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 honeycomb structure comprising:
a honeycomb body including a plurality of cells extending axially between first and second opposing end faces of the honeycomb body, the cells comprising intersecting porous walls;
a cement mixture deposited over a periphery of the honeycomb body, 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; and
wherein the first and second glass powders are amorphous fused silica.
2. The honeycomb structure according to claim 1 , wherein the cement mixture is a calcined cement mixture.
3. The honeycomb structure according to claim 2 , wherein an average coefficient of thermal expansion of the cement mixture from 600° C. on cooling to room temperature is equal to or less than 15×10 −7 /° C.
4. The honeycomb structure according to claim 2 , wherein an average coefficient of thermal expansion of the cement mixture from 600° C. on cooling to room temperature is equal to or less than 10×10 −7 /° C.
5. The honeycomb structure according to claim 2 , wherein after heating to a temperature of 600° C. for 30 minutes followed by unforced cooling to 23° C., no cracks are visible in the cement mixture under 10x magnification.
6. The honeycomb structure according to claim 2 , wherein the cement mixture is fully amorphous when examined by x-ray diffraction.
7. The honeycomb structure according to claim 1 , wherein the cement mixture is a calcined cement mixture and a coefficient of thermal expansion of the cement mixture is substantially equal to a thermal expansion coefficient of the honeycomb body.
8. The honeycomb structure according to claim 1 , wherein the cement mixture further comprises colloidal silica particles wherein a maximum particle size of the colloidal silica particles is less than 1 μm.
9. The honeycomb structure 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.
10. The honeycomb structure 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.
11. The honeycomb structure according to claim 1 , wherein the first glass powder filler material comprises between 20 wt % and 60 wt % of the total weight of the inorganic solid components of the cement composition.
12. The honeycomb structure according to claim 1 , wherein the second glass powder filler material comprises between 10 wt % and 40 wt % of the total weight of the inorganic solid components of the cement composition.
13. The honeycomb structure according to claim 1 , wherein a ratio of the second glass powder filler material to the first glass powder filler material is in a range from about 1:4 to about 1:1.