Processing Methods for Clay-Based Ceramics
The study of clay-based ceramics has an enduring legacy due to the science that developed to understand the rheological behavior of clay-water pastes. As stated repeatedly in this chapter, clays develop plasticity when mixed with water. Plasticity, as defined by Grim, is “the property of a material which permits it to be deformed under stress without rupturing and to retain the shape produced after the stress is removed” . For countless generations, clay-based ceramics were formed by mixing clay and other ingredients with some amount of water (determined by trial and error and/or experience) to get a consistency (i. e., rheology) that was acceptable for the forming method of choice. As new analytical tools were developed throughout the twentieth century, ceramists used them to examine the structure of clay minerals and to understand how clays interacted with water. Even though the emphasis in the field of ceramic engineering has shifted away from traditional ceramics to advanced materials, processing science still focuses on processing methods (dry pressing, extrusion, tape casting, and slip casting) that rely on controlled plastic deformation during forming, thus mimicking the behavior of clay – water pastes . The key difference is that advanced materials use organic additives to promote plasticity whereas plasticity develops naturally when water is added to clays.