THERMOELECTRIC INSTABILITY OF SOME NOBLE METAL THERMOCOUPLES AT HIGH TEMPERATURES
Abstract
Thermoelectric instabilities of noble metal thermocouples and individual thermoelements were studied from 1000 to 1700 deg C under oxidizing and neutral atmospheres. The principal source of instability was a contamination of the thermoelements by impurities from ceramic protection tubes. Several grades of alumina sheathing were tested, and thermocouple errors associated with each grade were determined. With alumina sheathing the principal contaminant was iron, and the instability generated was at least an order of magnitude greater in a neutral atmosphere than in an oxidizing atmosphere. Increasing the wire size increases stability in a neutral atmosphere, although not in an oxidizing atmosphere. Instability increases rapidly with temperature between 1000 and 1700 deg C, but the order of decreasing stability remains Pt-6%Rh/Pt-30%Rh, Pt-1%Rh/Pt-13%Rh, and Pt/Pt-10%Rh or Pt/Pt-13%Rh. The instability of pure rhodium thermoelements, and of Ir and Ir-50%Rh thermoelements, depends on internal changes, and not as much on iron contamination as the Pt-Rh series of thermoelements; hence the pure rhodium and the iridium thermoelements become preferable if gross iron contamination is expected.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 29, 1962
- Accession Number
- AD0282154
Entities
People
- B. E. Walker
- C. T. Ewing
- Roman R. Miller
Organizations
- United States Naval Research Laboratory