The Segregation of Particle Size in the Centrifugal Compaction Process of Submicron Alumina Powder

Abstract

An investigation was made of the characteristics of the green compacts, the compacts semisintered at 800°C and those sintered at 1250°C, in order to check the segregation of particle size in the centrifugal compaction process of ceramics.
Two alumina powders were used. One was a 0.22 μm powder (size range: 0.1-0.3μm) and the other was a 0.77 μm powder (size range: 0.2-1.0μm). These were dispersed with a ball mill. The coefficients of the viscosity of the slips were in the range of 40-2000mPa⋅s.
The fracture surfaces of the 0.22 μm powder compacts semi-sintered at 800°C were observed by S EM, and showed the particles 0.1-0.3 μm in size distributing uniformly from the bottom to the top in the compacts. On the other hand, the bigger particles of about 1.0μm in size were shown concentrating at the bottom in the 0.77 μm powder compacts.
When the compacts were made from the 0.22 μm powder which had a narrow particle size range, the moisture of the green compacts, relative green density, sintered density and dimensional change of the compacts, were uniform in the vertical direction. The compacts made from the 0.77 μm powder having a wide particle size range, however, showed no uniformity in those characteristics, and a particle size segregation was observed in them.
As a conclusion, a powder with a narrow particle size range must be used in order to obtain a uniform compact in the centrifugal compaction process.