Fabrication Of Fine Scale Piezoelectric Arrays By Novel Aqueous Gelcasting

Abstract:Gelcasting has many advantages such as near net shaping and high mechanical strength of the as-produced green body, which provides an effective means to the fabrication of ceramic components with mirco-or nano-structures. In this thesis, a gelling system based on the polymerization of Hydantion epoxy resin and3,3’-Diaminodipropylamine (DPTA) was developed for PZT gelcasting. And the preparation of PZT slurries, the gelation process and the fabrication of the green bodies with high reliabilities was systematically studied. Excellent piezoelectric micropillar arrays with different shapes and aspect ratio higher than5were successfully fabricated by combining with soft molding technique. The main results of the research are listed as follows:1. Hydantion epoxy resin was firstly developed for the aqueous gelcasting of PZT ceramics. The effect and mechanism of dispersant concentrations, ball-milling process, solid loading and epoxy resin concentrations were systematically studied. The relationship between the solid loading and relative viscosity was more consistent with the fitted results using German model. The rheological behavior of the PZT suspensions transformed from shear thinning to shear thickening as the solid loading of the suspension increased. The reason for this phenomenon was analysised from the point of agglomerates in suspensions. The cooperative adsorption mechanism of dispersant and epoxy resin on the surface of PZT particles was illustrated using Zeta potential analysis.2. The gelation behaviors of the premix solution and the slurries were characterized by probing the time-dependent evolution of the relative viscosities. The effect of temperature, epoxy resin concentrations and solid loading on the gelation process were systematically studied. The Arrhenius equation was used to quantitative analysis the gelation process. With the increase of the temperature and epoxy resin concentrations, the gelation rate accelerated, and the induction period and the idle time reduced. With the increase of solid loading, the activation energy of polymerization reaction reduced. The epoxy rings are susceptible to unlock and the energy barrier was lowered under alkaline conditions and in the presence of hydrated surfaces/ammonium groups derived from the dispersant or amines.3. The effect of solid loading and epoxy resin concentrations on the relability of the mechincal properties of the green and sintered bodies were studied using Weibull analysis. The highest Weibull modulus16.49and14.79for green and sintered bodies respectively, were obtained for55vol%PZT suspensions containing20wt%Hydantion epoxy resin.4. The silicon/SU-8micropillars arrays with different shapes and aspect ratio higher than5were successfully fabricated using ICP and UV lithography. The PDMS molds were replicated from corresponding silicon/SU-8masters. The polymer masters fabrication techinique and replication mold method were developed. The fabrication techinique of the polymer master with adjustable dimension was firstly developed using the shrinkage characteristic of the Hydantion epoxy resin hydrogel during the drying process. Excellent piezoelectric micropillar arrays with different shapes and aspect ratio higher than5molded from corresponding PDMS molds were successfully fabricated using gelcasting.