Graduate Thesis Or Dissertation
 

Neutron-induced autoradiography of lithiasilica microspecimens : Specimen preparation and preliminary alpha tracking

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  • Lithia-silica compositions between lithium disilicate and pure silica were explored theoretically and experimentally, with special emphasis on structural miscibility. Diffusion couples of vitreous materials were prepared and annealed. Best success in preparation was achieved by using electron-bombardment heating in vacuum to melt the less refractory glass and let it solidify around some of the more refractory material. Annealing was done with the protection of flowing argon at about 885° C for times up to 350.3 hours. Diffusion profiles were measured by neutron-induced autoradiography, but before this could be done, it was necessary to establish practical conditions for using the technique, and to calibrate it for lithia-silica compositions. This was the first known application of its sort for the method of neutron-induced autoradiography, and problems were encountered. This work represents a basis for improving several technical aspects. Results of the work completed can be considered only tentative, but it is believed that evidence of a liquid-liquid miscibility gap was observed for the lithia-silica compositions studied. Furthermore, it is suspected that the bounds of the miscibility gap at about 885° C are near 7 and 20 mol percent lithia, and that related spinodal compositions are near 11 and 15 mol percent lithia. The values on the lithium disilicate side of the gap are in general agreement with previous determinations, but no prior experimental evidence concerning the silica side of the gap has been reported. Both neutron-induced autoradiography and its application to basic investigation of the lithia- silica phase system were sufficiently promising to warrant repetition and extension of the work with improvements to increase confidence in the outcome.
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