Simultaneous XRD-DSC measurements of water-2-propanol at sub-zero temperatures.
A simultaneous low-temperature X-ray powder-diffractometric (XRD)-DSC technique was applied to the solid state and melting process of frozen aqueous solutions of 2-propanol. 1H NMR spectra were also obtained at low temperatures. The chemical shifts of the CH3 proton and the CH proton can be classified into four temperature regions: higher than -20 degrees C, around -20 degrees C, -50 to -20 degrees C, and lower than -50 degrees C. In the XRD data, five small diffraction peaks for 2 theta at 21.0 degrees, 25.2 degrees, 27.8 degrees, 31.1 degrees and 32.1 degrees can be attributed to the peritectic, while five diffraction peaks at 22.5 degrees, 24 degrees, 25.6 degrees, 33.4 degrees and 39.8 degrees can be attributed to ice; these peaks are due to the hexagonal form of ice, which disappears upon melting. However, the diffraction peak at 33.4 degrees showed a different pattern than the other peaks due to hexagonal ice. These results indicate that the temperature dependence of the diffraction peak at 33.4 degrees for 2 theta is related to the formation of hydrogen bonds between 2-propanol and water. The simultaneous XRD-DSC technique was effective for investigating this water-alcohol mixture at low temperatures.