Low density, resorcinol-formaldehyde aerogels

• US 4,997,804 A
• Filed: 09/12/1989
• Issued: 03/05/1991
• Est. Priority Date: 05/26/1988
• Status: Expired due to Term

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: United States Department of Energy
• Inventors: Pekala, Richard W.
• Primary Examiner(s): Foelak, Morton
• Application Number:
  US07/406,009
• Time in Patent Office: 539 Days
• Field of Search: 502/418, 502/402, 502/416, 502/437, 502/439, 521/64, 521/181, 521/918
• US Class Current: 502/418
• CPC Class Codes: B01J 20/20 comprising free carbon; comprising carbon obtained by carbonising processes
• CPC Class Codes: C08G 8/20 with polyhydric phenols
• CPC Class Codes: Y10S 521/918 Physical aftertreatment of a cellular product

Abstract

The polycondensation of resorcinol with formaldehyde under alkaline conditions results in the formation of surface functionalized polymer "Clusters". The covalent crosslinking of these "clusters" produces gels which when processed under supercritical conditions, produce low density, organic aerogels (density≦100 mg/cc; cell size ≦0.1 microns). The aerogels are transparent, dark red in color and consist of interconnected colloidal-like particles with diameters of about 100○. These aerogels may be further carbonized to form low density carbon foams with cell size of about 0.1 micron.

              TABLE I                                                     

______________________________________ Theo- [Form- retical Actual Formu- % alde- [Resor- density Density lation Solids hyde] cinol] Na₂ CO₃ (g/cc) (g/cc) ______________________________________ A 5.0% 0.29M 0.58M 0.0029M 0.050 0.079 B 5.0% 0.29M 0.58M 0.0019M 0.050 0.073 C 5.0% 0.29M 0.58M 0.0015M 0.050 0.070 D 4.0% 0.24M 0.47M 0.0012M 0.040 0.054 E 3.5% 0.21M 0.41M 0.0010M 0.035 0.044 F 2.0% 0.12M 0.24M 0.0006M 0.020 0.030 ______________________________________

Claims

1. A composition of matter comprising a low density, organic aerogel which is selected from the group of materials consisting of resorcinol-formaldehyde, hydroquinone-resorcinol-formaldehyde, phloroglucinol-resorcinol-formaldehyde, and catechol-resorcinol-formaldehyde with a uniform, pore size of less than about one micron and a density in the range of about 35 to 100 mg/cc.

2. The composition of claim 1, wherein the pore size of said aerogel is about 0.1 micron.

3. The composition of claim 1, wherein said aerogel is a resorcinol-formaldehyde aerogel.

4. The composition of claim 3, wherein said aerogel is carbonized to form a carbon foam with cell size of about 0.1 micron.

5. The composition of claim 1, further comprising a metal salt incorporated therein.

6. The composition of claim 5, wherein said metal salt is selected from the group consisting of thallium acetate, rubidium carbonate, chloroplatinic acid, palladium chloride, and lead acetate.

7. The composition of claim 1, further comprising the incorporation of a dihydroxy benzoic acid in said aerogel.

8. As an article of manufacture, an aerogel of claim 3, machined to a predetermined shape and size.

9. As an article of manufacture, a carbonized aerogel of claim 4, machined to a predetermined shape and size.

10. A low density, microcellular resorcinol-formaldehyde aerogel having a pore size of less than about one micron and a density in the range of about 35 to 100 mg/cc produced by the process comprising the steps of:

(a) mixing resorcinol and formaldehyde in a molar ratio of about 1;

2, in the presence of catalytic amounts of sodium carbonate;

(b) adjusting the pH of the mixture to a value in the range of about 6.5 to about 7.4.;

(c) decanting the mixture into a glass ampoule;

(d) sealing the glass ampoule;

(e) heating the mixture to about 85°

C. in an oven for about seven days to facilitate formation of a gel;

(f) removing the ampoule from the oven and cooling it to room temperature;

(g) breaking the ampoule and removing the gel from the ampoule;

(h) washing the gel in an agitated bath of trifluoracetic acid at 45°

C. for three days;

(i) transferring the gel from the acid bath to an agitated acetone bath maintained at about 45°

C., to remove water;

(j) removing the gel from the acetone bath and critical point drying the gel; and

(k) characterizing the gel.

11. A carbon foam produced by heating the aerogel of claim 10 in a nitrogen atmosphere to a temperature in the range of about 600°

to about 1200°

C. to carbonize said aerogel and form a low density, carbon foam.