Papers by Keyword: High Temperature Mass Spectrometry

Abstract: Chromium rich, nickel based alloys Haynes 230 and Inconel 617 are candidate materials for the primary circuit and intermediate heat exchangers (IHX) of (Very)-High Temperature Reactors. The corrosion resistance of these alloys is strongly related to the reactivity of chromium in the reactor specific environment (high temperature, impure helium). At intermediate temperature – 900°C for Haynes 230 and 850°C for Inconel 617 – the alloys under investigation are likely to develop a chromium-rich surface oxide scale. This layer protects from the exchanges with the surrounding medium and thus prevents against intensive corrosion processes. However at higher temperatures, it was shown that the surface chromia can be reduced by reaction with the carbon from the alloy [1] and the bare material can quickly corrode. Chromium appears to be a key element in this surface scale reactivity. Then, quantitative assessment of the surface requires an accurate knowledge of the chromium activity in the temperature range close to the operating conditions (T ≈ 1273 K). High temperature mass spectrometry (HTMS) coupled to multiple effusion Knudsen cells was successfully used to measure the chromium activity in Inconel 617 and Haynes 230 in the 1423- 1548 K temperature range. Appropriate adjustments of the experimental parameters and in-situ calibration toward pure chromium allow to reach accuracy better than ± 5%. For both alloys, the chromium activities are determined. Our experimental results on Inconel 617 are in disagreement with the data published by Hilpert [2]. Possible explanations for the significant discrepancy are discussed.

Abstract: In many elaboration furnaces, ceramics are used with other materials in vacuum atmospheres. If temperatures are sufficiently high, vaporizations occur. Depending on the thermodynamic stability of the investigated oxide, this vaporization can be congruent or not. In this last case, chemical reactions with the ceramic can take place which can lead to the destruction of it. One way to study these processes is the use of the High Temperature Mass Spectrometry (HTMS). This technique allows determining the composition of the gas phase and the partial pressures of the different gaseous species. By combining the spectrometer to a multiple Knudsen cell furnace, it is also possible to determine activities by direct comparison of the partial pressures of each gaseous species in equilibrium with a mixture and with pure components or compounds in the same experiment. Another recent development of the above technique is to characterize non equilibrium states by determining evaporation and condensation coefficients. These coefficients describe the difference between the real vaporization state of the system and the equilibrium state. To perform such determinations it is necessary to vary the shape of the Knudsen cell orifices in order to change the net evaporation process at the surface of the samples. Theses coefficients can be used to obtain better modeling in processing.