Date of Award

Summer 1965

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Physics

Abstract

The exploding wire phenomenon has been the subject of considerable scientific Interest. particularly during the last fifteen years. Most of the research In the area has been concerned with the phenomena which occur during the explosion Itself, and relatively little attention has been given to the residue of the explosion known as the smoke or aerosol. Exploding wire aerosols usually consist of submicron particles of pure metal, metal oxides or alloys In various combinations depending on the conditions of the explosion. The aerosols of exploded gold wires have been found to consist entirely of the pure metal. However, the unusual history of these gold particles, namely, vaporizatlon followed by condensation end then by a rapid quench to room temperature, produces significant modifications In the crystalline properties of the metal which can be observed by x-ray analysis. For this investigation, x-ray diffraction spectra of a series of gold aerosols were produced on an automatic recording diffractometer. The aerosol diffractograms are very similar to those obtained from ordinary gold powder, but with several striking differences. First, the diffraction peaks are shifted to the high-angle side, and the magnitude of this shift indicates an average decrease in the lattice parameter of the gold of about 0.2 percent. Second, the measured breadth of the diffraction peaks is several times that of pure instrumental broadening. The angular dependence of the observed broadening indicates that the effect is due to both small particles size and lattice imperfections, although the size broadening predominates in all cases. Finally, it is observed that after the aerosols are annealed at several hundred degrees centigrade, both the peak shift and the broadening are reduced considerably. This is due, at least partly, to an obvious crystal growth which occurs during the anneal. The fact that the lattice parameter of gold decreases with small particle size has been reported at least once in the literature. However, a satisfactory explanation for this phenomenon has not been reported. A solution to the problem would necessarily involve an analysis of the defect structure of gold, and any experimental evidence would be of considerable interest. It is undertaken in this thesis, therefore, to report on the investigation outlined above, and to interpret the results in terms of the existing theories of x-ray analysis and crystal structure.

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