Nitriding reactions with a Zr-Mn-Fe metal getter

The metal getter Zr-Mn-Fe (SAES ST909) is an important component of a metal hydride-based tritium clean-up system at Los Alamos National Laboratory (LANL). The system is normally used to clean a glovebox with a helium/nitrogen atmosphere. During start-up operations, it was found that the Zr-Mn-Fe alloy exhibited an anomaly during activation, namely an exotherm upon initial exposure to nitrogen. The purpose of this work is to better understand this nitriding reaction. Nitrogen absorption studies, temperature profile experiments, and powder X-ray diffraction (XRD) were used to study the nitriding reaction. An exothermic reaction between nitrogen and ST909 was observed at approx =450 deg C only when the getter was heated for the first time. ST909 that had been previously heated without nitrogen did not produce an exotherm when heated a second time with nitrogen. Based on the XRD evidence, it was speculated that nitrogen reacts exothermically with the zirconium in the ST909 material. After heating above approx =660 deg C, the aluminum binder in the ST909 melts and may alloy with the zirconium. The resulting alloy appears to be less reactive with nitrogen and does not produce an exotherm.