Cement and skinning material based on a water-swellable clay, and method for producing segmented or skinned ceramic honeycomb structures

Abstract

Skins and/or adhesive layers are formed on a porous ceramic honeycomb by applying a layer of a cement composition to a surface of the honeycomb and firing the cement composition. The cement composition contains a water-swellable clay, high aspect inorganic filler particles and water, and are nearly or completely devoid of particles smaller than 100 nm and a cellulosic polymer.

Claims

1. An uncured inorganic cement composition comprising: a) 1 to 18% by weight of a water-swellable clay; b) 20 to 70% by weight of non-water-swellable, non-fugitive, inorganic filler particles that have an equivalent diameter of greater than 250 nm; c) 20 to 60% by weight of water; d) larger than to less than 0.05% by weight of a water-soluble cellulosic polymer; e) Larger than 0 to less than 0.25% by weight of inorganic particles having an equivalent diameter of 250 nm or less; and f) 5 to 30% by weight of one or more porogens; wherein the uncured cement composition is self-supporting with a shear viscosity of 1 to less than 28 Pa*s when measured by oscillating shear rheometry methods at 20 C., 1 rad/s oscillation and 5 MPa amplitude.

2. The uncured inorganic cement composition of claim 1, wherein the water-swellable clay expands to a volume of at least 15 mL when 2 grams of the clay are added in small increments to room temperature distilled water.

3. The uncured inorganic cement composition of claim 1, which contains from 1 to 7 wt-% of the water-swellable clay.

4. The uncured inorganic cement composition of claim 1, wherein the inorganic filler particles include at least one high aspect ratio filler having an aspect ratio of 5 or greater.

5. The uncured inorganic cement composition of claim 4 which contains from 10 to 45 wt-% of the at least one high aspect ratio filler having an aspect ratio of 5 or greater.

6. The uncured inorganic cement composition of claim 4 wherein the at least one high aspect ratio filler having an aspect ratio of 5 or greater is a low-biopersistent fiber.

7. The uncured inorganic cement composition of claim 1 wherein the inorganic filler particles include alumina.

8. The uncured inorganic cement composition of claim 7 wherein the alumina and water-swellable clay are present in a weight ratio of from 0.25 to 2 parts of alumina to one part clay.

9. The uncured inorganic cement composition of claim 8 wherein the alumina and water-swellable clay are present in a weight ratio of from 0.3 to 1 part of alumina to one part clay.

10. The uncured inorganic cement composition of claim 7 wherein the alumina and water-swellable clay together constitute from 3 to 15 wt-% of the composition.

11. The uncured inorganic cement composition of claim 7 which contains from 10 to 35% by weight of low aspect ratio particles having an aspect ratio of less than 5 other than alumina or a water-swellable clay.

12. The uncured inorganic cement composition of claim 1 which includes: a) 1 to 7% by weight of the water-swellable clay; b) 0.75 to 4 parts by weight, per part by weight of the water-swellable clay, of alumina particles that have an effective diameter greater than 250 nm; c) 10 to 70% by weight of inorganic filler particles that have an aspect ratio of at least 10; d) 20 to 60% by weight of water; e) greater than 0 to less than 0.05% by weight of a water-soluble cellulosic polymer; f) greater than 0 to less than 0.25% by weight of inorganic particles having an equivalent diameter of 250 nm or less; and g) 10 to 25% by weight of the one or more porogens; wherein the composition is devoid of colloidal sol; wherein uncured cement composition is self-supporting with a shear viscosity of 3 to less than 10 Pa.Math.s when measured by oscillating shear rheometry methods at 20 C., 1 rad/s oscillation and 5 MPa amplitude.

13. The uncured cement composition of claim 1 which has a shear viscosity of 3 to 10 Pa.Math.s when measured by oscillating shear rheometry methods at 20 C., 1 rad/s oscillation and 5 MPa amplitude.

14. A method of forming a honeycomb structure comprising forming a layer of the uncured inorganic cement composition of claim 1 on at least one surface of a ceramic honeycomb having porous walls and then firing the uncured inorganic cement composition and the ceramic honeycomb to form a cured cement layer on said at least one surface of the ceramic honeycomb.

15. The method of claim 14, wherein the cured cement layer forms a peripheral skin on the ceramic honeycomb.

16. The method of claim 14, wherein the cured cement layer forms a cement layer between segments of a segmented honeycomb structure.

17. The method of claim 14, wherein fired cement composition has a CTE over the temperature range of 100 C.-600 C. that is within the range CTE.sub.honeycomb+1 ppm/ C. to CTE.sub.honeycomb5 ppm, where CTE.sub.honeycomb is the coefficient of thermal expansion of the honeycomb.

18. The method of claim 17 wherein the inorganic filler particles include low-biopersistent inorganic fibers and low aspect ratio particles other than alumina or a water-swellable clay which have a CTE equal to or lower than that of the ceramic honeycomb.

19. The uncured cement composition of claim 1, wherein the one or more porogens is wheat flour, wood flour, soy flour, potato starch, corn starch, corn meal, cellulose flour, and/or nut shell flour.

Description

EXAMPLE 1

(1) An uncured cement composition is made by mixing the following components:

(2) TABLE-US-00002 Alumina.sup.1 13.8 parts Bentonite Clay.sup.2 3.8 parts Inorganic fibers.sup.3 43.1 parts Water 39.3 parts .sup.1CT 3000 from Almatis, Inc., d50 = 0.5 m, d90 = 2.0 m, BET surface area = 7.8 m.sup.2/g. .sup.2Bentonite 34, Charles B. Chrystal Co., Inc. The particles range in size from 1 to about 500 m with a d50 in excess of 10 m. 2 grams of this material swells to at least 20 mL in water. .sup.3Fiberfrax Long Staple Fine fiber from Unifrax LLC, Niagara Falls, NY.

(3) The fibers and alumina are dry-blended in a blender for 60 minutes. The clay and the polyethylene glycol are then added and the mixture blended another 5 minutes. The water is then added to the resulting blend and mixed in on the blender for 25 minutes. This produces a foamy, lightweight uncured cement composition that is not self-leveling and does not drip when placed into an open container and held upside down. This cement composition is designated Example 1.

(4) A portion of cement composition Example 1 is applied to the periphery of an acicular mullite honeycomb that has 200 cells per square inch (31 cells/cm.sup.2) of cross-sectional area. A vacuum is then applied across the honeycomb for a period of two minutes at ambient temperature to dry the cement composition. The honeycomb is then inspected using scanning electron spectroscopy to determine the extent to which the cement composition has permeated into the honeycomb structure. Permeation is limited solely to the single outermost walls of the honeycomb to which the cement composition has been directly applied.

(5) For comparison, a conventional wet cement composition containing colloidal alumina, water, inorganic fibers and a water-soluble cellulose ether is applied to another specimen of the same honeycomb and dried in the same manner by applying a vacuum. The conventional wet cement composition is seen to have migrated 10 cells into the interior of the honeycomb structure.

(6) The periphery of another specimen of the same honeycomb is coated with cement composition Example 1 and dried for 2 hours at 120 C. No cracking is seen. When this experiment is repeated, except that vacuum is applied during the drying step, the dried cement again shows no cracking. Under these conditions, the conventional wet cement composition exhibits significant cracking, indicating that the conventional wet cement cannot be rapidly dried at these elevated temperatures.

(7) A portion of cement composition Example 1 is cast into 60 mm150 mm12 mm plates and dried overnight at 70 C. One of the plates is sanded smooth. The fracture strength of this plate is measured according to ASTM C1421-99; this value is the green strength of the cement composition. Other plates are fired at 1000 C. or 1100 C. for two hours. After cooling, the Young's modulus of the fired plates is measured according to ASTM C1259-94, and the fracture strength is measured according to ASTM C1421-99. Porosity of the fired cement is measured according to ASTM 830-00. Results of this testing are as indicated in Table 1.

(8) TABLE-US-00003 TABLE 1 Mechanical Properties, Green and Fired Cement Composition Ex. 1 Fired Fracture Fired Young's Fired Fracture Fired Young's Strength Modulus, Strength Modulus, Poros- (1000 C.), MPa (1000 C.), GPa (1100 C.), MPa (1100 C.), GPa ity 4 5.2 7.1 9.1 58%

(9) As shown in Table 1, both strength and modulus increase when the firing temperature is increased from 1000 to 1100 C. The lower strengths seen at the lower firing temperatures are advantageous because in general the strength of a cement or skin should be lower than that of the honeycombs. The data in Table 1 suggests that even lower firing temperatures, such as 900 to 950 C., will be sufficient to produce a cured cement having adequate but not excessive strength for ceramic honeycomb cement and skinning applications. Strength can be reduced further by increasing porosity.

EXAMPLE 2

(10) An uncured cement composition is made by mixing the following components:

(11) TABLE-US-00004 Alumina.sup.1 4.5 parts Bentonite Clay.sup.2 1.75 parts Low-biopersistent fibers.sup.3 42.0 parts 400 MW Polyethylene glycol 1.75 parts Water 50.0 parts .sup.1CT 3000 from Almatis, Inc., d50 = 0.5 m, d90 = 2.0 m, BET surface area = 7.8 m.sup.2/g. .sup.2Bentonite 34, Charles B. Chrystal Co., Inc. 2 grams of this material swells to at least 20 mL in water. .sup.3HT-95-SAB-T45 from Morgan Thermal Ceramics. This material contains 5% shot and has a tap density of 0.7 g/cc.

(12) The first four listed ingredients are dry blended on a blender for 60 minutes, and the water is then added to the resulting blend and mixed in on the blender for 30 minutes. This produces a foamy, lightweight uncured cement that is not self-leveling and does not drip when placed into an open container and held upside down. This composition is designated as Example 2.

(13) A portion of cement composition Example 2 is cast into 10 mm thick plates and dried overnight at 120 C. without vacuum. No cracks appear. The green strength of one of the dried plates is measured according to ASTM C1421-99, and found to be 0.75 MPa. Other plates are fired at 950 C. for two hours. After cooling, the modulus, strength and porosity of the fired plates are measured as before. The modulus is 5.39 GPa, the strength is 4.97 MPa and the porosity is 68.5%. In this example, the high porosity of the fired cement is attributable to the somewhat high water content (50% by weight).

EXAMPLES 3 AND 4

(14) Uncured cement composition Examples 3 and 4 are made by mixing the following components. In Example 3, the alumina is the CT3000 product from Almatis, Inc. described in previous examples. In Example 4, the alumina is A16SG from Almatis, Inc. (d50=0.5 m, d90=2.0 m, BET surface area=8.9 m.sup.2/g).

(15) TABLE-US-00005 Alumina 3.7 parts Bentonite Clay.sup.1 1.5 parts Inorganic fibers.sup.2 15.5 parts Water 31.8 parts Silicon carbide particles.sup.3 29.3 parts Porogen.sup.4 16.6 parts 400 MW poly(ethylene glycol) 1.6 .sup.1Bentonite 34, Charles B. Chrystal Co., Inc. .sup.2HT-95-SAB-T45 from Morgan Thermal Ceramics. .sup.3F1000 from US Abrasives, Northbrook, Illinois. This material contains at least 94% by weight of particles larger than 1 m, with most particles between 3.7 and 5.3 m. .sup.4A625 carbon flakes from Cummings-Moore.

(16) The cement compositions are prepared in the same general manner as described in Example 2, with all dry ingredients being mixed together before the water is added. Plates are prepared, dried and fired as described in Example 2, and green strength, calcined strength, calcined modulus and porosity are measured as described before. Results are as reported in Table 2 following.

(17) TABLE-US-00006 TABLE 2 Mechanical Properties, Green and Fired Cement Composition Ex. 3 and 4 Green Strength, Calcined Calcined Example MPa Modulus, GPa Strength, MPa Porosity 3 0.82 5.14 3.47 62.6% 4 0.65 4.85 3.68 63.5%

(18) These examples represent preferred formulations that contain a porogen and auxiliary filler particles. The porogen allows for high porosity to be obtained in the fired cement without using high water levels; higher porosities lead to lower calcined strengths and lower material thermal shock factors, each of which is beneficial. The lower water content allows one to obtain green strength values similar to that of Example 2 despite the much lower fiber content of Examples 3 and 4. The calcined strength of 3.4-3.7 MPa of these samples is lower than in Example 2, and represents a more preferred value as the cement is strong enough to perform its adhesive and skinning function while being well below that of the acicular mullite honeycomb.

(19) The auxiliary filler particles permit the amount of the more expensive fibers to be reduced, relative to Examples 1 and 2. In addition, these particles reduce the CTE of the cement to approximately 5.50 ppm/ C. over the temperature range of 200-600 C.; this CTE closely matches that of acicular mullite honeycombs. The MTSF values for Examples 3 and 4 are 123 C. and 138 C., respectively.

EXAMPLE 5

(20) Uncured cement composition Example 5 is made by mixing the following components.

(21) TABLE-US-00007 Alumina.sup.1 3.2 parts Bentonite Clay.sup.2 4.4 parts Inorganic fibers.sup.3 25.1 parts Silicon nitride particles.sup.4 23.8 parts Water 35.9 parts Porogen.sup.5 4.8 parts 400 MW poly(ethylene glycol) 2.8 parts .sup.1A16SG from Almatis, Inc. .sup.2Bentonite 34, Charles B Chrystal Co., Inc. .sup.3HT-95-SAB- T45 from Morgan Thermal Ceramics. .sup.4Grade L412S from HC Stark, Munich, Germany. .sup.5Graphite, Asbury Graphite Mills, Asbury, New Jersey.

(22) Cement composition Example 5 is prepared in the same general manner as described in Example 2, with all dry ingredients being mixed together before the water is added. Plates are prepared, dried and fired as described in Example 2, and green strength, calcined strength, calcined modulus and porosity are measured as described before. Results are as reported in Table 3 following.

(23) TABLE-US-00008 TABLE 3 Mechanical Properties, Green and Fired Cement Composition Ex. 5 Green Calcined Calcined CTE, Strength, Strength, Modulus, Porosity, MTSF, ppm/ C. MPa MPa GPa % C. 2.0 5.0 4.0 53 248

EXAMPLE 6

(24) Uncured cement composition Example 6 is made by mixing the following components.

(25) TABLE-US-00009 Alumina.sup.1 2 parts Bentonite Clay.sup.2 3 parts Inorganic fibers.sup.3 28.3 parts Cordierite particles.sup.4 19 parts Porogen.sup.5 11.3 parts 400 MW poly(ethylene glycol) 1.7 parts Water 34.7 parts .sup.1A16SG from Almatis, Inc. .sup.2Bentonite 34, Charles B Chrystal Co., Inc. .sup.3HT-95-SAB-T45 from Morgan Thermal Ceramics. .sup.4Pred Materials International, Inc, New York, New York. .sup.5A625 carbon flakes from Cummings-Moore.

(26) The cement composition is prepared in the same general manner as described in Example 2, with all dry ingredients being mixed together before the water is added. Plates are prepared, dried and fired as described in Example 2, and green strength, calcined strength, calcined modulus and porosity are measured as described before. Results are as in Table 4.

(27) TABLE-US-00010 TABLE 4 Mechanical Properties, Green and Fired Cement Composition Ex. 6 Green Calcined Calcined CTE, Strength, Strength, Modulus, MTSF, ppm/ C. MPa MPa GPa Porosity C. 5.5 1.3 2.5 2.6 64% 174

EXAMPLE 7

(28) Uncured cement composition Example 7 is made by mixing the following components.

(29) TABLE-US-00011 Alumina.sup.1 1.1 parts Bentonite Clay.sup.2 3.8 parts Bio-soluble Inorganic fibers.sup.3 17.9 parts SiC particles.sup.4 33.7 parts Porogen.sup.5 13.1 parts 400 MW poly(ethylene glycol) 1.6 parts Water 29.0 parts .sup.1A16SG from Almatis, Inc. .sup.2Bentonite 34, Charles B Chrystal Co., Inc. .sup.3HT-95-SAB-T45 from Morgan Thermal Ceramics. .sup.4F1000 from US Abrasives, Northbrook, Illinois. .sup.5A625 carbon flakes from Cummings-Moore.

(30) The cement compositions are prepared in the same general manner as described in Example 2, with all dry ingredients being mixed together before the water is added. Plates are prepared, dried and fired as described in Example 2, and green strength, calcined strength, calcined modulus and porosity are measured as described before. Results are as in Table 5.

(31) TABLE-US-00012 TABLE 5 Mechanical Properties, Green and Fired Cement Composition Ex. 7 Green Calcined Calcined CTE, Strength, Strength, Modulus, ppm/ C. MPa MPa GPa Porosity MTSF, C. 5.4 1.1 4.0 4.3 62% 187

EXAMPLE 8

(32) Uncured cement composition Example 8 is made by mixing the following components.

(33) TABLE-US-00013 Alumina.sup.1 3.2 parts Bentonite Clay.sup.2 4.4 parts Bio-soluble Inorganic fibers.sup.3 29.3 parts Cordierite precursor particles.sup.3 19.7 parts Water 33.5 parts Porogen.sup.5 7.0 parts 400 MW poly(ethylene glycol) 2.9 parts .sup.1A16SG from Almatis, Inc. .sup.2Bentonite 34, Charles B. Chrystal Co., Inc. .sup.3HT-95-SAB-T45 from Morgan Thermal Ceramics. .sup.4Pred Materials International, Inc, New York, New York .sup.5A625 carbon flakes from Cummings-Moore.

(34) The cement compositions are prepared in the same general manner as described in Example 2, with all dry ingredients being mixed together before the water is added. Plates are prepared, dried and fired as described in Example 2, and green strength, calcined strength, calcined modulus and porosity are measured as described before. Results are as in Table 6.

(35) TABLE-US-00014 TABLE 6 Mechanical Properties, Green and Fired Cement Composition Ex. 8 Green Calcined Calcined CTE, Strength, Strength, Modulus, ppm/ C. MPa MPa GPa Porosity MTSF, C. 5.4 1.8 4.1 3.7 64% 205

EXAMPLE 9

(36) Uncured cement composition Example 9 is made by mixing the following components.

(37) TABLE-US-00015 Alumina.sup.1 1.2 parts Bentonite Clay.sup.2 3.2 parts Mica platelete.sup.6 13.1 parts SiC.sup.4 24.7 parts Water 42.6 parts Porogen.sup.5 14.0 parts 400 MW poly(ethylene glycol) 1.2 parts .sup.1A16SG from Almatis, Inc. .sup.2Bentonite 34, Charles B. Chrystal Co., Inc. .sup.4F1000 from US Abrasives, Northbrook, Illinois. .sup.5A625 carbon flakes from Cummings-Moore. .sup.6Micro Mica 3000 Charles B. Chrystal Co.

(38) The cement compositions are prepared in the same general manner as described in Example 2, with all dry ingredients being mixed together before the water is added. Plates are prepared, dried and fired as described in Example 2, and green strength, calcined strength, calcined modulus and porosity are measured as described before. Results are as in Table 7.

(39) TABLE-US-00016 TABLE 7 Mechanical Properties, Green and Fired Cement Composition Ex. 9 Green Calcined Calcined CTE, Strength, Strength, Modulus, MTSF, ppm/ C. MPa MPa GPa Porosity C. 5.0 1.0 4.5 3.9 66% 229

EXAMPLE 10

(40) Uncured cement composition Example 10 is made by mixing the following components:

(41) TABLE-US-00017 Bentonite Clay.sup.2 7.9 parts SiC.sup.4 29.1 parts Water 47.1 parts Porogen.sup.5 15.9 parts .sup.2Bentonite 34, Charles B. Chrystal Co., Inc. .sup.4F1000 from US Abrasives, Northbrook, Illinois .sup.5A625 carbon flakes from Cummings-Moore.

(42) The cement composition is prepared in the same general manner as described in Example 2, with all dry ingredients being mixed together before the water is added. Plates are prepared, dried and fired as described in Example 2, and green strength, calcined strength, calcined modulus and porosity are measured as described before. Results are as in Table 8.

(43) TABLE-US-00018 TABLE 8 Green Calcined Calcined Strength, Strength, Modulus, MTSF, MPa MPa GPa Porosity C. 2.4 4.2 3.8 63% 220

EXAMPLE 11

(44) Uncured cement composition Example 11 is made by mixing the following components:

(45) TABLE-US-00019 Bentonite Clay.sup.2 9.1 parts SiC.sup.4 33.2 parts Water 39.7 parts Porogen.sup.5 18.1 parts .sup.2Bentonite 34, Charles B. Chrystal Co., Inc. .sup.4F1000 from US Abrasives, Northbrook, Illinois .sup.5A625 carbon flakes from Cummings-Moore.

(46) The cement composition is prepared in the same general manner as described in Example 2, with all dry ingredients being mixed together before the water is added. Plates are prepared, dried and fired as described in Example 2, and green strength, calcined strength, calcined modulus and porosity are measured as described before. Results are as in Table 9.

(47) TABLE-US-00020 TABLE 9 Green Calcined Calcined Strength, Strength, Modulus, MTSF, MPa MPa GPa Porosity C. 2.4 5.3 7.1 55% 149

EXAMPLE 12

(48) Uncured cement composition Example 12 is made by mixing the following components:

(49) TABLE-US-00021 Fibers 19.9 parts Bentonite Clay.sup.2 4.6 parts Si.sub.3N.sub.4 36.6 parts Water 29.4 parts Porogen.sup.5 6.0 parts Water reducer 3.5 parts .sup.2Bentonite 34, Charles B. Chrystal Co., Inc. .sup.5A625 carbon flakes from Cummings-Moore.

(50) The cement composition is prepared in the same general manner as described in Example 2, with all dry ingredients being mixed together before the water is added. Plates are prepared, dried and fired as described in Example 2, and green strength, calcined strength, calcined modulus and porosity are measured as described before. Results are as in Table 10.

(51) TABLE-US-00022 TABLE 10 Green Calcined Calcined CTE, Strength, Strength, Modulus, MTSF, ppm/ C. MPa MPa GPa Porosity C. 4.9 3.7 5.8 4.6 51% 253

EXAMPLE 13

(52) Uncured cement composition Example 13 is made by mixing the following components:

(53) TABLE-US-00023 Fibers 18.2 parts Bentonite Clay.sup.2 3.7 parts SiC.sup.4 34.0 parts Alumina 1.2 parts Water 29.7 parts Porogen.sup.5 13.2 parts .sup.2Bentonite 34, Charles B. Chrystal Co., Inc. .sup.4F1000 from US Abrasives, Northbrook, Illinois .sup.5A625 carbon flakes from Cummings-Moore.

(54) The cement composition is prepared in the same general manner as described in Example 2, with all dry ingredients being mixed together before the water is added. Plates are prepared, dried and fired as described in Example 2, and green strength, calcined strength, calcined modulus and porosity are measured as described before. Results are as in Table 11.

(55) TABLE-US-00024 TABLE 11 Green Calcined Calcined CTE, Strength, Strength, Modulus, MTSF, ppm/ C. MPa MPa GPa Porosity C. 5.4 1.7 7.4 8.3 59% 177

EXAMPLES 14-20

(56) Uncured cement composition Examples 14-20 are prepared for rheological testing from the ingredients listed in Table 12.

(57) TABLE-US-00025 TABLE 12 Ingredient Bentonite PEG Carbon Alumina.sup.1 Fibers.sup.2 Water SiC.sup.3 Clay.sup.4 400.sup.5 Black.sup.6 Parts by Weight Ex. 14 0 14.0 37.0 26.4 6.4 1.3 15.0 Ex. 15 6.6 14.3 32.2 26.9 3.4 1.4 15.3 Ex. 16 3.3 15.0 32.8 28.2 3.3 1.4 16.0 Ex. 17 6.2 12.4 37.2 23.4 6.2 1.2 13.3 Ex. 18 3.0 12.8 39.1 24.2 6.0 1.2 13.7 Ex. 19 0 15.5 33.9 29.2 3.3 1.5 16.6 Ex. 20 1.1 15.3 33.9 28.9 3.0 0 17.9 .sup.1CT 3000 from Almatis, Inc. .sup.2HT90-SAB-T45 low biopersistent fibers from Morgan Thermal Ceramics. .sup.3UK Abrasives, Inc., Northbrook IL. .sup.4Bentonite 34, Charles B. Chrystal Co., Inc. .sup.5400 molecular weight polyethylene glycol. .sup.6Asbury Graphite Mills, Asbury NJ.

(58) Rheological properties of each of these uncured cement compositions are evaluated using an oscillating shear rheometry method that employs a capillary rheometer apparatus. The capillary used for the tests is has an internal diameter of 4 mm and a length of 120 mm. The piston diameter is 4.5 cm, the piston area is 15.93 cm.sup.2, and the stroke length is 7.62 cm. A flow rate of 7.486 cm.sup.3/minute is used to measure extrusion pressure. Oscillating shear is applied at 1 rad/s oscillation and 5 MPa amplitude. The material temperature is 20 C. Viscosity and yield pressure are computed from the extrusion pressure. These values, together with the measurement temperature, are as reported in Table 13.

(59) In addition, the cement compositions are visually observed to see whether they are self-supporting or flow under their own weight. All of the compositions are self-supporting, even when the viscosity is as low as about 4 Pa.Math.s.

(60) TABLE-US-00026 TABLE 13 Temperature, Yield pressure, Viscosity, Self- Property C. pKa Pa .Math. s Supporting? Ex. 14 21.0 31.0 27.9 Yes Ex. 15 21.4 46.2 38.2 Yes Ex. 16 21.0 57.9 24.2 Yes Ex. 17 20.4 82.0 34.3 Yes Ex. 18 20.8 45.5 18.9 Yes Ex. 19 21.0 28.9 12.1 Yes Ex. 20 22.1 7.6 3.7 Yes