High-temperature X-ray diffraction and Raman spectroscopy of diopside and pseudowollastonite
High-temperature X-ray diffraction and Raman spectroscopy of diopside and pseudowollastonite
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DOI：
10.1007/s002690050130
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发表时间：
1998-06
影响因子：
1.4
通讯作者：
P. Richet;B. Mysen;J. Ingrin
中科院分区：
文献类型：
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作者：
P. Richet;B. Mysen;J. Ingrin
用X射线粉末衍射和拉曼光谱研究了透辉石(CaMgSi2O6)和假硅灰石(CaSiO_3)的熔点。与以往1100K以下的晶胞参数测定结果一致，透辉石沿轴向和轴向的热膨胀比沿轴向的热膨胀小得多。对于伪硅灰石，轴线膨胀率按b&a>；c顺序略有增加。两种矿物的晶胞角度变化都很小，熔点附近的其他晶胞参数也没有异常变化。随着温度的升高，拉曼光谱的主要变化是主要代表Si−O−Si弯曲(近6 0 0 cm−1)或涉及Ca−O或Mg−O伸缩的谱带的线宽显著增加，透辉石为2 70~5 0 0 cm−1，假硅灰石为2 40~450 cm−1。在接近量热预熔化效应开始的温度下，这种广泛的频带展宽导致了广泛的拉曼特征，不再能分解为其单独的成分。Si-−-O应变模式没有明显变化。对于透辉石和假硅灰石来说，预熔似乎与碱土元素的动力学增强有关。这一结论与偏硅酸钠的结论形成了鲜明的对比，偏硅酸钠中较弱的钠键使硅酸盐骨架扭曲和变形，从而预示了熔体中存在的硅酸盐实体。
Diopside (CaMgSi2O6) and pseudowollastonite (CaSiO3) have been studied by X-ray powder diffraction and Raman spectroscopy up to their respective melting points. In agreement with previous unit-cell parameters determinations below 1100 K, thermal expansion of diopside along theaandcaxis is much smaller than along thebaxis. For pseudowollastonite, the axis expansivity increases slightly in the orderb>a>c. For both minerals, the change in unit-cell angles is very small and there are no anomalous variations of the other unit-cell parameters near the melting point. With increasing temperatures, the main changes observed in the Raman spectra are strong increases of the linewidths for those bands which mainly represent Si−O−Si bending (near 600 cm−1) or involve Ca−O or Mg−O stretching, in the range 270–500 cm−1for diopside, and 240–450 cm−1for pseudowollastonite. At temperatures near the onset of calorimetric premelting effects, this extensive band widening results in a broad Raman feature that can no longer be deconvoluted into its individual components. No significant changes affect the Si−O streching modes. For both diopside and pseudowollastonite, premelting appears to be associated with enhanced dynamics of the alkaline-earth elements. This conclusion contrasts markedly with that drawn for sodium metasilicate in which weaker bonding of sodium allows the silicate framework to distort and deform in such a way as to prefigure the silicate entities present in the melt.