Porosity development of diatomite layers processed by tape casting

The processing from colloidal suspensions is a good method to obtain bodies with low microstructural heterogeneities, by careful control of the interfacial stresses. In previous papers we described the use of slip and tape casting techniques to obtain diatomite porous layers, having controlled morphology such as the amount and size of pores. The present work reports the use of tape casting bodies for filtration purposes. As the maximum thickness of the layers produced by tape casting is about 0.3 mm, their mechanical resistance is very low. It was necessary to produce thicker compacts made by several single layers (up to 20), obtained by thermocompression at different temperatures between 20 and 90 degrees C followed by sintering at 1200 degrees C. By selecting a careful heating programme, final bodies with 0.6-1.3 mm thickness were obtained, having porosity levels of about 44% and pore sizes between 0.1 and 1 mu m. High bending strength values (57 MPa) were obtained, enough to support mechanical stresses in use as a membrane. Permeability to an air flux was evaluated as a function of relevant morphological parameters (porosity, thickness, etc.). (C) 1998 Elsevier Science Limited and Techna S.r.l. All rights reserved.