An Investigation of Some Nuclear Properties and Applications of the Rare Gas Clathrate Compounds

JOHN EDWIN MOCK, Purdue University

Abstract

Because of possible pollution of the atmosphere, a need has arisen for a more satisfactory solution to the problem of containing the reactor off-gases, xenon and krypton. Moreover, investigation and utilization of the many unique properties of the rare-gas nuclides are severely handicapped since these elements are gases under normal conditions. This study was established, therefore, to investigate the possibility of forming useful rare-gas compounds which will exist in the solid state, with emphasis placed upon the clathrate compounds. It is believed that such rare-gas compounds should find use as a temporary (or permanent) storage medium for reactor waste gases, as a convenient form for handling and shipping rare-gas radioisotopes, and as a more satisfactory medium for containing the rare-gas radioisotopes to be used as radiographic and gaging sources of radiation.Several methods were investigated for preparing the rare-gas clathrates: crystallization from aqueous solutions of quinol, from non-aqueous solutions, from the quinol melt, and directly from the vapor phase. All methods were found to produce clathrate crystals in good yields. Correlations were obtained which outline the optimum operating conditions In each case. In general, high pressures, low quinol concentrations, and slow cooling rates favor the formation of crystals with high rare-gas content. Under identical operating conditions, crystals with much higher gas content are obtained from non-aqueous solutions than from aqueous solutions, and both methods give higher yields than do the solventless techniques. Of the latter techniques, the vapor- phase method was found to be more effective than the crystallization-from-melt method, e.g., at 250 psig the former method yielded crystals containing ten times the amount of gas contained in crystals from the latter method.Krypton and xenon were found to fill more clathrate vacancies than were filled by argon under identical conditions. Crystals containing 0.12% helium and 0.35% neon were prepared. The high density of these crystals precludes their being beta-quinol clathrates. It is postulated that they are interstitial crystals.It was found that almost any change to the quinol structure destroys its ability to form a clathrate compound, and that the amino group, either because of weaker hydrogen- bonding tendency or steric hindrance, cannot satisfactorily replace either of the quinol hydroxy groups. Other six-member ring systems (pyridazine, pyridine and pyrimidine) with para-hydroxy groups were found not to form the clathrate structure, which may be attributed to slight differences in size or configuration of the rings as compared to the benzene ring, or to directive influences of the nitrogen atoms. of the 21 matrix materials investigated, only p-fluorophenol apparently forms a clathrate compound with the rare gases.It was discovered that quinol does not form the clathrate structure in acetone solutions due to the preferential formation of a 1:1 acetone-quinol crystalline compound. Similarly, it was found that p,p'-biphenol and acetone also form a unique 1:1 crystalline compound.A theoretical analysis was made of the thermal stability of the radioactive rare-gas clathrates. Equations were developed to describe the temperature distribution in such slabs for various boundary conditions. A generalized plot was prepared for alpha emitters, and a general analysis based upon diffusion theory was accomplished for beta emitters. was found that a new dimensionless group plays a a dominant role in heat transfer when radioactive decay is involved. It has been proposed that this quantity be designated the nutherm number because of its fundamental significance. ItVarious rare-gas clathrate crystals were exposed to gamma radiation and found to be stable to a total dose of 1.14 x 108 rads as a minimum (the equivalent of an integrated thermal flux of 5 x 1017 nvt). The only perceptible change due to the radiation was a coloration effect which is apparently electronic in origin.This study was concluded with a discussion of several possible applications for these unique materials in the field of nuclear technology.

Degree

Ph.D.

Subject Area

Engineering

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