High-temperature silicon-29 NMR investigation of solid and molten silicates
High-temperature silicon-29 NMR investigation of solid and molten silicates
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固态和熔融硅酸盐的高温硅 29 NMR 研究
DOI：
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发表时间：
1990
期刊：
影响因子：
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通讯作者：
J. Stebbins
中科院分区：
文献类型：
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作者：
I. Farnan;J. Stebbins
对具有不同 SiO{sub 2} 含量的硅酸盐样品进行高温（高达 1250{deg}C）{sup 29}Si NMR T{sub 1} 和线形测量。该样品代表了从钠长石 (NaAlSi{sub 3}O{sub 8}) 中的 Q{sup 4} 到原硅酸锂和偏硅酸锂混合物 (Li{sub 4}SiO{sub 4}/Li{sub 2}SiO{sub 3}) 中的 Q{sup 2} 和 Q{sup 0} 的一系列桥接和非桥接氧分布。玻璃态样品的 T{sub 1} 弛豫数据与温度的关系表明玻璃化转变效率显着增加。这是由于当硅原子和杂质离子在高于 T{sub g} 的温度下开始扩散通过材料时，顺磁杂质的弛豫变得更加有效。在每个样品中都在高温下观察到化学交换，这表明熔体中硅酸盐四面体的寿命在核磁共振时间尺度上很短，即几微秒。四硅酸钾 (K{sub 2}Si{sub 4}O{sub 9}) 的变温线形数据允许对交换过程进行建模并模拟光谱，从而产生该过程的活化能。这与从粘度测量得出的粘性流的活化能非常一致。看来 {sup 29}Si NMR 已接近检测硅酸盐中粘性流动的基本步骤，并且 NMR 确定的交换过程的时间常数与四硅酸钾液体的剪切弛豫时间之间具有良好的一致性。« less
High-temperature (up to 1250{degree}C) {sup 29}Si NMR T{sub 1} and line-shape measurements were made on silicate samples with varying SiO{sub 2} contents. The sample represented a range of bridging and nonbridging oxygen distributions from Q{sup 4} in albite (NaAlSi{sub 3}O{sub 8}) to Q{sup 2} and Q{sup 0} in a mixture of lithium orthosilicate and metasilicate (Li{sub 4}SiO{sub 4}/Li{sub 2}SiO{sub 3}). T{sub 1} relaxation data as a function of temperature for glassy samples showed a dramatic increase in efficiency at the glass transition. This was ascribed to relaxation by paramagnetic impurities becoming more efficient as silicon atoms and impurity ions begin to diffuse through the material at temperatures above T{sub g}. In each sample chemical exchange was observed at high temperature, indicating that the lifetime of a silicate tetrahedron in the melt is short on the NMR time scale, i.e., a few microseconds. Variable-temperature line-shape data for potassium tetrasilicate (K{sub 2}Si{sub 4}O{sub 9}) allowed the exchange process to be modelled and spectra to be simulated, yielding an activation energy for the process. This was in good agreement with the activation energy for viscous flow derived from viscosity measurements. It appears that {sup 29}Si NMR is coming close to detecting the fundamentalmore » step in viscous flow in silicates with good agreement between the time constant of the exchange process determined by NMR and the shear relaxation time of the potassium tetrasilicate liquid.« less