Thermal and Composition Expansion of Clathrates in the Ethylene Oxide—Water System

Abstract

Nonstoichiometric clathrate compounds of ethylene oxide and water form cubic phases of composition xC2H4O·46H2O, where the theoretical maximum x is 8. Through x-ray diffraction experiments, thermal expansion relations were established for several specific compositions (x = 1.08, 2.32, 3.72, 6.75) over the temperature range from −140° to −20°C. It was found that in each case, the relative thermal expansion of the clathrate was greater than that of normal ice over matching ranges. At any given temperature in the range studied, a sharp break was observed in the composition expansion curve at about x = 3, for which a reasonable explanation has been provided.

Thermal expansion of structure I ethylene oxide hydrate

“…Our observations, however, differ significantly from the measurements of McIntyre and Peterson. 32 In this earlier work,32 the hydrate specimens were prepared by quenching aqueous solutions of ethylene oxide of different concentrations. From the measurment of the X-ray diffraction from only one Bragg peak ([732/651]) as a function of temperature, it was reported that the thermal expansion of the hydrate was dependent on the amount of ethylene oxide in the sample.…”

“…The type I structure was first established by von Stackelberg by X-ray powder diffraction.12 McIntyre and Peterson measured the cell parameter from 130 to 250 K as a function of the concentration of ethylene oxide in the specimens. 32 It was shown that the relative thermal expansion of the hydrate is greater than hexagonal ice at the same temperature range. Subsequently, Bertie and co-workers arrived at the same conclusion by comparing their unit cell parameter obtained at 110 K3 to that of McMullan and Jeffrey25 measured at 248 K. Except in the work of McIntyre and Peterson, thermal expansitivities were often estimated by uing the cell parameters determined by different laboratories and it is difficult to ascertain the absolute errors.…”