mm 206 06 ir spectroscopy
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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
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