Atom dynamics and Neutron Vibrational Spectroscopy NiNbZr Glassy Membranes

Crystalline Pd/Pd-Ag membranes are generally used in hydrogen separation from CO₂ and other gases in power generation applications. Inexpensive amorphous Ni-based alloys are being developed as an alternative to expensive Pd alloys. Amorphous membrane ribbons of (Ni_0.60Nb_0.40)_100-xZr_x fabricated by melt-spinning method exhibit high permeabilities of hydrogen between 200-400^oC [1-4]. Atom probe tomography (APT) revealed Nb-rich and Zr-rich clusters embedded in a Ni-rich matrix whose compositions that deviated from the nominal overall composition of the membrane. Fukuhara et al. [5] reported icosahedral cluster arrangement of Ni-Nb-Zr atoms; we also found clusters based on APT and neutron SANS data, which can be interpreted as icosahedral arrangement. Neutron vibrational spectroscopy of these alloy yielded possible positions of hydrogen. Atom dynamic studies by X-ray photon correlation spectroscopy (XPCS) revealed a dramatic reversible acceleration of the atomic motion under hydrogen atmosphere at low temperatures; these effects are observed by standard thermodynamic/kinetic measurements. Dynamic mechanical analyses (DMA) indicated amorphous to amorphous phase transitions well below the recrystallization temperature, as well as the change elastic modulus as a function of temperature. Devitrification kinetics of these amorphous ribbons by using the John-Mehl-Avrami method showed Avrami exponents ranging from 1.92 to 2.47 indicating diffusion controlled 3-D growth mechanism. In an attempt to develop new alloys we show liquidus profiles for the ternary system using CALPHAD methodology. Hydrogen permeation, atom probe tomography, small angle neutron scattering, neutron vibrational spectroscopy, dynamic mechanical analyses, XPCS and devitrification kinetic aspects of these membranes will be presented.
(This research is supported by US DOE-NNSA grant, DE-NA0002004 and DOE-NETL FE0000998).
 
References:

1. S. Sarker, D. Chandra et al, Applied Physics A, A 122, 168 (2016).
2. M.D. Dolan, N.C. Dave, A.Y. Ilyushechkin, L.D. Morpeth, K.G. McLennan, J. Membr. Sci. 285 (2006) 30
3. S.M Kim, D. Chandra et al, Journal of Non-Crystalline Solids, 358 (2012) 1165–1170.
4. S. Paglieri, N. Pal, D. Chandra, Journal of Membrane Science, 378 (2011) 42-50.
5. M. Fukuhara, N. H. Oji, A. Inoue, S. Emura, JALCOM,497 (2010) 182–187