Temperature Perturbation Infrared Spectroscopy of Minerals

A new method for variable temperature infrared spectroscopy studies of minerals is presented. A sample heating/cooling apparatus incorporating a modified button sample holder with thermoelectric temperature control is described. By employing different programs to heat and cool samples with temperatures varying in different ways, various aspects of mineral powders are investigated. Infrared spectroscopy methodologies for identifying sample structural changes as a function of temperature are described. The results obtained for a variety of minerals are provided as examples. The high precision and accuracy of this approach permit the detection of subtle crystallographic unit cell distortions as a function of temperature. A < 0.25% reduction in O-H stretching vibration band intensity associated with water desorption from a quartz sample is observed at 150 °C. By employing step temperature heating profiles, reversible and irreversible sample changes can be distinguished. Variable temperature infrared spectroscopy analyses demonstrate the utility of the technique for profiling sample dehydration processes and for elucidating interactions between mineral functionalities and absorbates as a function of temperature.