Thin layer activation: A technique for monitoring material loss during high temperature surface degradation processes☆

Abstract The potential of thin layer activation (TLA) to monitor in situ material loss from high temperature surface degradation processes has been assessed. For this purpose the spallation of the oxide scale formed on a 20wt.%Cr-25wt.%Ni-0.7wt.%Mn-0.6wt.%SiNb stainless steel during oxidation in CO 2 at 900°C and also on subsequent furnace cooling has been examined. The TLA technique was based on the production, by a deuteron beam, within a defined steel region of radioisotopes ( 51 Cr, 52 Mn, 54 Mn, 56 Co, 57 Co and 58 Co) of major constituent elements involved in scale formation. Measurement of the activity levels of the radioisotopes before, during and after oxidation, and comparison with concurrent continuous mass changes, confirmed that activity loss indicated oxide spallation. Transients in oxidation kinetics, during both the extended isothermal exposure and the initial period of furnace cooling, originated from scale cracking rather than from spallation. The involvement of the individual radioisotopes was ascertained in each type of scale formed and in the spall produced.