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Effect of the drying conditions on the microstructure of silica based xerogels and aerogels.
MedLine Citation:
PMID:  22962830     Owner:  NLM     Status:  In-Process    
Abstract/OtherAbstract:
Nanostructured silica based xerogels and aerogels are prepared by sol-gel technology, using methyltrimethoxysilane as precursor. The influence of the drying method and conditions on the microstructure of the obtained materials is investigated, since the drying stage has a critical influence on their porosity. Two types of drying methods were used: atmospheric pressure drying (evaporative), to produce xerogels, and supercritical fluids drying, to obtain aerogels. Although the supercritical fluids drying technique is more expensive and hazardous than the atmospheric pressure drying, it is well known that aerogels are less dense than the xerogels due to less pore shrinkage. However, the ideal situation would be to use atmospheric pressure drying in conditions that minimize the pore collapse. Therefore, in this work, different temperature cycles for atmospheric pressure drying and two heating rates for the supercritical fluids drying are tested to study the gels' shrinkage by analyzing the density and porosity properties of the final materials. The best materials obtained are aerogels dried with the lower heating rate (approximately 80 degrees C/h), since they exhibit very low bulk density (approximately 50 kg/m3), high porosity (95%)-mainly micro and mesopores, high surface area (approximately 500 m2/g), moderate flexibility and a remarkable hydrophobic character (>140 degrees). It was proved that the temperature cycles of atmospheric pressure drying can be tuned to obtain xerogels with properties comparable to those of aerogels, having a bulk density only approximately15 kg/m3 higher. All the synthesized materials fulfill the requirements for application as insulators in Space environments.
Authors:
L Durães; M Ochoa; N Rocha; R Patrício; N Duarte; V Redondo; A Portugal
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of nanoscience and nanotechnology     Volume:  12     ISSN:  1533-4880     ISO Abbreviation:  J Nanosci Nanotechnol     Publication Date:  2012 Aug 
Date Detail:
Created Date:  2012-09-11     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101088195     Medline TA:  J Nanosci Nanotechnol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  6828-34     Citation Subset:  IM    
Affiliation:
CIEPQPF Department of Chemical Engineering, University Coimbra, Pólo II, Rua Sílvio Lima, 3030-790 Coimbra, Portugal.
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