Method for controlling aluminum titanate ceramic filter properties

Abstract

A method for improving the thermo-mechanical properties of an aluminum-titanate composite, the composite including at least one of strontium-feldspar, mullite, cordierite, or a combination thereof, including: combining a glass source and an aluminum-titanate source into a batch composition; and firing the combined batch composite composition to produce the aluminum-titanate composite. Another method for improving the thermo-mechanical properties of the composite dips a fired composite article into phosphoric acid, and then anneal the dipped composite article. The resulting composites have a thin glass film situated between the ceramic granules of the composite, which can arrest microcrack propagation.

1 .- 11 . (canceled) 
     
     
         12 . A method for improving the thermo-mechanical properties of an aluminum titanate-based composite, comprising:
 dipping a fully fired aluminum titanate composite into an aqueous phosphoric acid solution of 0.5 to 10 wt %; and   annealing the dipped composite, to provide phosphorous incorporation into the resulting composite of 0.5 to 2 wt %, the weight % being based on a superaddition relative to the weight of the un-dipped composite.   
     
     
         13 . A method for toughening a microcracked aluminum titanate ceramic, comprising:
 creating an intergranular glass film within the ceramic, the film having a thickness of from about 20 nm to 500 nm, and the film interacts with the microcracks and limits uncontrolled growth of the microcracks.   
     
     
         14 . The method of  claim 13  wherein the ceramic is toughened from about 5 to about 25%, as demonstrated by an increase in the modulus of rupture measured by 4-point bending relative to a ceramic prepared without the intergranular glass film. 
     
     
         15 . The method of  claim 12  wherein the dipped and annealed aluminum titanate-based composite has an average CTE that is substantially unchanged by the dipping procedure, the microcrack density of the dipped and annealed aluminum titanate-based composite is increased, and the dipped and annealed aluminum titanate-based composite has a significantly larger hysteresis in a heating-cooling cycle compared to an undipped and annealed composite. 
     
     
         16 . The method of  claim 12  wherein the dipping is accomplished in aqueous 10 wt % phosphoric acid. 
     
     
         17 . The method of  claim 12  wherein the annealing is accomplished at 1400° C. 
     
     
         18 . The method of  claim 12  wherein the aluminum titanate-based composite comprises grains of an aluminum-titanate crystalline phase and grains of a strontium-feldspar crystalline phase, and an intergranular glass phase between the grains of the aluminum-titanate crystalline phase and the strontium-feldspar crystalline phase. 
     
     
         19 . The method of  claim 12  wherein the thermo-mechanical property of the dipped and annealed composite is material strength and the material strength is improved from 310 psi to 467 psi compared to an un-dipped composite. 
     
     
         20 . The method of  claim 12  wherein the thermo-mechanical property of the dipped composite is the CTE which is decreased from 8.4 10 −7 K −1  to 7.6 10 −7 K −1  over 25 to 1000° C. for a dipped and annealed composite having a pore size increased by 3 micrometers compared to an un-dipped and annealed composite. 
     
     
         21 . The method of  claim 12  wherein the resulting annealed aluminum titanate-based composite has a porosity greater than 42%, a median pore size greater than 16 micrometers, and a CTE of less than 9×10 −7 K −1  from 25 to 1000° C. 
     
     
         22 . The method of  claim 12  wherein the resulting annealed aluminum titanate-based composite is a honeycomb filter. 
     
     
         23 . The method of  claim 12  further comprising selectively plugging the ends of the honeycomb filter in an alternating checkerboard pattern to form a through wall filter for exhaust gas particle filtration. 
     
     
         24 . The method of  claim 22  further comprising washcoating the honeycomb filter with a catalyst suitable for catalytic conversion applications. 
     
     
         25 . The method of  claim 12  wherein the feldspar phase, prior to annealing, has a monoclinic structure. 
     
     
         26 . The method of  claim 12  wherein the annealing produces a strengthened product having a feldspar phase with a triclinic symmetry.