My Research – Part 2

The second analytical test I performed on the raw fly ash and the geopolymers was infrared spectroscopy. This method utilizes the FT-IR spectrometer instrument to acquire the broadband IR spectra, which can help to elucidate the structure of a compound. Note that infrared radiation is wedged between the visible and microwave regions on the electromagnetic spectrum. Infrared radiation is absorbed by molecules and transformed into molecular vibration energy—either bending or stretching. Specific bonds can be identified because they absorb IR of different wavelengths. There are known characteristic IR band positions for certain functional groups that can be used to analyze all kinds of materials. For example, the T-O-Si asymmetric stretching vibration (T either stands for Al or Si) is important for characterizing geopolymers. This specific band has been shown to shift to a lower wavenumber with an increasing degree of alkali-activation.

The sample preparation for this technique actually requires more time and effort than running the test.  Here are pictorial instructions on how to perform FT-IR:

First, an extremely small chunk of the solid sample is smashed with a spoonful of dried potassium bromide (KBr) in a mortar and pestle to form a very fine powder.

Second, the powder is poured into a circular metal plate and a metal rod is placed on top.

Third, the metal rod is compressed to form a thin plate of the sample.

Fourth, the thin plate or film is carefully removed. Note that KBr is transparent in the IR.

Fifth, the plate is placed on a metal holder.

Sixth, the metal holder is placed in the FT-IR for analysis. Note that this should be done as soon as possible to avoid hydration of the KBr, which interferes with the results.

The cover of the FT-IR is then closed to create the appropriate environment for analysis. After a few seconds of measuring the sample the machine outputs an IR spectrum, which is a plot of transmittance (or absorbance) vs. wavelength. This plot can reveal information on the molecular structure of the fly ash and geopolymers that would otherwise be impossible to determine

About Chris Shearer

Chris Shearer grew up in the great state of Ohio in America, and is currently pursuing his PhD in Civil Engineering at Georgia Institute of Technology. With support from the National Science Foundation East Asia and Pacific Summer Institutes (NSF EAPSI) program, he is currently researching fly ash geopolymers at The University of Melbourne under Dr. John Provis during the "summer" of 2011. In his spare time he is an avid movie-watcher, reader, traveler, musician, and supporter of Yellow Jackets sports.
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