Pressure Calibration to 60 kbar Based on the Resistance Change of a Manganin Coil under Hydrostatic Pressure

Abstract
The relative resistance change of a properly seasoned manganin coil was measured at the center of the region of indifference for the bismuth II‐III, thallium II‐III, and barium I‐II phase transformations in a hydrostatic system. The equilibrium pressures for these transformations were obtained from the relative resistance change of manganin which was calibrated with pressure by means of the mercury L‐I and bismuth I‐II transition pressures. Equilibrium pressures corrected to 25°C of 26.861±0.042, 36.569±0.153, and 56.273±0.521 kbar were determined for the bismuth II‐III, thallium II‐III, and barium I‐II phase transformations, respectively. Only the barium I‐II point deviated from the presently accepted high pressure scale. On the basis of the manganin pressure gauge, either the presently accepted value of the barium I‐II point is too high by about 2.5 kbar or the pressure coefficient of manganin resistance changes sharply between 37 and 59 kbar. A two‐point quadratic calibration curve was satisfactory for pressures to 37 kbar.

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