Thermal Diffusivity Measurement of Upper Mantle Minerals at Ultra-high Pressures and Temperatures

在本研究中，我们首先用埃法构建了一个热扩散率的测量系统，并利用可编程电源构建了一个加热系统，该电源可以调制电压，使电功率呈正弦变化。使用外部触发器，我们测量插入样品的两个热电偶的电动势，以确定两个不同点温度振荡之间的相位滞后。用光学方法测量两个热电偶的位置。根据这些位置和相位滞后计算热扩散系数。我们在高压和高温下测量了方长石、橄榄石、氧化锆和刚玉的热扩散系数。这些材料的热扩散系数随温度的升高而减小，随温度的升高而增大。方石的倒数热扩散系数与简单材料一样，随温度的升高而线性增加。其梯度随压力的增大而减小。与Fo89橄榄石一样，橄榄石的倒数热扩散率也表现出曲率。这可能是由于其复杂的晶体结构所致。刚玉的倒数热扩散系数与温度呈线性关系。但其梯度不随温度升高而变化。刚玉的热扩散系数非常高，可能是测量失败的原因。刚玉的热扩散系数比fo89橄榄石大30%。在6 GPa以上，森林石的热扩散系数提高了40%。这种压力依赖性比fo89橄榄石大40%左右。在高压下测量的氧化锆的热扩散系数比在环境条件下测量的结果大50%以上。

In this study, first we constructed a measurement system of thermal diffusivity by Angstrom method We constructed a heating system using a programmable power source which can modulate electric voltage such that electric power sinusoidally changes. Using an external trigger, we measure emf of two thermocouples inserted to a sample to determine phase lag between temperature oscillations at two different points. The positions of two thermocouples are measured opetically. Thermal diffusivity is calculated from these positions and the phase lag.We measured thermal diffusivity of periclase, forsterite, zircona and corundum at high pressures and temperatures. Thermal diffusivity of all of these materials decreases with increasing temperature and increases with increasing temperature. Reciprocal thermal diffusivity of periclase is linearly increases with increasing temperature as is the case of simple materials. Its gradient decreases with increasing pressure. Reciprocal thermal diffusivity of forsterite shows curvature as is the case of Fo89 olivine. This may be due to complex crystal structure of forsterite. Reciprocal thermal diffusivity of corundum shows a linear relation with temperature. However, its gradient does not change with increasing temperature. It is possible that measurement for corundum was failed because thermal diffusivity of corundum is very highThermal diffusivity of forsterite is 30% larger than that of fo89 olivine. Thermal diffusivity of forsterite increases by 40% over 6 GPa. This pressure dependence is about 40% larger than that of fo89 olivine.Thermal diffusivity of zirconia measured at high pressure is more than 50% larger than expected from the measurement at ambient conditions.