Colloidal processing and sintering of NANO-ZrO2 powders using polyethylenimine (PEI)

Abstract

A stable colloidal suspension is important for fabricating dense samples with uniform microstructure using colloidal processing methods. Aqueous nano-ZrO<inf>2</inf> suspensions were prepared using polyethylenimine (PEI) as a dispersant. PEI adsorption on nano-ZrO<inf>2</inf> surfaces was influenced by PEI content and suspension pH. The isoelectric point (IEP) shifts from pH 7 at 0 wt% PEI to pH 10.3 at 3 wt% PEI. Stable suspensions had mean particle sizes in the range of 100 to 150 nm and sedimentation rates less than 0.4 mm/h, as compared to 2-5.5 ?m and 10-50 mm/h for unstable suspensions. Electrostatic interactions, hydrogen bonding and PEI conformation were found to be controlling mechanisms on the colloidal stability of the suspensions. The amount of PEI adsorbed on nano-ZrO<inf>2</inf> surfaces was characterized using Thermogravimetric analysis (TG) and Fourier transform infrared spectrometer (FT-IR). The densification behavior of samples containing 3 wt% PEI at pH 7.1 sintered for 4 h at 1000 to 1300°C was characterized. Relative density was found to increase rapidly from 54 % at 1100°C to 92% at 1200°C and finally to 98 % at 1300°C. Therefore, pellets were sintered at 1300°C for 4 h to quantitatively correlate the processing conditions such as effect of pH and PEI content with densification. © 2008 Elsevier B.V., All rights reserved.