Characterisation of oxidising metal surfaces with a two colour pyrometer

Abstract

A miniature test system has been used to investigate the time dependence of the oxide scaling process on representative engineering materials, especially the magnitude of indicated temperatures using a parallel measurement setup of pyrometer and thermocouple. The miniature system uses direct current to heat long, thin, rectangular specimens, in both inert and oxidising atmospheres. Measurements showed that particular care has to be taken in interpreting pyrometer temperature measurements, particularly at the start of the scaling process when oxides are very thin. In some areas, differences of 100 K were noted between temperatures indicated by pyrometry and by thermocouples. Models have been developed to study the initial stages of the oxidation process and these clearly demonstrate the observed interference effects characteristic of a growing thin oxide layer.