a-Al2O3 is widely used and studied as high temperature structural material, electronic packaging, corrosion resistance ceramics and translucent ceramics. The surface state of a-Al2O3 powders cannot be regarded as a-Al2O3 but a hydrated state, and that the nature of this hydrate cannot be considered universal among different a-Al2O3, even produced by the same production method. One of these reasons is that water can be incorporated in the a-Al2O3 crystal structure resulting in the formation of aluminum hydroxides such as gibbsite. Although much research has shed light on the Al2O3-water interface and charging of a-Al2O3 surfaces, there is still much that we need to better understand a-Al2O3 structural property and surface characteristics. In this paper, general view of crystal-structural properties, manufacturing methods of high purity a-Al2O3, and surface characteristics on a-Al2O3 powders are introduced. Table 1: Soda impurity level required for different applications

/pdf/structural-properties-and-surface-characteristics-on-3i87ypgdb9.pdf

Structural properties and surface characteristics on aluminum oxide powders

Applications of grinding kinetics analysis to fine grinding characteristics of some inorganic materials using a composite grinding media by planetary ball mill

Wet dispersion mechanism of manometer-sized silica powder was investigated in a verticaltype beads mill using fine zirconium oxide (zirconia) beads. Zirconia beads of various sizes were used to disperse coagulated silica powders in nanometer size. The dispersed particles were measured by TEM and a dynamic light scattering technique and the contamination during the dispersion was also evaluated. Fine beads with the average diameters of 20μm and 50μm were found to be very effective for suppressing contamination from the beads as well as for achieving its homodispersity. 300μm-zirconia beads used in the present work had a very rough surface, which resulted in the silica powder contamination with zirconia in the level of 3250ppm. On the contrary, the surface of 20μm-beads was smooth and zirconia-contamination in the silica powder was decreased to 240ppm. The observation of bead surface and the amount of zirconia (impurity) suggested that the surface of large bead is easily worn away due to the collisions between the beads compared to smaller beads. The coagulated silica powder can be dispersed homogeneously using the beads with size smaller than 50μm, whereas coagulated silica particles were observed using the beads with size larger than 100μm. For coagulates of nanoparticles, main dispersion mechanism with large beads is pulverization while that with small beads is deflocculation. It is important not to give excessive energy to the coagulated particles for preventing the recoagulation and the contamination from the beads. Smaller beads (below 100μm) is suitable in this case.

Effect of Small Size Beads on Dispersion of Nanometer-Sized Silica Particle by Wet Beads Mill Process

Doping a small quantity of additive Bi2O3 is effective in suppressing the deliquescence of KNbO3 ceramics. When an optimized ball-milling process was included, dense and nondeliquescent KNbO3 ceramics were obtained by a conventional firing process. However, the presence of Bi prevented grain growth (

Processing and Electrical Properties of KNbO3 Ferroelectric Dense Ceramics Added with Small Amount of Bi2O3 and MnCO3

A series of wet grinding experiments by a vertical type planetary ball mill with various composite grinding balls were carried out using calcite powder as the sample. From comparison of particle size distribution of the ground products using monosized grinding balls and composite grinding balls, it was found that the grinding rate for composite grinding balls of q=0.1-0.3 was improved by 27% compared with that of the small monosized grinding balls of dB=2.58mm. The possibility of improvement was also confirmed from the experimental data using a high-G planetary ball mill of 150G.

https://www.jstage.jst.go.jp/article/sptj1978/33/9/33_9_747/_pdf

Grinding Rate Improvement Using a Composite Grinding Ball Size for an Ultra-fine Grinding Mill

Submicron grinding of BaTiO3 powder was studied by a ball mill with small alumina balls of 0.75mmφ to 30mmφ. BaTiO3 clinker which was obtained by calcining equimolar of TiO2 and BaCO3 was preground to 1.8μm. Submicron grinding of the BaTiO3 powder was possible by ball milling with several mmφ balls. In the case of ball diameter of 2mm, the specific surface area was maximum.An attempt was made to represent the specific surface area in terms of volume per ball and total surface area of used balls, and the following experimental equation with a time term was obtained.ln(SS)=-0.247lnr3-0.738/r+0.429lnt+1.57 where SS is the specific surface area, r is the ball radius and t is time. The multiple correlation coefficient R was found to be 0.982 when calculated by a computer.

Kichi Minai

Papers

Submicron Grinding of BaTiO3 by Ball Milling