High-temperature Resistant Lightweight Thermal Insulation Material with Dual-pore Structure and Preparation Method Thereof

Abstract

A high-temperature resistant lightweight thermal insulation material having a dual-pore structure and a preparation method thereof, wherein the material is prepared by adding a molding promoter and a pore former into raw materials including alumina, silica and aluminosilicate powders, stirring the resulting mixture evenly and extrusion molding the same, followed by sintering, whereby the high-temperature resistant lightweight thermal insulation material having a dual-pore structure comprising macroscopic through-pores and micro-pores is obtained, and wherein the ratio of the total volume of the through-pores to the total volume of the micro-pores is 0.5 to 25:1.

Claims

1. A high-temperature resistant lightweight thermal insulation material having a dual-pore structure, wherein the material is prepared by adding a molding promoter and a pore former into raw materials including alumina, silica and aluminosilicate powders, stirring the resulting mixture evenly and extrusion molding the same, followed by sintering, wherein the high-temperature resistant lightweight thermal insulation material having a dual-pore structure comprising macroscopic through-pores and micro-pores is obtained, wherein the ratio of the total volume of the through-pores to the total volume of the micro-pores is 0.5 to 25:1.

2. The high-temperature resistant lightweight thermal insulation material according to claim 1, wherein the ratio of the total volume of the through-pores to the total volume of the micro-pores is 1 to 15:1.

3. The high-temperature resistant lightweight thermal insulation material according to claim 1, wherein the total volume fraction of the through-pores and the micro-pores in the material is 18% to 80%.

4. The high-temperature resistant lightweight thermal insulation material according to claim 1, wherein the macroscopic through-pores are parallel to each other, and the direction of the through-pores is perpendicular to the direction of heat flow in use.

5. The high-temperature resistant lightweight thermal insulation material according to claim 1, wherein the macroscopic through-pores have a density of 900 to 640,000 pores/m.sup.2, a wall thickness of 0.2 to 20 mm, and a volume fraction of 15% to 70%.

6. The high-temperature resistant lightweight thermal insulation material according to claim 5, wherein the macroscopic through-pores have a density of 10,000 to 490,000 pores/m.sup.2.

7. The high-temperature resistant lightweight thermal insulation material according to claim 5, wherein the macroscopic through-pores have a volume fraction of 30% to 50%.

8. The high-temperature resistant lightweight thermal insulation material according to claim 1, wherein the total mass of aluminum element and silicon element in the raw materials is equal to or larger than 40%, and the mass ratio of aluminum element to silicon element is 2.8 to 10.2:1.

9. The high-temperature resistant lightweight thermal insulation material according to claim 1, wherein the macroscopic through-pores have a shape selected from the group consisting of a square, a circle, a hexagon, a triangle, and combinations thereof.

10. The high-temperature resistant lightweight thermal insulation material according to claim 1, wherein the micropores are evenly distributed throughout the thermal insulation material, with an average pore size of 0.05 to 100 m, and a microporosity of 3% to 35%.

11. The high-temperature resistant lightweight thermal insulation material according to claim 1, wherein the raw materials may be various crystalline or amorphous natural mineral powders or chemical synthetic raw material powders of alumina, silica, aluminosilicate, wherein the aluminosilicate includes but is not limited to mullite, andalusite, kyanite, flint clay, sillimanite, coal gangue, Suzhou clay, kaolin.

12. The high-temperature resistant lightweight thermal insulation material according to claim 1, wherein the molding promoter includes one or more selected from polyvinyl alcohol, polyvinyl butyral, polyethylene, polyvinyl chloride, methyl cellulose, hydroxypropyl methyl cellulose, glycerin, water, ethylene glycol, and stearic acid, the mass ratio of the raw materials to the molding promoter is 100:20 to 100:100.

13. The high-temperature resistant lightweight thermal insulation material according to claim 1, wherein the pore former is selected from the group consisting of graphite, activated carbon, wood chips, starch, carbonate particles, hydroxide particles, polystyrene beads, and combinations thereof and the mass ratio of the raw materials to the pore former is 100:0.5 to 100:5.

14. The high-temperature resistant lightweight thermal insulation material according to claim 1, wherein the sintering system comprises an increase from room temperature to 500 C. at a temperature increase rate of 0.5 to 2 C./min, an increase from 500 C. to 1000 C. at a temperature increase rate of 2 to 4 C./min, an increase from 1000 C. to 1300 to 1850 C., a warm keeping for 0.5 to 5 hours, and finally a cooling down to the room temperature.

15. A method for preparing the high-temperature resistant lightweight thermal insulation material according to claim 1, comprising: adding a molding promoter and a pore former into raw materials including alumina, silica and aluminosilicate powders, stirring the resulting mixture evenly and extrusion molding the same, followed by sintering, wherein the high-temperature resistant lightweight thermal insulation material having a dual-pore structure comprising macroscopic through-pores and micro-pores is obtained, wherein the ratio of the total volume of the through-pores to the total volume of the micro-pores is 0.5 to 25:1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 shows the direction of heat flow perpendicular to the direction of the through-pores when measuring the thermal conductivity of the sample.

[0026] FIG. 2 shows the direction of heat flow parallel to the direction of the through-pores when measuring the thermal conductivity of the sample.

[0027] FIG. 3 shows a standard brick sample.

[0028] FIG. 4 is a plate sample.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0029] The present invention is further illustrated by the following examples and comparative examples. The specific details of the embodiments are only for explaining the present invention and should not be construed as limiting the general technical solutions of the present invention.

[0030] The materials used in the following examples and comparative examples were prepared using a method comprising the steps of: mixing the raw material powders with water and milling balls at a mass ratio of 1:2:1.5, and subjecting the resulting mixture to ball-milling for 24 hours; subjecting the milled slurry to drying, crushing and sieving to obtain an evenly mixed raw material powder and stirring the obtained powder with activated carbon, polyvinyl alcohol solution (concentration: 10%), hydroxypropyl methylcellulose, glycerin, and water evenly in a kneader for 12 hours, wherein the mass ratio of the raw material powder, polyvinyl alcohol solution, hydroxypropyl methylcellulose, glycerin, and water is 100:10:10:10:10; subjecting the evenly stirred pug to vacuum pugging, followed by aging for 1 day, and extrusion molding in an extruder under a pressure of 100 to 150 MPa to obtain a Green body having a through-pore structure; and drying the Green body and sintering the same, wherein the sintering includes an increase from the room temperature to 500 C. at a temperature increase rate of 0.5 to 2 C./min, an increase from 500 C. to 1000 C. at a temperature increase rate of 2 to 4 C./min, an increase from 1000 C. to 1700 C. at a temperature increase rate of 0.5 to 2 C./min, a warm keeping for 4 hours, and finally a cooling down to the room temperature.

[0031] Tables 1 and 2 respectively list the main performance indexes of the products prepared in the respective examples and comparative examples.

TABLE-US-00001 TABLE 1 Performance comparison of products of respective examples Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Al/Si (mass ratio) 6.0 4.2 6.8 2.8 5.3 Through-pore density 25 (wall thickness: 0.5mm) 49 (wall 4 (wall (10000 pores/m.sup.2) thickness: 0.4mm) thickness: 1mm) Through-pore volume 36.0 46.2 25.0 fraction (%) Microporosity (%) 11.5 16.0 9.6 17.9 11.8 16.5 Total porosity (%) 47.5 52.0 45.6 53.9 58.0 41.5 Total volume of 3.1 2.3 3.8 2.0 3.9 1.5 through-pores / total volume of micro-pores Volumetric weight 1.10 0.95 1.14 0.87 0.86 1.19 Flexural strength at room 12.0 9.8 15.2 7.4 13.7 9.1 temperature (MPa) Thermal Perpendicular 0.85 0.78 0.88 0.75 0.65 1.01 conductivity to through- (W/m.Math.K) pores Parallel to 2.00 1.88 2.05 1.83 1.90 1.96 through-pores Volumetric heat 59 52 61 47 46 65 capacity (J/K.Math.m.sup.3) Creep index 1.65 2.64 1.98 2.91 1.74 2.54 Thermal shock 65 70 60 80 70 70 resistance index Note: Volumetric weight: Refers to the mass of refractory material per unit volume. The refractory material in this volume contains both solid materials, as well as micro-pores and macroscopic through-pores. Reference is made to FIG.1. Reference is made to FIG. 2. Volumetric heat capacity: Refers to the heat capacity value of refractory material per unit volume. The high temperature creep resistance of the sample is expressed by the creep index . The test method was as follows: a long strip sample with dimensions of 16 mm 12 mm 200 mm (width thickness length) was prepared and placed on two points spaced from each other by a distance of 160 mm; a load of 0.2 MPa was applied at a midpoint of the sample's length by hanging a weight or by pressing the sample's head; the sample was heated to 1600C. and held for 2 hours, and then naturally cooled to measure the amount of deformation [00001]$\mathrm{of}.Math..Math.\mathrm{the}.Math..Math.\mathrm{sample}..Math.\mathrm{The}.Math..Math.\mathrm{creep}.Math..Math.\mathrm{index}.Math..Math.\mathrm{is}.Math..Math.\mathrm{defined}.Math..Math.\mathrm{as}.Math..Math.=\left(\tan .Math..Math.\right)100=\frac{W}{L/2}100,$where a is the angle by which the geometric center point of the upper surface of the sample is rotated relative to the position before deformation, W is the deflection, and L is the distance between the two endpoints of the sample after deformation. The smaller the creep index, that is, the smaller the amount of creep, the better the sample's resistance to high temperature creep. (Yan Jie, Chen Han, Dai Haijun, Guo Lucun. Effect of oxide impurities on mechanical properties and creep resistance of Al.sub.2O.sub.3 ceramics. BullChinCeramSoc, 34(1), 2015: 6773) The thermal shock resistance of the sample is expressed as thermal shock resistance index F, which is defined as = (.sub.r / .sub.o) 100, where .sub.r = (.sub.5 + .sub.10 + .sub.20 + .sub.30) / 4 is the average value of the flexural strength of the sample after 5, 10, 20, and 30 thermal shocks, .sub.o is the flexural strength value of the sample without thermal shock. The greater the thermal shock resistance index, the better the thermal shock resistance of the sample. The thermal shock resistance test of the sample was as follows: the sample was held in an electric furnace at 600C. for 2 minutes, then rapidly immersed in flowing water for quenching (water temperature = room temperature) for 10 seconds, and then the sample was taken out and quickly placed in the electric furnace at 600C. again. One cycle of thermal shock was complete once one cycle of quenching from high temperature to room temperature was complete. (Kai Li, Dalei Wang, Han Chen, Lucun Guo. Normalized evaluation of thermal shock resistance for ceramic materials. Journal of Advanced Ceramics, 3(3), 2014: 250258).

TABLE-US-00002 TABLE 2 Performance comparison of products of respective comparative examples Comparative Comparative Comparative Comparative example 1 example 2 example 3 example 4 Al/Si (mass ratio) 4.2 4.2 16.7 2.3 Through-pore density (10000 pores/m.sup.2) 25 (wall thickness: 0.5 mm) Through-pore volume fraction (%) 36.0 Microporosity (%) 2.6 36.5 5.1 6.4 Total porosity (%) 38.6 72.5 41.1 42.4 Total volume of through-pores/ 13.8 1.0 7.1 5.6 total volume of micro-pores Volumetric weight 1.22 0.55 1.31 1.06 Flexural strength at room temperature 18.0 4.4 13.2 7.5 (MPa) Thermal conductivity Perpendicular to 1.00 0.45 1.55 0.72 (W/m .Math. K) through-pores.sup.{circle around (1)} Parallel to 2.23 1.35 3.11 1.79 through-pores.sup.{circle around (2)} Volumetric heat capacity (J/K .Math. m.sup.3) 66 30 71 57 Creep index 1.85 9.37 10.04 15.60 Thermal shock resistance index 30 85 20 30 Note: .sup.{circle around (1)}Reference is made to FIG. 1. .sup.{circle around (2)}Reference is made to FIG. 2.

EXAMPLE 1

[0032] In this example, the mass ratio of alumina, silica, electric melting mullite, andalusite, and Suzhou clay powders (as raw material) was 54:2:30:10:4. The mass ratio of the raw materials to the activated carbon pore former was 100:1.5. The Al/Si ratio in the raw materials in this example was 6.0:1, and the performance of the sample is listed in Table 1. The sample has a volumetric weight of 1.10, a flexural strength of 12 MPa, a thermal conductivity of 0.85 W/m.Math.K (perpendicular to the through-pores) and 2.00 W/m.Math.K (parallel to the through-pores), a volumetric heat capacity of 59 kJ/K.Math.m.sup.3, a creep index of 1.65, and a thermal shock resistance index of 65. In this example, a standard brick mold was used for extrusion molding, and a blank having a widththickness=137 mm78 mm was extruded and cut into a standard brick Green body having a length of 277 mm, and a standard brick sample having a lengthwidththickness=230 mm114 mm65 mm was obtained after sintering, as shown in FIG. 3.

EXAMPLE 2

[0033] In this example, the mass ratio of alumina, silica, electric melting mullite, andalusite, and Suzhou clay (as raw material powders) was 42:2:30:20:6. The mass ratio of the total raw materials to the activated carbon pore former was 100:1.5. The Al/Si ratio in the raw materials in this example was 4.2:1, and the performance of the sample is listed in Table 1. The sample has a volumetric weight of 0.95, a flexural strength of 9.8 MPa, a thermal conductivity of 0.78 W/m.Math.K (perpendicular to the through-pores) and 1.88 W/m.Math.K (parallel to the through-pores), a volumetric heat capacity of 52 kJ/K.Math.m.sup.3, a creep index of 2.64, and a thermal shock resistance index of 70. In this example, a flat mold was used for extrusion molding, and a blank having a widththickness=578 mm90 mm was extruded and cut into a flat Green body having a length of 963 mm, and a flat sample having a lengthwidththickness=800 mm480 mm75 mm was obtained after sintering, as shown in FIG. 4.

EXAMPLE 3

[0034] In this example, the mass ratio of including alumina, silica, electric melting mullite, kyanite, and Suzhou clay powders (as raw material powders) was 66:2:30:20:2. The mass ratio of the raw materials to the activated carbon pore former is 100:1.5. In this example, mullite and andalusite were replaced by kyanite as the main source of silica, and the amount of alumina used was more than that of Examples 1 and 2, the Al/Si ratio in the raw materials was 6.8:1. The performance of the sample is listed in Table 1.

EXAMPLE 4

[0035] In this example, the mass ratio of alumina, silica, and electric melting mullite (as raw material powders) was 35:15:50. The mass ratio of the raw materials to the activated carbon pore former was 100:1.5. In this example, only three raw material powders were used, and the Al/Si ratio in the raw materials was 2.8:1. The performance of the sample is listed in Table 1.

EXAMPLE 5

[0036] In this example, the mass ratio of alumina, silica, electric melting mullite, andalusite, and Suzhou clay (as raw material powders) was 50:2:30:15:3. The mass ratio of the raw materials to the activated carbon pore former was 100:1.5. The mass ratio of Al/Si in the raw materials in this example was 5.3:1. Due to the use of mold having a high through-pore density, the through-pore density of the sample in this example was larger than that of Examples 1 to 4, reaching 490,000 pores/m.sup.2, and the volume fraction of the through-pores was 46.2%. The microporosity was 11.8%. The performance of the sample is listed in Table 1.

EXAMPLE 6

[0037] In this example, the ratio of the respective raw materials and the amount of activated carbon pore former used were the same as in Example 5, so the Al/Si ratio was also the same. However, in this example, due to the use of a mold having a low through-pore density, the through-pore density of the sample was only 40,000 pores/m.sup.2, and the volume fraction of the through-pores was 25.0%. The microporosity was 14.6%, and the performance of the sample is listed in Table 1.

Comparative Example 1

[0038] In this example, the mass ratio of alumina, silica, electric melting mullite, andalusite, and Suzhou clay (as raw material powders) was 42:2:30:20:6. No pore former was added. The Al/Si ratio in the raw materials in this example was 4.2:1, but the microporosity was only 2.6%. The performance of the sample is listed in Table 2. Due to the too low microporosity, although the sample has a high flexural strength and good creep resistance, its volumetric weight, thermal conductivity and volumetric heat capacity are too large, resulting in an unsatisfactory high temperature energy-saving effect.

Comparative Example 2

[0039] In this example, the ratio of the respective raw materials was the same as in Comparative Example 1, so the Al/Si ratio was also the same. The mass ratio of the raw materials to the activated carbon pore former was 100:6. The microporosity was 36.5%. The performance of the sample is listed in Table 2. Due to the too high microporosity, although the volumetric weight, thermal conductivity and volumetric heat capacity of the sample were ideal, the flexural strength was too low and the high temperature creep was large. As a result, the sample has no practical use value.

Comparative Example 3

[0040] In this example, only two raw materials powders including alumina and andalusite were used, and the mass ratio of these two materials was 83:17. The mass ratio of the raw materials to the activated carbon pore former was 100:1.5. The mass ratio of Al/Si in the raw materials in this example was 16.7:1. The performance of the sample is listed in Table 2. The sample was poor in high temperature creep resistance and thermal shock resistance, thus cannot used at high temperatures.

Comparative Example 4

[0041] In this example, the mass ratio of alumina, silica, electric melting mullite, andalusite, and Suzhou clay raw material powders was 15:10:50:20:5. The mass ratio of the raw materials to the activated carbon pore former was 100:1.5. The mass ratio of Al/Si in the raw materials in this example was 2.3:1. The performance of the sample is listed in Table 2. The sample was poor in high temperature creep resistance and thermal shock resistance, thus cannot used at high temperatures.

[0042] The purity of the respective raw materials used in the examples and comparative examples is of industrial grade, and the raw material powder was passed through a 200-mesh sieve, with a maximum particle size of equal to or smaller than 75 m.