Production of macroporous ceramics from fibres dispersed mortars (FDM)

We examined the production of macroporous monolithic ceramic from mortars prepared using aluminate cements, one or two different types of alumina powders, superfluidificant, water and polyurethane fibres. Some relevant parameters for the preparation process of the mortar are: (i) the weight ratio between cement powder and water, (ii) the weight ratio between superfluidificant and cement powder and (iii) that between superfluidificant and water. Thirty-six percent is the upper limit for the volumetric content of the fibres that can be introduced into the mortar without leading to a material that breaks up by handling after the successive thermal cycle. We also optimized the thermal cycle that may be used in order to avoid the spontaneous break-up of the material during the sintering treatment. Materials containing fine and coarse particles of alumina powders exhibit extended ruptures probably dependent on the thermal stresses that grow on cooling after the sintering process, whereas in materials containing only fine alumina powders the presence of ruptures is more limited so that the fired materials have a sufficient strength and can be handled without a particular care. The ageing time at the maximum temperature plays an important role on the microstructure of the sintered material since it has been seen that after 2 h at 1250 degrees C the residual porosity seems to be completely closed and the large grain size shows the presence of structures which can be due to the presence of aluminates. (c) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.