Porous mullite bodies and methods of forming them

Abstract

A porous mullite composition is made by forming a mixture of one or more precursor compounds having the elements present in mullite (e.g., clay, alumina, silica) and a property enhancing compound. The property enhancing compound is a compound having an element selected from the group consisting of Mg, Ca, Fe, Na, K, Ce, Pr, Nd, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb, Lu, B, Y, Sc, La and combination thereof. The mixture is shaped and to form a porous green shape which is heated under an atmosphere having a fluorine containing gas to a temperature sufficient to form a mullite composition comprised substantially of acicular mullite grains that are essentially chemically bound.

1 - 29 . (canceled)  
   
   
       30 . A mullite composition comprised substantially of acicular mullite grains that are essentially chemically bound, wherein the mullite composition is substantially devoid of broomstick mullite grains.  
   
   
       31 . (canceled)  
   
   
       32 . The mullite composition of  claim 30 , wherein the mullite composition has a phase on at least a portion of the mullite grains wherein the phase is comprised of Fe and Mg such that the ratio of Fe/Mg in the mullite composition is from about 0.5 to 1.5 by weight.  
   
   
       33 . The mullite composition of  claim 32 , wherein the amount of Fe and Mg is from 0.5 percent to 5 percent by volume of the mullite composition. The volume being the volume of the Fe and Mg as an oxide.  
   
   
       34 . The mullite composition of  claim 33 , wherein the amount of Fe and Mg is at most bout 2 percent by volume of the mullite composition.  
   
   
       35 . The mullite composition of  claim 32  wherein the ratio is about 1.