Honeycomb structure comprising an outer cement skin and a cement therefor
Disclosed is a honeycomb catalyst support structure comprising a honeycomb body and an outer layer or skin formed of a cement comprising an amorphous glass powder with a multimodal particle size distribution applied to an exterior surface of the honeycomb body. The multimodal particle size distribution is achieved through the use of a first glass powder having a first median particle size and at least a second glass powder having a second median particle size. In some embodiments, the first and second glass powders are the same amorphous glass consisting of fused silica. The cement may further include a fine-grained, sub-micron sized silica in the form of colloidal silica. The cement exhibits a coefficient of thermal expansion less than 15×10 −7 /° C., and preferably about 5×10 −7 /° C. after drying.
1. A method of making a honeycomb structure comprising:
extruding a honeycomb body, the honeycomb body comprising a plurality of cells extending axially between first and second opposing end faces of the honeycomb body, the cells comprising intersecting porous walls;
shaping the honeycomb body, thereby exposing portions of the porous walls around a periphery of the honeycomb body;
coating the periphery of the shaped honeycomb body with a cement mixture, the cement mixture comprising a first glass powder filler material having a first particle size distribution with a D50 in a range from about 10 μm to about 50 μm, and a second glass powder filler material having a second particle size distribution with a D50 in a range from about 150 to about 300 μm, thereby forming a honeycomb structure;
drying the cement mixture; and
wherein an average coefficient of thermal expansion of the cement mixture from 600° C. on cooling to 23° C. is equal to or less than about 15×10 −7 /° C.
2. The method according to claim 1 , wherein a coefficient of thermal expansion of the cement mixture after drying is equal to or less than 10×10 −7 /° C.
3. The method according to claim 1 , wherein the first and second glass powder filler materials are amorphous fused silica.
4. The method according to claim 1 , wherein the first particle size distribution has a D10 in a range from about 1 μm to about 10 μm and a D90 in a range from about 25 μm to about 125 μm.
5. The method according to claim 1 , wherein the second particle size distribution has a D10 in a range from about 100 μm to about 150 μm, and a D90 in a range from about 250 μm to about 350 μm.
6. The method according to claim 1 , wherein a modulus of rupture of the cement mixture after drying is in a range from about 20 kg/cm 2 to about 60 kg/cm 2 .
7. The method according to claim 1 , wherein the first glass powder filler material comprises a range from about 20 wt. % to about 60 wt. % of the total weight of the inorganic solid components of the cement composition.
8. The method according to claim 1 , wherein the second glass powder filler material comprises a range from about 10 wt. % to about 40 wt. % of the total weight of the inorganic solid components of the cement composition.