Realization of the palladium freezing point for thermocouple calibrations

Abstract

A vertical alumina palladium (Pd) freezing-point cell was made and used for the calibration of noble metal thermocouples. Various characteristics of the freezing process were investigated using type B thermocouples, and the best method of freezing is discussed. It was found that the freezing behaviour was influenced by the thermal history: it is preferable to freeze the Pd melt completely before carrying out the next test. The thermocouple emfs during freezing were determined by calculating the average emf during the first 10 minutes of the plateau just after the depression in the supercooling curve. This emf was reproducible within a standard deviation of 0.1 C. The expanded uncertainty of calibrating a type B thermocouple in the Pd freezing-point cell was estimated to be 1.0 C at the 95 % confidence level .

The dependence of the melting temperatures of the eutectics Fe–C and Co–C, designed for thermocouple thermometry, on the furnace offset temperature during the preceding freeze

“…The pressure inside the cell was controlled slightly above the ambient to prevent oxidation of the eutectic elements during the fabrication of the cell and throughout the measurements. The temperature of the eutectic cells was measured by an alumina-sheathed Pt/Pd thermocouple that had been annealed and heat treated following a conventional procedure before the measurement [12]. The reference junction was made using the usual ice-water mixture.…”

A nickel freezing-point cell for thermocouple calibration

“…As described in previous reports, we have already successfully fabricated a cell for the pure-metal high-temperature xed point of palladium [2], and demonstrated the possibility that a similar cell for realizing the nickel freezing point could be fabricated for continuous xed-point realization [3]. In this work, we present the nal successful results on the realization of the nickel freezing point using an alumina crucible.…”

“…Melting and freezing were carried out at holding temperatures of 1465 C and 1453 C, respectively. The dynamic method was used for the realization, as in our previous work [2,3]. Melting lasted for about 130 min over a range of 3.64 m V. The initial and nal melting emfs were about 9567.82 m V and 9571.46 m V, respectively.…”

“…Extensive studies have recently been carried out on high-temperature xed-point materials for the calibration of thermocouples, some candidates being the metal-carbon eutectics [1] and pure metals [2,3]. Metalcarbon eutectic cells use graphite as a crucible material, and alumina for the tube to protect the thermocouple.…”

Realization of Fe–C Eutectic Point Using an Alumina Crucible

“…An alumina crucible is chemically immune to reaction with graphite and many metals, even though it is somewhat more difficult to machine than common graphite. Previously alumina crucibles were used to construct pure metal high-temperature fixed points such as Ni and Pd [8,9]. In our first approach to using the new crucible, we selected the Fe-C system, which is known to have the lowest melting temperature of all the M-C systems.…”