THERMOELECTRIC INSTABILITY OF SOME NOBLE METAL THERMOCOUPLES AT HIGH TEMPERATURES

Technical Report · Fri Jun 29 04:00:00 EDT 1962

OSTI ID:4805936

Walker, B E; Ewing, C T; Miller, R R

Thermoelectric instabilities of noble metal thermocouples and individual thermoelements (Pt, Rh, Ir, Ir-50% Rh, and several Pt--Rh alloys) were studied from 1000 to 1700 deg C under oxidizing and neutral atmospheres. The principal source of instability was found to be 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 or 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 thermo elements become preferable if gross iron contamination is expected. When compositional changes are expected in a thermoelement, immersion depth should be maintained constant or increased. (auth)

• Research Organization: Naval Research Lab., Washington, D.C.
• NSA Number: NSA-16-027261
• OSTI ID: 4805936
• Report Number(s): NRL-5792
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ALUMINUM ALLOYS
CERAMICS
COATING
ENGINEERING AND EQUIPMENT
HIGH TEMPERATURE
IMPURITIES
IRIDIUM
IRON
OXIDATION
PLATINUM
PLATINUM ALLOYS
RHODIUM
RHODIUM ALLOYS
TEMPERATURE
THERMOCOUPLES
THERMOELECTRICITY
TRANSITION METALS