MECHANICAL PROPERTIES OF SiO₂ - AEROGELS

Abstract

Resum4 : Le comportement m4canique des aerogels de silice a QB 6tudi6 par des mQhodes ultrasonores et par compression statique. Dans cat article nous presentons ies valeurs de la vitesse du son en fonction de la densite, de la charge externe et de la pression de gaz interne. Nous demontrons que la vkesse du son varie localement sur des distances de quelques millimbtres. De plus nous avons Uudie le frittage des aerogels en fonction de la temperature et de la dur6e du trakement et nous en dMuisons ainsi des lois d'echelle pour les constantes Blastiques.

Aerocellulose from cellulose–ionic liquid solutions: Preparation, properties and comparison with cellulose–NaOH and cellulose–NMMO routes

“…The open-cell regular foam model predicts n ≈ 2 (Gibson & Ashby, 1997); for aerogels the exponent was shown to be higher, n ≈ 2.5-4 (see, for example n = 2.7 for resorcinol-formaldehyde aerogels (Pekala, Alviso, & LeMay, 1990), n = 3.2 and n = 3.7 for silica aerogels (Cross, Goswin, Gerlach, & Fricke, 1989;Woignier, Phalippou, & Vache, 1989), respectively). The reason of this difference can be found in the formation of aerogel network itself during a sol-gel transition: gel structure has a lot of defects such as dangling ends and loops which do not participate to material response to mechanical stresses.…”

“…As mentioned in the previous section, the results obtained from mercury porosimetry can be used to deduce the mechanical properties of the porous material (Cross et al, 1989;Majling et al, 1995;Pirard & Pirard, 1997;Pirard et al, 1995;Scherer et al, 1995). The bulk modulus K is known to be a constant correlating applied pressure P and volumetric strain V/V: P = K( V/V).…”

Nanostructural damage associated with isostatic compression of silica aerogels

“…This phenomenon was initially observed in silica aerogels [1], but analogous behavior was also evidenced in carbon aerogels [2]. This behavior was consequently assumed to be associated with the specific porous texture of aerogels and not to the specific chemical nature of silica that is known to be an Ôanomalous' glass.…”

“…This behavior was consequently assumed to be associated with the specific porous texture of aerogels and not to the specific chemical nature of silica that is known to be an Ôanomalous' glass. The Ôknee model' [1] was proposed to account for this unusual mechanical behavior. The porous aerogel network is considered as a bar-like structure, where the most tenuous legs can Ôknee-bend' under the application of uniaxial stress.…”

Silica aerogels with enhanced durability, 30-nm mean pore-size, and improved immersibility in liquids

“…Unfortunately, these enticing opportunities are realized in a material with poor mechanical strength [3,11]. The fragility of undensified or nonstrengthened SiO 2 aerogels calls for gentle handling when the application requires a monolithic form, and limits the usefulness of silica aerogels as reaction platforms when repeated immersion in liquid media occurs [12].…”