However, the in situ measurement of mass gain, especially during fast temperature cycles, which is a problem of significant practical importance, remained a problem that was experimentally unsolved. The reason for this is that due to fast changes of temperature in close vicinity to the sample surface, thermal drifts begin to dominate the thermobalance signal, making a clear scientific interpretation of the mass changes impossible. This problem is well known to the community for more than a couple of decades but a sound solution of such an issue has never been presented so far. Instead, trials to combine fast heating by infrared furnace with thermobalance were so far unsuccessful, i.e. results obtained with set-ups caused a lot of doubts and controversies and hence this combination is up to now only used for long-term exposures of several hundred hours.
In addition to coupling of IR-heating and thermobalance, it was therefore decided at MPIE to eliminate the content of inert gas – which often represents up to 95 % of the atmosphere – and to perform thermal exposures in a low pressure environment instead. By this procedure, we can still establish the same amounts of all reactive components and reduce the buoyancy effects by more than a factor of 10.
Initial tests with exposures of pure iron samples in an argon atmosphere, as illustrated in Fig. 2, prove the success of this technique. Whereas in both experiments a clear reduction of the initial drop in the recorded mass signal has been observed, the fluctuations in a steady gas flow could also be reduced by several orders of magnitude. This enables extremely accurate measurements of in situ mass changes down to 0.1 µg. Please note, that a low oxygen contamination in the argon gas causes a residual mass increase and that this can be clearly seen at 30 mbar (Fig. 2, left), whereas this is not possible at ambient gas pressures.