Mechanism of Hard Agglomerate Formation in a High Purity Sub-micron .ALPHA.-Alumina Powder.

Abstract

A high purity, sub-micron, α-alumina powder produced by the hydrolysis of aluminum alkoxide method and a thermally hydrated product of the as-received powder have been investigated. The powders were divided into two particle size range fractions. The intensity of aluminum trihydroxide polymorph bands is larger in the diffuse reflectance infrared Fourier transform (DRIFT) spectra of the large particle size fractions of the as-received, as well as the hydrated product. The amount of aluminum trihydroxide polymorphs in the hydrated powder was large enough to be detected in the X-ray diffraction (XRD) pattern of the powder. Scanning electron microscope (SEM) observation of the powders shows the presence of large agglomerates in the hydrated powder. A smaller amount of agglomerates is also noticeable in the as-received powder. Transmission electron microscope (TEM) images of the as-received and hydrated alumina powders revealed the presence of a surface layer interconnecting neighboring α-alumina particles. It is concluded that Al(OH)3 surface structures of adjacent particles can form hydrogen bonding creating crystalline structures similar to the aluminum trihydroxide polymorphs. These structures are believed to be responsible for the formation of hard agglomerates even in the as-received alumina powder.