Infrared Spectroscopic Investigations of Calcium Oxalate Monohydrate (Whewellite) Dehydration/Rehydration

Variable-temperature infrared spectroscopy is employed to monitor molecular vibrations during dehydration of calcium oxalate monohydrate (COM) and hydration anhydrous (COA). A unique variable-temperature approach combines precise sample temperature control rapid (2 °C s−1) heating/cooling with high-sensitivity analysis. Infrared spectra are obtained at specific isothermal temperatures, while applying linear versus time heating cooling ramps, in coordination programmed steps. Spectrum vibration bands provide information regarding the symmetry local environments solid-state water molecules anions. When COM heated, liberated from different crystallographic sites selectively detected. Subtle anion configuration changes associated losses detected based on band shapes wavenumber trends. Dehydration rehydration processes occur lower temperatures over narrower ranges than conventional thermal analysis methods because samples consist thin layers small particles. Reversible irreversible distinguished by using a step program spectral subtractions. COA temperature-dependent structure variations that an atmosphere low vapor concentration characterized.