Extrudable mixture for forming a porous block

Abstract

An extrudable mixture is provided for producing a highly porous substrate using an extrusion process. More particularly, the present invention enables fibers, such as organic, inorganic, glass, ceramic or metal fibers, to be mixed into a mass that when extruded and cured, forms a highly porous substrate. Depending on the particular mixture, the present invention enables substrate porosities of about 60% to about 90%, and enables process advantages at other porosities, as well. The extrudable mixture may use a wide variety of fibers and additives, and is adaptable to a wide variety of operating environments and applications. Fibers, which have an aspect ratio greater than 1, are selected according to substrate requirements, and are mixed with binders, pore-formers, extrusion aids, and fluid to form a homogeneous extrudable mass. The homogeneous mass is extruded into a green substrate. The more volatile material is preferentially removed from the green substrate, which allows the fibers to interconnect and contact. As the curing process continues, fiber to fiber bonds are formed to produce a structure having a substantially open pore network. The resulting porous substrate is useful in many applications, for example, as a substrate for a filter or catalyst host, or catalytic converter.

1 . An extrudable mixture, comprising: 
 ceramic material consisting essentially of elongated fibers;    binder material;    fluid; and    wherein the elongated fibers, binder material, and fluid are a homogeneous, mass.    
   
   
       2 . The extrudable mixture according to  claim 1 , wherein the ceramic material is less than about 20% of the volume the homogenous mass.  
   
   
       3 . The extrudable mixture according to  claim 1 , wherein the extrudable mixture further comprises inorganic clays, nanoclays, colloidals, glass, or non-fiber ceramic precursors.  
   
   
       4 . The extrudable mixture according to  claim 1 , wherein the ceramic material is less than about 40% of the volume the homogenous mass.  
   
   
       5 . The extrudable mixture according to  claim 1 , wherein the ceramic material is in the range of about 15% to about 30% of the homogeneous mass by volume.  
   
   
       6 . The extrudable mixture according to  claim 1 , wherein substantially all of the elongated fibers have an aspect ratio greater than about 5 and less than about 200.  
   
   
       7 . The extrudable mixture according to  claim 1 , wherein substantially all of the elongated fibers have an aspect ratio in the range of about 10 to about 1000.  
   
   
       8 . The extrudable mixture according to  claim 1 , wherein the ceramic material includes ceramic precursors.  
   
   
       9 . The extrudable mixture according to  claim 1 , wherein the elongated fibers are ceramic fibers selected from the group identified in Table 1 of  FIG. 6 .  
   
   
       10 . An extrudable mixture, comprising: 
 fibers having an aspect ratio greater than 1;    binder material;    fluid; and    wherein the fibers, binder material, and fluid are a homogeneous mass.    
   
   
       11 . The extrudable mixture according to  claim 10 , wherein the fibers have a distribution of aspect ratios with a mode in the range of about 3 to about 1000.  
   
   
       12 . The extrudable mixture according to  claim 10 , wherein the fibers have a multi-modal distribution of aspect ratios with both modes in the range of about 3 to about 1000.  
   
   
       13 . The extrudable mixture according to  claim 10 , wherein the fibers are ceramic fibers.  
   
   
       14 . The extrudable mixture according to  claim 10 , wherein the fibers are substantially one fiber type selected from the group consisting of: organic fibers, polymeric fibers, inorganic fibers, metal fibers, glass fibers, glass-ceramic fibers, oxide ceramic, non-oxide ceramic, amorphous, polycrystalline, metallic alloy.  
   
   
       15 . The extrudable mixture according to  claim 10 , wherein the fibers are a mixture of a plurality of fiber types selected from the group consisting of: organic fibers, polymeric fibers, inorganic fibers, metal fibers, glass fibers, glass-ceramic fibers, oxide ceramic, non-oxide ceramic, amorphous, polycrystalline, metallic alloy.  
   
   
       16 . The extrudable mixture according to  claim 10 , wherein the fibers are coated.  
   
   
       17 . The extrudable mixture according to  claim 10 , wherein the fibers are about 15% to about 30% of the volume of the extrudable mixture.  
   
   
       18 . The extrudable mixture according to  claim 10 , wherein the fibers are about 8% to about 40% of the volume of the extrudable mixture.  
   
   
       19 . The extrudable mixture according to  claim 10 , wherein the homogenous mass has a rheology set in the area bounded by points a, b, c, and d of Table 5 of  FIG. 6 .  
   
   
       20 . The extrudable mixture according to  claim 10 , wherein the fibers are metal fibers.  
   
   
       21 . The extrudable mixture according to  claim 10 , wherein the fibers are ceramic fibers selected from the group identified in Table 1 of  FIG. 6 .  
   
   
       22 . The extrudable mixture according to  claim 10 , further including pore formers and wherein the inorganic fibers, binder material, pore formers, and fluid are in the homogeneous mass.  
   
   
       23 . The extrudable mixture according to  claim 22 , wherein the pore former is selected from the group identified in Table 3 of  FIG. 6 .  
   
   
       24 . An extrudable mixture, comprising: 
 a homogeneous and extrudable mass that comprises ceramic material, organic binders, and fluid;    wherein the ceramic material is less than about 40% of the volume of the mass.    
   
   
       25 . The extrudable mixture according to  claim 24 , wherein the ceramic material is less than about 20% of the volume of the mass.  
   
   
       26 . The extrudable mixture according to  claim 24 , wherein the ceramic material is a poly-crystalline fiber, a mono-crystalline whisker, or an amorphous fiber.