Hydrogenation properties of Ti–V–Mn alloys with a BCC structure containing high and low oxygen concentrations

• Published in: Journal of alloys and compounds Vol. 509; no. 5; pp. 1841 - 1847
• Main Authors: Nakamura, Y., Nakamura, J., Sakaki, K., Asano, K., Akiba, E.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 03.02.2011; Elsevier
• Subjects: Alloy; Alloys; BCC structure; Body centered cubic lattice; Concentration (composition); Condensed matter: structure, mechanical and thermal properties; Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder; Cross-disciplinary physics: materials science; rheology; Dihydrides; Exact sciences and technology; Formation enthalpy; Hydrogen storage; Hydrogenation; Inorganic compounds; Materials science; Occupation; Oxygen effect; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Phase transformations; Physics; P– C isotherm; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Thermal properties of condensed matter; Thermal properties of crystalline solids; Thermodynamic properties; BCC structure; Oxygen effect; Hydrogen storage; Formation enthalpy; Alloy; P– C isotherm; Scanning electron microscopy; P-C isotherm; Phase transformations; Enthalpy; X-ray spectra; XRD; Lattice parameters; Dispersive spectrometry; Hydrogenation; Nonstoichiometry; Quantity ratio; BCC lattices; Thermodynamic properties; Crystal structure
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2010.10.059

▶ Ti 1.0V 1.1Mn 0.9 alloys with two different oxygen concentrations have been studied. ▶ Increasing the oxygen concentration raises an equilibrium pressure for dihydride formation. ▶ The equilibrium pressure for formation of monohydride does not depend on the oxygen concentration. ▶ The change in the properties is caused by solved oxygen affecting hydrogen occupation directly. ▶ Oxygen also alters the properties as a result of promoting a composition change of the main phase. The hydrogenation properties of Ti 1.0V 1.1Mn 0.9 alloys with a BCC structure, prepared using two V materials with different oxygen concentrations, were studied. The sample prepared using a conventional-grade V material contained 0.530 mass% of oxygen, and the other sample prepared from a low-oxygen V material contained 0.051 mass% of oxygen. Both samples showed P– C isotherms with two plateaus corresponding to formation of monohydrides and dihydrides. The sample with the higher oxygen concentration had an equilibrium pressure for dihydride formation 6.7 times higher than that of the sample with the lower oxygen concentration at 0 °C. There was no significant difference between the two samples with regard to the equilibrium pressure for formation of monohydride or the hydrogen capacity. The formation enthalpies were calculated from the van’t Hoff plots: −30.2 kJ/molH 2 and −35.5 kJ/molH 2 for the dihydrides, and −39.7 kJ/molH 2 and −39.8 kJ/molH 2 for the monohydrides. Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM–EDX) and X-ray diffraction (XRD) indicated that the sample with the higher oxygen concentration contained a Ti-rich secondary phase, which caused changes in the composition and in the lattice parameter of the main phase. These results indicated that increasing the oxygen concentration altered the hydrogenation properties as a result of (1) the effect of oxygen solved in the main phase on hydrogen occupation and (2) a composition change resulting from secondary phase formation.