Ultra-High-Pressure Cold Isostatic Pressing of Barium Titanate Ultrafine Particles

Abstract

In this paper, we discussed the effect of isostatic pressure on the green density and sintering properties of green compact of BaTiO3 ultrafine particles with stoichiometric composition, prepared by sol-gel method. Fine powder compacts were formed by high pressure cold isostatic pressing ranging from 0.05 to 0.90 GPa for 2 min. The particle diameter of fine powder, derived from Ba(OH)2 aqueous solution and titanium alkoxide, was controlled by calcination at 700°C for 2h. Ultra-high isostatic pressure at 0.90 GPa led to closed packing green bodies of ultrafine BaTiO3 particles. The maximum density of 68% was reached in green compacts of BaTiO3 particles, which were calcined at 700°C and whose particle size increased to 59nm in diameter. On the other hand, in the case of as-dried BaTiO3 particles at 200°C, with no calcination and whose particle size was about 19nm in diameter, the relative density was almost equal to that of calcined particle after exposure to a relatively low isostatic pressure, ranging from 0.05 to 0.19 GPa. However, the relative density of as-dried powder compact was higher than that of calcined powder compacts by using isostatic pressure > 0.19 GPa, and the maximum density of green compact was 81% of theoretical by using a ultra-high isostatic pressure of 0.90 GPa. Densification of green compacts of as-dried BaTiO3 particles in the high-pressure range might mainly occur by viscous deformation at the contact points between ultrafine particles. Green compacts were sintered in the range 700 to 1100°C for 2h. Closely packed green compacts of BaTiO3 particles could be sintered to a density > 96% of theoretical at relatively low temperature.