Title of Paper:Structural characteristics and thermal conductivity of ambient pressure dried silica aerogels with one-step solvent exchange/surface modification

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Date of Publication:2009-01-15

Journal:MATERIALS CHEMISTRY AND PHYSICS

Included Journals:SCIE、EI、Scopus

Volume:113

Issue:1

Page Number:485-490

ISSN No.:0254-0584

Key Words:Silica aerogels; One-step solvent exchange/surface modification; Chemical synthesis; Thermal conductivity

Abstract:The paper reports the synthesis procedures as well as structural properties and thermal conductivity of the ambient dried hydrophobic silica aerogels with ethanol (EtOH)/trimethylchlorosilane (TMCS)/n-hexane as surface modification agent. One-step solvent exchange and surface modification were simultaneously progressed by immersing the hydrogels in EtOH/TMCS/n-hexane solution. When P(V(TMCS)/V(Hydrogels)) ranges from 10 to 20%, the final product is hydrophilic xerogel, which is porous material with porosity of 78-89% and the specific density is over 0.24 g cm(-3). When P(V(TMCS)/V(Hydrogels)) is at the scope of 75-100%, the specific densities of the aerogels range from 0.10 to 0.14 g cm(-3) and the porosity is in range of 93.5-95.8%. The silica aerogels modified with 75-100% TMCS (V/V) present good performance with the specific surface area in range of 745-770 m(2) g(-1) and the average pore sizes are about 20 nm. Furthermore, using granular silica aerogels (P(V(TMCS)/V(Hydrogels)) = 100%) as the fillings, the thermal conductivities of granular aerogels are analyzed by guarded hot plate method. When temperature ranges from 30 to 60 degrees C, thermal conductivity coefficients of the samples are lower than 0.03 W (m K)(-1). (C) 2008 Elsevier B.V. All rights reserved.