Influence of Alkali-Vapor Atmospheres on Pyrometrically Determined Temperatures: Cesium and Potassium

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Abstract
The conventional pyrometric measurement of wall, electrode, and probe temperatures through an alkali-vapor atmosphere (which is, in part, cooler than the surface) has been found to lead to significant under-estimation of the temperature. The error arises from optical absorption of the alkali-vapor dimers in the region of the pyrometer passband. As an example, the observation through 6 cm of saturated potassium vapor of a surface whose brightness temperature is 2500°K results in an error of from 50° to 500°K as the vapor temperature varies from 300° to 370°C. Thus, substantial errors may be introduced into the determination of properties such as electrical conductivities and reaction rates, which are exponentially dependent upon temperature. The reciprocal-temperature error was found to be roughly proportional to the dimer optical depth, and agreed with theoretical predictions utilizing dimer optical absorption coefficients measured during these experiments.

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