Accession Number : AD0284880

Title :   CATALYTIC EFFECTS OF THERMOCOUPLE MATERIALS

Corporate Author : NATIONAL BUREAU OF STANDARDS GAITHERSBURG MD

Personal Author(s) : OLSEN, LIEF O.

Report Date : JUN 1962

Pagination or Media Count : 1

Abstract : Under some conditions certain noble metal thermocouples produce erroneous indications when immersed in gas streams containing oxygen and combustible gases. These errors have been shown to be caused by catalysis of the gaseous mixture on the surfaces of the thermocouple elements. The object of this investigation was to determine the magnitude of the catalytic effects of all of the commonly used thermocouple materials in lean mixtures of H, CO, propane, and methane in air. Most of the work was conducted in an apparatus consisting of an electrically heated loop of the wire under study. Air and mixtures of air containing small quantities of combustible gases were alternately directed over the resistance loop. Changes in its resistance reflected a rise in temperature caused by the catalytic combustion of the mixture on the surface of the wire. Wires of Pt, Pd, Ir, Pt plus 15% Ir, and the two elements of the Platinel thermocouple catalyzed the combustion of mixtures of H, CO, and propane in air. Combustion of methane-air mixtures was not initiated by these materials at temperatures to 1800 F. Experiments with Au, Ag, Chromel, Alumel, and constantan wires showed no catalysis of any mixture at temperatures of the wires to 1800 F. Base-metal thermocouples are recommended for accurate determinations of temperatures of gaseous mixtures containing combustible materials. (Author)

Descriptors :   *THERMOCOUPLES, AIR, CARBON COMPOUNDS, CATALYSIS, CATALYSTS, COMBUSTION, GOLD, HYDROGEN, IRIDIUM, MATERIALS, METHANES (1 C), MONOXIDES, PALLADIUM, PLATINUM, PROPANES (3 C), SILVER.

Distribution Statement : APPROVED FOR PUBLIC RELEASE