Effect of Composite Ceramic Paste Velocity Profile on Extrudate Microstructure

Abstract

Composite ceramic materials prepared from a homogeneous mixture of basic components with optimal properties exhibit high mechanical strength. For preparation of a composite ceramic body with a high and uniform density in the body volume, proper technological processing of the mixture is necessary. Uniform microstructure and optimal particle distribution along with their orientation in the matrix volume are necessary for a positive effect of anisotropic particles. The objective of this work was to indicate the possibilities of controlling the microstructure in composite ceramic body at extrusion process in relation to resulting mechanical properties of the final material. Mathematical modeling of the flow of a composite ceramic paste through an extruder die was used to express the effect of forming parameters on the arising microstructure of the composite body. Orientation of the anisotropic particles can be influenced by the character of velocity field at the flow of composite ceramic paste through the circular extruder die. The velocity field established at the flow of ceramic paste can be described by a mathematical model of the non‐Newtonian liquid flow provided that its constitutive equation is known. The parameters of this mathematical function can be generally determined from the dependence of shear stress on the shear rate obtained by the capillary viscometer method. The velocity profiles of the flow of ceramics paste through the circular extruder die were calculated from a mathematical model and compared with experimentally determined profiles. The assumption concerning the influence of the velocity field on the anisotropic particle orientation during the paste flow was confirmed by a comparison of the evaluated anisotropic particle distribution with the corresponding shear rate profiles. The mathematical model of the paste flow allows for controlling the conditions under which various required particle orientations can be achieved. Those particle orientations range from a randomly oriented structure within the entire bulk to a structure of the oriented particles at the surface layer of the body. The model enables to control the preparation of composite ceramic materials to suit specific applications. The various orientations of the particles and their combinations aid to govern directional mechanical strength of composite ceramic materials.