Structure of volatile-containing silicate melts by multi-nuclear and multi-quantum NMR spectroscopy

1.含水玻璃的结构：为了研究水在硅酸盐熔体中的溶解机理，我们利用-^<29>Si和^1H MAS NMR和^1H-^<29>Si CP MAS NMR对CaO-MgO-SiO_2体系中的含水熔体进行了研究。我们在这些熔体中发现了游离OH以及SiOH和H_2O。在以前对富硅熔体进行的研究中未观察到游离OH。游离OH丰度随Mg/Ca和M/Si比值的变化有系统的变化。根据这些结果，我们认为游离OH在天然超镁质岩浆中可能很重要。含硫玻璃的结构：为了研究硫在硅酸盐熔体中的溶解，采用^<29>Si MAS NMR和微拉曼光谱对含硫玻璃进行了研究。我们合成了含不同价态硫（S^0 ~ S^<6+>）的水玻璃。当添加天然S时，熔体结构被聚合，而当添加硫酸盐时，聚合稍微减少。没有发现可检测到的Si-S键。从头计算化学位移：使用分子轨道理论，我们已经计算了各种硅酸盐，与熔融或具有挥发性成分的玻璃结构相关的簇。在含水体系中计算得到的^1H和^<29>Si核磁共振位移支持我们在核磁共振光谱中观察到的自由OH的分配。核磁共振和振动谱的类似计算有助于我们在含硫熔体中识别硫的种类。

1.Structure of hydrous glasses : In order to investigate water dissolution mechanisms in silicate melts, we have studied hydrous melts in CaO-MgO-SiO_2 system using-^<29>Si and ^1H MAS NMR and ^1H-^<29>Si CP MAS NMR. We found free OH as well as SiOH and H_2O in these melts. Free OH was not observed in previous studies which are conducted on silica-rich melts. There is systematic changes in abundance of free OH with Mg/Ca and M/Si ratio. From these results, we suggest that free OH could be important in natural ultramafic magmas.2.Structure of sulfur-bearing glasses : In order to study how sulfur dissolves in silicate melts, S-bearing glasses were studied by ^<29>Si MAS NMR and micro-Raman spectroscopy. We synthesized sodium silicate glasses containing sulfur of different valence states (S^0〜S^<6+>). When native S is added, melt structure was polymerized, whereas slightly less polymerized when sulfate is added. No detectable Si-S linkages are found.3.Ab initio calculation of chemical shifts : Using molecular orbital theory, we have calculated wide varieties, of silicate, clusters relevant to melt or glass structures with volatile components. Calculated shifts of^1H and ^<29>Si NMR in hydrous systems support our assignment of free OH observed in the NMR spectra. Similar calculations for NMR and also vibrational spectra help us to identify sulfur species in the sulfur-containing melts.