Sodium silicate aerogels

Naturally, also the type of silylation agent used plays a crucial role in determining the final properties of aerogels obtained by APD. HMDS and TMCS are the ones most commonly used, and that for a reason. They yield the lowest density and highest porosity materials and also are easily accessible through standard commercial retail channels. For a more comprehensive comparison of physicochemical properties of identically prepared sodium silicate aerogels sUylated with various surface modification agents, the reader is referred to [16]. 

Since the 1980s a new microporous insulation material based on silicic aerogels is in a test phase. About 60 years ago Kistler from Stanford University developed a method to produce aerogels from silicic material without shrinking them He reacted waterglass with hydrochloric acid, washed out the sodium and chloride ions from the gel, substituted the water with alcohol and dried the gel in an autoclave above the critical point. Other methods begin with tetramethoxysilane for the production of monolithic aerogels. 

Very finely divided colloidal silica powders can also be obtained by treating certain silicate minerals such as clay or calcium silicate with acid, followed by suitable heat treatment in an alkaline medium. Similarly, finely divided colloidal silicas can be produced by precipitating silica from a solution of sodium silicate with carbon dioxide. Such precipitated silicas are commonly used as reinforcing fillers, for elastomers because they are extremely finely divided, and the ultimate particles are easily broken apart. Finely divided aerogels of silicas may be employed, such as those described by Kistler in U.S. Pat. Nos. 2,093,454 and 2,249,767. 

Aerogels Sodium silicate -I- Acid Kistler 1931 Santocel, Nanogel... 

Parvathy Rao A, Venkastewara Rao A, Pajonk GM (2007) Hydrophobic and physical properties of the ambient pressure dried silica aerogels with sodium silicate precursor using various surface modification agents. Appl Surf Sci 253 6032-6040... 

Rao, A P, Rao, A V, Bangi, U K H (2008) Low thermalconductive, transparent and hydrophobic ambient pressure dried silica aerogels with various preparation conditions using sodium silicate solutions. J Sol-Gel Sci Technol 47(1) 85-94. 

Rao, A P, Rao, A V, Pajonk, G, Shewale, P M (2(X)7) Effect of solvent exchanging process on the preparation of the hydrophobic silica aerogels by ambient pressure drying method using sodium silicate precursor. J Mater Sci 42(20) 8418-8425. 

Sodium Silicate Based Aerogels via Ambient Pressure Drying... 

Bang , U. K.H. Rao, A. P. Hirashima, H. Rao, A. V., Physico-chemical properties of ambiently dried sodium sihcate based aerogels catalyzed with various acids, J. Sol-Gel Sci. Technol. 2009, 50, 87-97 Shewale, P. M. Rao, A. V. Gurav, J. L. Rao, A. P., Synthesis and characterization of low density and hydrophobic silica aerogels dried at ambient pressure using sodium silicate precursor, J. Porous Mater. 2009, 16 (1), 101-108... 

---