Cement to make thermal shock resistant ceramic honeycomb structures and method to make them

Abstract

A ceramic honeycomb structure comprised of at least two separate smaller ceramic honeycombs that have been adhered together by a cement comprised of inorganic fibers and a binding phase wherein the smaller honeycombs and fibers are bonded together by the binding phase which is comprised of an amorphous silicate, aluminate or alumino-silicate glass and the cement has at most about 5% by volume of other inorganic particles. The cement may be made in the absence of other inorganic and organic additives while achieving a shear thinning cement, for example, by mixing oppositely charged inorganic binders in water together so as to make a useful cement for applying to the smaller honeycombs to be cemented.

1 . A method of forming a honeycomb structure comprising contacting a first honeycomb segment on at least one of its outer surfaces with a cement comprised of inorganic fibers, a carrier fluid, a colloidal inorganic sol in the presence of at most 5% other inorganic particles by volume of the inorganic fibers and colloidal inorganic sol, wherein the fibers have a solids loading of at least about 10% by volume of the total volume of the cement, mechanically contacting a second honeycomb segment with the first honeycomb segment such that the cement is interposed between said honeycomb segments such that said honeycomb segments are adhered, heating the adhered segments sufficiently to form amorphous ceramic bonding between the fibers of the cement and the honeycomb segments to form the honeycomb structure. 
     
     
         2 . The method of  claim 1 , wherein the cement has an organic plasticizer. 
     
     
         3 . The method of  claim 2 , wherein the plasticizer is a polyethylene glycol, fatty acid, fatty acid ester or combination thereof. 
     
     
         4 . The method of  claim 1 , wherein the heating is at most 1100° C. 
     
     
         5 . The method of  claim 1 , wherein the heating is at most about 1050° C. 
     
     
         6 . The method of  claim 1 , wherein the segment honeycomb is first wetted prior to application of the cement. 
     
     
         7 . The method of  claim 1 , wherein the solids loading of the fibers in the cement is at least 15% by volume. 
     
     
         8 . The method of  claim 1 , wherein the cement has a porogen. 
     
     
         9 . The method of  claim 8 , wherein the porogen is present in an amount of at most about 20% by volume of amount of fiber and inorganic binder. 
     
     
         10 . The method of  claim 1 , wherein the ceramic segments are mullite and the inorganic sol is comprised of a silica sol mixed with an alumina sol such that the coefficient of thermal expansion is within 10% of the thermal expansion of the mullite segments. 
     
     
         11 . The method of  claim 10 , wherein the weight ratio of silica sol to alumina sol on a solids basis is from 1:99 to 99:1. 
     
     
         12 . The method of  claim 1 , wherein the cement is shear thinning. 
     
     
         13 . The method of  claim 12 , wherein the cement has a viscosity of at least about 1 Pa·s at a shear rate of 5 s −1  and a viscosity of at most about 0.05 Pa·s at a shear rate of 200 s −1 . 
     
     
         14 . The method of  claim 1 , wherein the cement is made in the absence of other inorganic particles and in the absence of organic additives. 
     
     
         15 . The method of  claim 1 , wherein each of the segments has been exposed to a colloidal sol separate from the colloidal particles in the cement. 
     
     
         16 . The method of  claim 15 , wherein the colloidal sol has the same carrier fluid as the cement. 
     
     
         17 . The method of  claim 16 , wherein the colloidal sol is a silica sol, alumina sol or combination thereof. 
     
     
         18 . A process for making a ceramic cement comprising
 (a) mixing inorganic fibers with a first colloidal sol having negative or positive surface charge and then subsequently   (b) mixing in to the mixture of step (a) a second colloidal sol having a surface charge opposite that of the first colloidal sol to form the ceramic cement.   
     
     
         19 . The process of  claim 18 , wherein the process is performed in the absence of any other additives. 
     
     
         20 . The process of  claim 18 , wherein the ceramic cement is shear thinning.