JOURNAL OF MATERIALS SCIENCE 37 (2 0 0 2 ) 929 – 934 Effect of type of solvent and dispersant on NANO PZT powder dispersion for tape casting slurry S. BHASKAR REDDY, P. PARAMANANO SINGH Department of Metallurgical Engineering, Indian Institute of Technology, Madras, Chennai 600 036, India E-mail: ps@iitm.ac.in N. RAGHU, V. KUMAR Centre for Materials for Electronics Technology (C-MET), Thrissur 680 771, India Dispersion of PZT powder of average particle size ∼75 nm in commonly used solvent systems for tape casting namely, toluene-ethanol and MEK-ethanol (azeotropic), xylene-ethanol (zeotropic) along with triton x-100, menhaden fish oil and phosphate ester as dispersants has been studied using simple sedimentation experiments. The relative merits of these three solvent systems and dispersants in dispersing PZT powder was analyzed. In all the three solvent systems, phosphate ester was found to be the best dispersant. Xylene-ethanol with phosphate ester gave the excellent dispersion characteristics for nano-PZT powder. The results of initial dispersion studies were confirmed by the formation of defect free, denser and smooth green tapes using xylene-ethanol and phosphate ester, while the other two solvent systems gave defective green tapes. The influence of phosphate ester on dispersion is explained by the dissociation and ionization, and the dominance of electrostatic repulsion even though organic solvent systems were used. C  2002 Kluwer Academic Publishers 1. Introduction Lead zirconate titanate Pb(Zr x Ti 1-x )O 3 (PZT) are of interest owing to their ferroelectric and piezoelectric properties [1–3]. Piezoelectric actuators are of great interest as micro-displacement transducers. Multilayer technology is used to fabricate these devices, which brings the drive voltages down to ∼75–150 V [4]. The increasing demand for miniaturization of multi- layer actuators requires the improvements in processing techniques, the starting materials and their characteris- tics. There are techno-economic pressures to reduce the layer thickness to around 20 μm, which demands the use of well-dispersed sub-micron sized ceramic pow- ders. Such thin layers are produced using tape casting technique [5]. Tape casting slurry consists of ceramic powders dispersed in solvents and dispersants together with binder and other additives. In achieving uniform, dense, dimensionally accurate ceramic sheets, the col- loidal processing of tape casting slurry is the critical step [6]. A well dispersed and highly stable slurry sys- tem, shear thinning behavior and optimized low viscos- ity, high solid content to control the shrinkage during further densification by sintering are the required char- acteristics of the tape casting slurry to obtain defect free green tapes and hence, the slurry preparation requires a more thorough investigation [7–9]. Slurry preparation usually involves particle defloc- culation and dispersion in a solvent using dispersants and slurry homogenization with the aid of binders and plasticizers. The first stage strongly influences green tape characteristics whereas second stage influences the final product properties such as density and mi- crostructure homogeneity [8]. There is ample evidence that systems which are not fully deflocculated contain voids in the cast tape, which are difficult to eliminate during firing and results in porosity in final product [10]. Thus, full dispersion of tape casting slurry is necessary for uniform, high-density dielectrics. It is in this con- text that recently, stabilization of dispersions of oxide particles in organic liquids has become a major con- cern in tape casting. Stable suspensions are achieved due to steric stabilization or electrostatic stabilization or both depending upon the type of dispersant used. Steric stabilization is caused by polymeric dispersant of long chain molecule whereas electrostatic stabilization is caused by surfactants [11, 12]. Binders in the slurry may also provide some dispersion effect [13–15]. Measurement of sedimentation height and packing density of particles in suspension is a well-accepted method to establish the degree of particle dispersion and packing. The efficiency of dispersion is evaluated by slower rate of settling of particles and higher final settling density. The state of particle dispersion has very sensitive role to play in the rheological properties of the slurry. Usually the slurry viscosity decreases with in- crease in flocculation of particles. Powder dispersion is not only dependent on the dispersant but also on the type of solvent used [9]. Tsurumi [16] studied the dispersability of PZT powders in different pure organic solvents. It is well established that a slurry composed 0022–2461 C  2002 Kluwer Academic Publishers 929