Effect of pressure on the viscosity of molten iron : experimental study on the viscosity of the outer core

压力对铁水粘度的影响：外芯粘度的实验研究

• 批准号: 08640524
• 负责人: YASUDA Atsushi
• 金额: $ 1.54万
• 依托单位: University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1996
• 资助国家: 日本
• 起止时间: 1996 至 1997
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08640524/
• 关键词: viscosity; molten metal; diffusivity; silicate melt; melt structure

The viscosity of the earth's outer core is one of the most important physical property of the earth because it has significant influence on the thermal and material transport in the deep earth. In spite of its importance, it is probably the least well-known property of the earth. The purpose of the present study is to give a constraint on the viscosity of outer core from high pressure experiments. Effect of pressure on the physical property and structure of melt was studied.Water diffusivities in basaltic and rhyolitic melts were determined at 2 and 3 GPa and 1450ﾟC.Contrary to previous studies at low pressures, water diffusivity is not sensitive to the water content at 3 GPa, and the measured total water concentration profiles can be practically fitted by a single constant diffusion coefficient for total water. Water diffusivities are 4.7_x10^<-10>m^2/s in the basaltic melt (0.14-2.3 wt% water) and 1.8_x10^<-10>m^2/s in the rhyolitic melt (1.5-3.1 wt% water) at 3 GPa and 1450ﾟC.On the other hand, water diffusivity at 2 GPa and 1450ﾟC in the basaltic melt depends on the water-concentration ; 1.4_x10^<-10>m^2/s at 0.4 wt% water and 5.6_x10^<-10>m^2/s at 1.6 wt% water. However, this dependence is smaller than that expected from previous studies at lower pressures. Present experimental results suggest that the diffusivity of OH species increases with increasing pressure whereas that of molecular H_2O decreases, and consequently the former becomes comparable to the latter at about 3 GPa.Diffusion of Ni in molten Au was measured up to 3 GPa and it is 2.3+-0.4_x10^<-9>m^2/s at 1 GPa and 1200ﾟC,and 2.3-3.7_x10^<-9>m^2/s at 3 GPa snd 1300ﾟCApplying Sutherland-Einstein equation to the measured diffusivity, viscosity of Au at high pressure was calculated. The resultant viscosity is consistent with viscosities using theoretical estimation such as Andrade's formula.

地球外核的粘度是地球最重要的物理特性之一，因为它对地球深处的热量和物质传输具有重大影响，尽管它很重要，但它可能是最不为人所知的特性。本研究的目的是通过高压实验给出外核粘度的约束，研究压力对熔体物理性质和结构的影响。测定了玄武岩和流纹岩熔体中的水扩散率。在 2 和 3 GPa 和 1450°C 下。与以前在低压下的研究相反，水扩散率对 3 GPa 下的水含量不敏感，并且测量的总水浓度分布实际上可以通过总扩散系数的单一恒定扩散系数来拟合。水在玄武岩熔体中的扩散率为 4.7_x10^<-10>m^2/s（0.14-2.3 wt% 水）并且在 3 GPa 和 1450°C 下，流纹岩熔体（1.5-3.1 wt% 水）中的水扩散率为 1.8_x10^<-10>m^2/s。另一方面，在玄武岩熔体中，水扩散率在 2 GPa 和 1450°C 下取决于水浓度；0.4 时 1.4_x10^<-10>m^2/s wt% 水和 1.6 wt% 水时为 5.6_x10^<-10>m^2/s 然而，这种依赖性小于先前研究在较低压力下的预期。压力增加，而分子 H_2O 减少，因此前者在约 3 GPa 时与后者相当。测量到 Ni 在熔融 Au 中的扩散高达 3 GPa，如下： 1 GPa 和 1200ﾟC 时为 2.3+-0.4_x10^<-9>m^2/s，3 GPa 和 1300ﾟC 时为 2.3-3.7_x10^<-9>m^2/s 应用 Sutherland-Einstein 方程测量的扩散率，计算出Au在高压下的粘度，所得粘度是一致的。使用安德拉德公式等理论估计来计算粘度。