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Astron. Astrophys. 328, 419-425 (1997)

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2. Materials and their characteristics

The solid [FORMULA] used in the original study (Nuth et al. 1985), obtained from Pfaltz and Bauer Chemicals [P&B] was a gray solid with a "rocky" texture consisting of hard, brittle, irregularly- shaped granules a few millimeters across. This sample was also used in the present study. In addition, samples of [FORMULA] were purchased from ICN Biomedical [ICN]. The ICN samples exhibited a wide range of physical appearance both for different lot numbers and even for two different bottles of the same lot number. Some resembled the "gray rocky" P&B sample, some "white crusty" samples consisted of plates about a millimeter across and two millimeters thick with a white crust on one side and a dark gray surface on the other side while a third sample consisted of thin needle-like "white fluffy" crystals. This last material resembles the "long, white, flexible, asbestos-like needles" described as chain-like orthorhombic crystals by Rochow (1973). The "gray rocky" samples from both P&B and ICN appeared to be less uniform in composition and probably contain small quantities of both free elemental silicon and free elemental sulfur in a glassy matrix. Elemental sulfur was detected in the ICN "white crusty" sample by x-ray diffraction and close microscopic examination revealed variations in color from dark gray to pure white and pure yellow. This sample appears to be an amorphous mixture of [FORMULA] with sulfur and silicon impurities but with a greater degree of compositional variation within the sample than in the "gray rocky" samples. Nonetheless both the "gray rocky" and "white crusty" samples may well be more representative of the type of material formed by secondary reactions between solids and gas in a circumstellar outflow than the crystalline "white fluffy" [FORMULA] sample. Despite the differences in color and texture noted above, the infrared spectra of these disparate samples were remarkably similar as noted below.

A third sample of [FORMULA] was obtained from Strem Chemicals in order to check the possibility that features observed near 10 microns in our other samples might be due to [FORMULA] impurities on the surfaces of the [FORMULA] grains (Begemann et al. 1996). Strem Chemicals synthesized crystalline [FORMULA] in "cotton-like lumps" of greater than 99.5% purity and delivered the sample double sealed under dry nitrogen. Upon opening this sample in a dry nitrogen-filled glove bag samples were removed for XRD and FTIR analyses that will be discussed in detail below.

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© European Southern Observatory (ESO) 1997

Online publication: March 24, 1998

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