagnetic Radiation with Matter
X-rays Photoionization,Compton scattering
ultraviolet
Core-level XPS
Electron shift to excited states, valence-band photoemission
UPS
visible
infrared
microwave
Molecular rotation, torsion
Molecular vibrational statesFTIR
Symmetricstretching
Anti-symmetricstretching
Bending
Relative energy of electromagneticradiation
Inspired by HyperPhysics (©C.R. Nave, 2000), Department of Physics and Astronomy, Georgia State University
UV-vis
Laboratory for Surface Analysis and Corrosion Science
Comparison of Techniques for Surface Analysis
Secondary Ion Mass Spectroscopy (SIMS) Advantages: Sub-micron resolution, ppb detection levels, dynamic (profiling) and static (mapping)
modes Disadvantages: Sample charging, UHV
X-ray Photoelectron Spectroscopy (XPS) Advantages: Surface sensitivity, oxidation state data Disadvantages: Low signal in microanalysis mode, some photodegradation, UHV
Auger Electron Spectroscopy Advantages: Surface sensitivity, sub-micron spatial resolution Disadvantages: Sample charging, damage, UHV
Raman microscopy Advantages: Can sample through aqueous media, sub-micron resolution, non-vacuum Disadvantages: Possible photochemical damage, Raman effect weak in some cases
Laboratory (globar) FTIR microspectroscopy Advantages: Inexpensive, 10-15 micron spatial resolution, non-vacuum Disadvantages: Micron surface sensitivity, long data collection to improve signal-to-noise, difficult in
aqueous or humid environment SIRMS
Advantages: 3 to 5 micron spatial resolution, rapid data collection, good signal-to-noise ratio due to bright,coherent source (1000x globar), non-vacuum technique
Disadvantages: Requires synchrotron, aqueous environment still a problem
Laboratory for Surface Analysis and Corrosion Science
Principles
The Beer-Lambert Law:
A=ebc
Where A is absorbance (no units, since A = log10 P0 / P )
e is the molar absorbtivity with units of L mol-1 cm-1
p is the path length of the sample - expressed in centimeters.
c is the concentration of the compound in solution, expressed in mol L-1Infrared Ranges:
Near IR: 13,000 – 4,000 cm-1 (0.78 – 2.5 m)
Mid IR: 4,000 – 200 cm-1 (2.5 – 50 m)
Far IR: 200 –10cm-1 (50 – 1000 m)
Laboratory for Surface Analysis and Corrosion Science
Fourier Transform Infrared Spectroscopy
Choice of beamsplitter and detector determinesregion of spectralanalysis available
Design and qualityof IR source and opticscontrols spot size,quality of data,speed of acquisition
Choice of sampling accessory determinesapplicability to sample, depth of analysis
Laboratory for Surface Analysis and Corrosion Science
Beamsplitters and Detectors
Determine range of analysis MCT – Mercury cadmium telluride
Cooled quantum detectors (also InSb, etc.): photon promotion of electron across semiconductor bandgap to conduction band
Requires liquid nitrogen cooling A or B: relates to degree of doping to change
bandgap DTGS – Deuterated tri-glycine sulfate
Thermal detector (pyroelectric) detects heat through changes in capacitance caused by thermal distortion of polarized structure
Slower, less sensitive, but does not require cooling
Laboratory for Surface Analysis and Corrosion Science
Beamsplitters
High (cm-1)
Low (cm-1)
Ge-on-KBr 7,400 350
XT-KBr 11,000 375
CsI 6,400 200
Quartz 25,000 2,800
Si-on-CaF2 14,500 1,200
ZnSe 6,000 650
Solid Substrate
700 20
Beamsplitters
(from www.thermonicolet.com)
Laboratory for Surface Analysis and Corrosion Science
Detectors
Detectors High (cm-1) Low (cm-1)
Temperature-Stabilized DTGS
12,500 350
TE Cooled DTGS 12,500 350
MCT-High D* 11,700 800
MCT-A 11,700 600
MCT-B 11,700 400
Time Resolved MCT 11,700 650
DTGS/CsI 6,400 200
Silicon 25,000 8,600
PbSe 13,000 2,000
InSb 11,500 1,850
InGaAs (1.9 m) 12,000 5,300
InGaAs (2.6 m) 12,000 3,800
DTGS/PE 700 50
Si Bolometer 600 20
Photoacoustic 10,000 400
(from www.thermonicolet.com)
MCT – Mercury cadmium tellurideDTGS – Deuterated tri-glycine sulfate
Laboratory for Surface Analysis and Corrosion Science
FTIR Microspectroscopy
Detector(MCT-A,B)
interferometer
synchrotron
Continuum IR Microscope (Spectr-Tech, Inc.)
visible light
viewer
sample
Dichromicmirror
Infinitycorrected objective
Infinitycorrected condenser
Dichromicmirror
aperature
6504000
abso
rpti
on
wavenumbers
Fourier transform
Mapping by scanning sample stage while collecting data at multiple points
interferogram
Laboratory for Surface Analysis and Corrosion Science
Advantage of Synchrotron IR Source
Synchrotron Radiation News (2000): 13 (5), 31-38.
L.M. Miller,*1 G.L. Carr,1 M. Jackson,2 P. Dumas,3 and G.P. Williams4
Laboratory for Surface Analysis and Corrosion Science
Synchrotron-based Infrared Microspectroscopy (SIRMS)
Beamline U10BNational Synchrotron Light Source
Reflection mode
Laboratory for Surface Analysis and Corrosion Science
Applications of SIRMS
Mechanism of Al alloy corrosion and the role of chromate inhibitors (MURI)Lt. Col. Paul Trulove, contract officer
Mechanisms of military composite coatings degradation (SERDP)Dr. Stephen McKnight, contract officer
Mechanisms of radionuclide-hydroxycarboxylic acid interactions for decontamination of metallic surfaces (EMSP)Dr. Richard Gordon, project officer
Laboratory for Surface Analysis and Corrosion Science
SIRMS of Surface Treatments on AA2024-T3
Mechanism of Al alloy corrosion and the role of chromate inhibitors (MURI)Lt. Col. Paul Trulove, contract officer
Develop a model of the mechanisms of operation and the structure of chromate conversion coatings (CCC) on aluminum-copper aerospace alloy (AA2024-T3)
Model can provide guidelines for replacement of CCC with benign surface treatments
Requires an understanding of alloy surface cleaning and preparation Characterize depth-dependent and spatial variations in the structure of
CCC’s Determine the role of intermetallic compounds on the structure and
homogeneity of CCC’s
Laboratory for Surface Analysis and Corrosion Science
SIRMS of Acetone-Induced Pitting in AA2024-T3
Optical micrograph of AA2024-T3 ultrasonically rinsed in acetoneand exposed to sodium chloride mist showing a typical pit across which a FTIR line scan was performed. The line scan was 150mand was along the line shown
Carboxyl groups and hydroxidesignal intensity increase as edgeof pit is approached, but vanishwithin pit
Possible evidence of oxides, hydroxides, oxychlorides in pit
Laboratory for Surface Analysis and Corrosion Science
SIRMS of Acetone-Induced Pitting in AA2024-T3: Initiation of Pitting
Microns0 20 40 60 80 1000
20
40
60
80
100
Mic
ron
s
25 30 35 40 45 50 55 60 65 70 75
%R
efl
ec
tan
ce
500 1000 1500 2000 2500 3000 3500 4000
SIRMS results for a AA2024-T3 sample that had been degreased with acetone prior to exposure to a salt mist in an area whichshowed initiation of pitting
The dotted-outline box in the optical
digimicrograph (a) indicates the region of
analysis, which was centered about a site
The FTIR map (b) and representative
component spectra (b) emphasize
the spectral region for carboxyl groups.
Laboratory for Surface Analysis and Corrosion Science
SIRMS of Acetone-Induced Pitting in AA2024-T3: Initiation of Pitting
0 20 40 60 80 100
0
20
40
60
80
100
Map of Aliphatic Hydrocarbon Bond Deformation Near a Pit
Map of Carboxyl Group BondStretching Near a Pit
0 20 40 60 80 100
0
20
40
60
80
100
Microns
Mic
ron
s
Pitting expected to occur on the intermetallic particles containing copperCopper acts as a photocatalyst for the reaction between acetone and water Leads to the formation of acetic acid, which reacts with aluminum,copper forming acetates. Eventually copper chlorides and other corrosion products form.
Devicharan Chidambaram and Gary P. Halada, “Infrared Microspectroscopic Studies on the Pitting of AA2024-T3 Induced by Acetone Degreasing”, submitted to Surf. Inter. Analysis
Laboratory for Surface Analysis and Corrosion Science
1
1
2
11
2
2
The ions shown, except Cr, are likely associated with IMC
SIMS Maps of CCC on AA2024-T32 min of sputtering (~1/5 of total coating thickness)
Region in boxes associated with IMC:
1- ‘Blocky’ AlxCuy(MnFe)z
2- ‘ Spherical’ Al2CuMg
Individual intermetallic particles appear to have different levels of CCC coverage
Mg Si
CrCrFeFe Cu
AlO2
25 m
1
2
1
2
1
2
1
2
Halada, G.P., C.R. Clayton, M.J. Vasquez, J.R. Kearns, M.W. Kendig, S.L. Jeanjaquet, G.G. Peterson and G. Shea-McCarthy. Spatially Resolved Microchemical Analysis of Chromate Conversion Coated Aluminum Alloys and Constituent IMC, in Critical Factors in Localized Corrosion III -–Jerome Kruger 70 th Birthday Symposium, The Electrochemical Society (1998)
Laboratory for Surface Analysis and Corrosion Science
SIRMS of a Chromate Conversion Coating (CCC) on AA2024-T3
Chromate CN
Microns0 50 100 1500
50
100
150
Microns
Mic
ron
s
0 50 100 1500
50
100
150
--indicates heterogeneity of non-converted chromate and retained cyano
activator on treated surface (54 mg2/ft CCC on Sanchem treated AA2024-T3)
175x175 microns
Laboratory for Surface Analysis and Corrosion Science
Following 30 minutes Ar+ ion etch
Chromate CN
175x175 microns
0 50 100 1500
50
100
150
Microns
Mic
ron
s
0 50 100 1500
50
100
150
Microns
-- indicates variations in coating thickness (in agreement with data from SIMS)
Laboratory for Surface Analysis and Corrosion Science
Attachment to FTIR micro-scope for the analysis of thin films on metallic surfaces.
Provides infrared radiation at grazing incidence angles (65 to 85 degrees) for the analysis of sub-micron films
Analyzes areas as small as 50 microns in diameter
Viewing Mode Grazing Mode
Grazing Angle Objective
-- need to analyze early stages of CCC
Laboratory for Surface Analysis and Corrosion Science
97.5 98.0
98.5
99.0
99.5
100.0
100.5 101.0
101.5
500 1000 1500 2000 2500 3000 3500 4000
Wavenumbers (cm-1)
100
150
200
250
300
350
0 50 100 150 200 250 300 3500
50
Distribution of CN Infrared Feature
CN Cr-OH-O-H CHx
OH
M-CH3
Grazing Angle Infrared Microspectroscopy from 10 Sec. Alodine on Sanchem Treated
AA2024-T3
-- shows inhomogeneity of coverage in early stage CCC
Laboratory for Surface Analysis and Corrosion Science
SIRMS Analysis of Composite Paint Systems
Mechanisms of military composite coatings degradation (SERDP)Dr. Stephen McKnight, contract officer
Determine the chemical mechanisms of degradation of military composite paint coatings systems
Comparison of failure mechanisms for VOC versus new water-based, environmentally benign CARC primer/topcoat systems
Relate to chalking, adhesion failure, chipping and disbondment Artificially age coatings through UV/humidity exposure Apply data to development of Life Cycle Analysis models to predict
service life and aid in scheduling of maintenance/repainting
Laboratory for Surface Analysis and Corrosion Science
Microtoming of Paint Coatings for SIRMS Analysis
Step 1) Embrittlement via liquid nitrogen immersion.
Step 2) Separate coating by bending substrate.
Step 3) Microtome 4-micron thick cross-section.
Step 4) Transmission analysis.
Topcoat
Primer
Wax embedding compound
Laboratory for Surface Analysis and Corrosion Science
Transmission SIRMS of Composite Paint System Topcoat
Waterborne CARC Polyurethane Topcoat IR Spectrum
1695 cm-1, Carbonyl group C=O
1550 cm-1, Amide II
1470 cm-1, Alkane, CH2 Bend
40 x 120 m
Laboratory for Surface Analysis and Corrosion Science
SIRMS of Incorporated Radionuclide Contamination and Decontamination
Low carbon steels (1010) were cleaned and sprayed with uranyl nitrate. They were placed in a humidity chamber and allowed to rust over a period of 4 days. They were then exposed again to uranium and underwent another humidity treatment.
Some of the steels were then sprayed with 0.1M citric acid and rinsed with deionized water.
Determine how uranium associates with the iron oxides/oxyhydroxides that are formed when steel is exposed to a humid environment.
Investigate the effectiveness of cleaning the contaminated and corroded steel surfaces with citric acid.
Optimization of bio/photodegradation to recover radionuclides.
Mechanisms of radionuclide-hydroxycarboxylic acid interactions for decontamination of metallic surfaces (EMSP)Dr. Richard Gordon, project officer
Laboratory for Surface Analysis and Corrosion Science
SIRMS Analysis of Uranium Interaction with Corroded Steel
0 10 20 30 40 50 60 700
10
20
30
40
50
60
70
microns
microns
0 10 20 30 40 50 60 700
10
20
30
40
50
60
70
microns
microns
OH stretching U-O stretching (UO2)2
Synchrotron FTIR microspectroscopy chemical maps from (a) –OH stretching frequency and (b) U-O stretching frequency associated with uranyl groups from corroded steel surface exposed to uranyl nitrate solution.
-- shows spatial incorporation of contaminant uranium at thick corrosion area
G.P.Halada, C. Eng, C.R. Clayton, A.J. Francis, C.J. Dodge and J.B. Gillow, “A Spectroscopic Study of the Association of Contaminant Uranium with Corroded Carbon Steel Surfaces and Subsequent Removal Using Citric Acid”, submitted to Env.Sci. Tech.
Laboratory for Surface Analysis and Corrosion Science
SIRMS of Microtomed Corrosion Product Layer
lepidocrocite1020 cm-1
goethite796 cm-1
O-U-O920 cm-1
Microtomed corrosion sample shows lepidocrocite layer over goethite layer.Uranium is found throughout the sample.
Laboratory for Surface Analysis and Corrosion Science
Decontamination of Uranium on Corroded Steel Using 0.1M Citric Acid
3760 3780 3800 3820 3840
-8300
-8280
-8260
-8240
-8220
-8200
-8180
X Axis
Y A
xis
4160 4180 4200 4220 4240 4260
-7840
-7820
-7800
-7780
-7760
-7740
X Axis
Y A
xis
3760 3780 3800 3820 3840
-8300
-8280
-8260
-8240
-8220
-8200
-8180
X Axis
Y A
xis
4160 4180 4200 4220 4240 4260
-7840
-7820
-7800
-7780
-7760
-7740
X Axis
Y A
xis
4160 4180 4200 4220 4240 4260
-7840
-7820
-7800
-7780
-7760
-7740
X Axis
Y A
xis
Synchrotron-based infrared chemical maps of the O-U-O stretching frequency feature at approximately 900 wave numbers from a portion of the surface of a contaminated carbon steel surface corroded in a cyclic humidity chamber, before (left) and after (right) decontamination using a citric acid treatment (0.1M followed by rinse with distilled water)
Laboratory for Surface Analysis and Corrosion Science
Correlation to XPS and Rutherford Backscattering Data
In corroded, contaminated samples, uranium, oxygen, and iron is found throughout the oxide layer.
RBS – conducted at Army Research Laboratory , APG, MD
U4f5/2 U4f7/2
U6+
(UO3)
U6+ (U2O5)
U6+
(UO3)
U6+ (U2O5)
U4+ (U2O5)
U4+ (U2O5)
XPS
Uranium XPS spectra for the corroded, contaminated sampleindicates presence of both U4+ and U6+.
Laboratory for Surface Analysis and Corrosion Science
Future Directions – Far Infrared Synchrotron Microspectroscopy (FIRMS), Improvements in
Spatial Resolution Extension of spectral region for microspectroscopy
Current range approximately 4000 to 650 cm-1 (2.5 to 16 m) With use of large optics, Si beamsplitter, may be able to
extend range to longer wavelengths (far infrared down to 100-200 cm-1 (25 m))
Will allow for identification of many inorganic features, including more metal-oxide stretching vibrations (i.e. strongest features for Cr2O3 and Al2O3 are from 550-650 cm-1 )
Problems include need for better purge of water vapor
Improvements in spatial resolution Experiments underway at U4IR (NSLS-BNL) to characterize
below the diffraction limit (around 3 microns) Use of confocal optics (30% improvement), deconvolution of
the diffraction pattern, precise sample preparation G.L. Carr, Rev. Sci. Instr., vol. 72, no. 3 (March 2001), 1613-
1619
Laboratory for Surface Analysis and Corrosion Science
Future Directions – Infrared Spectroscopy using a Free Electron Laser
Thomas Jefferson National Accelerator Facility, IR Demo FEL
Schematic drawing of IR Demo FEL accelerator. The electron beam originates in a 350 keV photocathode gun, is accelerated in a 10 MeV cryounit, and is injected into a 40 MeV cryomodule. The beam is steered around the cavity mirrors and through the FEL wiggler.
Applications include: transient IR absorption microspectroscopy for timeresolved experiments near-field infrared microspectroscopy – uses sub-wavelength size source
Laboratory for Surface Analysis and Corrosion Science
Conclusions
Synchrotron-based infrared microspectroscopy is a powerful tool for the spatially-resolved characterization of surface and interfacial chemistry.
Applicability can be enhanced through novel sample preparation techniques and choice of optics.
Combination with other techniques, including XPS, SIMS, RBS, optical analysis and laboratory-based FTIR, is essential for the creation of comprehensive and consistent models of surfaces and coatings
Limitations of synchrotron-based infrared analysis arise from availability of detector/beamsplitter combinations, quality of IR source, physics of diffraction limits and aqueous environments.
Studies currently underway at synchrotron and FEL facilities to overcome these limitations show great promise
Laboratory for Surface Analysis and Corrosion Science
Additional Acknowledgements
In addition to the funding programs shown earlier, we wish toacknowledge the students who have worked on these measurements:
Marvin Vasquez, Devicharan Chidambaram , Lionel Keene, Charlotte Eng and Michael Cuiffo
as well as our collaborators at the National Synchrotron Light SourceAt Brookhaven National Laboratory:
Gwyn Williams, Larry Carr and Lisa Miller
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