Hydrogenation Properties Of Ti Research Articles

Hydriding properties of Ti–Mg alloy with BCC structures synthesized from α-Ti and β-Ti by ball-milling

The structure and hydrogenation properties of Ti–Mg alloy synthesized by ball-milling have been investigated. In this study, α-Ti powder (HCP) was successfully transformed into β-Ti (BCC) powder by ball-milling for 216 ks. This composition was obtained to mix elemental powder of each Ti (HCP or BCC) and Mg by ball-milling with the ratio of 12.5, 25, 37.5, and 50 at% Mg. The structure and thermal stability of these samples were analyzed by means of X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). In this results, Ti–Mg alloy with β-Ti maintained BCC phase as much as the ratio of 37.5 at% Mg, and it was the steady state until 573 K. Furthermore, from the comparison of hydride properties of Ti75Mg25 alloy with BCC phase synthesized from β-Ti and α-Ti, alloy with β-Ti easily absorbed hydrogen at the room temperature, while alloy with α-Ti hardly reacted with hydrogen. In addition, the lattice parameter of Ti–Mg with β-Ti was 0.326 nm, and the strain was lower than alloy with α-Ti. However, Ti75Mg25 after hydrogenation was transformed into TiH2.

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

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.

Relationship between microstructure and hydrogenation properties of Ti 0.85Zr 0.15Mn 1.5V 0.5 alloy

The hydrogenation properties of Ti 0.85Zr 0.15Mn 1.5V 0.5 alloy for four different microstructures obtained by as-cast arc melting, high-temperature annealing, ball-milling, and recrystallization after milling, have been determined. The as-cast alloy reaches a hydrogen content of 1 H/M with absorption kinetics of less than 10 s at room temperature. Sloping plateau pressures are obtained for as-cast, and annealed arc-melted alloys due to the persistence of chemical heterogeneity. Mechanical milling causes formation of amorphous phase, and improves chemical homogeneity. Milled alloy exhibits no plateau pressure, a lower hydrogen capacity (0.7 H/M), and slower kinetics. Annealing of the milled alloy at 800 °C for 30 min restores the hydrogenation capacity up to 1 H/M with a flat plateau pressure, and fast kinetics. Mechanical milling is an efficient method to obtain a chemically homogenous alloy. Subsequent annealing of the milled alloy produces homogeneous AB 2 crystalline phase.

Hydrogenation of TiFe by high-energy ball milling

The hydrogenation properties of TiFe, TiFe 2 and pure Ti during high-energy ball milling in hydrogen atmosphere were studied. By ball milling, TiFe could absorb hydrogen without activation treatment. For Ti powder, a single phase TiH 1.924 was formed. In addition, TiFe 2 could also be hydrided by ball milling in hydrogen, which was ascribed to decomposition to form TiFeH x , TiH 1.924, and Fe. Based on the hydrogenation properties of Ti, TiFe, and TiFe 2 during dynamic ball milling and the thermal stability of the milled powders, it is proposed that the reactions in the milling of TiFe in hydrogen involve four steps: (1) fresh surfaces created by collision with the balls; (2) absorption of hydrogen by the powder; (3) oversaturation of hydrogen in the powder; (4) decomposition of TiFeH x to TiH 1.924 and Fe.