Permeability of diatomite layers processed by different colloidal techniques

Recently, efforts have been directed towards the development of ceramic fil ters for water treatment systems in which the microstructure is tailored to the application, is well characterised and is reproducible. This work repo rts on the use of slip and tape casting techniques, as well as a new "direc t consolidation technique", to obtain porous diatomite layers for filtratio n purposes. Diatomite has been chosen because of its low price, abundance, and intrinsic properties such as high porosity and small grain size. Layers prepared by tape casting and lamination, with a bending strength of 57 MPa , were almost 3 times stronger but less permeable than those produced by sl ip casting, due to the presence of binders and to the lamination step that promoted particle rearrangement. However, both forming techniques gave rela tively low permeable layers due to fine (0.25-0.6 mu m) and monomodal pore size distributions. The use of starch granules (30-50 wt%) as pore former a nd consolidator agents enabled to increase the permeability of sintered bod ies for almost one order of magnitude as a result of the increasing amount and average size of pores. As expected, porosity and average pore size valu es show a direct dependence on the starch content. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.