ISSN: 0090-3973
Page Count: 15

A New Stable Nickel-Base Thermocouple
Starr, CD
Vice-President, Engineering and Research, and research director, Wilbur B. Driver Co., N.J.

Wang, TP

Abstract

The change in magnitude and direction of electromotive force (EMF) and the accompanying structural changes of nickel-chromium (Ni-Cr), nickel-silicon (Ni-Si), and nickel-silicon-magnesium (Ni-Si-Mg) alloy thermoelements at 1800°F (982°C) in air were studied in comparison with a standard type K thermocouple of the same size. The Ni-Cr versus Ni-Si-Mg couple changes only +200 µV versus +600 µV for the Type K couple after 21 200 hours at that temperature. The EMF changes of K+ and the Ni-Cr alloy are attributed to the simultaneous oxidation of Cr and Si and to the increase in oxygen. The EMF change of K- is caused by the preferential oxidation of silicon, aluminum, manganese, and iron and to the increase in oxygen. The EMF changes of Ni-Si and Ni-Si-Mg are caused by the preferential oxidation of Si and to the increase in oxygen. The presence of magnesium increases the stability of the Ni-Si system by blocking the reaction of silicon and oxygen.

Keywords:
electric potential, thermal conductivity, stability, drift (instrumentation), thermocouples, thermoelements, type K, nickel-based alloys, nickel-chromium, nickel-silicon, nickel-silicon-magnesium, oxygen, oxides, oxidation, preferential oxidation, internal oxidation, air atmosphere, surface morphology, microprobe analysis

Paper ID: JTE10507J
DOI: 10.1520/JTE10507J
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