Infrared (IR) spectroscopy is a useful technique for characterizing materials and providing information on the molecular structure, dynamics, and environment of a compound.

When irradiated with infrared light (photons), a sample can transmit, scatter, or absorb the incident radiation.

Absorbed infrared radiation usually excites molecules into higher energy vibrational states.

This can occur when the energy (frequency) of the light matches the energy difference between two vibrational states (or the frequency of the corresponding molecular vibration).

Infrared spectroscopy is particularly useful for determining functional groups present in a molecule.

Many functional groups vibrate at nearly the same frequencies independent of their molecular environment.

This makes infrared spectroscopy useful in materials characterization. Further, many subtle structural details can be gleaned from frequency shifts and intensity changes arising from the coupling of vibrations of different chemical bonds and functional groups.

Infrared Spectroscopy (IR)

For a molecular vibration to absorb infrared radiation, dipole moment must change during the vibration.

The infrared photon frequency must resonate with the vibrational frequency to excite the molecule into the higher vibrational state.

In addition, the electric dipole-transition moment associated with the molecular vibration being excited must have a component parallel to the polarization direction of the incident infrared photon.

Infrared spectra are typically presented as plots of intensity versus energy (in ergs), frequency (in s-1), wavelength (in microns), or wavenumber (in cm-1).

Intensity can be expressed as percent transmittance (%T) or absorbance (A). If I0 is the energy, or radiant power, reaching the infrared detector with no sample in the beam, and I is the energy detected with a sample present, transmittance is:

Strong and weak bands are more easily visualized simultaneously without changing scale when spectra are plotted in transmittance, because the absorbance scale ranges from zero to infinity, while transmittance ranges from 0 to 100% T (0% T corresponds to an absorbance of infinity).

Molecular vibrations are complicated, because individual bond stretches or bond anglebends are often highly coupled to each other. Progress in understanding the nature of molecular vibrations has derived mainly from empirical observation.

Fortunately, certain functional groups consistently produce absorption bands inthe same spectral regions independent of the remainder of the molecular structure.

These molecular vibrations are known as group frequencies. For example, methylenestretching vibrations always occur from 3000 to 2800 cm-1, methylene deformations from 1500 to 1300 cm-1, and methylene rocking motions from 800 to 700 cm-1.

A few general rules are useful when applying the mechanical ball and spring model to molecular vibrations:

· Stretching vibrations generally have a higher frequency than bending vibrations· The higher the bond order, the higher the stretching frequency· The lighter the atoms involved in the vibration, the higher the vibrational frequency

Capillary rheometer

Die

Feeder

Heaters

Single screw extruder

Die entry Die exit

Screw

SEM images of feedstocks

Feedstock F1

Feedstock F4

Feedstock F3

Feedstock F5

F1 F2F3

SEM image of sintered sample of F1

Sintered alumina tubes

SEM image of thermal debinded tube of F1

Chemisorption treatment

Adsorption isotherm

Derived from the TGA

data of chemisorbed and

washed powders

Alumina BET surface area

6.75 m2/gm

Saturation of stearic acid

quantity at 0.66 wt.%

alumina

FTIR results

FTIR of alumina

Bond Peak

Al-O 458

Al-O 794

OH 3336

Molecularwater

1608

FTIR of stearic acid

Bond Peak

C=O 1697

CH2 2915

CH2 2850

OH 937

FTIR of alumina with physisorbed stearic acid (0.7 wt.% of

alumina)

Bond Peak

CH2 2915

CH2 2850

FTIR of alumina with chemisorbed stearic acid (0.7 wt.% of

alumina)

Bond Peak

CH2 2915

CH2 2850

10

100

20

40

60

80

4000 400100020003000

%T

Wavenumber [cm-1]

1.5 wt.%

0.7 wt.%

1.0 wt.%1700

2900

FTIR of alumina with chemisorbed stearic acid (0.7, 1.0 and

1.5 wt.% of alumina)

XPS works by irradiating atoms of a surface of any solid material with X-Ray photons, causing the ejection of electrons.

The Ultra High Vacuum environment will prevent contamination of the surface and aid an accurate analysis of the sample.

The binding energies can be determined from the peak positions and the elements present in the sample identified.

X-Ray photoelectron spectroscopy

Electron beams with a diameter of less than 10nm can be achieved resulting in high spatial resolution

X-Rays and the Electrons

X-RayElectron without collision

Electron with collision

The noise signal comes from the electrons that collide with other electrons of different layers. The collisions cause a decrease in energy of the electron and it no longer will contribute to the characteristic energy of the element.

XPS Instrument

X-Ray Source

Ion Source

SIMS Analyzer

Sample introductionChamber

XPS Spectrum

O 1s

O becauseof Mg source

C

AlAl

O 2s

O Auger

Sample and graphic provided by William Durrer, Ph.D.Department of Physics at the Univertsity of Texas at El Paso