Aerogel compositions and methods
The present disclosure provides an aerogel composition which is intrinsically hydrophobic without surface modification by a hydrophobizing agent, is durable and easy to handle, which has favorable performance in aqueous environments, and which also has favorable combustion and self-heating properties. Also provided is a method of preparing an aerogel composition which is intrinsically hydrophobic without surface modification by a hydrophobizing agent, is durable and easy to handle, which has favorable performance in aqueous environments, and which has favorable combustion and self-heating properties.
1 . A composition comprising a silica-based aerogel including hydrophobic-bound silicon, wherein:
the silica-based aerogel comprises surface groups consisting essentially of hydrophobic groups of the formula Si—R, where R is a single alkyl group;
the silica-based aerogel has a content of from about 0.1 wt % to about 2 wt % of guanidinium cations;
the silica-based aerogel has a content of ammonium salts of about 100 ppm or less;
the silica-based aerogel is not surface-treated by a hydrophobizing agent; and
the silica-based aerogel has a liquid water uptake of less than 5 wt % as determined by ASTM C1511.
2 . The composition of claim 1 , where R is a methyl group.
3 . The composition of claim 1 , wherein the silica-based aerogel has a water uptake of less than 2 wt %.
4 . The composition of claim 1 , wherein a heat of combustion of the composition is less than 717 cal/g.
5 . The composition of claim 1 , wherein the composition has an onset of thermal decomposition of hydrophobic organic materials of 350° C. or higher.
6 . The composition of claim 1 , wherein the composition has an onset of thermal decomposition of hydrophobic organic materials of 400° C. or higher.
7 . The composition of claim 1 , wherein the composition has an onset of thermal decomposition of hydrophobic organic materials of 500° C. or higher.
8 . The composition of claim 1 , wherein the silica-based aerogel has a thermal conductivity of less than about 45 mW/M*K.
9 . The composition of claim 8 , wherein the thermal conductivity is about 40 mW/M*K or less.
10 . The composition of claim 1 , further comprising a reinforcement material.
11 . The composition of claim 10 , wherein the reinforcement material comprises a fiber reinforcement material or a foam reinforcement material.
12 . The composition of claim 1 , further comprising an opacifying or fire-class additive.
13 . The composition of claim 12 , wherein the opacifying or fire-class additive is present in amount from about 0.1 wt % to about 10 wt %.
14 . The composition of claim 12 , wherein the opacifying or fire-class additive is present in an amount from about 0.5 wt % to about 3.0 wt %.
15 . The composition of claim 12 , wherein the opacifying or fire-class additive is selected from the group consisting of boron carbide, diatomite, manganese ferrite, manganese oxide, nickel oxide, tin oxide, silver oxide, bismuth oxide, titanium carbide, tungsten carbide, carbon black, titanium oxide, iron titanium oxide, zirconium silicate, zirconium oxide, iron oxide, iron (II) oxide, iron (III) oxide, manganese dioxide, iron titanium oxide, chromium oxide, silicon carbide, phyllosilicate clay, kaolin or kaolinite, metakaolin, halloysite, meta-halloysite, endellite, mica, diaspore, gibbsite, boehmite, montmorillonite, beidellite, pyrophyllite, nontronite, bravaisite, smectite, leverrierite, rectorite, celadonite, attapulgite, chloropal, volkonskoite, allophane, racewinite, dillnite, severite, miloschite, collyrite, cimolite and newtonite, sodium bicarbonate, magnesium hydroxide, magnesium dihydroxide, alumina trihydrate, gypsum, barringtonite, nesquehonite, lansfordite, hydromagnesite, dolomite, lithium carbonate or mixtures thereof.