laboratory for surface analysis and corrosion science applications of synchrotron infrared...

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


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


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


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)


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


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


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)


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


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


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


Synchrotron-based Infrared Microspectroscopy (SIRMS)

Beamline U10BNational Synchrotron Light Source

Reflection mode


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


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


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


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.


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


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)


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


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)


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


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


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


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


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


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


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.


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.


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)


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+.


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


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


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


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

laboratory for surface analysis and corrosion science applications of synchrotron infrared...

Documents