DEFECTS IN LARGE HOLLOW POROUS CYLINDRICAL FILTERS MADE BY SHS

Abstract

The relevance of research is connected with the use of ceramic filters in biology and medicine for fine filtration of air and biological fluids abroad. Due to the unique combination of chemical and thermal resistance, high strength and thermal conductivity, ceramic filters are used to clean aggressive liquids, superheated high pressure steam and other gases. The dependence of burning rate on the relative density and granulometric composition of FeTiO 3 –Al–Si–SiO 2 –C powder mixtures is studied. The paper provides experimental results on the influence of initial charge compact density and composition on the quality of products obtained. The main types of defects appearing in the synthesis are identified. The causes of defects are found. Feedstock with particle sizes larger than specified values results in penetrations (cavities) occurring in the product. Their formation is caused by the increased liquid phase content in these regions due to decelerating reaction rate and rising temperature. Higher density results in transverse and longitudinal laminations in the product. Such laminations are formed under the pressure of gaseous products with the low gas permeability of the sample that declines as density increases. The technology of self-propagating high-temperature synthesis of large porous products is developed with the photographs of filtering elements presented: for the typical industrial gas burner GG-2, for superheated steam and demineralized water purification (filtering elements used in polyvinyl chloride process vessels at JSC «Sayanskkhimplast»), for iron removal from artesian water. Defect-free large porous products can be obtained with an optimal ratio of the sample grain size distribution and density, as well as reaction rate and heat removal rate.