PhD Scholar, IIT-Bombay
Investigation on hydrogen absorption in doped BCC alloys for hydrogen storage varying particle size
I am working on Ti-V-Cr based materials(metal hydrides) for storing hydrogen at room temperature under 2 bar(very low compared to other metal types of metal hydrides). We choose the composition which has body centered cubic crystal structure as has high void. These materials absorbs/desorbs hydrogen so quickly after first time exposure for hydrogenation but first time hydrogen absorption is very difficult. There is some waiting period before first time hydrogen absorption. This waiting period may be couple of minutes or days. My task is to find out parameters affecting this waiting period and optimize the favorable material synthesizing technique for quicK hydrogenation. The waiting period during first hydrogenation is mainly affected by chemical composition, phase system, phase compositions, crystal structure, surface properties. In this investigation, I searched for effect of particle size and doping on hydrogen absorption of 52Ti-12V36Cr doped with 4wt%Zr. We found
Abstract: The electrochemical reactions of multi-phase metal hydride (MH) alloys were studied using a series of Laves phase-related body-centered-cubic (BCC) Ti15.6Zr2.1V43Cr11.2Mn6.9Co1.4Ni18.5Al0.3X (X = V, B, Mg, Y, Zr, Nb, Mo, La, and Nd) alloys. These alloys are composed of BCC (major), TiNi (major), C14 (minor), and Ti2Ni (minor) phases. The BCC phase was found to be responsible for the visible equilibrium pressure plateau between 0.1 MPa and 1 MPa. The plateaus belonging to the other phases occurred below 0.005 MPa. Due to the synergetic effects of other non-BCC phases, the body-centered-tetragonal (BCT) intermediate step is skipped and the face-centered-cubic (FCC) hydride phase is formed directly. During hydrogenation in both gaseous phase and electrochemistry, the non-BCC phases were first charged to completion, followed by charging of the BCC phase. In the multi-phase system, the side with a higher work function along the grain boundary is believed to be the first region that becomes hydrogenated and will not be fully dehydrided after 8 h in vacuum at 300 °C. While there is a large step at approximately 50% of the maximum hydrogen storage for the equilibrium pressure measured in gaseous phase, the charge/discharge curves measured electrochemically are very smooth, indicating a synergetic effect between BCC and non-BCC phases in the presence of voltage and charge non-neutrality. Compared to the non-BCC phases, the C14 phase benefits while the TiNi phase deteriorates the high-rate dischargeability (HRD) of the alloys. These synergetic effects are explained by the preoccupied hydrogen sites on the side of the hydrogen storage phase near the grain boundary.
Pub.: 19 May '16, Pinned: 30 Jul '17
Abstract: The system for fuel supply of a hydrogen-air fuel cell on the basis of the aluminum-water hydrogen generator and hydride-forming alloy as an intermediate gas storage has been developed. For a series of general composition alloys LaNi4.5 − xAlxCO0.5 service life evaluation tests with the use of highly wet hydrogen were carried out. The possibility of absorption and release of hydrogen by hydride-forming alloys with the rate that corresponds to technical parameters of the system has been shown, and it was found that hydrogen storage capacity is unaffected by high wetness of hydrogen.
Pub.: 05 Jan '11, Pinned: 30 Jul '17
Abstract: Zr substituted Ti2CrV alloy with Ti0.43Zr0.07Cr0.25V0.25 composition was synthesized by arc melting method and its crystal structure, microstructure and hydrogen storage performance were investigated. XRD and microstructural analyses confirmed that the alloy forms Laves phase related BCC solid solution. The enthalpy of hydride formation as derived from pressure composition absorption isotherms is −56.33 kJ/mol H2. The desorption temperature of the hydride is significantly lower (by ∼50 K) than that of Ti2CrV hydride indicating lower thermal stability of the hydride compared to its unsubstituted analogue. The alloy shows better cyclic stability over the unsubstituted one. This work also offers mechanistic insight into hydrogen absorption reaction of Ti0.43Zr0.07Cr0.25V0.25 alloy by analyzing the hydriding kinetics data with standard kinetic models. The rate-determining steps of hydrogen absorption reaction were identified as random nucleation and growth of hydride followed by 1D and 3D diffusion of hydrogen atoms through the hydride layer. The present study is expected to provide valuable information for the better development of Ti–Cr–V based hydrogen storage alloys.
Pub.: 21 Mar '17, Pinned: 30 Jul '17
Abstract: The effect of chemical composition and particle size on the first hydrogenation of BCC alloy 52Ti-12V-36Cr were investigated. The alloy was studied in the undoped state and doped with 4%Zr. Three particle size ranges were selected: less than 0.5 mm, between 0.5 mm and 1 mm, and bigger than 1 mm. It was found that doping reduced the incubation time by more than two orders of magnitudes. Smaller particle size also reduces incubation time but only by a factor of three. The intrinsic hydrogenation kinetics were also significantly enhanced by doping. Moreover, there is some synergetic effect between doping and reduction of particle size. It was also found that incubation time depends on the average particle size and not on the distribution of particle sizes.
Pub.: 18 Mar '17, Pinned: 30 Jul '17
Abstract: In this investigation the commercial ZK60 magnesium alloy modified with 2.5 wt.% of mischmetal was processed by melt spinning (MS) and equal-channel angular pressing (ECAP), both followed by extensive cold rolling (CR). The results indicate that MS was effective to produce small grain sizes in the order of 700 nm, while specimens prepared only by ECAP reached about 50 μm. However, melt spun ribbons showed long activation (first hydrogenation) times of more than 30 h in contrast to ECAP, which took about 10 h. In addition, after the activation process, the hydrogen storage capacity of ECAP was poorer than MS (2.5 and 3.3 wt.% of H2, respectively). Additional processing by CR caused further grain refinement and breakage of intermetallic particles, as well as favoring crystallographic texture in the (002) direction. All these features promoted a significant improvement in the hydrogen storage capacity, and in the absorption kinetics of the specimens processed by MS and ECAP.
Pub.: 24 May '16, Pinned: 30 Jul '17
Abstract: In this paper, we report the microstructure and hydrogen storage properties of Ti0.95FeZr0.05, TiFe0.95Zr0.05 and TiFeZr0.05 alloys prepared by arc melting. We found that all these alloys are made of a TiFe phase with small amount of zirconium in solid solution and a secondary phase which is zirconium rich. This special microstructure is actually responsible for the enhanced activation (first hydrogenation) kinetics of these alloys. First hydrogenation of Ti0.95FeZr0.05 alloy proceed faster than for the other two alloys. This is probably due to a finer distribution of the bright secondary phase. Pressure-composition isotherms of TiFeZr0.05 and Ti0.95FeZr0.05 alloys are similar while the alloy TiFe0.95Zr0.05 shows the highest capacity. These results demonstrate that a very slight variation of composition could have an important effect of microstructure and hydrogen storage behaviours.
Pub.: 29 Jul '16, Pinned: 30 Jul '17