Formation Of TiH Research Articles

The impact of ambient gas on the magnetic properties of Ti 40Zr 40Ni 20 powders during mechanical alloying

Ti 40Zr 40Ni 20 in the form of elemental powders was mechanically alloyed in a planetary ball-mill under argon and hydrogen atmospheres at an acceleration of 55 m s −2 for different time intervals. The samples were analyzed by X-ray diffraction (XRD), vibrating-sample magnetometry (VSM) and scanning electron microscopy (SEM), which revealed the large impact of the ambient gas, i.e. argon and hydrogen, on the magnetic properties, morphology and structure. Namely, during mechanical alloying in argon the saturation magnetization decreased due to the modification of the Ni d-states upon alloying with paramagnetic Ti and Zr, whereas in hydrogen the Ni d-states remained largely unmodified, since the formation of TiH 2 and ZrH 2 was faster than the alloying with the ferromagnetic nickel. However, after 40 h we obtained a mixture of nanocrystalline Ni and ZrH 2/TiH 2 hydrides, which in equilibrium contained 1.55 mass% of hydrogen. In the case of argon we determined welding of the Ti 40Zr 40Ni 20 amorphous particles, whereas in hydrogen such a process was suppressed by the brittle ZrH 2/TiH 2 hydrides. In addition, we revealed that the mechanical alloying of pure Ni powder for 100 h in argon does not affect its magnetic properties.

TiCl3-Enhanced NaAlH4: Impact of Excess Al and Development of the Al1-yTiy Phase during Cycling

NaAlH(4) with TiCl(3) and Al were mixed by ball-milling and cycled three times. The hydrogen storage properties were monitored during cycling, and the products were characterized by synchrotron X-ray diffraction. Because of the previously described formation of Al(1)(-)(y)Ti(y) with y approximately 0.15 during cycling that traps Al beyond the amount associated with the formation of NaCl, some Na(3)AlH(6) has no free Al to react with to form NaAlH(4). This was counteracted in the present work by adding a stoichiometric amount of Al that increases the theoretical storage capacity. Due to limitations in metal diffusion small amounts of Na(3)AlH(6) were still detected. When approximately 7 mol % more Al than the stoichiometric amount was added, the observed storage capacity increased significantly, and the Na(3)AlH(6) content was negligible after prolonged rehydrogenation. Cycled NaAlH(4) + 10 mol % TiCl(3) were desorbed to two different levels, and the diffraction patterns were compared. There is no change in unit-cell dimensions during desorption, and there is no sign of changes in the bulk composition of the Al(1)(-)(y)Ti(y) phase during a cycle. Adding pure Ti to a NaH + Al mixture by ball-milling in argon or hydrogen results in formation of TiH(2) that is stable during at least one cycle.

Electrochemical properties of amorphous and icosahedral quasicrystalline Ti 45Zr 35Ni 17Cu 3 powders

Ti 45Zr 35Ni 17Cu 3 amorphous and single icosahedral quasicrystalline powders were synthesized by mechanical alloying and subsequent annealing at 855 K. Microstructure and electrochemical properties of two alloy electrodes were characterized. When the temperature was enhanced from 303 to 343 K, the maximum discharge capacities increased from 86 to 329 mAh g −1 and 76 to 312 mAh g −1 for the amorphous and quasicrystalline alloy electrodes, respectively. Discharge capacities of two electrodes decrease distinctly with increasing cycle number. The I-phase is stable during charge/discharge cycles, and the main factors for its discharge capacity loss are the increase of the charge-transfer resistance and the pulverization of alloy particles. Besides the factors mentioned above, the formation of TiH 2 and ZrH 2 hydrides is another primary reason for the discharge capacity loss of the amorphous alloy electrode.

Formation of magnesium nanocomposite via mechanical milling

Nanocomposite Mg5wt%Al has been synthesized via mechanochemical milling of elemental Mg, Al and Ti powders with polyethylene–glycol. TiH 2 phase was formed through the reaction between Ti and polyethylene–glycol during the milling as well as the sintering processes. Formation of ultra-fine particles of a few nanometer in size was observed within the matrix grains. The formation of TiH 2 particles is hypothesized to occur through two stages. In the first stage, Ti is supersaturated in the Mg matrix during high energy milling while polyethylene–glycol decomposes to react with Mg as well as Ti which is not solid solute in the Mg matrix. In the second stage during sintering, the hydrogen and Ti released from the Mg react with each other, thus forming nanoparticles. As a result of the nanoparticles, the nanocomposite manifests improved yield strength and ductility in comparison to it counterpart.

Magnesium nanocomposite via mechanochemical milling

Nanocomposite Mg5wt%Al–10.3%Ti was synthesized via mechanochemical milling of elemental powders of Mg, Al and Ti with polyethylene–glycol. Formation of TiH 2 was observed after milling and the concentration of TiH 2 was found to further increase after sintering. The nanocomposite shows an improvement in yield strength and ductility compared to its counterpart fabricated using a conventional powder metallurgy (P/M) process. The increase in mechanical properties is associated with the ultra fine grain size and the presence of nano-dispersoids in the matrix.

Development of nanocrystalline Al–Ti alloy powders by reactive ball milling

Elemental powders of Al and Ti were mechanically alloyed in a hydrogen atmosphere to produce nanocrystalline Al–Ti alloys. A brittle hydride phase(TiH 2) was formed and well dispersed by a solid–gas reaction during initial milling. The particle size was effectively reduced by the formation of TiH 2 and the grain size in the particles became nanoscale with progression of the milling. High resolution transmission electron spectroscopy (HREM) analysis showed the presence of TiH 2 at the boundaries of Al or Al 3Ti grains. This phase is considered to not only reduce the particle size but also to impede the grain growth during the heat treatment. Decomposition of TiH 2 and subsequent formation of Al 3Ti occurred at 440∼480 °C. However, the heat treated powders maintained their nano-sized structure.

Microstructural correlations with the hydrogenation kinetics of FeTi 1+ξ alloys

The influence of β-Ti on the hydrogenation properties of FeTi 1+ξ alloys (0.1 ⩽ ξ⩽0.5) was investigated. The surface morphologies and chemical compositions before and after hydrogenation were examined. From the cracking features of the surfaces and X-ray diffraction analysis, it was concluded that the hydride of β-Ti was formed prior to hydrogenation of the FeTi matrix in these alloys. Formation of TiH 2 induced cracking into the FeTi matrix. Hydrogen was then transported through the cracks and absorbed by FeTi. Therefore, activation treatment was not required. In addition, the rate of hydrogen absorption of these alloys in the first few cycles was faster than that of FeTi 1.0. The difference in the kinetics of the first hydrogenation cycle of these alloys can be explained on the basis of the amount and distribution of the eutectic strips.

Thermochemistry of Ti + hydrocarbon bonds: translational energy dependence of the reactions of Ti + with ethane, propane, and trans-2-butene

The reactions of Ti + with ethane and propane are studied as a function of translational energy in a guided ion beam tandem mass spectrometer. By varying the conditions for forming Ti +, the effect of electronic excitation is studied. In contrast to previous results for reaction of Ti + with methane, little change in reactivity with electronic state is seen here. With ethane, TiC 2H + 2 and TiC 2H + 2 are formed in exothermic reactions. Endothermic processes observed are formation of TiH + and TiCH + n , n = 1–3. With propane, the same products as well as TiC 2H + 3, TiC 2H + 5, and TiC 3H + n , n = 2, 4, 6, are observed. Analyses of the kinetic energy dependence of these reactions are used to derive the following 298 K thermochemistry: D ⦵(Ti +  CH) = 5.27 ± 0.15 eV, D ⦵(Ti +  CH 3) = 2.33 ± 0.08 eV, D ⦵(Ti +  C 2H 2) ⩾ 3.08 eV, D ⦵(Ti +  C 2H 3) = 3.46 ± 0.25 eV, D ⦵(Ti +  C 2H 4) ⩾ 1.38 eV, D ⦵(Ti +  C 2H 5) = 2.28 ± 0.07 eV, D ⦵(Ti +  C 3H 4) = 2.85 ± 0.15 eV, and D ⦵(Ti +  C 3H 6) ⩾ 1.16 eV. The reaction of Ti + with trans-2-butene is also studied to derive thermochemistry for the dimethylitanium ion, D ⦵(H 3CTi +  CH 3) = 2.80 ± 0.26 eV.