Rheological characterization and tape casting of aqueous zircon slips
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Mater. Res. Soc. Symp. Proc. Vol. 1243 © 2010 Materials Research Society
Rheological characterization and tape casting of aqueous zircon slips M. León Carriedo, C. A. Gutiérrez Chavarría, J. L. Rodríguez Galicia, M. I. Pech Canul and J. López Cuevas. Centro de Investigacion y de Estudios Avanzados del IPN. Carretera Saltillo-Monterrey Km. 13,5 C.P. 25900, Ramos Arizpe, Coahuila, México. e-mail: [email protected] ABSTRACT In this work, a commercial zircon flour of 99% purity and mean particle size of 10µm is used. Suspension stabilization process is carried out using the electrostatic stabilization mechanism at pH 11 employing Tetramethylammonium hydroxide (TMAH). Tape casting suspensions are formulated with binding systems obtained by the combination of polyvinyl alcohol with polyethylene glycol, additionally the binding system is added at different binder:plasticizer ratio ranging from 1:1 to 3:1. Suspensions are characterized rheologically determining its type and flow properties by obtaining flow and viscosity curves. Suspensions are tape cast on vinyl-acetate substrates and are dried at room conditions to determine some physical properties of the obtained tapes and to correlate the rheological with the physical properties. The experimental results show that tape casting suspensions have a shear thinning flow type, yield points and flow indexes varying as a function of binder system combination and binder:plasticizer ratio. Also, the binder system has a strong influence on the green tapes characteristics. INTRODUCTION Zircon is a material that can be employed in a wide range of industrial and advanced applications at high temperature as structural material and/or in highly corrosive environments. Also, zircon has a low thermal expansion coefficient, which provides high thermal shock resistance and remains structurally stable up to its dissociation temperature at 1676°C. These properties make zircon a very attractive refractory structural material [1-3] and production of zircon tapes would widen its high temperature structural applications. The tape casting process is a method in use to transform suspensions into tapes with large area and low thickness [4]. The suspension of well stabilized ceramic particles is cast onto a flat surface and, after drying, the tapes can be cut in the proper shapes to produce different pieces or multilayer components [5]. A suspension adequate for the tape casting process requires large additions of binders and plasticizers. Binders and plasticizers modify the flow behavior of suspensions since they act as rheological modifiers. Thus they make possible to design the proper rheological flow behavior that requires the processing method [6]. For dry tapes, binders are responsible to ensure good particle cohesion and packing, providing tapes with sufficiently high green mechanical strength to resist handling and storage. On the other hand, plasticizers modify the properties of binders to give them enough flexibility to resist subsequent forming stages and handling. Ther
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