Accession Number : ADP007773

Title :   Use of A TM010 Microwave Cavity at 2.45 GHz for Aerosol and Filament Drying,

Corporate Author : LOS ALAMOS NATIONAL LAB NM

Personal Author(s) : Christiansen, D. E. ; Unruh, W. P. ; Hawley, Martin C.

Report Date : 27 APR 1992

Pagination or Media Count : 8

Abstract : As part of the development of a generic spray-drying process for aerosol preparation of homogeneous powders of complex metal oxide systems, we have investigated the use of 2.45 GHz power in a high-Q single-mode TM010 cavity coupled directly to aerosols of aqueous solutions. Partial success was attained with a concentrated solution of ferric nitrate. Although all particulates showed drying, only a few percent of the particles were fully dried prior to collection. The cavity operated at a power level just below that sufficient to cause electric field breakdown in the carrier gas (dry nitrogen). The large inherent dielectric shielding of the spherical droplets makes it difficult to couple enough power into an aerosol at 2.45 GHz to overcome the heat loss from individual droplets to the surrounding gas and achieve full particulate drying. The calculated and measured dielectric shielding of a thin cylinder of water aligned with the cavity electric field is very much smaller. We have produced heating rates in water approx. 600 times more rapid than could be achieved with aerosols. This suggests using 2.45 GHz microwave power for drying extruded filaments and then calcining those dried filaments to ceramic fiber.

Descriptors :   *MICROWAVES, *POWDER METALS, *CERAMIC MATERIALS, *DRYING APPARATUS, AEROSOLS, CAVITIES, CERAMIC FIBERS, COLLECTION, DIELECTRICS, DRYING, ELECTRIC FIELDS, FIBERS, FILAMENTS, HEAT, HEAT LOSS, HEATING, METALS, NITRATES, NITROGEN, OXIDES, PARTICLES, PARTICULATES, POWDERS, POWER, POWER LEVELS, PREPARATION, RATES, SHIELDING, SPRAYS, WATER, MAGNETRONS, SYMPOSIA.

Subject Categories : Ceramics, Refractories and Glass
      Metallurgy and Metallography
      Electrical and Electronic Equipment

Distribution Statement : APPROVED FOR PUBLIC RELEASE