T. I. Bratanich

Reversible Hydriding of LaNi5 − xAlx ― Pd Composites in the Presence of Carbon Monoxide

Carbon monoxide is one of the most dangerous impurities in gas mixtures involved in the hydriding of intermetallic compounds, and up to the present time the concentration limit 0.03 vol.% CO has not been surmounted. The objective of the present work was to investigate the possibility of reversibly hydriding LaNi5 − xAlx ― Pd composites in gas mixtures containing up to 5 vol.% CO. The experimental specimens were mixtures of palladium black and LaNi5, LaNi4.7Al0.3, LaNi4.5Al0.5, LaNi4.2Al0.8, and LaNi4Al powders cold pressed at 300 MPa. The intermetallics were preliminarily dispersed by hydriding and mechanical grinding. The concentration of palladium black in the powder mixtures was varied from 0 to 1.5 mass%. It was shown that it is possible to reversibly hydride LaNi5 − xAlx ― Pd composites in mixtures of hydrogen and carbon monoxide containing up to 5 vol.% CO at the temperatures 423 and 473 K. It was established that alloying LaNi5 with aluminum in amounts which raised the stoichiometric concentration above 0.5 stabilized the absorption properties of LaNi5 − xAlx ― Pd in the presence of CO. The composition LaNi4Al was optimal. Palladium additions to LaNi5 − xAlx ― Pd composites also increased the stability of hydrogen absorption by the intermetallic. It is noted that the effect of palladium was more positive than that of aluminum.

Phase Transformations in Ti3Sn and Ti2Sn Intermetallics During Hydrogenation

The sequence of phase transformations in Ti3Sn and Ti2Sn intermetallics during their interaction with hydrogen is studied. The mechanism whereby Ti3Sn hydride phases form is clarified. It is shown that Ti3Sn reacts with hydrogen at 373–1173 K through hydrogen ordering of the initial intermetallic structure, subsequent amorphization, and restructuring during the formation of hydride phases in the following sequence: hcp Ti3Sn → diamond Ti3SnH0.8 → hcp Ti3SnH0.8–0.9 → fcc Ti3SnH0.9–1.0 → bcc Ti3SnH1+x. A new hydride phase, Ti3SnH1+x (bcc, a = 0.538 nm), with high hydrogen capacity compared to the known fcc Ti3SnH hydride, which decomposes when heated to 1073 K, has been found. Destructive hydrogenation of Ti3Sn at 298–1173 K and hydrogen pressures of 1.0–6.0 MPa is not revealed. It is found that intermetallic Ti2Sn reacts with hydrogen through destructive hydrogenation to form a solution of hydrogen in β-titanium, hydride of a face-centered tetragonal solid solution of tin in titanium, and intermetallic Ti5Sn3.

Structural and phase mechanism and rate of interaction between TiCu, Ti3Cu4, and Ti2Cu3 intermetallics and hydrogen. II. Destructive hydrogenation of intermetallics

The structural and phase mechanism and the rate of TiCu, Ti3Cu4, and Ti2Cu3 destructive hydrogenation (DH) are studied at 773 K under a hydrogen pressure of 1.0 MPa. The mechanism of destructive hydrogenation of the intermetallics consists in the formation of a hydrogen solid solution, selective hydrogenation of titanium, and subsequent formation of intermediate intermetallics and copper. The destructive hydrogenation products are nondestructive TiH1.9–Cu matrix composites. The rate of TiCu, Ti3Cu4, and Ti2Cu3 destructive hydrogenation is limited by the rates of hydrogen dissociation on the intermetallic surface and the diffusion of titanium hydride. The products of TiCu, Ti3Cu4, and Ti2Cu3 destructive hydrogenation are recombined in vacuum and hydrogen atmosphere.

Structural and phase transformations and rate of Ti2Co and TiCo interaction with hydrogen and synthesis of nondestructive nanostructured titanium hydride composites

The paper examines the sequence of structural and phase transformations and the rate of Ti2Co and TiCo interaction with hydrogen. Destructive hydrogenation of Ti2Co is used to produce nondestructive nanostructured titanium hydride composites. Thermodynamic analysis has shown that Ti2Co and TiCo destructive hydrogenation is thermodynamically favored in the temperature range 298–973 K. In the temperature range 773–973 K, Ti2Co interacts with hydrogen by destructive hydrogenation reaction, in which hydrogen is dissolved in the intermetallic compound, titanium is selectively hydrogenated to cubic TiH1.9, and titanium-depleted TiCo and TiCo2 intermetallics are successively formed in accordance with the Ti–Co phase diagram. The rate of Ti2Co destructive hydrogenation is proportional to temperature, hydrogen pressure, and surface area of the starting samples. Compound TiCo is hydrogenated to form a solution of hydrogen in Ti1+yCo, intermetallic TiCo2, and a solution of hydrogen in β-titanium. Nondestructive composites with nanostructured components are synthesized by Ti2Co destructive hydrogenation.

Reaction of Powder Systems LaNi5 _ xAlx ― Pd with Hydrogen in the Presence of Carbon Dioxide

The possibility of reversible hydrogenation of LaNi5 _ xAlx ― Pd powder systems from mixtures of hydrogen and carbon dioxide containing up to 90 vol.% CO2 in the temperature range 293-423 K is demonstrated. It is established that alloying LaNi5 with aluminum increases the stability of its adsorption capacity in the presence of CO2 and that this is greater, the higher the aluminum content in the material. The most stable composition is LaNi4Al. Dosing of palladium powder in the composite LaNi5 _ xAlx ― Pd with a CO2 content in the gas mixture of more than 50 vol.% promotes an increase in the level of hydrogen capacity for the material and its hydrogenation rate.