ANALYSIS OF Nb - Ni AND V - Ni BASED MEMBRANE CHARACTERISTICS

Для получения сверхчистого водорода мембранной технологией вместо дорогостоящих сплавов Pd рассмотрены более дешёвые на основе металлов Nb и V . Накапливаемый в матрицах обычных мембран водород формирует специфические полиэдрические плотноупакованные гидридные образования особенно с повышение температур от 473 до 673 К и риском разрушения мембран. Благодаря легированию титаном этих сплавов повысились рабочие характеристики мембран: диффузия и проницаемость водорода, прочность, износоустойчивость и термостабильность. В кристаллических аналогах проблема образования гидридов также была решена повышением концентрации Ti с формированием эвтектических фаз в тройных составах сплавах, например, NbTiNi и VTiNi. С формированием в указанных составах соединений NiTi и NiTi образование гидридов блокируется даже при нагреве, благодаря устойчивым процессам водородной селективности. To obtain ultrapure hydrogen by membrane technology, instead of expensive membranes made of Pd alloys, cheaper ones based on metals (Nb - Ni) and (V - Ni) are considered. Due to alloying of these Ti alloys, the performance of the membranes increased - diffusion and permeability of hydrogen, wear resistance and thermal stability, exceeding the Pd alloys. For crystalline analogs, the problem was also solved by increasing the Ti concentration with the formation of eutectic phases in ternary alloy compositions (NbTiNi and VTiNi). Hydrogen accumulated in membrane matrices forms specific polyhedral eutectic TCP hydrides up to phase transitions, and upon cooling from 673 to 303K under conditions of thermal expansion from 473 to 673K, it increases the temperature of P-hydride formation and forms NiTi and NiTi compounds, which stabilize and protect nano- and crystalline membranes from brittle destruction.

The Crystal Structures in Hydrogen Absorption Reactions of REMgNi4-Based Alloys (RE: Rare-Earth Metals)

REMgNi4-based alloys, RE(2−x)MgxNi4 (RE: rare-earth metals; 0 < x < 2), with a AuBe5-type crystal structure, exhibit reversible hydrogen absorption and desorption reactions, which are known as hydrogen storage properties. These reactions involve formation of three hydride phases. The hydride formation pressures and hydrogen storage capacities are related to the radii of the RE(2−x)MgxNi4, which in turn are dependent on the radii and compositional ratios of the RE and Mg atoms. The crystal structures formed during hydrogen absorption reactions are the key to understanding the hydrogen storage properties of RE(2−x)MgxNi4. Therefore, in this review, we provide an overview of the crystal structures in the hydrogen absorption reactions focusing on RE(2−x)MgxNi4.

Mayenite-Based Electride C12A7e−: A Reactivity and Stability Study

Ru supported on mayenite electride, [Ca24Al28O64]4+(e−)4 a calcium aluminum oxide denoted as C12A7e−, are described in the literature as highly active catalysts for ammonia synthesis, especially under conditions of low absolute pressure. In this study, we investigated the application of recently reported plasma arc melting synthesized C12A7e− (aluminum solid reductant) as supports of Ru/C12A7e− catalysts in ammonia synthesis up to pressures of 7.6 MPa. Together with the plasma-arc-melting-based catalyst support, we investigated a similar plasma-synthesized C12A7e− (graphite solid reductant) and a vacuum-sintering-based C12A7e−. Complementary to the catalytic tests, we applied 2H solid-state NMR spectroscopy, DRUVVis-spectroscopy, thermal analysis and PXRD to study and characterize the reactivity of different plasma-synthesized and vacuum-sintered C12A7e− towards H2/D2 and H2O. The catalysts showed an immediate deactivation at pressures > 1 MPa, which can be explained by irreversible hydride formation at higher pressures, as revealed by reactivity tests of C12A7e− towards H2/D2. The direct formation of C12A7:D from C12A7e− is proven. It can be concluded that the application of Ru/C12A7e− catalysts at the industrial scale has limited prospects due to irreversible hydride formation at relevant pressures > 1 MPa. Furthermore, we report an in-depth study relating to structural changes in the material in the presence of H2O.