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The static method, developed at IMT, for determining sorption properties of NEGs is based on establishing constant test gas flow by the rate of pressure rise technique followed by measuring sorption pressure above NEG after exposing its surface to the gas flow. A spinning rotor gauge is used for both pressure measurements. During the test, the gas flow is few times interrupted to measure a background pressure increase due to accumulation of inert gases.
A new method enabling continuous monitoring the behaviour of the background pressure has been derived from the method described above. Firstly, the test gas flow is reduced for more than three orders of magnitude. Using SS inner walls of the test chamber as a constant RT H2 source, the corresponding sorption pressure throughout the test becomes much smaller in comparison with the increasing background pressure. Secondly, an accumulated gas composition is analysed by slow opening a valve to continuously pumped RGA.
NEG samples of 2 cm2 surface area were cut from a 60 Mu thick NiCr20Ti foil covered with a 200 Mu thick, highly porous layer consisting of sintered Ti and Zr-V-Fe alloy particles. Before starting NEG activation the test chamber was baked at 150°C for 6 h while keeping NEG at 200°C. With the test chamber kept at RT the NEG activation took place at 450°C for 1 h by means of either local radiation heating or resistance heating. These precautions were taken to minimize the influence of residual H2O vapour on the build-up of C on the NEG surface.
Before performing the new, 18 h long sorption test at RT in the 0.8 l test chamber, the H2 outgassing rate of SS walls was measured, which amounted to 4.2x10-9 mbarl/s. In case of NEGs activated by radiation heating the background pressure increasing was slightly parabolic, into the mid 10-7 mbar range, while in case of resistively heated NEGs the same increasing was clearly parabolic, into the highest 10-7 mbar range. After completing the standard H2 sorption test, reactivated NEGs exhibited linear increasing, in first case in the mid 10-8 mbar range while in second case in the lowest 10-8 mbar range (outgassing rate of 1x10-13 mbarl/scm2). In all cases the gas composition analysis using RGA in dynamic mode gave CH4 as a main constituent of the residual atmosphere.
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