A comparison of mechanical properties and scaling law relationships for silica aerogels and their organic counterparts

Conference · Wed Aug 01 00:00:00 EDT 1990

OSTI ID:6824462

Pekala, R W; Hrubesh, L W; Tillotson, T M; Alviso, C T; Poco, J F; LeMay, J D

Aerogels are a special class of open-cell foams derived from the supercritical extraction of highly crosslinked, inorganic or organic gels. The resultant materials have ultrafine cell/pore sizes (< 100 nm), high surface areas (350--1000m{sup 2}/g), and a microstructure composed of interconnected colloidal-like particles or polymeric chains with characteristic diameters of 10 nm. TEM and SAXS show that this microstructure is sensitive to variations in processing conditions that influence crosslinking chemistry and growth processes prior to gelation. Traditional silica aerogels are prepared via the hydrolysis and condensation of tetramethoxy silane (TMOS) or tetraethoxy silane (TEOS). Factors such as pH and the (H{sub 2}O)/(TMOS) ratio affect the microstructure of the dried aerogel. It is generally accepted that polymeric' silica aerogels result from acid catalysis while colloidal'silica aerogels result from base catalysis. Recently, Hrubesh and Tillotson developed a new condensed silica' procedure for obtaining silica aerogels with densities as low as 0.004g/cc, i.e. only 3{times} the density of air. Organic aerogels are formed from the aqueous, polycondensation of (1) resorcinol/formaldehyde or (2) melamine/formaldehyde. The microstructure of the resorcinol-formaldehyde (RF) aerogels is dictated by the amount of base catalyst used in the sol-gel polymerization. In addition, these materials can be pyrolyzed in an inert atmosphere to form vitreous carbon aerogels. Melamine- formaldehyde (MF) aerogels that are both colorless and transparent are only formed under acidic conditions (i.e. pH = 1--2). In this paper, the microstructural dependence and scaling law relationships for the compressive modulus of silica, carbon, RF, and MF aerogels will be discussed in detail. 17 refs., 1 fig.

• Research Organization: Lawrence Livermore National Lab., CA (USA)
• Sponsoring Organization: DOE/DP
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 6824462
• Report Number(s): UCRL-JC-104279; CONF-901105-13; ON: DE91000282
• Resource Relation: Conference: Fall meeting of the Materials Research Society, Boston, MA (USA), 24 Nov - 1 Dec 1990
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
GELS
MECHANICAL PROPERTIES
SYNTHESIS
FOAMS
FORMALDEHYDE
MELAMINE
MICROSTRUCTURE
RESORCINOL
SILICA
ALDEHYDES
AMINES
AROMATICS
AZINES
CHALCOGENIDES
COLLOIDS
CRYSTAL STRUCTURE
DEVELOPERS
DISPERSIONS
HETEROCYCLIC COMPOUNDS
HYDROXY COMPOUNDS
MINERALS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHENOLS
POLYPHENOLS
SILICON COMPOUNDS
SILICON OXIDES
TRIAZINES
360603* - Materials- Properties
360601 - Other Materials- Preparation &amp; Manufacture