Method for preparing spherical ferrite beads and use thereof
The invention allows the fabrication of small, dense, highly polished spherical beads of hexagonal ferrites with selected compositions for use in nonreciprocal microwave and mm-wave devices as well as in microwave absorbent or reflective coatings, composites, and the like. A porous, generally spherical bead of hydrous iron oxide is made by a sol-gel process to form a substantially rigid bead having a generally fine crystallite size and correspondingly finely distributed internal porosity. The resulting gel bead is washed and hydrothermally reacted with a soluble alkaline earth salt (typically Ba or Sr) under conditions of elevated temperature and pressure to convert the bead into a mixed hydrous iron-alkaline earth oxide while retaining the generally spherical shape. This mixed oxide bead is then washed, dried, and calcined to produce the desired (BaFe12O19 or SrFe12O19) crystal structure. The calcined bead is then sintered to form a dense bead of the BaFe12O19 and SrFe12O19 phase suitable for polishing and incorporation into various microwave devices and components.
UT-Battelle, LLC
Y C H Y C Y C C Y C
Y10T C01P H01F Y10T C01G Y10T C01P C01P Y10T C01P
additional additional inventional additional inventional additional additional additional additional additional
Frederick C. Jack L. Robert J. Kimberly K.
Montgomery Collins Lauf Anderson