FLUIDIZED BED SURFACE MODIFICATION OF FINE POWDERS

FLUIDIZED BEDS ARE AN IDEAL TOOL FOR PRODUCING OR MODIFYING POWDER MATERIALS. UNFORTUNATELY, THE MOST DESIRABLE POWDERS FOR PRODUCING ENGINEERING MATERIALS ARE OF SUCH A FINE SIZE (<30 MICRONS, CORRESPONDING TO GELDART CLASS C POWDERS) THAT THEY ARE VERY COHESIVE AND DIFFICULT TO FLUIDIZE. SOME CLASS C POWDERS ARE FLUIDIZED BY AGGLOMERATE FORMATION, AND MANY DIELECTRIC POWDERS CAN BE FLUIDIZED IN THIS MANNER. HOWEVER, APPLICATIONS OF COATINGS OR SURFACE MODIFICATIONS AT ELEVATED TEMPERATURES CAN FORM HARD AGGLOMERATES, AN UNDESIRABLE TRAIT. OPERATING A FLUIDIZED BED ABOVE THE TRANSPORT LIMIT (FAST FLUIDIZATION) OR IN THE TURBULENT FLUIDIZATION REGION MAY ENABLE CLASS C POWDERS INCLUDING FINE POWDERS AND WHISKERS, CHOPPED FIBERS, AND THE LIKE, TO BE FLUIDIZED WITH HIGH PRODUCT YIELDS. RESEARCHERS ARE DEMONSTRATING THE FEASIBILITY OF USING A FAST-FLUIDIZED OR TURBULENT FLUIDIZED BED FOR THE APPLICATION OF COATINGS TO FINE PARTICLES AND WHISKERS. THIS WILL ALLOW THE PRODUCTION OF IMPROVED STARTING MATERIALS FOR POWDER METALLURGY, CERAMIC, AND COMPOSITE MATERIALS, AS WELL AS IMPROVED CONDUCTIVE FILLERS, REINFORCEMENTS, AND ELECTRONIC MATERIALS.