Supercritical fluid extraction as a means of reducing the carbon contamination inherent in samples of silica aerogel destined for the capture of CHON cosmic dust particles in space

Details Supercritical fluid extraction as a means of reducing the carbon contamination inherent in samples of silica aerogel destined for the capture of CHON cosmic dust particles in space Supercritical fluid extraction as a means of reducing the carbon contamination inherent in samples of silica aerogel destined for the capture of CHON cosmic dust particles in space

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994p%26ss...42..947h&link_type=abstract

Planetary and Space Science (ISSN 0032-0633), vol. 42, no. 11, p. 947-954

Physics

2

Aerogels, Carbon, Cosmic Dust, Decontamination, Extraction, Silicon Dioxide, Supercritical Fluids, Water, Carbon Dioxide, Methyl Alcohol, Temperature Gradients

Scientific paper

Silica aerogel represents an ideal material for use as a cosmic dust capture medium. Its low density enables impacting particles to decelerate and stop within a small quality of the material, but without any severe heating. Hence the particles, which remain unmelted, can subsequently be removed and studied. Since a large proportion of the prospective cosmic dust is likely to be enriched in elements such as carbon and hydrogen (typically 5 wt% C, 20 wt% H2O), it is imperative that the aerogel used in the capture cell contains minimal quantities of these elements. Unfortunately the lowest density aerogels contain carbon at levels of 5 wt%; water is present in even greater amounts. Thus, techniques need to be identified to remove these contaminants. Herein, an attempt is made to use supercritical fluid extraction to remove carbon (and water). The investigation was tried to identify the most suitable parameters (i.e. CO2 density, solvating power using single or multiple extractions, use of modifier, etc.) necessary for removal of contaminants. A set of conditions was derived which was able to remove 90% of carbon contaminants from an aerogel of 0.12 g/cu cm density. This involved the use of multiple extractions with gradient temperatures (i.e. variable CO2 density), but without the use of a methanol modifier. Unfortunately, the same technique was less efficacious at removing carbon from aerogels with densities less than 0.12 g/cu cm. At present the extraction procedure has only been tried on a laboratory scale, but clearly this could be scaled-up in the future.

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