BINDER-FREE BULK SILICA AEROGEL MATERIAL, METHOD OF PRODUCING THE SAME AND USES THEREOF

Abstract

A method of preparing a binder-free bulk silica aerogel material, comprising the steps of: (i) providing an amount of granular silica aerogel material, and (ii) carrying out a curing step wherein the granular silica aerogel material is contacted with a curing medium, thereby converting the granular silica aerogel material to the bulk silica aerogel material. According to the invention, the granular silica aerogel material is hydrophobic, and the curing medium is an aqueous curing medium which is either acidic with a pH<4 or basic with a pH>10. A resulting binder-free bulk silica aerogel material comprises silica aerogel granules which are interface-bonded and has the following properties: a thermal conductivity below 24 mW/(m.Math.K), a compressive strength of at least 5 kPa, a 3-point flexural stress (f), determined with a specimen having a longest dimension which is four times the specimen thickness, of at least 0.5 kPa.

Claims

1. A method of preparing a binder-free bulk silica aerogel material, comprising the steps of: providing an amount of granular silica aerogel material, carrying out a curing step wherein the granular silica aerogel material is contacted with a curing medium, thereby converting the granular silica aerogel material to the bulk silica aerogel material, the granular silica aerogel material is hydrophobic, and the curing medium is an aqueous curing medium which is either acidic with a pH<4, or basic with a pH>10.

2. The method according to claim 1, wherein the curing medium further comprises an additive acting to catalyse hydrolysis of alkoxy groups present at the surface of the silica aerogel material.

3. The method according to claim 1, wherein the granular silica aerogel material is wetted with a surfactant.

4. The method according to claim 1, wherein at least part of the curing step is carried out under compression, whereby the silica aerogel material is compressed from an initial volume to a compressed volume of 30% to 90% of the initial volume.

5. The method according to claim 4, wherein the curing step is carried out at ambient temperature.

6. The method according to claim 1, wherein the curing step is carried out at a temperature of at least 110 C.

7. The method according to claim 6, wherein the curing step is carried out in a microwave oven.

8. The method according to claim 1, wherein the granular silica aerogel material has a grain size distribution ranging from 0.001 mm to 10 mm.

9. The method according to claim 8, wherein the granular silica aerogel material is a mixture of silica aerogel powder and silica aerogel granules, with a volume fraction of granules to powder that ranges from 55:45 to 75:25.

10. A binder-free bulk silica aerogel material obtainable by a method of preparing inder-free el material, the method comprising the steps: providing an amount of granular silica aerogel material, carrying out a curing step wherein the granular silica aerogel material is contacted with a curing medium, thereby converting the granular silica aerogel material to the bulk silica aerogel material, wherein the granular silica aerogel material is hydrophobic, and the curing medium is an aqueous curing medium which is either acidic with a PH<4, or basic with a pH>10, wherein the material comprises silica aerogel granules which are interface-bonded, and the material has the following properties: a thermal conductivity below 24 mW/(m.Math.K), a compressive strength of at least 5 kPa, a 3-point flexural stress (.sub.f), determined with a specimen having a longest dimension which is four times the specimen thickness, of at least 0.5 kPa.

11. The bulk silica aerogel material according to claim 10, having a board shape with a board length, a board width and a board thickness, wherein the board length and the board width each are at least four times the board thickness.

12. The bulk silica aerogel material according to claim 11, which is configured as a surface laminate comprising at least one reinforcement sheet, the surface laminate having a 3-pount flexural stress (.sub.f) of at least 100 kPa.

13. The bulk silica aerogel material according to claim 11, further containing a fibrous or particulate reinforcement material.

14. (canceled)

15. The method according to claim 1, wherein the curing medium is an aqueous curing medium which is either acidic with a pH<3, or basic with a pH>11.

16. The bulk silica aerogel material according to claim 11. wherein the material has at least one of: a thermal conductivity below 19 mW/(m.Math.K). a compressive strength above 40 kPa. a 3-point flexural stress (.sub.f) of at least 10 kPa, or a combination thereof.

17. The bulk silica aerogel material according to claim 11, wherein the material has at least one of: a thermal conductivity below 17 mW/(m.Math.K). a 3-point flexural stress (.sub.f) of at least 20 kPa, or a combination thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

Example 1

[0032] 2.17 g of aerogel granules produced by Cabot (P300) with a size between 1.2 and 4.0 mm were mixed with 1.27 g of aerogel powder (<0.1 mm, produced from Cabot P300 by mechanical crushing). Separately, 2.97 g of deionised water were well mixed with 0.74 g of 1-molar hydrochloric acid and 0.06 g of BASF Pluronic PE9200, resulting of a solution pH of about 0.7 to be used as curing medium. All ingredients were merged and mixed with a spatula until a gluey consistency was achieved. The mixture was compressed into a plastic mould of a volume of about 505010 mm.sup.3. It was cured in the mould in a kitchen microwave for 10 minutes at 700 W, subsequently carefully removed from the mould and microwaved at the same power for another 10 minutes. The resulting small insulation board of approximate dimensions of 505012 mm.sup.3 had a thermal conductivity of about 17.3 mW/(m.Math.K), measured with a custom-built guarded hot plate device.

Example 2

[0033] In the same proportions and with the same procedure as in Example 1 except for a lower microwave power of 350 W, a cylindrical sample of diameter 20 mm and height 30 mm was created with a compressive strength at failure of about 24.3 kPa.

Example 3

[0034] With the same amounts and with the same procedure as in Example 1, except using 3.35 g of deionised water and 0.38 g of 1-molar hydrochloric acid, a sample of dimensions 505012 mm.sup.3 was created. The sample was cut along the long direction and a mean 3-point flexural stress (.sub.f) of 11.9 kPa was measured.

Example 4

[0035] 2.16 g of aerogel granules and 1.28 g of aerogel powder were mixed as in Example 1. Separately, 2.70 g of deionised water, 0.06 g of BASF Pluronic PE9200 and 0.32 g of 0.01-molar sodium hydroxide, resulting in a pH of about 11, were well mixed. The curing medium thus formed was merged and mixed with the aerogel as in Example 1 and cured in the same way. The material was bound cohesively and a thermal conductivity of 19.9 mW/(m.Math.K) was measured.

Example 5

[0036] 2.15 g of aerogel granules and 1.27 g of aerogel powder were mixed as in Example 1. Separately, 10 g of 1-molar hydrochloric acid was mixed with 10 g of deionised water. The aerogel and acid solution were placed in a suitable plastic container with a valve to apply pressurised air of about 2 bar. The pressure in the container was then gently released. This pressurising process was repeated two more times. Subsequently, the mixture was filtered with a sieve to removed excess liquids and then cured as in Example 1. A thermal conductivity of 17.0 mW/(m.Math.K) was measured.

Example 6

[0037] In the same proportions and with the same procedure as in Example 5, a sample of dimensions 303030 mm.sup.3 was prepared for compression testing. The compressive strength at failure was about 23.6 kPa.

Example 7

[0038] With the same amounts, but using 2.50 g of deionised water and 1.00 g of hydrochloric acid, and with the same mixing procedure as in Example 1, a sample was created. However, instead of curing the sample in the microwave, it was left for seven days at ambient conditions. The measured thermal conductivity of this sample was 16.7 mW/(m.Math.K).

Example 8

[0039] Aerogel granules and powder were mixed as in Example 1. Separately, 3.08 g of deionised water, 0.67 g of 1-molar hydrochloric acid and 0.06 g of BASF Pluronic PE9200 were mixed, then combined with the aerogel and placed in a mould as in Example 1. The sample was subsequently cured in an oven at 130 C. for 1.3 h inside the mould and then again for 1.3 h outside the mould.

Example 9

[0040] With the same amounts as in Example 7 and the procedure as in Example 1 a sample was created. The sample was modified by gluing a glass fibre mesh with a surface weight of 25 g/m.sup.2 on both faces of the sample using a polyurethane glue. A mean 3 point flexural stress (.sub.f) of 121.0 kPa was measured.

Example 10

[0041] With the same amounts and the same procedure as in Example 1, but with the addition of 0.1 g of glass fibres, a fibre-reinforced sample was created in order to improve mechanical properties.

[0042] Comparative Example 11

[0043] With the same material proportions and the same mixing procedure as in Example 1, a mixture was made to fill a cavity in a fired clay brick. The mixture was compressed into the cavity and the brick with the mixture was cured in an oven at 130 C. for 8 hours. This resulted in a cohesive filling of the cavity.

[0044] Comparative Example 12

[0045] With the same amounts and the same procedure as in Example 1, a mixture was made to loosely fill a mould of about 505020 mm.sup.3 by slightly pressing the material into the mould. Like that no pressure was applied during curing in a microwave as in Example 1. This resulted in a cohesive sample.

Comparative Example 13

[0046] With the same amounts and the same procedure as in Example 1 but substituting hydrochloric acid with water, a mixture with neutral pH was produced. Curing the mix in the microwave as in Example 1 did not result in binding of the granules and hence not in a cohesive sample.