HT-FTIR micro-spectroscopy of cordierite: the CO2 absorbance from in situ and quench experiments

In this work, we address the intensity evolution of the CO2 FTIR bands of cordierite as a function of increasing T, by comparing data obtained from in situ versus quenching measurements. A natural well-characterized cordierite from Kragero (Arendal region, Norway) was studied up to 1200 °C using a heating stage fitted on a FTIR microscope. Two different oriented sections (001) and (010), respectively, were examined in order to check for the effect of the channel orientation on the CO2 release from the matrix. Spectra collected in situ show that increasing temperatures induces an increase in peak width for all CO2-related bands. The effects on the integrated absorbance A i are different for the different modes. Most notably, the integrated intensity A i of the anti-symmetric stretching mode (ν3) increases significantly up to 800 °C and then progressively decreases to 1000/1200 °C, depending on the sample orientation. Data obtained on quenched samples reveal that there is no variation in the band intensity for T < 900 °C, and thus, the absorbance increase observed for in situ measurements may be related to an increase in the molar absorption coefficient e. Combination of in situ with quenched data reveals that the CO2 loss from the cordierite matrix starts around 800 °C and is strongly dependent on the thickness and shape of the examined sample: It is favored for small and tabular-shaped grains, while being significantly reduced for large and prismatic grains. Fracturing along direction normal to [001] multiplies the diffusion interfaces, thus enhancing the CO2 loss from the matrix.