The present invention relates to particulate
alumina ball and to an industrial, economical method for producing particulate alumina which is particularly useful for materials, such as substrate material and sealing material for electronic parts, fillers, finish lapping material and aggregates incorporated into refractory, glass, ceramic, or composites thereof; has a narrow particle size distribution profile (i.e., containing few coarse particles and microparticles); causes little wear; and exhibits excellent flow characteristics. The invention also relates to particulate alumina produced through the method and to a composition containing the particulate alumina.
There has also been known a thermal spraying method in which
alumina ball produced through the Bayer method is jetted into high-temperature plasma or oxygen-hydrogen flame to thereby produce roundish crystal particles through melting and rapid quenching. However, the thermal spraying method has a drawback that unit heat energy requirement is large, resulting in high costs. In addition, the thus produced alumina, although predominantly containing -alumina, includes by-products, such as -alumina. Such an
alumina ball by-product is not preferred since the product exhibits low thermal conductivity.
Electronic parts used in a cellular phone or in a similar apparatus are required to be adapted to modularization and higher-speed, higher-frequency operation. A multi-layer substrate used in the apparatus, particularly a glass-ceramic substrate, having a low dielectric constant is particularly advantageous from the viewpoint of, for example, conductor loss of wiring and incorporation of a passive part in the substrate. However, the glass-ceramic substrate is inferior to an alumina-ceramic substrate in terms of properties, such as mechanical strength and dielectric loss. In order to ensure enhanced characteristics of the glass-ceramic substrate, particulate alumina having a roundish shape and a smaller particle size, exhibiting a narrow particle size distribution profile and containing an active chemical component must be used as a filler. These features cannot be attained by conventionally employed
alumina ball.
