Several LaNi5-based hydrogen storage alloys were studied using secondary ion mass spectrometry (SIMS) technique. Ar+ ions with the energy of 10 - 18 keV were used as primary ions. The study of the initial stages of the processes of LaNi5-based alloys interaction with hydrogen under the experimental conditions showed that on the areas of clean surface, hydrogen formed chemical compounds with the both of the main components of the alloy: nickel and lanthanum. As hydrogen accumulates on the surface and in the near-surface region, a hydrogen-containing structure is formed, which is characterized by a certain stoichiometric ratio of components. Nickel in this structure has strong chemical bonds with two hydrogen atoms, and lanthanum – with two or more hydrogen atoms. Along with such compounds, some structures with lower hydrogen content are also formed. The formed hydrogen-containing structure includes both main alloy components, La and Ni for all the studied samples, even though only lanthanum is generally accepted to be the hydride-forming element in such alloys. The SIMS studies of the chemical composition of the surface monolayers of the intermetallic alloy LaNi5, in the process of its interaction with oxygen, showed the following. As a result of the oxygen interaction with the alloy, a complex chemical structure including oxygen, lanthanum and nickel is formed on the surface and in the near-surface region of LaNi5. Oxygen in such a structure, similarly to hydrogen, forms strong chemical bonds with both components of the alloy. This is indicated by the presence in the mass spectra of a large set of oxygen-containing emissions of positive and negative secondary ions with lanthanum and nickel, as well as oxygen-containing lanthanum-nickel cluster secondary ions. The formed oxide compounds have a three-dimensional structure and occupy tens of monolayers. Oxygen poisoning of the surface of the hydride-forming alloy LaNi5 can occur regardless of whether the surface of the alloy was clean from the very beginning or it was covered with a layer of hydrogen-containing chemical compounds.
The paper describes a simple analytical model that allows the calculation of hydrogen surface coverage under the influence of several processes that can co-occur during the ion-beam bombardment/sputter analysis of a sample surface, in particular during analysis by secondary ion mass spectrometry (SIMS). The model considers processes of dissociative adsorption, desorption, absorption from the surface into the sample volume, and removal by ion bombardment. After describing the model, we provide some examples of its practical applications for interpretation of the experimental results obtained during in situ SIMS studies of hydrogen interaction with the hydrogen-storage alloys TiFe, Zr2Fe, and with nickel. In the examples, some quantitative characteristics of surface-related processes involving hydrogen, such as hydrogen sputtering rate, activation energy of hydrogen desorption and absorption, have been successfully determined using various model approaches.
The changes in chemical composition of the intermetallic alloy LaNi5 surface monolayers were studied using secondary ion mass spectrometry (SIMS) in the process of the alloy interaction with oxygen. The investigated samples were pellets made by pressing the fine-grained LaNi5 alloy. Ar+ ions having energies of 10-18 keV were used as primary ions. The primary beam current density was 9-17 μA·cm-2, which corresponds to the dynamic SIMS mode. The emission intensities of secondary ions were measured within the dynamic range of at least 6 orders of magnitude. Before the measurements, the samples were annealed in residual vacuum at a temperature of ~ 1000 K. After the annealing, the sample surface was cleaned using the primary ion beam until the mass-spectrum composition and secondary ion emission intensity stabilized completely. The gas phase composition was monitored using a gas mass spectrometer. The conducted studies showed that a complex chemical structure including oxygen, lanthanum, and nickel is formed on the surface and in the near-surface region of LaNi5 as a result of its exposure to oxygen. Oxygen forms strong chemical bonds in such a structure with both components of the alloy. This is evidenced by the presence of a large set of oxygen containing emissions of positive and negative secondary ions with lanthanum, with nickel, and oxygen containing lanthanum-nickel cluster secondary ions in mass spectra. The resulting oxide compounds have a bulk structure and occupy dozens of monolayers. In such a bulk oxide structure, the outer monolayers are characterized by the highest ratio of oxygen atom number to the number of matrix atoms. This ratio decreases along the transition from the surface to the underlying monolayers. This process occurs uniformly, without any phase transformation. The observed secondary ions are not a product of association between sputtered surface fragments and oxygen in the gas phase at the fly-off stage after sputter-ejection, but they are products of the oxide compounds being sputtered, hence they characterize the composition of surface and near-surface region.
У роботi представлено результати дослiдження поверхнi сплаву LaNi5 методом мас-спектрометрiї вторинних iонiв. Показано, що одночасний вплив водню i кисню на поверхню сплаву приводить до утворення складної поверхневої хiмiчної структури, що складається з гiдридiв, гiдроксидiв i оксидiв лантану та нiкелю. Стехiометричнi спiввiдношення у цих сполуках визначаються долями водню i кисню у газовiй сумiшi. Взаємодiя кисню з поверхнею сплаву викликає поверхневу сегрегацiю i угруповання атомiв нiкелю з утворенням великих нiкелевих кластерiв. Доки на поверхнi таких кластерiв є вiльнi вiд оксидiв i гiдроксидiв дiлянки, вони виступають каталiтично активними центрами для дисоцiативної хемосорбцiї молекул водню i, таким чином, сприяють процесам гiдрування.
Secondary ion mass spectrometry (SIMS) analysis is used to investigate the composition of surface monolayers of the hydride forming intermetallic TiFe alloy during its interaction with oxygen. Oxygen, which is chemisorbed on the surface, is shown to form strong chemical bonds with both alloy components. As a result, on the surface and in the subsurface region of the alloy, a joint oxide structure forms with a certain stoichiometric ratio between titanium, iron and oxygen. With an increasing partial pressure of oxygen in the oxide structure being formed, the ratio of the number of oxygen atoms to the number of matrix atoms increases. This process occurs uniformly without any abrupt phase transformations.
In the work a technology of tungsten films and two-layer copper-tungsten coatings deposition on stainless steel substrates was developed. The coatings were deposited by magnetron and arc sputtering of materials with condensation of them on the testing substrates. The deposition objects were probe of the ICRF antenna on fusion devices and reference samples, on which the properties of obtained coatings were studied. The possibility of tungsten coatings forming on long-length elements of functional blocs was considered.
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