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The reaction mechanisms of C3H8 dehydrogenation and subsequent metathesis on a TiH2 surface were investigated using an automated reaction path search method. The predicted pathway suggests that dehydrogenation could occur at the H vacancies present on the TiH2 surface. The propylidene species formed by the initial dehydrogenation reaction are crucial intermediates in butane formation; this compound is in turn required by the subsequent metathesis reaction on the surface of the metal hydrides. [ABSTRACT FROM AUTHOR]

The formation of titanium hydrides is closely related to the hydrogen embrittlement in titanium and its alloy. In this work, a comprehensive study on the stable and metastable structures of TiH x (x=0.5, 1, 1.5 and 2) has been performed by means of first-principles calculations in combination with the evolutionary algorithm. The structural features, dynamical stability and elastic properties of these searched titanium hydrides have been systematically investigated. The influence of temperature on the structure stability and phase transition of the Ti 2 H, TiH, Ti 2 H 3 and TiH 2 phases is considered using the quasi-harmonic approximation theory. Our calculations predict that Ti 2 H, Ti 2 H 3 and TiH 2 undergo temperature-driven phase transitions. The reason that the theoretical calculation overestimates the critical temperature of the tetragonal to cubic phase transition in TiH 2 within the quasi-harmonic approximations approach is also explored and discussed. The thermodynamic stability of these TiH x (x=0.5, 1, 1.5 and 2) structures is further analyzed over the temperature range of 0–1100 K. TiH 2 is the only stable structure in the Ti–H system and Ti 2 H, TiH, and Ti 2 H 3 are thermodynamically metastable within 900 K. [Display omitted] [ABSTRACT FROM AUTHOR]

Multifunctional materials based on a combination of permanent and degradable metals open new perspectives for medical implants combining osseoconductivity and drug-delivery functions which can significantly decrease the number of implants’ revision. In this work, hybrid magnesium-titanium materials were produced via sintering, and the properties of the permanent titanium component before and after the degradation of the temporary magnesium part were evaluated. The changes of chemical composition and mechanical parameters were determined. Loading of hydrogen into the titanium part at room temperature was observed, which deteriorated the mechanical characteristics but could also simultaneously improve the biocompatibility of the permanent titanium implant. The control of degradation of the magnesium part and the modification of the titanium part are required for the development of partly degradable hybrid implants.

The behavior of hydrogen in metals and their alloys is of great interest, since hydrogen-metal systems are used in practice for absorption of nuclear radiation, in neutron sources, and for hydrogen storage. This study is focused on simulation of the behavior of hydrogen in titanium hydrides at ultrahigh concentrations of H in TiH2 + x. Numerical methods of continuum mechanics are used. The structure of the hydrogen sublattice of titanium hydride is taken into account in the model of diffusion and thermal desorption of H. This makes it possible to model the thermal desorption of hydrogen under irradiation with a beam of hydrogen ions. [ABSTRACT FROM AUTHOR]

In this work we have studied transgranular cleavage and the fracture toughness of titanium hydrides by means of quantum mechanical calculations based on density functional theory. The calculations show that the surface energy decreases and the unstable stacking fault energy increases with increasing hydrogen content. This is consistent with experimental findings of brittle behaviour of titanium hydrides at low temperatures. Based on Griffith-Irwin theory we estimate the fracture toughness of the hydrides to be of the order of 1 MPa⋅m 1/2 , which concurs well with experimental data. To investigate the cleavage energetics, we analyse the decohesion at various crystallographic planes and determine the traction-separation laws based on the Rose's extended universal binding energy relation. The calculations predict that the peak stresses do not depend on the hydrogen content of the phases, but it is rather dependent on the crystallographic cleavage direction. However, it is found that the work of fracture decreases with increasing hydrogen content, which is an indication of hydrogen induced bond weakening in the material. [ABSTRACT FROM AUTHOR]