Hydriding and dehydriding kinetics

Abstract The processes involved in the first few hydriding-dehydriding cycles, referred to as activation, are discussed. The controversial activation of TiFe is reviewed and new H2-D2 isotope scrambling results are presented which indicate that metallic iron does not play a catalytic role. The hydriding-dehydriding kinetics are resolved into three interacting processes: intrinsic kinetics, heat flow and mass flow. The intrinsic kinetics are further resolved into three processes occurring simultaneously and in series: a surface process, diffusion and phase transformation. The problem of determining the rate-limiting intrinsic process from the time-temperature-pressure (tTP) dependences of the different processes is discussed. The employment of surface modification techniques to complement the tTP analysis is emphasized. Most kinetics analyses that have identified an intrinsic process as rate limiting are criticized as being invalid because 1. (1) the rate theory used has been inappropriate. 2. (2) heat flow has not been adequately taken into account. The viewpoint adopted is that only nucleation and growth (NG) theory is applicable. The NG formalism is developed and is employed to treat the interplay between the simultaneous intrinsic processes which is generally ignored. NG theory is also employed to model kinetics behavior in order to discuss heat flow. The control of heat flow by the previously overlooked, but very useful, control of heat capacity is discussed.

[1]  T. Flanagan,et al.  The slow step for hydrogen absorption (desorption) by activated LaNi5 , 1977 .

[2]  E. L. Huston,et al.  Kinetic and dynamic aspects of rechargeable metal hydrides , 1980 .

[3]  Dieter M. Gruen,et al.  Preparation and properties of porous metal hydride compacts , 1980 .

[4]  K. Nakamura.  Hydrogen absorption kinetics of niobium with an ionplated nickel overlayer , 1981 .

[5]  P. Rudman,et al.  Hydrogen desorption from uhv-cleaved vanadium hydride , 1980 .

[6]  B. Achar,et al.  Numerical Data for Some Commonly Used Solid State Reaction Equations , 1966 .

[7]  J. Pryde,et al.  Thermodynamic data and kinetics of evolution for dilute solution of hydrogen in tantalum , 1969 .

[8]  M. A. Pick,et al.  Enhancement of Hydrogen Uptake Rates for Nb and Ta by Thin Surface Overlayers , 1979 .

[9]  S. Suda,et al.  Reaction kinetics of metal hydrides and their mixtures , 1980 .

[10]  T. Schober,et al.  The activation of FeTi for hydrogen storage: A different view☆ , 1981 .

[11]  L. Belkbir,et al.  Comparative study of the formation-decomposition mechanisms and kinetics in LaNi5 and magnesium reversible hydrides , 1981 .

[12]  P. Rudman,et al.  The Catalytic Role of Mg2 Cu in the Hydriding and Dehydriding of Mg , 1979 .

[13]  H. Imamura,et al.  Mechanism of hydrogen absorption by lanthanum-nickel (LaNi5) , 1979 .

[14]  P. Rudman,et al.  Hydriding and dehydriding rates of the LaNi5-H system , 1983 .

[15]  L. Belkbir,et al.  Kinetics of hydrogen absorption and desorption by ternary LaNi5-type intermetallic compounds , 1979 .

[16]  J. Sheridan,et al.  The effect of surface nickel on the hydriding-dehydriding kinetics of MgH2 , 1980 .

[17]  P. Rudman,et al.  Hydriding and dehydriding kinetics of Mg in a Mg/Mg2Cu eutectic alloy: Pressure sweep method , 1979 .

[18]  R. Bowman,et al.  Hydrogen diffusion in β-phase titanium iron hydride , 1979 .

[19]  R. Sabatini,et al.  The “activation” of FeTi for hydrogen absorption; An electron microscopic study☆ , 1980 .

[20]  L. Schlapbach,et al.  Surface effects and the formation of metal hydrides , 1980 .

[21]  P. Rudman.  Hydrogen‐diffusion‐rate‐limited hydriding and dehydriding kinetics , 1979 .

[22]  D. Lindner.  Mechanism for the isothermal decomposition of iron titanium hydride , 1978 .

[23]  M. Amano,et al.  The hydriding of FeTi during an activation treatment - by in-situ X-ray diffraction - , 1981 .

[24]  T. Flanagan,et al.  Kinetics of hydrogen absorption by lanthanum-nickel (LaNi5) , 1977 .