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Aerogels are a unique type of ultrafine cell size, low density foam. Traditional aerogels are inorganic, but the synthesis of organic aerogels has also been reported. In all cases, solution chemistry can be used to tailor the structure and properties of the resultant aerogels. This study examines the microstructural dependence of the compressive mechanical properties of silica, resorcinol-formaldehyde, carbon, and melamine-formaldehyde aerogels.

A stable mixture of partially condensed polysilicates is formed from the substoichiometric, acid catalysed hydrolysis of tetramethoxysilane [Si(OCH3)4] and the removal of the reaction- generated methanol by distillation. This mixture has been used as a precursor to make silica aerogels that show microstructural differences from base catalysed TMOS aerogels. In this paper, we report the analysis of this mixture for a determination of the type and distribution of the polysilicate species formed, and we include measurements of some physical properties of this fluid.

Aerogels are highly porous solids derived from the hypercritical drying of covalently crosslinked gels. SEM, TEM and scattering studies reveal that these materials have an open-cell morphology with a solid matrix composed of interconnected colloidal-like particles (30–200 A) Processing variables and synthetic conditions largely determine the microstructure and morphology. In this study, the structure-mechanical property relationships of silica, resorcinolformaldehyde, and carbon aerogels are examined.

Silica aerogels having densities in the range of 0.003 to 0.05 g/cm3, have been prepared from a condensed silica formulation involving a two-step hydrolysis/condensation process with tetramethoxysilane (TMOS). This work describes the preparation of these unique ultralow-density aerogels, and compares several of their properties with those of aerogels made by a single step, base catalysed process.

The classical sol-gel process for synthesizing SiO2 aerogels involves the hydrolysis/condensation of tetraethyoxysilane (TEOS) and/or teramethyoxysilane (TMOS) to produce a gel which can then be super-critically extracted to a low density, highly porous aerogel glass. Controlled hydrolysis of TEOS and TMOS leads to partially hydrolyzed compounds that can be subsequently water processed to form silica aerogels in the density range from .020 to .500 gms/cc. The partially hydrolyzed compounds are stable when sealed from moist air and can be stored for future use.We discuss the controlled conditions used to obtain these compounds and present data that characterize their structure. We detail the procedures for preparing the wide range of aerogel densities. We also report on their use as an adhesive.