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

在本研究中，我们首先建构了一套热扩散率的量测系统，并利用一个可程式化的电源来调整电压，使电功率呈正弦变化。使用一个外部触发器，我们测量电动势的两个热电偶插入到一个样品，以确定在两个不同点的温度振荡之间的相位滞后。两个热电偶的位置是光学测量的。我们测量了方镁石、镁橄榄石、锆英石和刚玉在高温高压下的热扩散率。所有这些材料的热扩散率随着温度的升高而降低，并且随着温度的升高而增加。方镁石的倒数热扩散率与简单材料的情况一样，随温度的升高而线性增加。它的梯度随着压力的增加而减小。镁橄榄石的倒数热扩散率与Fo89橄榄石一样呈曲率变化。这可能是由于镁橄榄石复杂的晶体结构所致。导热系数倒数与温度呈线性关系。然而，其梯度不随温度的升高而改变。镁橄榄石的热扩散系数比fo89橄榄石的热扩散系数大30%，这可能是由于镁橄榄石的热扩散系数很高而导致测量失败的原因。镁橄榄石的热扩散系数在6GPa以上增加了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率比在环境条件下测量的预期值大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.