A high sensitivity variable temperature infrared spectroscopy investigation of kaolinite structure changes.

Abstract

A new approach for thermal analysis based on variable temperature infrared spectroscopy is described and evaluated. Diffuse reflection optics are employed with a sample heating system that does not employ a sealed environmental chamber. Rather than using a sample cup, a thin layer of solid particles is loaded into a "button" sample holder. The new design minimizes spectral artifacts and provides enhanced optical throughput compared to other designs, but necessitates a more restrictive sample heating temperature range. Results obtained while monitoring solid-state temperature-dependent changes are used to assess the sensitivity of the method. Infrared spectrum changes associated with reversible and irreversible kaolinite structure changes are described and characterized. Subtle temperature-dependent sample changes are revealed by positive and negative difference spectrum residuals, which are obtained by subtracting infrared spectra obtained at different temperatures. Scan-to-scan infrared spectrum relative standard deviations at 30 and 150°C were less than 1.0%, which was slightly higher than the ambient temperature reproducibility.