X-RAY DIFFRACTION STUDY OF THE STRUCTURE OF BORON IN VAPOR-DEPOSITED BORON FIBERS
BHARDWAJ, JAYANT VENKATKRISHNA
Doctor of Philosophy thesis
The structure of vapor-deposited fiber boron is studied using x-ray diffraction and computer modeling. The diffraction pattern displays broad peaks which have been interpreted in previous studies to arise from a microcrystalline material having an average crystallite size of about 30 (ANGSTROM). This study was initiated by quantitatively investigating the microcrystalline models suggested by workers. The Debye equation was used to compute the intensity scattered by randomly oriented crystallites. Crystallites with diameters up to 26 (ANGSTROM) were considered. An additional computer program was written to calculate the different interatomic distances and their multiplicities, and to compute their contributions to the various peaks. This method of analysis was utilized to drive the atoms in the microcrystal towards positions which gave a more favorable fit of the computed intensity profile to the experimentally obtained profile. Chapter I describes boron, the production of boron fiber and its properties and includes a survey of previous work. Chapter II addresses the experimental techniques used to obtain the diffraction pattern. In Chapter III, the methods utilized the model and compute the interference patterns are described. Chapter IV summarizes and discusses the results which indicate that a complex atomic arrangement is present, involving distorted nearest-neighbor distances, partial icosahedra and individual atoms. Some of the icosahedra display orientations present in alpha-rhombohedral boron, while others display those observed in tetragonal boron. The average size of the region of local atomic ordering is approximately 20 (ANGSTROM).
Engineering, Materials Science