Rheology of Glaze Suspensions

Abstract

In chemical engineering and related industries, there are many cases involving the processing of suspensions such as paint, ceramic, drilling mud, coal and food. The presence of filler particles in elastomers and molten plastics are examples of such suspension systems. The design of pumps, pipelines, mixing, and heat transfer of suspensions requires a good understanding of the rheological behaviour of such materials.There are four forces that affect the rheology of suspensions, viz. i) the ever existing thermal, i.e. Brownian forces, ii) colloidal forces causing repulsion or attraction between particles, iii) viscous or hydrodynamic forces depending on the velocity field of the suspension medium and iv) inertial forces that become important for large particles and higher velocities. For small particles, i.e. smaller than roughly 1 µm, Brownian forces become noticeable (Russel et al. 1989;Macosko, 1994). Colloidal forces include repulsion and dispersion forces. The former originates from the interaction between similar charge sites on the particles and/or steric forces between adsorbed or grafted polymer molecules to the particles surfaces. The latter is composed of the attractive London-van der Waals forces resulting from the formation of spontaneous dipoles on the solid surfaces. Since these forces are surface forces, therefore they are more significant when dealing with small particles. The balance between colloidal, Brownian and hydrodynamic forces determines the rheology of the suspensions.The important role of colloidal forces in the rheology of suspensions has been addressed by many authors, however, their application into the modeling processes has been hindered by the difficulty in introducing them into the expressions for the suspension viscosity. The objective of this work is to provide a model that incorporates the influence of the colloidal forces on the rheology of such suspensions by introducing their contribution into the expression for the relative viscosity. Besides, the effects of kaolin, and a flocculating agent, calcium ion, have been investigated. Material and MethodSamples of dry frit were ground in five different lengths of grinding time using a laboratory ball mill. The grinding times were 14, 22, 38, 46, and 62 h. Thus, five samples with different particle size distributions were prepared. The particle size distributions were measured with a Fritsch particle size analyzer. Calculated mean particle diameters were 14, 6, 2.7, 1.6, and 0.9 µm in the order of increasing grinding time. By the measurement of the volume of the predetermined mass of glaze powder under pressure in a graduated cylinder, the values of maximum packing *Author to whom correspondence may be addressed. E-mail address: S_Savarmand@email.com Rheology of Glaze SuspensionsSaeid Savarmand*, Mohammad-Reza Golkar-Narenji and Kourosh Saedi Department of Chemical Engineering, Amirkabir University of Technology, Tehran 15914, I. R. IranRheological properties of suspensions and ceramic glaze slurries under steady flow conditions h...