Smelting in the Age of Nano: Iron Aerogels
Mesoporous interpenetrating networks of resorcinol-formaldehyde (RF) and iron oxide aerogels (FeOx) were prepared by one-pot gelation of ferric chloride hexahydrate with epichlorohydrine, resorcinol and formaldehyde. The strength of the monoliths was increased by crosslinking the skeletal nanoparticles with a triisocyanate-derived polymer according to well-established procedures in our laboratory. That process casts a conformal polymer coating over the entire skeletal framework of the composite material, leaving the mesopores open. In a smelting-like process, pyrolysis at 800-1000⁰C under Ar of both the native (n-RF-FeOx) and the crosslinked (X-RF-FeOx) composites yields porous materials in monolithic form with compositions closely resembling that of pig iron. However, as it turns out crosslinking alters the thermolytic behavior of the two materials. The triiisocyante derived conformal coating melts at around 300⁰C causing partial collapse of the skeletal frameowork creating macropores. Most importantly though, the molten crosslinker plays the role of a "solvent" where RF and FeOx nanoparticles undergo more efficient mixing, depressing their reaction temperature by as much as 400⁰C. Overall, although the chemical compositions of the resulting n-C-Fe and X-C-Fe aerogels are similar, the former are mesoporous and ferromagnetic, while the latter are macroporous and superparamagnetic. The method has been extended to RF-SnOx and RF-CuOx aerogels.
N. Chandrasekaran et al., "Smelting in the Age of Nano: Iron Aerogels," Abstracts of Papers of the American Chemical Society, American Chemical Society (ACS), Mar 2009.
237th ACS National Meeting (2009 : Mar. 22-2, Salt Lake City, UT)
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