Known porous bodies employed for filter materials or catalytic carriers include those consisting of various materials such as resin, metals or ceramics. Among these, a filter or a catalytic carrier consisting of a ceramics material is generally employed in high temperature or strongly corrosive environments which other materials cannot withstand. A filter or a catalytic carrier consisting of oxide ceramics such as alumina (Al.sub.2 O.sub.3) has already been put into practice.
As to a porous body consisting of nonoxide ceramics, on the other hand, only small examples have been put into practice while Japanese Patent Laying-Open No. 63-291882 discloses a silicon nitride based or silicon carbide based porous body prepared by a heat treatment. Further, Japanese Patent Laying-Open No. 1-188479 discloses a method of compacting mixed powder of silicon powder and silicon nitride powder of relatively coarse particles and thereafter nitriding the same thereby preparing a porous body as a solid target.
As hereinabove described, it is difficult to use a porous body consisting of resin or a metal in a high temperature or corrosive atmosphere. It is inevitably necessary to employ a porous body made of ceramics for a filter for removing foreign matter from a high-temperature exhaust gas or for a carrier serving as a catalyst for decomposing a harmful matter.
As an example of such porous bodies made of ceramics, porous bodies made of alumina have been put into practice. While the porous bodies of alumina are varied in pore size, porosity and bending strength, a porous body having a porosity of 35 to 40% and a mean pore size of 25 to 130 .mu.m has a bending strength of 20 to 35 MPa, whereby the strength of the porous body is insufficient depending on its use.
In the silicon nitride based porous body disclosed in the aforementioned Japanese Patent Laying-Open No. 63-291882, the porosity is less than 30% and fluid permeability is insufficient. In general, the strength of ceramics tends to be reduced following an increase in the porosity, and it has been extremely difficult to attain compatibility between the porosity and the strength.