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

Silica aerogel represents an ideal material for use as a cosmic dust c apture medium. Its low density enables impacting particles to decelera te and stop within a small quantity of the material, but without any s evere heating. Hence the particle, which remain unmelted, can subseque ntly be removed and studied. Since a large proportion of the prospecti ve 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 a erogel used in the capture well contains minimal quantities of these e lements. Unfortunately the lowest density aerogels contain carbon at l evels of 5 wt%; water is present in even greater amounts. Thus, techni ques need to be identified to remove these contaminants. Herein, an at tempt 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 multipl e extractions, use of modifier etc.) necessary for removal of contamin ants. A set of conditions was derived which was able to remove 90% of carbon contaminants from an aerogel of 0.12 g cm(-3) density. This inv olved the use of multiple extractions with gradient temperatures (i.e. variable CO2 density), but without the use of a methanol modifier. Un fortunately, the same technique was less efficacious at removing carbo n from aerogels with densities <0.12 g cm(-3). At present the extracti on procedure has only been tried on a laboratory scale, but clearly th is could be scaled-up in the future.