PULSED-FIELD DESORPTION MASS-SPECTROMETRIC STUDY OF THE OXIDATION OF HYDROGEN-DOPED NI3ZR

The oxidation of a Ni3Zr field emitter, electrochemically doped with h ydrogen, has been studied over a temperature range from 100 degrees C to 250 degrees C in an oxygen atmosphere with pressures ranging from 1 0(-4) Torr to 3 X 10(-1) Torr using PFDMS. Water was observed immediat ely after the first oxidation at 100 degrees C and 10(-4) Torr O-2 and was observed throughout the series of oxidations, Pulse field desorpt ion produced a wide range of ions: Ni+, Ni2+, H+, O+, O2+, O-2(+), H2O + Ni(OH)(2)(+), NiOH+, NiOH2+, NiOH3+, Ni2O2+, Ni(CO)(+), Ni(CO)(2)(+) , Ni(CO)(3)(+), Zr+, ZrO23+, ZrO22+, ZrO2+, ZrO3+, ZrO2+ and ZrO+; whi ch differ substantially from an atom probe investigation of the oxidat ion (dry, no H-abs same alloy. The data show, for all oxidation temper atures and pressures, an initial strong enrichment of Ni at the surfac e. At lower temperatures and oxygen pressures this layer appears to be very thin. Previous low temperature/pressure thermal oxidation experi ments performed on Ni3Zr (no H-abs) resulted in the preferential oxida tion and segregation of Zr to the surface. only at higher temperatures and/or oxygen pressures has preferential Ni oxidation and segregation been previously observed. This behavior is indeed observed during the se experiments after the 250 degrees C and 3 x 10(-1) Torr O-2 oxidati on. The unusual H-doped Ni3Zr behavior at low temperatures/pressures a ppears to involve the formation of a thin layer of Ni(OH)(x) which is more stable than NiO. The results from the study of H-doped Ni3Zr yiel d some important new findings regarding the effect of hydrogen absorpt ion on the alloy oxidation. In addition, the reaction of absorbed hydr ogen with oxygen provides a unique way of introducing water on a sampl e in a UHV environment.