Applications of Synchrotron Infrared
Microspectroscopy (SIRMS) to Corrosion,
Contamination and Coatings
Gary P. Halada and Clive R. Clayton
199th Meeting of the Electrochemical Society
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
Laboratory for Surface Analysis and Corrosion Science
Interaction of Electromagnetic
Radiation with Matter
Photoionization,
Compton scattering
X-rays
Core-level XPS
Electron shift to excited
states, valence-band photoemission
UPS
ultraviolet
Relative
energy of
electromagnetic
radiation
UV-vis
Molecular vibrational states
FTIR
visible
infrared
Symmetric
stretching
Anti-symmetric
stretching
Bending
microwave
Molecular rotation,
torsion
Inspired by HyperPhysics (©C.R. Nave, 2000), Department of Physics and Astronomy, Georgia State University
Laboratory for Surface Analysis and Corrosion Science
Comparison of Techniques for Surface
Analysis

Secondary Ion Mass Spectroscopy (SIMS)



X-ray Photoelectron Spectroscopy (XPS)





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: Surface sensitivity, sub-micron spatial resolution
Disadvantages: Sample charging, damage, UHV
Raman microscopy


Advantages: Surface sensitivity, oxidation state data
Disadvantages: Low signal in microanalysis mode, some photodegradation, UHV
Auger Electron Spectroscopy


Advantages: Sub-micron resolution, ppb detection levels, dynamic (profiling) and static (mapping)
modes
Disadvantages: Sample charging, UHV
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-1
Infrared 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 determines
region of spectral
analysis available
Choice of sampling
accessory determines
applicability to sample,
depth of analysis
Design and quality
of IR source and optics
controls spot size,
quality of data,
speed of acquisition
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
Beamsplitters
High
(cm-1)
Low (cm1)
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
700
20
(from www.thermonicolet.com)
Solid Substrate
Laboratory for Surface Analysis and Corrosion Science
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
Detectors
(from www.thermonicolet.com)
– Mercury cadmium telluride
DTGS – Deuterated tri-glycine sulfate
MCT
Laboratory for Surface Analysis and Corrosion Science
FTIR Microspectroscopy
interferogram
Continuum IR Microscope (Spectr-Tech, Inc.)
Detector
(MCT-A,B)
viewer
Fourier transform
Dichromic
mirror
Infinity
corrected
objective
aperature
sample
650
4000
wavenumbers
Infinity
corrected
condenser
synchrotron
Dichromic
mirror
interferometer
visible light
Mapping by scanning sample stage while collecting data at multiple points
Laboratory for Surface Analysis and Corrosion Science
Advantage of Synchrotron IR Source
L.M. Miller,*1 G.L. Carr,1 M. Jackson,2 P. Dumas,3 and G.P. Williams4
Synchrotron Radiation News (2000): 13 (5), 31-38.
Laboratory for Surface Analysis and Corrosion Science
Synchrotron-based Infrared
Microspectroscopy (SIRMS)
Beamline U10B
National 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 acetone
and exposed to sodium chloride mist showing a typical pit across
which a FTIR line scan was performed. The line scan was 150m
and was along the line shown
Carboxyl groups and hydroxide
signal intensity increase as edge
of pit is approached, but vanish
within 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
100
Microns
SIRMS results for a AA2024-T3 sample that
had been degreased with acetone prior to
exposure to a salt mist in an area which
showed initiation of pitting
80
60
40
20
0
0
20
40
60
80 100
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.
%Reflectance
Microns
75
70
65
60
55
50
45
40
35
30
25
4000 3500 3000 2500 2000 1500 1000 500
Laboratory for Surface Analysis and Corrosion Science
Microns
SIRMS of Acetone-Induced Pitting in
AA2024-T3: Initiation of Pitting
100
100
80
80
60
60
40
40
20
20
0
0
0
20
40
60
80
100
0
20
40
60
80
100
Microns
Map of Aliphatic Hydrocarbon
Bond Deformation Near a Pit
Map of Carboxyl Group Bond
Stretching Near a Pit
Pitting expected to occur on the intermetallic particles containing copper
Copper 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
SIMS Maps of CCC on AA2024-T3
2 min of sputtering (~1/5 of total coating thickness)
are likely associated
MgThe ions shown, except
Si with IMC
AlOCr,
2
Region in boxes
associated with
IMC:
11
2
22
2
Cu
Fe
1
1
2- ‘ Spherical’
Al2CuMg
1
1
1
1
2
Individual
1- ‘Blocky’
AlxCuy(MnFe)z
Cr
25 m
2
2
intermetallic particles appear to have different levels of CCC coverage
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 70th Birthday Symposium, The Electrochemical Society (1998)
Laboratory for Surface Analysis and Corrosion Science
SIRMS of a Chromate Conversion
Coating (CCC) on AA2024-T3
CN
Microns
Chromate
150
150
100
100
50
50
0
0
0
50
100
Microns
150
0
50
100
Microns
150
175x175 microns
--indicates heterogeneity of non-converted chromate and retained cyano
activator on treated surface (54 mg2/ft CCC on Sanchem treated AA2024-T3)
Laboratory for Surface Analysis and Corrosion Science
Following 30 minutes Ar+ ion etch
Microns
Chromate
CN
150
150
100
100
50
50
0
0
0
50
100
Microns
150
0
50
100
Microns
150
175x175 microns
-- indicates variations in coating thickness (in agreement with data from SIMS)
Laboratory for Surface Analysis and Corrosion Science
Grazing Angle Objective
-- need to analyze early stages of CCC
Attachment to FTIR microscope for the analysis of thin
films on metallic surfaces.
Viewing Mode
Grazing Mode

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
Laboratory for Surface Analysis and Corrosion Science
Grazing Angle Infrared Microspectroscopy
from 10 Sec. Alodine on Sanchem Treated
AA2024-T3
350
101.5
101.0
100.5
100.0
99.5
99.0
98.5
98.0
97.5 H-O-H
300
250
200
150
M-CH3
OH
Cr-O
CN
CHx
4000 3500 3000 2500 2000 1500 1000 500
Wavenumbers (cm-1)
100
50
0
0
50 100 150 200 250 300 350
Distribution of CN Infrared Feature
-- 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.
Wax embedding
compound
Topcoat
Primer
Step 3)
Microtome
4-micron
thick crosssection.
Step 4)
Transmission
analysis.
Laboratory for Surface Analysis and Corrosion Science
Transmission SIRMS of Composite
Paint System Topcoat
Waterborne CARC Polyurethane
Topcoat IR Spectrum
40 x 120 m
1695 cm-1,
1550 cm-1,
1470 cm-1, Alkane,
Carbonyl group
Amide II
CH2 Bend
C=O
Laboratory for Surface Analysis and Corrosion Science
SIRMS of Incorporated Radionuclide
Contamination and Decontamination
Mechanisms of radionuclide-hydroxycarboxylic
acid interactions for decontamination of metallic
surfaces (EMSP)
Dr. Richard Gordon, project officer





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.
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.
Laboratory for Surface Analysis and Corrosion Science
SIRMS Analysis of Uranium Interaction
with Corroded Steel
U-O stretching (UO2)2
70
70
60
60
50
50
40
40
microns
microns
OH stretching
30
30
20
20
10
10
0
0
0
10
20
30
40
microns
50
60
70
0
10
20
30
40
50
60
70
microns
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
lepidocrocite
1020 cm-1
goethite
796 cm-1
Microtomed
O-U-O
920 cm-1
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
-8180
-7740
-8200
-7760
-8220
Y Axis
Y Axis
-7780
-8240
-7800
-8260
-7820
-8280
-7840
-8300
3760
3780
3800
X Axis
3820
3840
4160
4180
4200
4220
4240
4260
X Axis
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
RBS – conducted at Army Research Laboratory , APG, MD
XPS
U4f5/2
U4f7/2
U6+
(UO3)
U6+
(UO3)
U6+
(U2O5)
U6+
(U2O5)
U4+
(U2O5)
U4+
(U2O5)
 Uranium XPS spectra for the
corroded, contaminated sample
indicates presence of both
U4+ and U6+.
 In corroded, contaminated samples,
uranium, oxygen, and iron is found
throughout the oxide layer.
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
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 time
resolved experiments
 near-field infrared
microspectroscopy – uses
sub-wavelength size source
Thomas Jefferson National Accelerator Facility, IR Demo FEL
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 to
acknowledge 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 Source
At Brookhaven National Laboratory:
Gwyn Williams, Larry Carr and Lisa Miller
Laboratory for Surface Analysis and Corrosion Science