화학공학소재연구정보센터
International Journal of Hydrogen Energy, Vol.36, No.11, 6689-6697, 2011
Study of the diffusion kinetics and mechanism of electrochemical hydriding of Mg-Ni-Mm alloys
Electrochemical hydriding in a 6 M KOH solution at 20 and 80 degrees C for 480 min was applied on a series of as-cast binary Mg-Ni and ternary Mg-Ni-Mm alloys (Mm = mischmetal containing 45% Ce, 38% La, 12% Nd and 4% Pr) containing 11-24 wt. % Ni and 0-6 wt. % Mm. The kinetics and mechanism of the hydriding process, as well as hydrogen release temperatures, were studied by glow discharge spectrometry hydrogen profiling, scanning electron microscopy, energy dispersion analysis, X-ray diffraction and mass spectrometry. A maximum hydrogen concentration of 1.1% was achieved in the eutectic MgNi24Mm5 alloy hydrided at 80 degrees C. In all cases, the main hydriding product was binary MgH(2) hydride. Mass spectrometry revealed its destabilization due to Ni and Mm because its decomposition temperature was lowered by about 100 degrees C. Both nickel and mischmetal showed positive effects on hydriding and dehydriding kinetics. These effects are discussed in relation to the hydriding mechanism, electronic structure and atomic size of additives and structural variations of the alloys. Based on the H-concentration profiles, the diffusion coefficients of hydrogen were estimated. For the eutectic MgNi24Mm5 alloy, the H diffusion coefficient at 20 degrees C was 4 . 10(-10) cm(2) s(-1). Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.