Hydrogen Sorption Properties of Ti$_{0,475}$Zr$_{0,3}$Mn$_{0,225}$ Eutectic Alloy Alloyed with 2 at.% and 5 at.% of Vanadium

Abstract

Sorption properties and kinetic parameters of hydrogenating and dehydrogenating processes of Ti 0.475 Zr 0.3 Mn 0.225 eutectic alloy, in which partial substitution of each of its component with 2% and 5% of vanadium is performed, are investigated by Sieverts' method. As determined, the introduction of vanadium within the specified limits results in decrease of the temperature of the start of intensive hydrogen absorption, decrease of the duration of hydrogenating process, and also in substantial increase of sorption capacity (up to 2.85% wt.). As shown, the alloys, which are subjected to the sorptiondesorption cycling, possess as much activated surface that behave themselves with regard to hydrogen similar to intermetallic compounds and can absorb hydrogen at the room temperature and the pressure of 0.23 MPa from the first seconds of the contact of the specimen with the hydrogen-containing medium with the average rate of (2-4)10 3 wt.%/s. Сівертсовою методою досліджено сорбційні властивості і кінетичні параметри процесів гідрування і дегідрування виливаного евтектичного стопу Ti 0,475 Zr 0,3 Mn 0,225 , в якому було виконано часткову заміну кожного з його компонентів на 2% і 5% Ванадію. Встановлено, що введення Ванадію в зазначених межах приводить до зниження температури початку інтенсивного вбирання Гідроґену, зменшення тривалости процесу гідрування, а також до істотного збільшення сорбційної місткости (до 2,85% мас.). Показано, що стопи, які пройшли циклування сорбція-десорбція, мають настільки активовану поверхню, що ведуть себе щодо водню неначе інтерметаліди і здатні вбирати Гідроґен за кімнатної температури і тиску у 0,23 МПа з перших секунд контакту зразка з водневим середовищем із середньою швидкістю у (2-4)10 3 мас.%/с. Методом Сивертса исследованы сорбционные свойства и кинетические параметры процессов гидрирования и дегидрирования литого эвтектического сплава Ti 45,5 Zr 30 Mn 22,5 , в котором была произведена частичная замена каждого из его компонентов на 2% и 5% ванадия. Установлено, что

Structure, Phase Composition, and Hydrogen Absorption Properties of Multiphase Alloys of Ti–Zr–Mn–V System Alloyed with Holmium

“…To determine the temperature of active hydrogenation of alloys of the Ti-Zr-Mn-V-Ho system, they were heated in a hydrogen atmosphere up to 450-550°C at a rate of 4-5°C/min and at a constant pressure of 0.6 MPa. According to the literature [20,28], the alloys without holmium in the first hydrogenation actively absorb hydrogen at 450°C; the amounts of hydrogen absorbed after isothermal exposure H/Me were ∼ 1.81 and 1.70 for the alloys Ti 47.5 Zr 30 Mn 17.5 V 5 and Ti 44.18 Zr 27.9 Mn 20.93 V 7 , respectively (Fig. 4, a, b).…”

“…Our previous studies [20,21] of multiphase alloys of the Ti-Zr-Mn-V and Ti-Zr-Mn-V-Cr systems confirmed that adding the elements with a larger atomic radius, which can form stable chemical compounds with hydrogen, usually leads to enhanced hydrogen absorption. Nevertheless, it is necessary to take into account other factors that can limit this pattern.…”

“…The coarse crystallites of Laves phase in multiphase alloys of the Ti-Zr-Mn-V system are known to promote the interaction of the material with hydrogen at room temperature [32,33]. Therefore, active hydrogenation of the alloys with holmium (Table 1) was expected, as they had much larger surface area of Laves phase crystallites (80-300 2 ) compared to the base alloys (2-8 µm 2 ) [20,28]. The alloys of the Ti-Zr-Mn-V-Ho system, as well as the base alloys [20,28], were exposed at room temperature and an absolute hydrogen pressure of 0.6 MPa for 24-48 hours; however, this did not lead to surface activation and to the expected active hydrogen absorption.…”

“…Despite the fact that holmium (Ho) has the smallest atomic radius among these RE elements (atomic radii of Ho and La are 0.179 and 0.187 nm, respectively [18]), it meets all the conditions that are needed to increase the hydrogen capacity of the alloy: its atomic radius is larger compared to other components of the Ti-Zr-Mn-V system (0.160 nm for zirconium and lower for other elements), and holmium can form with hydrogen a chemical compound НоН 3 . To clarify the effect of holmium addition, the previously studied alloys of hypoeutectic Ti 47.5 Zr 30 Mn 17.5 V 5 [20,27] and hypereutectic Ti 44.18 Zr 27.9 Mn 20.93 V 7 [28] compositions were selected. The studies were carried out by comparing the structure, phase composition and hydrogen adsorption properties of the alloys (Table 1) with those without holmium (Ti0 47.5 Zr 30 Mn 17.5 V 5 and Ti 44.18 Zr 27.9 Mn 20.93 V 7 ) as a reference which were studied in detail in [27,28].…”

“…solid solution in the Ti 47.5 Zr 30 Mn 17.5 V 5 alloy, while the Ti 44.18 Zr 27.9 Mn 20.93 V 7 alloy contained the Laves phase. The range of holmium content was chosen the same as for the multiphase alloys of the Ti-Zr-Mn-V system [20,21], i.e., 2 and 5 at.% (Table 1). Holmium replaced only manganese, and so it increased the total amount of hydride-forming constituent in the alloy (Table 1, alloys 1, 2); in order to maximize the unit cell volume, all 916V.…”