Study of Morphological Changes in MgH(2) Destabilized LiBH(4) Systems Using Computed X-ray Microtomography

The objective of this study was to apply three-dimensional x-ray microtomographic imaging to understanding morphologies in the diphasic destabilized hydride system: MgH(2) and LiBH(4). Each of the single phase hydrides as well as two-phase mixtures at LiBH(4):MgH(2) ratios of 1:3, 1:1, and 2:1 were prepared by high energy ball milling for 5 minutes (with and without 4 mol % TiCl(3) catalyst additions). Samples were imaged using computed microtomography in order to (i) establish measurement conditions leading to maximum absorption contrast between the two phases and (ii) determine interfacial volume. The optimal energy for measurement was determined to be 15 keV (having 18% transmission for the MgH(2) phase and above 90% transmission for the LiBH(4) phase). This work also focused on the determination of interfacial volume. Results showed that interfacial volume for each of the single phase systems, LiBH(4) and MgH(2), did not change much with catalysis using 4 mol % TiCl(3). However, for the mixed composite system, interphase boundary volume was always higher in the catalyzed system; increasing from 15% to 33% in the 1:3 system, from 11% to 20% in the 1:1 system, and 2% to 14% in the 2:1 system. The parameters studied are expected to govern mass transport (i.e., diffusion) and ultimately lead to microstructure-based improvements on H(2) desorption and uptake rates.