High strength air-dried aerogels
View Patent ↗A method for the preparation of high strength air-dried organic aerogels. The method involves the sol-gel polymerization of organic gel precursors, such as resorcinol with formaldehyde (RF) in aqueous solvents with R/C ratios greater than about 1000 and R/F ratios less than about 1:2.1. Using a procedure analogous to the preparation of resorcinol-formaldehyde (RF) aerogels, this approach generates wet gels that can be air dried at ambient temperatures and pressures. The method significantly reduces the time and/or energy required to produce a dried aerogel compared to conventional methods using either supercritical solvent extraction. The air dried gel exhibits typically less than 5% shrinkage.
1. A process for the synthesis of a low density, organic aerogel the process comprising the steps of:
mixing a hydroxy benzene and an aldehyde in a solvent in the presence of a catalyst, the hydroxy benzene and aldehyde present in a molar ratio of 1:4 or less wherein the hydroxy benzene and catalyst are added in a molar ratio of greater than 1000:1;
heating the mixture to sufficient temperature for a sufficient time to form a stable gel; and
allowing the gel to air dry whereby a stable, low-density monolithic structure exhibiting less than about 5% shrinkage results,
wherein the resulting monolithic structure has a density of about 30-250 mg/cm 3 .
2. The process of claim 1 wherein the hydroxy benzene is selected from the group consisting of resorcinol, catechol, hydroquinone, phloroglucinol and mixtures thereof; and
the aldehyde is selected from the group consisting of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde and mixtures thereof.
3. The process of claim 1 wherein the solvent is water.
4. The process of claim 1 wherein the ratio of hydroxy benzene and aldehyde is between 1:4 and 1:8.
5. The process of claim 1 wherein the ratio of hydroxy benzene and aldehyde is less than 1:5.
6. The process of claim 1 wherein the ratio of hydroxy benzene and aldehyde is between 1:4 and 1:8, wherein the resulting monolithic structure has an unpyrollized density of about 30-190 mg/cm 3 , wherein the resulting monolithic structure exhibits less than about 3% shrinkage.
7. The process of claim 6 wherein
the hydroxy benzene is selected from the group consisting of resorcinol, catechol, hydroquinone, phloroglucinol and mixtures thereof; and
the aldehyde is selected from the group consisting of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde and mixtures thereof.
8. The process of claim 7 wherein the hydroxyl benzene is resorcinol and the aldehyde is formaldehyde.
9. The process of claim 1 and further including the step of curing the mixture.
10. The process of claim 1 wherein the solvent is selected from the group consisting of acetone, amyl acetate, dimethylsulfoxide, glycol, methanol, ethanol, propanol, isopropanol, amyl acetate and mixtures thereof.
11. The process of claim 1 wherein said catalyst is sodium carbonate.
12. The process of claim 1 wherein the drying step occurs at substantially room temperature.
13. The process of claim 1 wherein the drying step occurs at a temperature of between about 20° C. and 150° C.
14. The process of claim 13 wherein the aerogel is substantially dried within 1 day.
15. The process of claim 1 wherein the resulting monolithic structure has at least about 90% of a total pore volume in pores of a diameter from about 2 nanometers to about 10 microns, a solids portion of the monolithic structure having at least 90% of a total particle size of diameter from about 100 nm to about 5 microns.
16. The process of claim 1 wherein the resulting aerogel has a density of less than about 190 mg/cm 3 .
17. The process of claim 1 wherein the resulting aerogel has a density of between about 50-240 mg/cm 3 .
18. The process of claim 1 , further comprising the step of heating said aerogel in a nitrogen atmosphere, to a temperature in the range of about 600° C. to about 1200° C. to carbonize said aerogel and form a low density, carbon foam.
19. An aerogel produced by the process of claim 1 .
20. A process for the synthesis of a low density, high strength organic aerogel of fine pore size, said process comprising the steps of:
mixing in a predetermined ratio a polyhydroxy benzene and formaldehyde in the presence of a base catalyst;
heating the mixture to a predetermined temperature for a sufficiently long period of time to form a stable gel; and
air drying the gel whereby a low density, high strength monolithic aerogel, exhibiting less than about 8% shrinkage, results,
wherein the resulting monolithic structure has an unpryrollized density of about 30-240 mg/cm 3 .
21. The process of claim 20 wherein the hydroxyl benzene is resorcinol, the aldehyde is formaldehyde, the solvent is water, the catalyst is a base catalyst, and the molar ratio of hydroxylated benzene to formaldehyde is less than about 1:4.
22. A process for forming a low density, high strength organic aerogel, comprising
forming a reaction mixture comprising at least one hydroxylated benzene compound, at least one aldehyde, a catalyst and solvent; wherein the molar ratio of the hydroxylated benzene compound to aldehyde is less than about 1:5;
reacting said reaction mixture at a temperature and for a time sufficient to form an organic gel;
heating said organic gel at a curing temperature for a curing time to form a cured organic gel; and
allowing the resultant gel to air dry at a temperature of between about 20° C. and 150° C. whereby an uncracked, low density, high strength monolithic aerogel, exhibiting less than about 5% shrinkage, results,
wherein the resulting monolithic structure has an unpyrollized density of 50-190 mg/cm 3 ,
wherein the resulting monolithic structure has at least about 90% of a total pore volume in pores of a diameter from about 2 nanometers to about 10 microns,
wherein a solids portion of the monolithic structure having at least 90% of a total particle size of diameter from about 100 nm to about 5 microns.
23. The process of claim 22 wherein the hydroxyl benzene is resorcinol, the aldehyde is formaldehyde, the solvent is water, the catalyst is a base catalyst, and the molar ratio of hydroxylated benzene to formaldehyde is between 1:4 and 1:8.
24. An aerogel made by the process of claim 23 .
25. An unpyrollized organic resorcinol formaldehyde aerogel, characterized by a high strength, non friable monolithic structure, having a density of between about 30 and 190 mg/cm 3 and a surface area of at least about 400 m 2 /g, wherein the aerogel is derived from air drying an organic resorcinol formaldehyde gel.