SGER: Preliminary Experiments on the Grain Boundary Diffusivity of Water

SGER：水的晶界扩散率的初步实验

• 批准号: 0741354
• 负责人: Rhea Workman
• 金额: --
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-08-15 至 2009-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0741354&HistoricalAwards=false
• 关键词: SGER; Preliminary; Experiments; Grain; Boundary

Hydrogen content may be the single most important chemical parameter within the mantle, and hence it is very important to quantify its distribution and rates of transport. Volume diffusion measurements for H in mantle minerals indicate extremely fast diffusive equilibration times, unlike that for nearly all other elements. The added component of grain boundary diffusion has the potential to speed equilibration times by an order of magnitude at moderate temperatures (~300-1000°C). However, to date there is no information on effective diffusion rates of water through the upper mantle. These are urgently needed data, as geoscientists are already making calculations based on assumptions about bulk water diffusivity.In this Small Grant for Exploratory Research, the investigator proposes to do the preliminary experiments to determine the magnitude of grain boundary diffusivity of water through olivine aggregates. The choice of olivine is critical as this is the most abundant upper mantle mineral. Deuterium will be used as a proxy for hydrogen in order to avoid contamination by sample preparation and to improve the analytical background/detection limit. Doubt about the feasibility of these experiments is significant enough to warrant an initial test of the specific aspects of the experimental design, including the quality of olivine aggregates synthesized in the piston-cylinder, the mechanical integrity of aggregates during hydrothermal anneals, and the detection limit of deuterium by SIMS (Secondary Ion Mass Spectrometry) probing in the context of the proposed experiments.

氢含量可能是地幔中唯一最重要的化学参数，因此量化其分布和迁移速率非常重要。地幔矿物中H的体积扩散测量表明扩散平衡时间非常快，与几乎所有其他元素不同。添加的晶界扩散成分有可能在中等温度（~300-1000°C）下将平衡时间加快一个数量级。然而，迄今为止，没有关于水通过上地幔的有效扩散速率的信息。这些都是迫切需要的数据，因为地球科学家已经在进行计算的基础上对散装水扩散率的假设。在这个探索性研究的小额赠款，研究人员建议做初步实验，以确定水通过橄榄石聚集体的晶界扩散率的大小。 橄榄石是上地幔中含量最丰富的矿物，因此选择橄榄石至关重要。氘将用作氢的替代物，以避免样品制备过程中的污染，并提高分析背景/检测限。怀疑这些实验的可行性是显着的，足以保证实验设计的具体方面的初步测试，包括在活塞缸中合成的橄榄石聚集体的质量，在水热退火过程中的聚集体的机械完整性，和氘的检测限由西姆斯（二次离子质谱）探测在所提出的实验的背景下。