Journal of Colloid and Interface Science 259 (2003) 391–397 www.elsevier.com/locate/jcis Effect of solvent composition on dispersing ability of reaction sialon suspensions Xin Xu, Marta Oliveira, and José M.F. Ferreira ∗ Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal Received 20 May 2002; accepted 19 December 2002 Abstract This work focuses on the optimization of the rheological behavior of suspensions considering different solvent compositions. The effects of methyl ethyl ketone (MEK)/ethanol (E) solvent mixtures on reaction sialon suspensions were investigated by measuring sedimentation behavior, adsorption of dispersant, and flow behavior. It was shown that both the flow behavior and the sedimentation behavior strongly depended on selection of solvent composition. Using 3 wt% KD1 as dispersant, well-dispersed colloidal suspensions could be obtained in MEK-rich solvents. The suspensions with 60 vol% MEK/40 vol% E as solvent could be fitted to the Bingham model with very low yield stress, while suspensions with pure MEK or ethanol-rich mixtures as solvent showed pseudoplastic behavior with relatively high yield stress values. A model was proposed to explain the different flow behaviors of suspensions considering the different configurations of dispersant at particles’ surfaces.  2003 Elsevier Science (USA). All rights reserved. Keywords: Colloidal processing; Steric stabilization; Solvents; Rheology; Sialon 1. Introduction Sialon ceramics are considered the most promising ma- terials, with great potential for advanced structural applica- tions, due to their unique combination of excellent proper- ties [1]. However, the widespread use of sialon ceramics and strides forward in industrialization have been limited by low stability, difficulty in machining, and high manufac- turing costs of components, especially for fabricating parts with complex shapes. The colloidal forming technology is not only a prerequisite for assuring the design of a com- ponent but also a key processing step for improving the reliability and decreasing the production costs of ceramic materials [2]. Homogeneous, high concentrated ceramic sus- pensions with low viscosity are the key controlling factors for the production of ceramic components through colloidal processing. Achieving these properties requires precise con- trol of interparticle forces. This is done either by engineering an electric surface charge on the particles, resulting in elec- trostatic repulsion, or by adsorption of macromolecules onto the particles’ surfaces, resulting in steric repulsion [3]. * Corresponding author. E-mail address: jmf@cv.ua.pt (J.M.F. Ferreira). The dispersion of sialon powders in aqueous media has been studied by many authors [4–6]. However, reaction sialon suspensions containing Si 3 N 4 , Al 2 O 3 ,Y 2 O 3 , and AlN should be prepared in nonaqueous solvents through steric repulsion to avoid the hydrolysis of AlN [7]. Many authors have extensively studied the colloidal behavior of silicon nitride-based suspensions in organic media [8–10]. Their works have been mainly focused on the selection of suitable dispersants. However, the thickness of the adsorbed layers, the relative affinity of the dispersant to the surface, the adsorbed amount, and the solvency of the dispersant in the media are all strongly interrelated [11], indicating that powder dispersion is affected not only by the dispersant but also by the selection of solvent. Therefore, the selection of a proper solvent is also a key point in achieving highly stable suspensions. It has been shown that the xylenes/ethanol solvent mix- ture influenced the dispersion of PLZT suspensions [12]. It has also been observed that different mixtures of methanol and methyl isobutylketone resulted in different adsorption levels of long-chain poly(vinyl butyral) (PVB) resin and af- fected the rheological properties of Al 2 O 3 suspensions [13]. One of the most common solvent combinations used is an azeotropic mixture of methyl ethyl ketone (MEK) and 0021-9797/03/$ – see front matter  2003 Elsevier Science (USA). All rights reserved.