Permeability of diatomite layers processed by different colloidal techniques

Recently, efforts have been directed towards the development of ceramic filters for water treatment systems in which the microstructure is tailored to the application, is well characterised and is reproducible. This work reports on the use of slip and tape casting techniques, as well as a new “direct consolidation technique”, to obtain porous diatomite layers for filtration 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 slip casting, due to the presence of binders and to the lamination step that promoted particle rearrangement. However, both forming techniques gave relatively low permeable layers due to fine (0.25–0.6 μm) and monomodal pore size distributions. The use of starch granules (30–50 wt%) as pore former and consolidator agents enabled to increase the permeability of sintered bodies 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 values show a direct dependence on the starch content.