Microstructure of kaolin spheres produced by a gel-casting process with a biopolymer

Over the past few years due to increased environmental awareness, there has been great interest in improving ceramic processing to reduce the use of organic solvent and synthetic binders. This work is focused on a gel-casting process using a biopolymer that is environmentally friendly, easy to burn out and inexpensive. Starch was employed as a binder and kaolin clay was used as the starting material. To fabricate kaolin spheres, aqueous kaolin slurry was mixed with a starch solution. A small volume of the kaolin-starch solution was added to a vegetable oil at high temperature. The starch then formed a strong, cross-linked gel and immobilized the clay powders into the desired spherical shape. The kaolin spheres were then dried and sintered at different temperatures for 1 h. The phases present in the spheres was identified by X-ray diffraction (XRD) analysis. The microstructure and dimensions of the kaolin spheres were examined using a field emission scanning electron microscope (FE-SEM) in conjunction with energy dispersive spectrometry (EDS). An image analysis technique was used to identify the pore volume of the spheres. Copyright (C) 2006 John Wiley & Sons, Ltd.