A STUDY OF THE KINETICS OF HYDROGEN ABSORPTION IN LaNi_5
Lu Manqi;Qi Zhenzhong;Wu Pingsen Institute of Metal Research; Academia Sinica
Cite this article:
Lu Manqi;Qi Zhenzhong;Wu Pingsen Institute of Metal Research; Academia Sinica. A STUDY OF THE KINETICS OF HYDROGEN ABSORPTION IN LaNi_5. Acta Metall Sin, 1980, 16(1): 65-72.
Abstract The kinetics of hydrogen absorption in LaNi_5 has been investigated at initialpressures of 15--30 atm and temperatures in the range of 20--85℃. LaNi_5 was pre-pared in a ZrO_2 crucible in a graphite-tube furnace under vacuum. It is shownthat a linear relationship exists between the amount of hydrogen absorbed, W,and the time of reaction on a logarithmic scale and the rate of hydrogen absorp-tion depends on the initial pressure and the test temperature. The P-X-T curves of the LaNi_5 system have been determined. For each testtemperature there is a corresponding pressure plateau P_0 and it is therefore as-sumed that for every initial pressure P_0 there is a corresponding balance temperatureT_0, and T_0-T may be taken as the driving force of hydrogen absorption processin LaNi_5 at initial pressure P_0 and test temperature T. The absorption of hydro-gen takes place in three steps: (1) surface reaction, which seems to be rather com-plicated; (2) diffusion of hydrogen atoms and (3) phase transformation f LaNi_5 toa hydride phase. All these steps are thermal activation processes, and thereforethe e~(-U/RT) can be introduce in the hydrogen absorption process. The relatioshipbetween the absorption rate, the initial pressure, the test temperature and time isgiven as follow: dW/dt=A_0(T_0-T)e~(-U/RT)·1/tThe activation energy of the rate limiting step U is about 2 or 3.2 kcal/molaccording to whether the amount of hydrogen absorbed is less or more than 70%respectively. The parameter U of the rate-limiting step during hydrogen absorptionin LaNi_5 can be obtained as shown by our experiments.
[1] Zijlstra, J.H. and Westerdorp, F.F., Solid State Commun., 7 (1969) , 857． [2] Van Vucht, J.H.N., Kuijpers, F.A. and Bruning, H.C.A.M., Philips Res. Rep., 25 (1970) , 133． [3] Reilly, J.J. and Wiswall, R.H., Inorg. Chem., 6 (1967) , 2220． [4] Reilly, J.J. and Wiswall, R.H., The Formation and Properties of FeTi Hydride, BNL-177711, 1973． [5] Kuijpers, F.A., Philips Res. Rep. Suppl., 1970, № 2, p. 28． [6] Reilly, J.J., Hoffman, K.C., Strickland, G. and Wiswall, R.H., 26th Power Sources Symp., 1974, Atlantic City, New Jersey, p. 11． [7] Klein, M. and George, M., 26th Power Sources Symp., 1974, Atlantic City, New Jersey, p.18． [8] Tanaka, S., Clewley, J.D. and Flaragan, T. B., J. Less-Common Metals, 56 (1977) , 137． [9] Boser, O. and Lehrfeld, D., Record of the 10th Intersociety Energy Conversion Engineering Conference, 1975, Published by IEEE, New York, Newark Delaware, p. 1363． [10] Lundin, C.E. and Lynch, F.E., Record of the 10th Intersociety Energy Conversion Engineering Conference, 1975, Published by IEEE, New York, Newark Delaware, p. 1380． [11] Boser, O., J. Less-Common Metals, 46 (1976) , 91． [12] Buschow, K.H.J. and Van Mal, H.H., J. Less-Common Metals, 29 (1972) , 203． [13] Pryde, J.A. and Titcomb, C.G., J. Phys. C: Solid State Phys., 5 (1972) , 1293． [14] Birnbaum, H.K. and Wert, C.A., Ber. Bunsenges. Phys. Chem., 76 (1972) , 806．
