Translated Research Paper
High-pressure Cold Isostatic Pressing of Ultra-fine Oxide Powders [Translated]†
1994 Volume 12 Pages 161-172
Details
1994 Volume 12 Pages 161-172
Fine Al2O3, MgO and SiO2 powders of various sizes were consolidated into a dense and uniform structure by high-pressure cold isostatic pressing. Although the average particle diameter was less than 21 nm, Al2O3, MgO and SiO2 powder compacts were compressed to 60% of their theoretical density by cold isostatic pressing at 1 GPa, because the open and strong aggregate structure collapsed under the cold isostatic pressure. The pore size of these compacts decreased below the primary particle size. Especially, in the case of MgO powders, the maximum relative density increased to 80% and the ratio of pore size to primary particle size was less than 20%. However, in the case of Al2O3 powders, whose size was more than 100 nm, a slight increase in relative density and decrease in pore size in the compacts occurred with an increase in isostatic pressure up to 1 GPa. In the case of particles larger than 100 nm and high-hardness materials, high cold isostatic pressure was not effective in increasing the packing density.
The mean vertical force and compressive stress at the contact point between particles in compacts and the maximum tensile stress in a particle during isostatic pressing were estimated using Rumpf's and Hertz's equation. Because these stresses were smaller than the hardness and tensile strength of Al2O3 or MgO materials, no viscous deformation or fracture of particle took place during compacting. The relations between the ratio of mode pore diameter to particle diameter and the relative density of Al2O3, MgO and SiO2 compacts agreed with those of spherical and monosized particle beds. The main mechanism of densification of compacts during isostatic pressing was the collapse of aggregates and rearrangement of particles.
† This report was originally printed in KAGAKU KOGAKU RONBUNSHU 19(2), 220-229 (1993) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Chemical Engineers, Japan.
