(261d) Porous Ceramic Foams By Emulsified Alumina Powder Suspensions in Water

Porous ceramics have applications in a wide variety of technologies such as filters for hot liquids or gases, supports for catalysts and batteries, thermal and acoustic insulation, biomaterials and many others. Porous ceramics are synthesized by different methods which are typically based on the use of a polymeric matrix.  However, these approaches have known disadvantages especially in terms of the consolidation process, the pore size and distribution, and overall porosity. An alternative processing methodology for attaining porous ceramics is the use to emulsified powder ceramic suspensions that, when stabilized, can yield high porosity, varying pore sizes, and excellent sinterability without the use of polymeric matrices.

The emulsified suspension process involves three steps: conformation of the suspension, which is fundamental for the stability of the colloidal system; the emulsification of the suspension, where the droplets of disperse phase are distributed in the aqueous phase; and the forming and sintering of the ceramic body. 

Here we will discuss effect of processing variables in the emulsified suspensions and its relationship with the microstructure of the sintered ceramic.  In particular, the effects of homogenization speed, simple and double emulsification, and type and percentage difference of oil dispersed phase will be presented.  The material system focus of this work is comprised of alumina powder, deionized water and sodium polyacrylate to form a suspension combined with mineral oil and surfactants to stabilize the emulsified suspension. 

In a typical process, the ceramic powder is mixed with water and the dispersant in a homogenizer to ensure a homogenous suspension.  Next, the oil phase is incorporated into the suspension with surfactants at different homogenization speeds. Finally, the system is dried under controlled conditions of temperature and humidity.  Afterwards, a sintering profile optimized to reduce thermal stresses is used to prevent cracks and the collapse of the porous ceramic body. 

The analysis of the rheology and emulsified oil phase size distribution of the colloidal systems will be presented and correlated with the pore size distribution and morphology of the sintered ceramic.

We will show that changes in the speed of homogenization results in differences in the oil phase size distribution and the viscosity of the emulsified system regardless of the type of oil phase dispersed.  Further, we will demonstrate that double emulsification processes enhances the polydispersity of the emulsified suspensions and the pore size distribution in the sintered ceramic.