Upscaling effect in the preparation of metal hydride materials
The preparation of Ti-Zr based AB2 alloys where A=Ti, Zr ; B= Mn,Cr, Ni, Fe, V, Cu for use in hydrogen storage was investigated. In Ti-Zr based AB2 metal hydrides, the effects of composition, microstructure, and hydrogen sorption properties were examined using Scanning electron microscope (SEM), Energy dispersive x-ray spectroscopy (EDS), X-ray diffraction (XRD), and Sievert’s type Pressure composition temperature (PCT) measurements. Alloys were prepared by arc melting and induction melting. Ti0.85Zr0.15Cr0.2Mn1.22Ni0.22V0.3Fe0.06 alloy prepared by arc melting served as the base alloy. The EDS and XRD revealed that the alloy contained no impurities with a single C14 Laves phase and had a maximum storage capacity of 1.8 wt.% H2 at 20C . The base alloy additionally doped with Lanthanum (Ti0.85Zr0.15Cr0.2Mn1.22Ni0.22V0.3Fe0.06La0.02) was prepared by induction melting with an alumo-silica crucible and graphite crucible, respectively. The alumo-silica crucible was coated with a Y2O3 slurry, whereas the graphite crucible was coated with Mo slurry + (Y2O3 + Mo) + Y2O3 slurry. However, even though coated with Y2O3, the XRD revealed an impurity phase in both alloys (La2TiO5) with an additional impurity phase in the alloy prepared by alumo-silica crucible (Ti,Zr)O2. The transmission electron microscope (TEM) results showed that the alloy prepared with alumo silica crucible had the poorest crystallinity due to the additional impurity phase, whereas the alloy prepared with graphite crucible had the highest degree of crystallinity. In addition, the atomic emission spectroscopy (AES) results showed that alloy prepared by alumo silica crucible had the maximum amount of oxygen whereas the oxygen content decreased by 3% for the alloy prepared with graphite crucible. Finally, the hydrogen storage capacity decreased from the initial 1.8 wt.% to 1.36 wt.% and 1.5 wt.%, for alloy prepared with the alumo silica crucible and graphite crucible, respectively. Oxygen was introduced to the base alloy (Ti0.85Zr0.15Cr0.2Mn1.22Ni0.22V0.3Fe0.06O0.05) to investigate its influence on the alloy’s performance. The SEM/EDS results of the alloy modified by oxygen showed that the surface contained more cracks than the unmodified alloy (base alloy). In addition, the total oxygen impurity was 0.78% from EDS data. The XRD revealed that both the unmodified and modified oxygen alloy consisted of the main C14 Laves phase and also an impurity phase of η-phase (Ti4Fe2O1-x). The reason for the impurity phase in the unmodified alloy was due to the commercial use of ferrovanadium (FeV). The hydrogen absorption kinetics revealed that the hydrogen intake for the oxygen-modified alloy was slower after activation by vacuum heating. However, in the non-activated state, the hydrogen intake was immediate due to the impurity phase acting as a catalyst, but this ultimately caused a decrease in hydrogen storage capacity. The effect of changing the Ti/Zr ratio on hydrogen sorption performance of TixZryCr0.2Mn1.22Ni0.22V0.3Fe0.06 (x=0.9,0.8; y=0.1, 0.2) was also studied. The EDS data revealed that despite having Cr and Fe in the composition, it was absent in the EDS data. This may be due to the increase in Ti content since the atomic radii is larger than Cr and Fe and may occupy the B-sites of Cr and Fe. By increasing the Zr content, the lattice parameter and unit cell volume increased due to the larger Zr atomic radius than the Ti one. However, this led to a decrease in hydrogen storage capacity. A substitution of a cheaper alternative material such as FeV was also investigated. The Ti0.85Zr0.15Cr0.2Mn1.2Ni0.22Cu0.02FeV0.42 showed to exhibit a single C14 phase in the XRD, however in the EDS data a minor silicon impurity was found. The hydrogen storage capacity compared to the base alloy, decreased to 1.5 wt.%. Finally, the effect of changing Mn/Cr ratio by Ti0.85Zr0.15CrxMnyNi0.22V0.3Fe0.06 (x=0,0.3,0.6; y=1.4, 1.1, 0.8) showed to have a decrease in hydrogen storage capacity with increasing Cr content. However, the hydrogen capacity with the alloy containing no Cr, showed to have a higher maximum hydrogen storage capacity than the base alloy.
Alloy, Arc melting, Hydrogen storage, HySA, Induction melting
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