In Situ Raman Spectroscopic Study of Gypsum (CaSO4•2H2O) and Epsomite (MgSO4•7H2O) Dehydration Utilizing an Ultrasonic Levitator

We present an original apparatus combining an acoustic levitator and a pressure-compatible process chamber. To characterize in situ the chemical and physical modifications of a levitated, single particle while heated to well-defined temperatures using a carbon dioxide laser, the chamber is interfaced to a Raman spectroscopic probe. As a proof-of-concept study, by gradually increasing the heating temperature, we observed the variations in the Raman spectra as 150 mu g of crystals of gypsum and epsomite were dehydrated in anhydrous nitrogen gas. We display spectra showing the decreasing intensities of the nu(1) symmetric and nu(3) asymmetric stretching modes of water with time and the simultaneous shift of the nu(1)(SO42-) symmetric stretch mode to higher wavenumbers. Our results demonstrate that the new apparatus is well suited to study the dehydration of levitated species such as minerals and offers potential advantages compared with previous experiments, on bulk samples.