Laboratory study of annealed amorphous MgSiO3 silicate using IR spectroscopy and synchrotron X-ray diffraction
Laboratory study of annealed amorphous MgSiO3 silicate using IR spectroscopy and synchrotron X-ray diffraction
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使用红外光谱和同步加速器 X 射线衍射对退火非晶 MgSiO3 硅酸盐进行实验室研究
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发表时间：
2002
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通讯作者：
C. Tang
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作者：
S. P. Thompson;S. Fonti;C. Verrienti;A. Blanco;V. Orofino;C. Tang
本文介绍了在1000 K退火的非晶态辉石粉末样品的原位高分辨同步辐射X射线粉末衍射和红外光谱测量相结合的结果。我们发现，使用这两种技术，在退火过程中形成的晶体结构是Mg 2SiO 4（镁橄榄石），但在10 μm波段的某些功能的存在通常归因于结晶顽火辉石（MgSiO 3）是矛盾的光谱在20 μm区域（沿着与某些其他10 μm波段的功能）和X射线衍射。两者都表明结晶镁橄榄石是在该温度下形成的唯一结晶相。我们讨论了从无定形辉石形成镁橄榄石的可能机制，并确定在无定形起始材料中存在原镁橄榄石结构。我们认为10 μm波段的“晶态顽火辉石”特征可能是由于非晶MgSiO 3网络有序性的短程改善，而这种改善不一定伴随着晶态顽火辉石结构的形成。这些结果不仅表明，在这个温度下，通过退火形成结晶顽火辉石尘埃颗粒可能很难实现，而且还强调了在没有额外的确凿证据的情况下，在彗星等天体的光谱中观察时，错误识别10 μm“顽火辉石”特征载体性质的可能性。我们还讨论了15 ~ 16 μm区域的精细结构演化，它可能作为恒星源颗粒加工的观测指标。
We present the results of combining in situ high resolution synchrotron X-ray powder diffraction and infrared spectroscopic measurements on an amorphous pyroxene powder sample annealed in the region of 1000 K. We find using both techniques that the crystalline structure formed during annealing is Mg 2 SiO 4 (forsterite), but that the presence of certain features in the 10 μm band normally attributed to crystalline enstatite (MgSiO 3 ) is contradicted by spectroscopy in the 20 μm region (along with certain other 10 μm band features) and X-ray diffraction. Both indicate crystalline forsterite as the only crystalline phase formed at this temperature. We discuss the possible mechanism of forsterite formation from amorphous pyroxene and identify the presence of proto-forsteritic structures in the amorphous starting material. We suggest the likely origin of the 10 μm band "crystalline enstatite" features as being due to short-range improvements in the amorphous MgSiO 3 network ordering which are not necessarily accompanied by the formation of crystalline enstatite structure. These results not only suggest that the formation of crystalline enstatite dust grains via annealing may be difficult to realise at this temperature, but also highlight the possibility, in the absence of additional corroborating evidence, of misidentifying the nature of the carrier of the 10 μm "enstatite" features when observed in the spectra of objects such as comets. We also discuss the evolution of fine structure in the region of 15 to 16 μm, which may serve as an observational indicator of grain processing in stellar sources.