PROCESS FOR PRODUCING ORGANICALLY MODIFIED AEROGELS

Abstract

It is an object of the invention to provide an economically viable process for the production of hydrophobized aerogels which works both inexpensively and in a resource-conserving manner. 2.2. This object is achieved by the provision of a process for producing organically modified aerogels by producing a sol containing [SiO.sub.4/2] units and [R.sub.xSiO.sub.(4X)/2] a units, where x may be the same or different and is 1, 2 or 3, and R may be the same or different and is hydrogen or an organic substituted or unsubstituted radical, using the sol to form a gel, surface-modifying the gel obtained in the presence of more than 0.1% by weight of a phase modifier in a mixture comprising organosiloxane and initiator, wherein the mixture contains at least 20% by weight of organosiloxane and wherein the initiator consists of acid or organosiloxane or mixtures thereof and the gels obtained are dried. 2.3. The aerogels provided can be used as insulating materials, especially in thermal insulation.

Claims

1. A process for producing organically modified aerogels, said process comprising: i) preparing a sol comprising [SiO.sub.4/2] units and [R.sub.xSiO.sub.(4x)/2] units, wherein a compatibilizer is admixed in the step of preparing the sol or a compatabilizer is formed out of the sol, ii) forming a gel out of the sol, wherein a compatabilizer content of a pore liquid is between 1 and 50 wt %, iii) surface modifying the gel in a presence of more than 0.1 wt % of a compatibilizer in a mixture comprising an organosiloxane and an initiator, wherein the mixture comprises not less than 20 wt % of the organosiloxane, and wherein the initiator consists of an acid or a chlorosilane or mixtures thereof, iv) and drying the gels obtained, wherein each X is 1, 2 or 3 and may be the same or different and wherein each R is hydrogen or a substituted or unsubstituted organic moiety and may be the same or different.

2. (canceled)

3. The process as claimed in claim 1, wherein the step of preparing the sol (step i) is carried out by later admixing not less than 1 wt % of starting materials to form [R.sub.xSiO.sub.(4x)/2] units to already initially charged starting materials.

4. (canceled)

5. The process as claimed in claim 1, wherein step iii takes place without a solvent exchange beforehand.

6. The process as claimed in claim 1, wherein the initiator consists of trimethylchlorosilane or hydrochloric acid or mixtures thereof.

7. The process as claimed in claim 1, wherein shaping is effected concurrently with the step of gel formation.

8. The process as claimed in claim 1, wherein the organosiloxane used is hexamethyldisiloxane.

9. The process as claimed in claim 7, wherein said shaping is effected by dispersing the sol in a continuous phase, wherein the continuous phase comprises not less than 20 wt % of the organosiloxane and simultaneously serves as a reagent for surface modification.

10. The process as claimed in claim 1, wherein alcohols are used as the compatibilizer.

11. The process as claimed in claim 10, wherein ethanol is used as the compatibilizer.

12. The process as claimed in claim 1, wherein not more than 20 g of the initiator are used per 100 g of the gel.

13. The process as claimed in claim 1, wherein [SiO.sub.4/2] starting material used is tetraethoxysilane (TEOS) and a [R.sub.xSiO.sub.(4x)/2] starting material used is methyltriethoxysilane (MTES) or hydrolysis products thereof.

14. The process as claimed in claim 3, wherein step iii takes place without a solvent exchange beforehand.

15. The process as claimed in claim 14, wherein the initiator consists of trimethylchlorosilane or hydrochloric acid or mixtures thereof.

16. The process as claimed in claim 15, wherein shaping is effected concurrently with the step of gel formation.

17. The process as claimed in claim 16, wherein the organosiloxane used is hexamethyldisiloxane.

18. The process as claimed in claim 17, wherein said shaping is effected by dispersing the sol in a continuous phase, wherein the continuous phase comprises not less than 20 wt % of the organosiloxane and simultaneously serves as a reagent for surface modification.

19. The process as claimed in claim 18, wherein alcohols are used as the compatibilizer.

20. The process as claimed in claim 19, wherein ethanol is used as the compatibilizer.

21. The process as claimed in claim 20, wherein not more than 20 g of the initiator are used per 100 g of the gel.

22. The process as claimed in claim 21, wherein a [SiO.sub.4/2] starting material used is tetraethoxysilane (TEOS) and a [R.sub.xSiO.sub.(4x)/2] starting material used is methyltriethoxysilane (MTES) or hydrolysis products thereof.

Description

EXAMPLES

[0094] Suppliers Applicable to All examples: [0095] Tetraethyl orthosilicate (WACKER TES28 from Wacker Chemie AG), methyltriethoxysilane (SEMICOSIL M3E from Wacker Chemie AG), dimethyldimethoxysilane (Sigma-Aldrich, Grade: 95%), waterglass (Sigma-Aldrich: SiO.sub.2 content: 26.5 wt %, Na.sub.2O content: 10.6 wt %), potassium methylsiliconate (SILRES BS 16 from Wacker Chemie AG), hexamethyldisiloxane (WACKER AK 0.65 SILICONOEL from Wacker Chemie AG), trimethylchlorosilane (SILAN M3 from Wacker Chemie AG).
All other laboratory chemicals were obtained from Sigma-Aldrich, unless otherwise mentioned.
Aerogel production in emulsions (Examples 1-3), unless otherwise stated, utilized a KPG stirrer in the stirred steps at a speed of 400 revolutions per minute (rpm).

Example 1

[0096] A round-bottom flask was initially charged with 675 ml of water and 3.3 ml of 1 M hydrochloric acid before heating to 60 C. Under intensive stirring, a mixture formed from 156 g of TEOS and 134 g of MTES was admixed and stirred at 60 C. for 2 hours. The molar ratio of TEOS:MTES was 1:1.

[0097] In a second flask, 2000 ml of hexamethyldisiloxane were intensively stirred.

[0098] The warm sol was intensively stirred while being admixed with 40 ml of 0.25 M ammonia solution and transferred within a minute into the second round-bottom flask holding the HMDSO.

[0099] The reaction mixture was stirred for 1 hour at room temperature and then for 2 hours at 60 C. Gel formation and aging took place during this period. Then, 100 g of concentrated hydrochloric acid were admixed with stirring and the reaction mixture was stirred at 60 C. for 60 minutes during which an aqueous phase was formed.

[0100] The gel particles were subsequently separated off by filtration using a Bchner funnel (Whatman Filter, 125 mm, Grade 40).

[0101] The gel particles were finally dried in a vacuum drying cabinet (10 mbar, 80 C.). The following values were determined as described in the analytical methods: [0102] bulk density: 0.11 g/cm.sup.3 [0103] BET: 750 m.sup.2/g [0104] BJH pore volume: 4.0 cm.sup.3/g [0105] median pore diameter: 22 nm [0106] yield: 117.3 g

Example 2

[0107] A round-bottom flask was initially charged with 675 ml of water and 3.3 ml of 1 M hydrochloric acid before heating to 60 C. Under intensive stirring, a mixture formed from 226 g of TEOS and 64 g of MTES was admixed and stirred at 60 C. for 2 hours. The molar ratio of TEOS:MTES was 3:1.

[0108] In a second flask, 2000 ml of hexamethyldisiloxane were intensively stirred.

[0109] The warm sol was intensively stirred while being admixed with 36 ml of 0.25 M ammonia solution and transferred within a minute into the second round-bottom flask holding the HMDSO. The reaction mixture was stirred for 1 hour at room temperature and then for 2 hours at 60 C. Gel formation and aging took place during this period. Then, 100 g of concentrated hydrochloric acid were admixed with stirring and the reaction mixture was stirred at 60 C. for a further 2 hours, during which an aqueous phase was formed as a result of the hydrophobicization and the associated solvent exchange.

[0110] The gel particles were subsequently separated off by filtration using a Bchner funnel (Whatman Filter, 125 mm, Grade 40).

[0111] The gel particles were finally dried in a vacuum drying cabinet (10 mbar, 80 C.). The following values were determined as described in the analytical methods: [0112] bulk density: 0.14 g/cm.sup.3 [0113] BET: 850 m.sup.2/g [0114] BJH pore volume: 4.2 cm.sup.3/g [0115] median pore diameter: 15 nm [0116] yield: 108.7 g

Example 3

[0117] A round-bottom flask was initially charged with 650 ml of water and 3 ml of 1 M hydrochloric acid before heating to 60 C. Under intensive stirring, a mixture formed from 271 g of TEOS and 26 g of MTES was admixed and stirred at 60 C. for 1.5 hours. The molar ratio of TEOS:MTES was 9:1.

[0118] In a second flask, 1500 ml of hexamethyldisiloxane were heated to 60 C. and intensively stirred.

[0119] The warm sol was intensively stirred while being admixed with 37 ml of 0.25 M ammonia solution and transferred within a minute into the second round-bottom flask holding the HMDSO. The reaction mixture was stirred at 60 C. for 3 hours. Then, 100 g of concentrated hydrochloric acid were admixed with stirring and the reaction mixture was stirred at 60 C. for a further 2 hours, during which an aqueous phase was formed as a result of the hydrophobicization and the associated solvent exchange. The gel particles were subsequently separated off by filtration using a Bchner funnel (Whatman Filter, 125 mm, Grade 40). The gel particles were finally dried in a vacuum drying cabinet (10 mbar, 80 C.). The following values were determined as described in the analytical methods: [0120] bulk density: 0.12 g/cm.sup.3 [0121] BET: 840 m.sup.2/g [0122] BJH pore volume: 4.2 cm.sup.3/g [0123] median pore diameter: 16 nm [0124] yield: 113 g

Example 4

[0125] A round-bottom flask was initially charged with 449 g of water and 0.7 ml of 1 M hydrochloric acid before heating to 60 C. Under intensive stirring, a mixture formed from 104 g of TEOS and 89 g of MTES was admixed and stirred at 60 C. for 2 hours. The molar ratio of TEOS:MTES was 1:1.

[0126] After cooling down to room temperature, the sol was mixed in a glass beaker with 25 ml of 0.25 M ammonia solution. For aging, the gel obtained was incubated in a sealed vessel in a drying cabinet at 60 C. for 3 hours. The gel was subsequently divided into pieces about 10 mm in size. 50 g of the gel pieces were overlayered with 100 ml of HMDSO and, at 50 C., admixed with 5.0 g of TMCS and incubated in a sealed screw top flask for 2 hours at 50 C. in a drying cabinet. Then, the gel pieces were separated off by filtration via a Bfunnel (Whatman Filter, 125 mm, Grade 40) and dried to constant weight in a vacuum drying cabinet (80 C. and 10 mbar). Run 1 and Run 2 represent two independent replications of Example 4. The following values were determined as described in the analytical methods:

Run 1:

[0127] Mass density: 0.12 g/cm.sup.3 [0128] BET surface area: 795 m.sup.2/g [0129] BJH pore volume: 4.23 cm.sup.3/g [0130] Median pore diameter: 22.4 nm [0131] Thermal conductivity: 0.011 W/m*K

Run 2:

[0132] Mass density: 0.11 g/cm.sup.3 [0133] BET surface area: 804 m.sup.2/g [0134] BJH pore volume: 3.97 cm.sup.3/g [0135] Median pore diameter: 18.2 nm [0136] Thermal conductivity: 0.01 W/m*K

[0137] Thermal conductivity has the unit of watt per meter per kelvin (W/m*K).

Example 5

Determination of Hydrophobicization and Solvent Exchange Rates in Gels With Basic Hydrophobicization and Presence of Compatibilizer

[0138] A round-bottom flask was initially charged with 449 g of water and 0.7 ml of 1 M aqueous hydrochloric acid and heated to 60 C. Under intensive stirring, a mixture formed from 104 g of TEOS and 89 g of MTES was admixed and stirred at 60 C. for 2 hours. After cooling down to room temperature, the sol was admixed in a glass beaker with 25 ml of 0.25 M ammonia solution. The gel obtained was subsequently aged, i.e. incubated in a sealed vessel for 3 hours at 60 C. in a drying cabinet. Subsequently, the gel was pressed through a sieve having a mesh size of 5 mm in order to obtain pieces below 5 mm in size. The gel pieces were subsequently reacted as per versions a), b) and c). [0139] a) In a sealed screw top flask, 50 g of gel and 100 ml of HMDSO at 50 C. were admixed with 5.0 g of trimethylchlorosilane, shaken and the amount of the aqueous phase displaced out of the gel was read off on a scale. The results are listed in Table 1. It transpired that the hydrophobicization, displacing the aqueous pore liquid, was complete after one hour. [0140] b) In a sealed screw top flask, 50 g of gel and 100 ml of HMDSO at 50 C. were admixed with 5.0 g of concentrated hydrochloric acid, shaken and the amount of the aqueous phase displaced out of the gel was read off on a scale. The results are listed in Table 1. It transpired that the hydrophobicization, displacing the aqueous pore liquid, was complete after one hour. [0141] c) In a sealed screw top flask, 50 g of gel and 100 ml of an HMDSO solution (50 wt % in n-hexane) at 50 C. were admixed with 5.0 g of trimethylchlorosilane, shaken and the amount of the aqueous phase displaced out of the gel was read off on a scale. It transpired that the hydrophobicization, displacing the aqueous pore liquid, was complete after two hours.

Example 6

[0142] In a glass beaker, 150.0 g of water, 75.0 g of waterglass and 75.0 g of potassium methylsiliconate were mixed and cooled to 10 C. in an ice bath.

[0143] In a screw top flask, 200 g of hydrochloric acid (7.5 wt %) were initially charged, cooled to below 10 C. in an ice bath and stirred at 500 rpm with a magnetic stirrer.

[0144] The cooled waterglass-potassium methylsiliconate solution was gradually added via a dropping funnel to the hydrochloric acid solution with stirring. Care was taken with the metered addition to ensure that the temperature does not rise above 10 C. At pH 5.3 the admixture was stopped and the reaction mixture heated to room temperature, resulting in gel formation taking place. For aging, the gel obtained was incubated in a sealed vessel in a drying cabinet at 60 C. for 3 hours.

[0145] Subsequently, the gel was pressed through a sieve having a mesh size of 5 mm in order to obtain pieces below 5 mm in size. To remove the salts, the gel pieces were incubated in hot water (300 ml of water per 100 g of gel) at 60 C. three times for 12 hours at a time. The incubating water was decanted off after 12 hours in each period, to then be replaced by fresh water. Before the surface-modifying step, 100 g of the moist gel were overlayered with 200 ml of an ethanol-water mixture (50 wt % ethanol) and incubated in a sealed vessel at room temperature for 16 hours. The gel was subsequently separated off by filtration using a Bfunnel (Whatman Filter, 125 mm, Grade 40). For surface modification, the gel pieces obtained were admixed, shaken and incubated in a drying cabinet at 60 C. for 4 hours with 200 ml of HMDSO and 10.0 g of trimethylchlorosilane in a sealed screw top flask. The gel pieces were subsequently separated off by filtration using a Bfunnel (Whatman Filter, 125 mm, Grade 40) and dried to constant weight under reduced pressure in a vacuum drying cabinet (10 mbar, 120 C.). The following values were determined as described in the analytical methods: [0146] mass density: 0.11 g/cm.sup.3 [0147] BET: 511 m.sup.2/g

Example 7

[0148] In a glass beaker, 108.8 g of water and 108.8 g of waterglass were mixed and cooled to 10 C. in an ice bath. In a second glass beaker, 11.6 g of water and 11.6 g of potassium methylsiliconate were mixed and cooled to 10 C. in an ice bath. In a screw top flask, 200 g of hydrochloric acid (7.5 wt %) were initially charged, cooled to below 10 C. in an ice bath and stirred at 500 rpm with a magnetic stirrer.

[0149] The cooled waterglass solution was gradually added via a dropping funnel to the hydrochloric acid solution with stirring. Care was taken with the metered addition to ensure that the temperature does not rise above 10 C. After admixture, the reaction mixture was stirred at room temperature for two hours and cooled back down to below 10 C. before admixing the second component. Then, the cooled potassium methylsiliconate solution was gradually added via a dropping funnel with stirring, care being taken with the metered addition to ensure that the temperature does not rise above 10 C. Then, the stirrer was removed and the sol warmed to room temperature, resulting in gel formation taking place.

[0150] For aging, the gel obtained was incubated in a sealed vessel in a drying cabinet at 60 C. for 3 hours. Thereafter, the gel was pressed through a sieve having a mesh size of 5 mm in order to obtain pieces below 5 mm in size. To remove the salts, the gel pieces were incubated in hot water (300 ml of water per 100 g of gel) at 60 C. three times for 12 hours at a time. The incubating water was decanted off after 12 hours in each period, to then be replaced by fresh water. Before the surface-modifying step, 100 g of the moist gel were overlayered with 200 ml of an ethanol-water mixture (50 wt % ethanol) and incubated in a sealed vessel at room temperature for 16 hours. The gel was subsequently separated off by filtration using a Bfunnel (Whatman Filter, 125 mm, Grade 40). For surface modification, the gel pieces obtained were admixed, shaken and incubated in a drying cabinet at 60 C. for 2 hours with 200 ml of HMDSO and 10.0 g of trimethylchlorosilane in a sealed screw top flask. The gel pieces were subsequently separated off by filtration using a Bfunnel (Whatman Filter, 125 mm, Grade 40) and dried to constant weight under reduced pressure in a vacuum drying cabinet (10 mbar, 120 C.). The following values were determined as described in the analytical methods: [0151] mass density: 0.11 g/cm.sup.3 [0152] BET: 498 m.sup.2/g [0153] BJH pore volume: 3.25 cm.sup.3/g [0154] median pore diameter: 22.1 nm

Example 8

[0155] In a screw top flask, 84 g of water and 0.2 ml of aqueous hydrochloric acid 1 M were initially charged and heated to 60 C. Under intensive agitation (magnetic stirrer, 500 rpm), a mixture of 41.2 g of TEOS and 2.40 g of dimethyldimethoxysilane (DMDMS) was admixed and stirred at 60 C. for 2 hours. The molar ratio of TEOS:DMDMS was 9:1. The sol was subsequently admixed with 5 ml of 0.25 M ammonia solution. For aging, the gel obtained was incubated in a sealed vessel in a drying cabinet at 60 C. for 3 hours. The gel was subsequently divided into pieces about 10 mm in size. 50 g of the gel pieces were overlayered with 100 ml of HMDSO and, at 50 C., admixed with 5.0 g of TMCS and incubated in a sealed screw top flask for 2 hours at 50 C. in a drying cabinet. Then, the gel pieces were separated off by filtration via a Bfunnel (Whatman Filter, 125 mm, Grade 40) and dried to constant weight in a vacuum drying cabinet (80 C. and 10 mbar). The following values were determined as described in the analytical methods: [0156] mass density: 0.17 g/cm.sup.3 [0157] BET surface area: 790 m.sup.2/g

Comparative Example 1

Determination of Hydrophobicization and Solvent Exchange Rates Without Basic Hydrophobicization of the Gel, in the Presence of a Compatibilizer

[0158] In a round-bottom flask, 451 g of water and 0.7 ml of 1 M aqueous hydrochloric acid were initially charged and heated to 60 C. Under intensive agitation, 208 g of TEOS were admixed and stirred at 50 C. for 2 hours. After cooling down to room temperature, the sol was admixed in a glass beaker with 25 ml of 0.25 M ammonia solution. For aging, the gel obtained was incubated in a sealed vessel in a drying cabinet at 60 C. for 3 hours. Subsequently, the gel was pressed through a sieve having a mesh size of 5 mm in order to obtain pieces below 5 mm in size. The gel pieces were subsequently reacted according to versions a) and b). [0159] a) In a sealed screw top flask, 50 g of gel and 100 ml of HMDSO at 50 C. were admixed with 5.0 g of trimethylchlorosilane, shaken and the amount of the aqueous phase displaced out of the gel was read off on a scale. The results are listed in Table 1. It transpired that the hydrophobicization, displacing the aqueous pore liquid, was complete after two hours. [0160] b) In a sealed screw top flask, 50 g of gel and 100 ml of HMDSO at 50 C. were admixed with 5.0 g of concentrated hydrochloric acid, shaken and the amount of the aqueous phase displaced out of the gel was read off on a scale. The results are listed in Table 1. It transpired that the hydrophobicization, displacing the aqueous pore liquid, was complete after three hours.

Comparative Example 2

Determination of Hydrophobicization and Solvent Exchange Rates With Basic Hydrophobicization of the Gel, in the Absence of a Compatibilizer

[0161] The gel pieces below 5 mm were prepared as described under Example 5.

[0162] Instead of silylation according to versions a), b) or c), the gel pieces were incubated in hot distilled water (300 ml of water per 100 g of gel) at 60 C. five times for 24 hours at a time to remove the ethanol. The incubating water was decanted off after 24 hours in each period, to then be replaced by fresh water. The gel pieces were subsequently reacted according to versions a) and b). [0163] a) In a sealed screw top flask, 50 g of gel and 100 ml of HMDSO at 50 C. were admixed with 5.0 g of trimethylchlorosilane, shaken and the amount of the aqueous phase displaced out of the gel was read off on a scale. The results are listed in Table 1. It transpired that 24 hours later 85% by volume of the pore liquid quantity to be expected had been displaced out of the gel. [0164] b) In a sealed screw top flask, 50 g of gel and 100 ml of HMDSO at 50 C. were admixed with 5.0 g of concentrated hydrochloric acid, shaken and the amount of the aqueous phase displaced out of the gel was read off on a scale. The results are listed in Table 1. It transpired that 24 hours later 70% by volume of the pore liquid quantity to be expected had been displaced out of the gel.

Comparative Example 3

Determination of Hydrophobicization and Solvent Exchange Rates Without Basic Hydrophobicization of the Gel, in the Absence of a Compatibilizer

[0165] The gel pieces below 5 mm were prepared as described under Comparative Example 1.

[0166] Instead of silylation according to versions a), b) or c), the gel pieces were incubated in distilled water (300 ml of water per 100 g of gel) at 60 C. five times for 24 hours at a time to remove the ethanol. The incubating water was decanted off after 24 hours in each period, to then be replaced by fresh water. The gel pieces were subsequently reacted according to versions a) and b). [0167] a) In a sealed screw top flask, 50 g of gel and 100 ml of HMDSO at 50 C. were admixed with 5.0 g of trimethylchlorosilane, shaken and the amount of the aqueous phase displaced out of the gel was read off on a scale. Over a period of 24 hours no reaction took place in the form of pore liquid displacement. [0168] b) In a sealed screw top flask, 50 g of gel and 100 ml of HMDSO at 50 C. were admixed with 5.0 g of concentrated hydrochloric acid, shaken and the amount of the aqueous phase displaced out of the gel was read off on a scale. Over a period of 24 hours no reaction took place in the form of pore liquid displacement.

Comparative Example 4

Determination of Hydrophobicization and Solvent Exchange Rates For Same Amount of Trimethylchlorosilane as in Example 5a and Comparative Examples 1a, 2a and 3a by Substitution of n-Hexane For Hexamethyldisiloxane

[0169] a) In a sealed screw top flask, 50 g of aged and comminuted gel obtained as described in Example 5 and 100 ml of n-hexane were, at 50 C., admixed and shaken with 5.0 g of trimethylchlorosilane and the amount of the aqueous phase displaced out of the gel was read off on a scale. Over a period of 24 hours no reaction took place in the form of pore liquid displacement. [0170] b) In a sealed screw top flask, 50 g of aged and comminuted gel obtained as described in Comparative Example 2 and 100 ml of n-hexane were, at 50 C., admixed and shaken with 5.0 g of trimethylchlorosilane and the amount of the aqueous phase displaced out of the gel was read off on a scale. Over a period of 24 hours no reaction took place in the form of pore liquid displacement. [0171] b) In a sealed screw top flask, 50 g of washed gel obtained as described in Comparative Example 2 and 100 ml of n-hexane were, at 50 C., admixed and shaken with 5.0 g of trimethylchlorosilane and the amount of the aqueous phase displaced out of the gel was read off on a scale. Over a period of 24 hours no reaction took place in the form of pore liquid displacement. [0172] d) In a sealed screw top flask, 50 g of washed gel obtained as described in Comparative Example 3 and 100 ml of n-hexane were, at 50 C., admixed and shaken with 5.0 g of trimethylchlorosilane and the amount of the aqueous phase displaced out of the gel was read off on a scale. Over a period of 24 hours no reaction took place in the form of pore liquid displacement.

Example 9

[0173] In a glass beaker, 80.0 g of waterglass and 65.0 g of water were mixed and cooled to 10 C. in an ice bath.

In a screw top flask, 100 g of hydrochloric acid (7.5 wt %) were initially charged, cooled to below 10 C. in an ice bath and stirred at 500 rpm with a magnetic stirrer.

[0174] The cooled waterglass solution was gradually added via a dropping funnel to the hydrochloric acid solution with stirring. Care was taken with the metered addition that the temperature does not rise above 15 C. The addition was stopped at pH 2.5. Then, under agitation, 6.25 g of MTES were admixed and the mixture removed from the ice bath. Once the sol was clear, 40.0 g of ethanol were admixed. Lastly, 0.25 M ammonia solution was admixed to establish pH 5.5, resulting in gel formation taking place. For aging, the gel obtained was incubated in a sealed vessel in a drying cabinet at 60 C. for 3 hours. Subsequently, the gel was pressed through a sieve having a mesh size of 5 mm, to obtain pieces below 5 mm.

[0175] For surface modification, 100 g of the gel pieces obtained were admixed, shaken and incubated with 200 ml of HMDSO and 10.0 g of hydrochloric acid (32% strength) in a sealed screw top flask at 70 C. in a drying cabinet for 4 hours during which the reaction vessel was shaken every 15 min or so. The gel pieces were subsequently separated off by filtration, washed with water and dried to constant weight at reduced pressure in a vacuum drying cabinet (10 mbar, 120 C.). The following values were determined as described in the analytical methods: [0176] bulk density: 0.09 g/cm.sup.3 [0177] BET: 790 m.sup.2/g

Example 10

[0178] In a glass beaker, 82.0 g of waterglass, 5.0 g of potassium methylsiliconate and 50.0 g of water were mixed and cooled to 10 C.

[0179] In a screw top flask, 100 g of hydrochloric acid (7.5 wt %) were initially charged, cooled to below 10 C. in an ice bath and stirred at 500 rpm with a magnetic stirrer.

[0180] The cooled waterglass-potassium methylsiliconate solution was gradually added via a dropping funnel to the hydrochloric acid solution with stirring. Care was taken with the metered addition that the temperature does not rise above 15 C. The addition was stopped at pH 1.5. Then, under agitation, 100.0 g of the compatibilizer were admixed (85 g of ethanol (a), 100 g of methanol (b), 100 g of isopropanol (c)) and the mixture was removed from the ice bath. Lastly, 0.25 M ammonia solution was admixed to establish pH 5.5, resulting in gel formation taking place. For aging, the gel obtained was incubated in a sealed vessel in a drying cabinet at 60 C. for 3 hours. Subsequently, the gel was pressed through a sieve having a mesh size of 5 mm, to obtain pieces below 5 mm.

[0181] For surface modification, 100 g of the gel pieces obtained were admixed, shaken and incubated with 200 ml of HMDSO, 10.0 g of hydrochloric acid (32% strength) and in a sealed screw top flask at 70 C. in a drying cabinet for 4 hours during which the reaction vessel was shaken every 15 min or so. The gel pieces were subsequently separated off by filtration, washed with water and dried to constant weight at reduced pressure in a vacuum drying cabinet (10 mbar, 120 C.). The following values were determined as described in the analytical methods: [0182] a) Bulk density: 0.09 g/cm.sup.3 [0183] b) Bulk density: 0.06 g/cm.sup.3 [0184] c) Bulk density: 0.06 g/cm.sup.3

Example 11

[0185] In a glass beaker, 115 g of water and 1.5 g of 1 M aqueous hydrochloric acid were initially charged. Under agitation, a mixture formed from 47.5 g of TEOS and 1.4 g of trimethylethoxysilane was admixed and stirred at room temperature for 16 hours.

[0186] For gel formation, the sol was admixed with 5.0 g of 0.5 M ammonia solution. For aging, the gel obtained was incubated in a sealed vessel in a drying cabinet at 60 C. for 4 hours. The gel was subsequently divided into pieces about 5 mm in size. For surface modification, 100 g of the gel pieces obtained were admixed, shaken and incubated with 200 ml of HMDSO, 10.0 g of hydrochloric acid (32% strength) and 10 g of ethanol in a sealed screw top flask at 70 C. in a drying cabinet for 3 hours during which the reaction vessel was shaken every 15 min or so. The gel pieces were subsequently separated off by filtration, washed with water and dried to constant weight at reduced pressure in a vacuum drying cabinet (10 mbar, 120 C.). The following values were determined as described in the analytical methods: [0187] bulk density: 0.11 g/cm.sup.3 [0188] BET: 715 m.sup.2/g

TABLE-US-00001 TABLE 1 Amount of displaced pore liquid [ml] Time Example Comparative Example [h] 5a 5b 1a 1b 2a 2b 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.08 0.00 0.00 nd nd nd nd 0.33 28.00 0.00 nd nd nd nd 0.50 nd 0.00 0.00 nd nd nd 0.67 nd 24.00 nd nd nd nd 0.83 nd nd 13.00 0.00 nd nd 1.00 nd nd nd nd 0.00 0.00 1.17 49.00 47.00 nd nd nd nd 1.20 nd nd 31.00 0.00 nd nd 1.50 49.00 nd nd nd nd nd 2.00 nd 49.00 nd nd 0.00 0.00 2.10 nd nd nd 0.00 nd nd 2.20 nd nd nd 19.00 nd nd 2.40 nd nd 49.00 38.00 nd nd 3.00 nd nd nd nd 15.00 0.00 3.20 nd nd 49.00 50.00 nd nd 6.00 nd nd nd nd 28.00 0.00 24.00 nd nd nd nd 42.00 35.00 nd = not determined