PLASTIC EXTRUSION FORMING OF NANOMETER-SIZE TETRAGONAL ZIRCONIA POWDER

Plastic extrusion forming of nanometre size (20 nm) tetragonal zirconi a powder with polyvinyl alcohol (PVA) as binder has been studied. Plas tic bodies had plasticity indices of 1.0-4.0 kg cm, comparable with cl ay, when 2-6 wt-% PVA and a water content of 40-60 wt-% were used. The plastic bodies also exhibited high plasticity at low stress levels in stress-strain curves. Green samples had a low relative density (<27%) and underwent a large linear shrinkage (47%) on sintering at 1350-165 0 degrees C for 4 h. The grain size of samples sintered at 1650 degree s C for 4 h was 3-10 mu m and the density 99.5% theoretical. The obser ved high plasticity and low green density are attributed to the very s mall particle size of the powder, the large specific surface area of t he powder absorbing a great amount of wafer (>80 vol.-%) as an interfa cial film between the particles.