Monolithic honeycomb structure made of porous ceramic material, and use as filter for particulates

摘要

The monolithic structure having channels opening at its end faces comprises 70-97 wt.% alpha - or beta -silicon carbide and 3-30% wt.% binder ceramic phase of at least one of B2O3, Al2O3, SiO2, MgO, K2O, Li2O, Na2O, CaO, BaO, TiO2, ZrO2 and Fe2O3 and/or a mixed oxide selected from alkali(ne earth) metal aluminosilicates, clays, bentonite, feldspars and other natural aluminosilicate materials. The external shape of the structure is defined by a cylindrical surface bearing on two extreme surfaces having any form. The structure has porosity 35-65 cm3/g and pore size distribution of 5-60 microns . The monolithic structure has 7.75-62 channels per cm2. The channels have a cross-section of 0.5-9 mm2, and the walls separating the channels have a thickness of 0.3-1.5 mm. The channels can be alternately open and closed at either of their ends. The alpha - or beta -silicon carbide has at least one, preferably at least two, more preferably two to five, particle size distributions. The average particle size of the silicon carbide is 3-125 microns . Preferably, most of the silicon carbide particles are of size 15-125 microns and a minor part of the silicon carbide particles are of average size less than 15 microns . The ceramic binder phase has an overall composition that is adjusted so that it has a coefficient of expansion close to that of the silicon carbide within a margin of 50%. Independent claims are given for (a) a method of producing the monolithic structure; and (b) use of the monolithic structure as a filter for filtering particles from diesel engine exhaust gas. Production of the monolithic structure involves: (i) mixing the components to form a homogeneous product in the form of a bound paste; (ii) extruding the product through a die so as to form a monolithic honeycomb structure; (iii) drying the obtained structure; (iv) calcining the structure at not more than 1650 degrees C in an oxygen-containing atmosphere; and (v) plugging one channel out of two at each end of the structure. The latter stage (v) can be carried out at any stage of the process after extrusion.