Preparation of Sizable and Uniform-Sized Spherical Ceramic Foams: Drop-in-Oil and Agar Gelation

Abstract

We propose a simple and environmentally friendly method to prepare uniform-sized spherical ceramic foams (SCFs) with excellent pore properties by combining a drop-in-oil method with agar gelation. In addition, the change in size distribution and uniformity (characterized as coefficient of variation (C.V.)) and the corresponding pore-related properties for the SCFs were systematically investigated as functions of agar concentration (i.e., 0.50-1.50 wt% with respect to dry alumina). The results showed that uniform-sized SCFs were successfully fabricated regardless of agar concentration, that pore-related properties were gradually improved by increasing the agar content, and that the most uniform-sized SCFs were obtained when the agar concentration was 1.00 wt%. The extent of the improvement in size uniformity was evaluated by comparing the C.V. value for the drop-in-oil method with that for the pseudodouble-emulsion (PDE) method, which is an alternative method to fabricate SCFs. The C.V. values for the SCFs prepared by the drop-in-oil and the PDE method were determined to be 7% and 31%, respectively. The results clearly indicate that the size uniformity of the SCFs has been much improved for the drop-in-oil method as compared to the PDE method.