Diffusion of H bearing species in silicate glasses at low temperatures - development of a newexperimental technique

氢在玻璃中的低温输运（低于200 °C）与许多应用有关，例如考古文物的黑曜石定年、古气候研究、高放射性核废料的储存、火山灰的产生、玄武岩的地球化学风化及其对各种地球化学循环的影响、玻璃机械性能的工程设计、理解玻璃电极在化学分析中的行为，以及理解一些光学数据存储设备。在这些条件下，含H物质的扩散系数的实验测量是困难的，因为水，最常用的H源，通过溶解-沉淀反应与玻璃反应，并且难以分离扩散过程。低温下缓慢的扩散速率增加了进一步的复杂性。然而，外推在较高温度下测得的扩散系数被证明是不足以描述所观察到的形状的低温过程中产生的浓度梯度。我们已经开发了几个新的实验方面，特别是（a）的能力，产生H轴承的非晶薄膜作为一个来源的H不存在的自由H2O，和（B）的能力，以测量低浓度的H，独立的物种，具有高的空间分辨率在纳米尺度上。在这个项目中，它打算利用这些发展来探索的扩散H-轴承物种的条件下，一直无法访问到目前为止。一个具体的目标是表征在这些条件下H-扩散的组成依赖性，并了解导致在较高温度下观察到的行为不同的扩散机制的变化。

The transport of H in glasses at relatively low temperatures (below 200 °C) is relevant for a number of applications such as obisidian dating of archaeological artefacts, palaeoclimate studies, storage of high level nuclear waste, production of volcanic ash, biogeochemical weathering of basalts and its implications for various geochemical cycles, engineering the mechanical properties of glasses, understanding the behaviour of glass electrodes in chemical analysis, and the understanding of some optical data storage devices.Experimental measurement of diffusion coefficients of H-bearing species has been difficult to impossible at these conditions because water, the most commonly used source of H, reacts with glass by dissolution - precipitation reactions and it is difficult to isolate the process of diffusion. Sluggish diffusion rates at low temperatures add further complications. Yet, extrapolation of diffusion coefficients measured at higher temperatures is shown to be inadequate for describing the observed shapes of concentration gradients produced by low temperature processes. We have developed several new experimental aspects, and in particular (a) the ability to produce H-bearing amorphous thin films to act as a source of H without the presence of free H2O, and (b) the ability to measure low concentrations of H, independent of the speciation, with a high spatial resolution on the nanometer scale. In this project it is intended to use these developments to explore the diffusion of H-bearing species at conditions that have been inaccessible so far. A specific goal is to characterize the compositional dependence of H-diffusion at these conditions and understand the change of diffusion mechanism that leads to a different behaviour from those observed at higher temperatures.