Chihara Hiroki

According to infrared astronomical observation, the silicates of circumstellar dust are an amorphous material and a crystal of olivine and pyroxene while the silicate of interstellar dust is amorphous material. And the crystal hardly contains iron. We synthesized an amorphous silicate with the solar composition by the sol-gel method, and did the heating experiments. Each sample was analyzed by Infrared absorption spectroscopy and X-ray diffraction. We found that the olivine takes magnesium in preference to iron in the process of crystallization from an amorphous silicate.

We produced sub-micron silicate particles as cosmic dust simulants to examine changes in infrared absorption spectra by particle size, shape, and distortion. Quartz from Andhra Pradesh, India and olivine from San Carlos, USA were used as samples. The crystals were crushed in a WC mortar first, and then powdered in an alumina mortar. Sub-micron particles were formed successfully by using a planetary ball mill with zirconia balls in the final step. The sizes and shapes of the particles were observed under an SEM and latticed distortion by crushing was evaluated by XRD. Infrared absorption spectra of the particles were changed by the particle size, shape and lattice distortion compared with result of samples without crushing by the ball mill. Sub-micron powder of olivine crystals obtained in the present experiments will be used as samples in reproduction experiments for Stardust sample recovery in aerogel collectors.