Abstract
Much studies have been carried on the compaction of powder. However, fine powder has high cohesiveness and is considerably different in its behavior from usual powder of above several microns in particle size. In order to investigate the compaction process of high cohesive fine powder, the compacted samples were made from silicon nitride by the following methods:
(1) uniaxial compaction of dried powder,
(2) uniaxial compaction of dried granulated powder,
(3) centrifugal compaction of slurry using ethanol as a medium,
(4) uniaxial compaction of granulated powder wetted with ethanol, and
(5) isotactic compaction of dried powder
Each columner sample so obtained was cut into three equal parts in the longitudinal direction, and the apparent density, pore size distribution and compression strength of each specimen were measured. In the dried powder the compressive force was not transmitted enough through powder to the lower part because it was dissipated due to the internal friction of powder bed. Accordingly, the lower the position, the more are the porosity and heterogeneity of the body. In the wetted powder in which liquid filled up the pore volume of interparticles, the compressive force was transmitted enough through powder to the lower part because the granulated powder was deformed easily with compression, and therefore the powder can be formed into a uniform body having high strength. Although in isotactic compaction the applied force spread uniformly throughout, the mechanical strength of the resulting fabricated body was not so good. This suggests that some sliding planes are formed locally during compaction. The compaction process of each sample was discussed based on Cooper's equation representing the relationship between pressure and compressibility ratio.
