Inelastische Neutronenstreuung bei hohen Temperaturen und Drücken zur Aufklärung der Lösungs- und Transportmechanismen von Wasser in wasserhaltigen Silikatschmelzen

我们已经成功地构建了一个高温/压力室，用于中子散射谱仪，在样品位置提供高达1250K的温度和高达2kbar的压力。这是通过内部加热的NbZr高压灭菌器实现的。到目前为止，已经在FRM II的飞行时间光谱仪TOFTOF上对含水的Na2O·3SiO_2熔体进行了实验。测量的密度关联函数显示了质子的非相干动力学。用准弹性线宽推导了自扩散系数。Q2的依赖性甚至高达1.5A−1。这可能是一种通过通道结构的扩散机制，类似于无水碱性硅酸盐熔体中的碱离子。与H2O/D2O的对比变化允许测量纯氢动力学，因为H的总散射截面比D大得多。通过这一分析，我们有望对水物种的旋转动力学以及水的添加对Na动力学的影响有新的认识。对于含水的SiO_2和Al_2O_3·Na_2O·6SiO_2体系，在压力室的工作温度范围内，水的扩散速度不足以在TOFTOF的仪器能量分辨率范围内被分解。然而，计划在更高分辨率的中子背向散射谱仪上进行的实验应该允许研究水物种的扩散动力学和扩散机制。

We have successfully constructed a high temperature/pressure cell for the application on neutron scattering spectrometers provides temperatures up to 1250 K and pressures up to 2 kbar at the sample position. This has been achieved with an internally heated NbZr autoclave. So far experiments on hydrous Na2O•3SiO2 melts with 10 mol% water have been performed on the time-of-flight spectrometer TOFTOF at FRM II. The measured density correlation functions exhibit the incoherent dynamics of the proton. The quasielastic line width is used to derived the self diffusion coefficient. The Q2 dependence even holds up to 1.5 A−1. This might be an indication of the diffusion mechanism via channel structures, similar to the alkali ions in anhydrous alkali silicate melts. A contrast variation with H2O/D2O allows to measure pure hydrogen dynamics since the total scattering cross-section for H is much larger than for D. With this analysis we expect to gain new insight of rotational dynamics of the water species and of the influence of the water addition on the Na dynamics. For the hydrous SiO2 and Al2O3•Na2O•6SiO2 systems, the water diffusion is not fast enough to be resolved within the instrument energy resolution of TOFTOF at the working temperature range of the pressure cell. However, experiments scheduled on the neutron backscattering spectrometer with higher resolutions should allow to study diffusive dynamics and diffusion mechanisms of the water species.