長時間クリープ試験に使用した PR 熱電対の劣化原因とばらつき要因

概要

論文の詳細を見る
The drift (or decrease) of electromotive force (EMF) in the calibration of PR thermocouples used for long-time creep testing at various temperatures up to 100000h in air is investigated. The magnitude of resistivity, ρ, which is considered to be one of indices to the inhomogeneity of thermocouples, and its distribution from the measuring junction are measured. The change in ρ together with the results of X-ray diffraction and spectroscopic analysis indicate that the inhomogeneity is very small in Pt but considerable in Pt-12.8%Rh limbs. The oxides found on the surface of thermocouples with notable drifts are the mixture of Rh_2O_3 types. The effect of drift on the measured temperature is rather small if the ratio of immersion depth is less than unity (when it is more than unity, the scatter in the drift among thermocouples after virtually same times is pronounced). For the thermocouples used 30000 to 50000h at 1000℃ the drift is also responsible to the evaporation of Pt and Rh elements. For the thermocouples with the immersion depth of 250mm, the annealing treatment is effective to recover the drift provided that the test temperature is below 500℃ ; above 500℃ it is recommended to cut off a part of thermocouple limbs up to 100mm from the measuring junction in order to get the complete recovery of EMF.
社団法人日本鉄鋼協会の論文
1989-04-01