Papers by Keyword: Isotopic Exchange

Abstract: MgH2-LiBH4 system is one of the promising hydrogen storage materials. In the system, it was found that there was a mutual interaction between the two hydrides, but its mechanism has not been clarified yet. In this work, we found an “H-D” exchange between MgD2 and LiBH4 during heating. IR absorption spectroscopy revealed that the peak of “B-D” vibration appeared at 275 °C below the melting and hydrogen desorption of the system, indicating that this exchange proceeded even in solid phases. The hydrogen desorption properties of the composite of catalyst-doped MgH2 and LiBH4 under inert gas were investigated by mass spectroscopy. The results showed that the hydrogen desorption temperature of the first step was over 300 °C, in spite of catalyst-doped MgH2 can release hydrogen at 200 °C. The above results might suggest the hydrogen desorption from catalyst-doped MgH2 is somehow suppressed by the exchange effect between MgH2 and LiBH4.

Abstract: K2NiF4 type oxides have received considerable attention in recent years as possible mixed conducting membranes for technologically important applications such as solid oxide fuel cells and oxygen generators. Much of this interest has focused on the oxygen interstitial containing oxides such as La2NiO4+δ. This contribution will review some of the recent work on these and related materials and will present new data on the La2MO4+δ (M= Ni, Co or Mn) systems. In particular data on the oxide ion diffusivity of these systems, as determined by oxygen isotopic exchange and SIMS analysis highlighting the fast oxide ion diffusion (1 x 10-7 cm2s-1 at 750oC) present, will be discussed and the significance of these data evaluated in relation to solid oxide fuel cell systems. A further section of the presentation will consider the oxygen defect species present and discuss the nature of the mobile oxygen ions. Finally some preliminary data on the application of these materials as cathodes will be presented and the performance of the cathodes on intermediate temperature electrolytes discussed.

Abstract: Grain boundary diffusion coefficients of oxygen (δDgb) at 1793K in high purity α-alumina bicrystals with Σ7{2 _ ,310}/[0001] and Σ31{7 _ ,1140}/[0001] symmetric tilt grain boundaries were measured by means of the isotopic exchange and diffusion depth profiling using SIMS. δDgb of both grain boundaries were determined to be 7.1x10-24 [m3/sec] for Σ7 grain boundary and 5.3 x10-24 [m3/sec] for Σ31 grain boundary, respectively. These results indicate that Σ values do not directly relate to grain boundary diffusion properties.