Other
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21725013w&link_type=abstract
American Astronomical Society, AAS Meeting #217, #250.13; Bulletin of the American Astronomical Society, Vol. 43, 2011
Other
Scientific paper
Many astrophysical environments exhibit spectral features around 10µm and 18µm that have long been attributed to amorphous (glassy) silicates. However existing laboratory spectral data for amorphous silicates do not cover a wide enough compositional range to allow astronomers to interpret their observations without large uncertainty. In particular, while magnesium-rich silicates have been studied extensively, the effect of some other likely components (e.g. calcium, aluminium) have been largely neglected, even though these elements are expected to play a major role in dust condensation.
We present laboratory spectra for a series of 8 glasses, produced by quenching silicate melts of calcium-bearing pyroxene composition. The samples range from the Mg end-member (enstatite; MgSiO3) to the Ca end-member (wollastonite; CaSiO3). The halfway composition corresponds to the mineral diopside (CaMgSi2O6), which has previously been proposed to explain observed spectral features. CaMgSi2O6 glass has a much broader 10µm peak than Mg2Si2O6 glass, due to the more varied bonding environments resulting from two different network modifying cations, and its peak extends to longer wavelengths, consistent with the greater mass of Ca. The presence of other elements is likewise expected to result in broader features and subtle changes in peak position. In addition to a systematic study of the effect of Ca substitution for Mg, we present some more complex glasses that include Na, Al and Fe as minor constituents. In addition we present measurements of the viscosity of these glasses to determine the glass transition temperature (Tg), which provides an important constraint on the thermal history of observed glassy silicate.
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