Application of Infrared Spectroscopy in the Study of Thermal Decomposition of Materials

Introduction

Infrared spectroscopy (IR) is a powerful analytical technique used to study the interaction of infrared light with matter.

It is particularly useful in identifying unknown materials, examining sample quality, and determining the amount of components in a mixture.

IR spectroscopy is divided into three subregions: Near-infrared, Mid-infrared, and Far-infrared, with mid-infrared being the most commonly used.

The technique is capable of analyzing samples in almost any phase (liquid, solid, or gas) and can be used alone or in combination with other instruments.

In the study of Thermal decomposition, IR spectroscopy helps in identifying the functional groups and molecular structures of the decomposition products.

It provides qualitative and quantitative analysis by measuring the absorption or transmittance of light at each frequency.

The technique is non-destructive and can be used to monitor the thermal stability and decomposition pathways of materials under various conditions.

Principles of Infrared Spectroscopy

Infrared spectroscopy studies the interaction of infrared light with matter.

Infrared light refers to electromagnetic radiation with wavenumbers ranging from 13000 to 10 cm-1.

The infrared region is divided into near-infrared, mid-infrared, and far-infrared subregions.

Molecules absorb infrared radiation, causing vibrational excitation of functional groups.

The resulting infrared spectrum provides information on molecular structure and composition.

Instrumentation

Dispersive infrared spectrometer and Fourier transform infrared (FTIR) spectrometer are commonly used.

Dispersive spectrometers use radiation sources like Globar, Nernst glower, and tungsten-halogen lamps.

FTIR spectrometers employ an interferometer to handle all frequencies simultaneously, increasing speed and sensitivity.

Detectors in FTIR spectrometers include pyroelectric and Photoconductive detectors.

FTIR spectrometers convert interferograms to spectra using Fourier transform.

Qualitative Analysis

IR spectroscopy is used to identify substances by their unique spectra.

Functional groups have characteristic vibrational frequencies that appear as peaks in the spectrum.

The mid-infrared region is most useful for qualitative analysis due to strong fundamental vibrations.

The fingerprint region (1500-650 cm-1) is particularly useful for identifying specific compounds.

Reference spectra databases, such as NIST Chemistry WebBook, aid in compound identification.

Quantitative Analysis

Absorbance is used for quantitative analysis due to its linear dependence on concentration.

Beer-Lambert law relates absorbance to concentration and pathlength of the sample.

Calibration curves are used to determine the concentration of unknown samples.

Quantitative analysis can be performed on liquid and solid samples.

Multi-component analysis is feasible due to different molar absorptivity values of components.

Applications in Thermal Decomposition

IR spectroscopy helps in identifying the functional groups and molecular structures of decomposition products.

It provides insights into the thermal stability and decomposition pathways of materials.

The technique is non-destructive and can be used to monitor changes in materials under various conditions.

IR spectroscopy is used to study the thermal decomposition of Pharmaceuticals, polymers, and other materials.

It can detect volatile decomposition products and provide information on their chemical nature.

Case Studies

Studies have shown IR spectroscopy's effectiveness in analyzing building materials like cement and carbonated compounds.

It is used to identify phases in hydrated cementitious materials and detect Carbonates in materials.

IR spectroscopy has been applied to study the thermal stability of pharmaceutical compounds.

The technique has been used to analyze the thermal decomposition of imidazoline/dimethyl succinate hybrids.

Case studies demonstrate the technique's ability to provide detailed insights into material composition and decomposition pathways.