Effect of pressure on temperature measurements using WRe thermocouple and its geophysical impact

Publication date: Available online 12 November 2019Source: Physics of the Earth and Planetary InteriorsAuthor(s): Yu Nishihara, Shunta Doi, Sho Kakizawa, Yuji Higo, Yoshinori TangeAbstractOur understanding of the Earth's interior strongly depends on the physical and chemical properties of the Earth's constituent materials, which have been determined using high-pressure/high-temperature experiments involving thermocouples. Thus, knowledge of the pressure effect on the thermocouple electromotive force (EMF) is indispensable for an accurate understanding of the Earth's interior. We have determined the effect of pressure on a W3Re-W25Re thermocouple up to 16 GPa and 1173 K by the single-wire method using a multi-anvil apparatus in conjunction with synchrotron radiation. The difference between the nominal temperature and the real temperature was determined to be −29 K at 16 GPa and 1173 K when using this thermocouple. There have been many debates addressing the discrepancy between the depth of the 660-km seismic discontinuity in the Earth's mantle and the pressure–temperature conditions of the postspinel phase boundary in Mg2SiO4. This discrepancy disappears when the temperature value is corrected. The transport properties (e.g. rheology, element diffusion, electrical conductivity) in the Earth appear to slow down with depth more rapidly than was previously estimated because of the effect of pressure on the thermocouple.

Source: Physics of the Earth and Planetary Interiors - November 13, 2019 Category: Physics Source Type: research