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TiH2 is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ti2+ is bonded in a body-centered cubic geometry to eight equivalent H1- atoms. All Ti–H bond lengths are 1.92 Å. H1- is bonded to four equivalent Ti2+ atoms to form a mixture of corner and edge-sharing HTi4 tetrahedra.
TiH2 is Fluorite structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ti2+ is bonded in a body-centered cubic geometry to eight equivalent H1- atoms. All Ti–H bond lengths are 1.92 Å. H1- is bonded to four equivalent Ti2+ atoms to form a mixture of corner and edge-sharing HTi4 tetrahedra.
TiH2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Ti2+ is bonded in a 9-coordinate geometry to nine H1- atoms. There are a spread of Ti–H bond distances ranging from 1.90–2.10 Å. There are two inequivalent H1- sites. In the first H1- site, H1- is bonded to four equivalent Ti2+ atoms to form HTi4 tetrahedra that share corners with twelve equivalent HTi5 square pyramids, corners with four equivalent HTi4 tetrahedra, edges with four equivalent HTi5 square pyramids, and edges with four equivalent HTi4 tetrahedra. In the second H1- site, H1- is bonded to five equivalent Ti2+ atoms to form distorted HTi5 square pyramids that share corners with four equivalent HTi5 square pyramids, corners with twelve equivalent HTi4 tetrahedra, edges with eight equivalent HTi5 square pyramids, and edges with four equivalent HTi4 tetrahedra.
Ti2ZrH4 is Spinel structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Zr is bonded to four equivalent H atoms to form ZrH4 tetrahedra that share corners with twelve equivalent TiH6 octahedra. The corner-sharing octahedral tilt angles are 62°. All Zr–H bond lengths are 2.04 Å. Ti is bonded to six equivalent H atoms to form TiH6 octahedra that share corners with six equivalent ZrH4 tetrahedra and edges with six equivalent TiH6 octahedra. All Ti–H bond lengths are 1.89 Å. H is bonded to one Zr and three equivalent Ti atoms to form a mixture of edge and corner-sharing HZrTi3 tetrahedra.
The electrochemical nitrate reduction reaction (NO3RR) on titanium introduces significant surface reconstruction and forms titanium hydride (TiH x , 0 < x ≤ 2). With ex situ grazing-incidence X-ray diffraction (GIXRD) and X-ray absorption spectroscopy (XAS), we demonstrated near-surface TiH2 enrichment with increasing NO3RR applied potential and duration. This quantitative relationship facilitated electrochemical treatment of Ti to form TiH 2 /Ti electrodes for use in NO3RR, thereby decoupling hydride formation from NO 3 RR performance. A wide range of NO 3 RR activity and selectivity on TiH2/Ti electrodes between -0.4 and -1.0 VRHE was observed and analyzed with density functional theory (DFT) calculations on TiH 2 (111). Finally, this work underscores the importance of relating NO 3 RR performance with near-surface electrode structure to advance catalyst design and operation.
Commercially pure titanium and heats of Armco ingot iron and steels containing from 0.008-1.23 w/oC were annealed or normalized and machined into hollow cylinders. Coefficients of diffusion for alpha-Ti and alpha-Fe were determined by the lag-time technique. Steady state permeation experiments yield first power pressure dependence for alpha-Ti and Sievert's law square root dependence for Armco iron and carbon steels. As in the case of diffusion, permeation data confirm that alpha-titanium is subject to at least partial phase boundary reaction control while the steels are purely diffusion controlled. The permeation rate in steels also decreases as the carbon content increases. As a consequence of Sievert's law, the computed hydrogen solubility decreases as the carbon content increases. This decreases in explained in terms of hydrogen trapping at carbide interfaces. Oxidizing and nitriding the surfaces of alpha-titanium membranes result in a decrease in the permeation rate for such treatment on the gas inlet surfaces but resulted in a slight increase in the rate for such treatment on the gas outlet surfaces. This is explained in terms of a discontinuous TiH2 layer.
Different hydrides are investigated to find a system with a sufficiently high storage density (at least 3%). The formation of hydrides with light alloys is examined. Reaction kinetics for hydride formation were defined and applied to the systems Mg-Al-H, Mg-Al-Cu-H, Ti-Al-H, Ti-Al-Cu-H, and Ti-Al-Ni-H. Results indicate that the addition of Al destabilizes MgH2 and TiH2 hydrides while having only a limited effect on the storage density.
The recovery of hydrogen from such metal hydrides as LiH, MgH2, TiH2, CaH2 and FeTiH compounds is studied, with the aim of evaluating the viability of the technique for the storage of hydrogen fuel. The pressure-temperature dependence of the reactions, enthalpies of formation, the kinetics of the hydrogen absorption and desorption, and the mechanical and chemical stability of the metal hydrides are taken into account in the evaluation. Economic aspects are considered. Development of portable metal hydride hydrogen storage reservoirs is also mentioned.
The Ti-24Al-11Nb (Ti-24-11) alloy heat treated to the fine basketweave microstructure was shown previously to be hydrogen tolerant. In order to assess its limit of hydrogen tolerance, the tensile, creep, fracture toughness, and sustained load crack growth behaviors of this alloy were studied as a function of hydrogen content. All test specimens were thermally charged with internal hydrogen and tested at 25 and 600 C. Coupon specimens were used for developing the hydrogen charging procedures and for studying compatibility of the alloy with high temperature, high pressure gaseous hydrogen. The mechanical test results indicated that the fine basketweave microstructure was tolerant to hydride embrittlement for hydrogen contents up to approximately 1500 wt. ppm, providing that the hydride formed was of the TiH2 type. On the other hand, hydrogen charging experiments indicated that the Ti-24-11 alloy was severely cracked and pulverized under zero load when the hydrogen content exceeded 3000 wt. ppm. X-ray diffraction results revealed that the dichotomous behaviors might be due to the formation of TiH(1.924) type hydrides at higher hydrogen contents. Thus, hydrogen embrittlement in the Ti-24-11 alloy with the fine basketweave microstructure depends on hydrogen content and the nature of the hydrides formed.
A method (500) for producing a titanium product is disclosed. The method (500) can include obtaining TiO2-slag (501) and reducing impurities in the TiO2-slag (502) to form purified TiO2 (503). The method (500) can also include reducing the purified TiO2 using a metallic reducing agent (504) to form a hydrogenated titanium product comprising TiH2 (505). The hydrogenated titanium product can be dehydrogenated (506) to form a titanium product (508). The titanium product can also be optionally deoxygenated (507) to reduce oxygen content.