Development of a textured and tabular grain microstructure in alumina fibers via seeded sol-gel processing

The development of an textured and/or elongated grain microstructure can be desirable for improving mechanical, electrical, or magnetic properties. In this thesis, seeded sol-gel processing was examined as a means of producing a textured and elongated microstructure in an alumina fiber. Seeded sols have previously been used to obtain dense, fine grain microstructures from alumina precursors such as boehmite. Furthermore, the addition of certain dopants to alumina has lead to anisotropic grain growth and the formation of elongated grains in situ. This study is the first to control the orientation of the seed particle so as to produce a textured materials which forms aligned and elongated grains in situ during thermal processing.;Alpha-iron oxide particles, hematite, were used to seed the formation of alpha-alumina from a boehmite precursor. For comparison, iron nitrate was used as a randomly oriented seed. The effectiveness of the seed particle was studied using DTA and TEM. Hematite particles decreased the temperature at which ;The acicular seed particles aligned parallel to the fiber axis during fiber drawing. Epitaxial growth of ;The addition of 1% iron nitrate resulted in isometric grains. Six percent iron nitrate seeding and 5% acicular particles plus 1% iron nitrate yielded tabular grains in a fine grain matrix. In fibers drawn from sols containing acicular particles, the tabular grains were aligned parallel to the fiber axis.