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© 2006 by Taylor & Francis Group, LLC

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146 Corrosion Control Through Organic Coatings<br />

Absorbance<br />

0.05<br />

0.04<br />

0.03<br />

0.02<br />

0.01<br />

0<br />

−0.01<br />

FIGURE 8.8 Example of FTIR fingerprinting.<br />

Photo courtesy of SCI.<br />

The most important FTIR techniques include:<br />

• Attenuated total reflectance (ATR), in which a sample is placed in close<br />

contact with the ATR crystal. ATR is excellent on smooth surfaces that<br />

do not degrade during the test.<br />

• Diffuse internal reflectance (DRIFT). DRIFT uses potassium bromide<br />

pellets for sample preparation and, therefore, has certain limitations in<br />

use with hygroscopic materials.<br />

• Photoacoustic spectroscopy (PAS). In PAS, the sample surface absorbs<br />

radiation, heats up, and gives rise to thermal waves. These cause pressure<br />

variations in the surrounding gas, which are transmitted to a microphone<br />

— hence the acoustic signal [32].<br />

8.2.6.4 Electron Spectroscopy<br />

4000 3500 3000 2500 2000 1500 1000 500<br />

Wavenumber(cm−1 )<br />

Electron spectroscopy is a type of chemical analysis in which a surface is bombarded<br />

with particles or irradiated with photons so that electrons are emitted from it<br />

[26, 33]. Broadly speaking, different elements emit electrons in slightly different<br />

ways; so an analysis of the patterns of electrons emitted — in particular, the kinetic<br />

energy of the electron in the spectrometer and the energy required to knock it off<br />

the atom (binding energy) — can help identify the atoms present in the sample.<br />

There are several types of electron spectroscopy techniques, each differing in<br />

their irradiation sources. The one most important to coatings research, XPS (or<br />

electron spectroscopy for chemical analysis [ESCA]), uses monochromatic x-rays.<br />

XPS can identify elements (except hydrogen and helium) located in the top 1 to 2 Nm<br />

of a surface [2, 26, 33]. It can also yield some information about oxidation states<br />

because the binding energy of an electron is somewhat affected <strong>by</strong> the atoms around<br />

<strong>©</strong> <strong>2006</strong> <strong>by</strong> <strong>Taylor</strong> & <strong>Francis</strong> <strong>Group</strong>, <strong>LLC</strong>

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