Porous body, honeycomb filter, and method for producing porous body

Abstract

A porous body has a flow-rate-weighted mean diameter Ru of 10 μl or more and 24 μm or less, which is obtained as follows: with reference to porous-body data obtained by a CT scan in which positional information is associated with voxel-type information, a plurality of virtual curved surface solids, which are each a curved surface solid made up of a plurality of virtual spheres, are placed to fill space voxels (Step S 100 ); fluid analysis is carried out to obtain information regarding the flow rates of a fluid in individual space voxels during passing of the fluid through the porous body (Step S 110 ); and, the flow-rate-weighted mean diameter Ru is obtained, which is a weighted mean obtained by weighting the equivalent diameter R′ i of each virtual curved surface solid with the volume V i and average flow rate U i of each virtual curved surface solid (Step S 120 ).

What is claimed is: 
     
         1 . A porous body having a flow-rate-weighted mean diameter Ru of 10 μm or more and 24 μm or less, wherein the flow-rate-weighted mean diameter Ru is obtained as follows:
 based on an image obtained by three-dimensionally scanning the porous body, porous-body data is created in which positional information indicating position of a voxel in the image is associated with voxel-type information indicating whether the voxel is a space voxel representing space or a matter voxel representing object; 
 a process is carried out in which a single parent virtual sphere is placed in the porous-body data so as to have as large a diameter as possible so that the parent virtual sphere fills the space voxels without overlapping the matter voxel, at least one child virtual sphere whose center overlaps the parent virtual sphere that has been placed is placed such that voxels occupied by the at least one child virtual sphere do not overlap the matter voxel and fill space voxels, and a single virtual curved surface solid made up of the parent virtual sphere and the at least one child virtual sphere is placed such that curved surface solid voxels, which are voxels occupied by the virtual curved surface solid, fill space voxels; this process is repeated to place a plurality of the virtual curved surface solids such that voxels occupied by different virtual curved surface solids do not overlap each other; 
 based on the porous-body data, fluid analysis is carried out by the lattice Boltzmann method in terms of a fluid flowing through a predetermined inflow plane into the porous body, to obtain flow-rate vectors of the fluid in individual space voxels during passing of the fluid through the porous body; and 
 based on information regarding the virtual curved surface solids that have been placed and information regarding the flow-rate vectors in individual space voxels, the flow-rate-weighted mean diameter Ru is obtained by an expression (1) below 
 
       
         
           
             
               
                 
                   
                     
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         where 
         Ru: flow-rate-weighted mean diameter [μm] 
         n: number of virtual curved surface solids that have been placed [number] 
         R′ i : equivalent diameter of each virtual curved surface solid [μm] (i=1, 2, . . . , n) 
         V i : volume of each virtual curved surface solid [cc] (i=1, 2, . . . , n) 
         U i : average flow rate of fluid passing through each virtual curved surface solid [mm/s] (i=1, 2, . . . , n). 
       
     
     
         2 . The porous body according to  claim 1 , wherein, based on the information regarding the virtual curved surface solids that have been placed, an arithmetic mean diameter Rc=(R′ 1 +R′ 2 + . . . +R′ n )/n is obtained, and
 a difference ΔR (=|Ru−Rc|) is 2 μm or less. 
 
     
     
         3 . A honeycomb filter comprising
 a partition that include the porous body according to  claim 1  and form a plurality of cells of which one end is open and the other end is sealed and serving as a fluid channel.   
     
     
         4 . A method for producing a porous body, comprising:
 a raw-material mixing step of mixing talc having an average particle size of 1 μm or more and 18 μm or less, alumina, an auxiliary raw material containing a material that undergoes a eutectic reaction with talc and being prepared in an amount so as to satisfy a weight ratio of 0.5% or more and 1.5% or less by weight relative to the talc, and a pore-forming agent, to provide green body; and   a molding and firing step of molding the green body to provide a compact and firing this compact at a firing temperature of 1350° C. to 1440° C.   
     
     
         5 . The method for producing a porous body according to  claim 4 ,
 wherein the talc has an average particle size of 5 μm or more and 12 μm or less.   
     
     
         6 . The method for producing a porous body according to  claim 4 ,
 wherein the weight ratio of the auxiliary raw material relative to the talc is 0.5% or more and 1.0% or less by weight.   
     
     
         7 . The method for producing a porous body according to  claim 4 ,
 wherein the auxiliary raw material is at least one selected from zirconium oxide, cerium oxide, and yttrium oxide.   
     
     
         8 . The method for producing a porous body according to  claim 4 ,
 wherein the firing temperature is 1410° C. to 1430° C.