Characterisation of ceramic membranes

The performance of porous ceramic membranes is typically expressed by the permeate flux (throughput) and the selectivity (separation ability), which in turn are governed by the pore size distribution, porosity and intrinsic membrane surface properties, and as such there are a variety of direct and indirect characterisation techniques used to evaluate the potential of a membrane and predict its performance. In this way new membranes can be efficiently and effectively screened and later optimised without the need for lengthy permeation experiments, reducing overall development time. Similarly, these techniques can be used to understand and/or verify a new membrane s transport and separation mechanisms. 

The separation characteristics and performances of the composite ceramic membranes are ultimately determined by the morphology and underlying microstructure of the membrane, whether it be a symmetric macroporous filter element or an asymmetric microporous composite membrane for gas 

13 Electron microscopy images of porous ceramic membranes taken with SEM (a) andTEM (b). 

Hie characterisation of porous membranes is, for the most part, no different from the characterisation of porous solids, although in the case of membranes, the nature of the percolative network of pores is crucial for understanding transport of the desired species through the membrane and rejection of undesired species. The most common and accurate method for determining pore size and structure is by employing probe molecules to adsorb the pore walls and/or condense within the pores themselves. 

The technique of gas adsorption/desorption is perhaps the most widely used for characterisation of porous materials for the determination of pore size, specific surface area and pore size distribution. The adsorption/ 

---

J. Rocek and P. Uchytil, Evaluation of selected methods for the characterisation of ceramic membranes. /. Membr. Sci., 89 (1994) 119. 

---