Pressure effect on the electromotive force of the type R thermocouple

ABSTRACT

The pressure effect on the electromotive force (EMF) of a Pt13Rh–Pt (type R) thermocouple was examined to determine the temperature measurement accuracy of solid pressure medium apparatuses in high-pressure experiments. Single-wire EMFs were measured up to pressure of 13 GPa and temperature of 1173 K with a Kawai-type multi-anvil apparatus for Pt13Rh and Pt based on the single-wire method. The pressure conditions along the wires were evaluated by in situ X-ray diffraction using synchrotron X-ray radiation. The pressure effect of the Seebeck coefficients of Pt13Rh and Pt were determined by the analysis of the single-wire EMFs and pressure–temperature profiles along the wires and was virtually consistent with those determined in previous studies at lower pressures and temperatures. For type R thermocouple, the difference between the nominal and real temperatures was determined to be as large as –75 K at 13 GPa and 873 K.

KEYWORDS:

• Type R thermocouple
• electromotive force
• platinum–rhodium
• pressure effect
• Seebeck coefficient

Acknowledgements

The authors acknowledge K. Ueki for constructive discussions. The in situ X-ray experiments were performed with the SPEED-1500 system at BL04B1 in SPring-8 (proposal no. 2017B1345). This work was supported by the Japan Society for the Promotion of Science (JSPS) under Grant-in-Aid for Scientific Research (B) (15H03749) and Grant-in-Aid for Innovative Areas (15H05827) and the Cooperative Research Program of the Earthquake Research Institute, University of Tokyo (ERI JURP 2018-B-01). H. H. was partly supported by the Japan Science and Technology Agency (JST) under Core Research for Evolutional Science and Technology (CREST) (JPMJCR1761). Constructive comments by an anonymous reviewer are appreciated.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Japan Society for the Promotion of Science (JSPS) under Grant-in-Aid for Scientific Research (B) (15H03749) and Grant-in-Aid for Innovative Areas (15H05827); the Japan Science and Technology Agency (JST) under Core Research for Evolutional Science and Technology (CREST) (JPMJCR1761).