Scientific Research and Essays Vol. 6(11), pp. 2302-2305, 4 June, 2011 Available online at http://www.academicjournals.org/SRE DOI: 10.5897/SRE10.686 ISSN 1992-2248 ©2011 Academic Journals Full Length Research Paper Investigation of the effects of different deflocculants on the viscosity of slips A. Evcin Materials Science and Engineering Department, Engineering Faculty, Afyon Kocatepe University, 03200 Afyonkarahisar, Turkey. E-mail: evcin@aku.edu.tr. Tel: +90 (272) 228 14 23. Fax: +90 (272) 228 14 22. Accepted 20 September, 2010 Various parameters like the solid concentration of the slip, chemical and mineralogical composition, particle size and distribution and shape, density of slip, type and content of electrolyte, temperature and pH, affect the rheological parameters of slip. In this study, the effect of various electrolytes on Söğüt and Konya clays have been assessed. Slips were prepared by adding various amounts of the electrolytes sodium carbonate, sodium silicate and sodium triployphosphate and their viscosity were measured. The slip used in this study had solid concentration about 65%. The results of the experiments have shown that the lowest viscosity is attained in clay and slip prepared with sodium triployphosphate. Key words: Viscosity, slip, rheology, deffuloculant, clay. INTRODUCTION Slip casting method has been used in classic or modern ceramic industry for two hundred years. In this method, determining the rheologic features of slips is vital for controlling the process (Özel et al., 2002). Slip casting is known to be a suitable and inexpensive compaction process to produce material with high green densities and micro structural homogeneity, even for complex geometries (Xu et al., 2003). The slip casting process is widely used to consolidate ceramic particles from aqueous suspensions. In this process a porous mould is filled with a slip, consisting of a ceramic powder mixed with water. The capillary action due to the pores in the mould withdraws the liquid medium from the slip. Excellent fluidity, low water content, high stability, and high water permeability are essential properties in ceramic slip casting. The main factor for successful wet processing of slips that contain clay is the interactions between the particles. Chemical additions strongly affect the surface chemistry of the ceramic powder by increasing or decreasing the interaction forces between the particles (Deliormanli and Yayla, 2004). Many scientists have studied the effects of different chemical materials such as sodium tripolyphosphate, sodium hexameta phosphate, sodium polymethacrylates, ammonium phosphate, sodium citrate, polysulfonate on the dispersion behaviour of clay particles in aqueous systems (Papo et al., 2002; Guler and Balcı, 1998; Corradi et al., 1994). Sodium carbonate and sodium silicate are well known deflocculants used for sanitary ware ceramic slips. Mixtures of these two chemical agents are usually the most satisfactory. Sodium hydroxide is also as active as sodium carbonate and sodium silicate, but it is not used to a great extent because of its corrosiveness (Deliormanli and Yayla, 2004). Rheology is the branch of science concerning the fluidity and deformation properties of materials. Therefore it is indicated as the deformation of body under tension. Especially wet mixing, grinding, slip casting, glazing and decorative processes are related to rheology intensely. Moreover, rheologic behaviours of colloidal suspensions depend on the key factors distinctly mentioned as follows: 1. Viscosity of dispersing media 2. Particle concentration 3. Size and shape of particle 4. Interaction of particle-particle and particle-dispersing media (Özel et al., 2002). The most common electrolyte used in the sanitary ware slips is sodium silicate (Na 2 SiO 3 ). Some alkaline silicates and carbonates such as calcium silicate (CaSiO 3 ), calcium carbonate (CaCO 3 ), sodium carbonate (Na 2 CO 3 ) are also used as electrolytes to provide the fluidity. Anionic poly-electrolytes such as poly-acrylates and poly- phospates are used in some case to regulate slip viscosity. Lowering the viscosity with alkaline–silicate and