X-Ray Diffraction Studies of Dense Fluids

Citation

Honeywell, Wallace Irving (1964) X-Ray Diffraction Studies of Dense Fluids. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/E2BS-WS38. https://resolver.caltech.edu/CaltechETD:etd-09182002-140103

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Radial distribution functions supply useful information for the investigation of the structure of liquids. An x-ray cryostat and supporting equipment have been developed for determination of these functions experimentally. The apparatus has been tested on confined fluids at pressures up to 2000 psia and temperatures to 77 [degrees] K. Although a cylindrical beryllium sample cell is currently used in a geometry of the Debye-Scherrer type, the equipment is adaptable to parafocusing methods and to a wide variety of cell configurations. Except for self-absorption in the sample and cell, absorption of the incident and scattered x rays is less than 1%. The cryostat and supporting equipment maintain automatic temperature control to ?0.006[degrees] C. The sample temperature is measured to ?0.05[degrees] C with a miniature platinum resistance element placed directly in the sample fluid; temperature homogeniety of the irradiated sample is better than 0.003[degrees] C. The sample pressure is transmitted through a steel diaphragm to an oil system where it is measured to 1:10,000 on a pressure balance of the dead weight variety. A pressure transducer incorporating the diaphragm is used to balance the sample and oil pressures. The transducer has a sensitivity of 3.27 volts per differential psi. The analysis of x-ray diffraction data from highly absorbing samples is extended to include losses of incoherent scattering in the sample and cell and in the detection system. Methods for treating incident or scattered beams with nonuniform intensities are also presented. The scattering geometry represents an optimum choice for highly absorbing samples in cylindrical cells. The sample position is determined experimentally to within 0. 001 in. X-ray diffraction measurements made with molybdenum radiation are presented for liquid argon at -130.00[degrees]C for the densities 0.9098, 0.9818, and 1.0052 gm/[cubic centimeter]. Scintillation detection was employed; monochromatization was effected with [beta] filtering and pulse height selection. Radial distribution functions are derived from the intensity curves for data to S=9[Angstroms][superscript -1)]. The coordination numbers and shell distances show good agreement with previous work at a nearby state, but suggest the possibility of systematic error in the older data.

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