Laboratory X-ray Diffraction Complex for In Situ Investigations of Structural Phase Evolution of Materials under Gaseous Atmosphere

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Nanoscale multilayer coatings (NMCs) with different crystal structures are considered as capable of self-healing after radiation damage due to the recombination of vacancies and interstitials. This work is focused on a defect distribution study of NMCs based on Zr/Nb layers (25/25 nm and 100/100 nm) after proton irradiation. Coatings with a total thickness of 1.05 ± 0.05 µm were irradiated by 900-keV protons using a pelletron-type electrostatic accelerator with an ion current of 2 µA for durations of 60 min to 120 min. The influence of the irradiation effect was studied by X-ray diffraction analysis (XRD), glow discharge optical emission spectrometry (GD–OES), and Doppler broadening spectroscopy using a variable energy positron beam. The results obtained by these methods are compatible and indicate that defect concentration of Zr/Nb NMCs remains unchanged or slightly decreases with increasing irradiation time.

Section: Materials and Research Methodsmentioning

confidence: 99%

Effect of Proton Irradiation on the Defect Evolution of Zr/Nb Nanoscale Multilayers

Laptev

Ломыгин

Krotkevich

et al. 2020

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“…The structural and phase state was investigated by X-ray diffraction analysis (XRD) on a Shimadzu XRD-7000S diffractometer (Shimadzu, Kyoto, Japan) in Bragg-Brentano geometry with Cu K α radiation (λ = 0.154 nm) [31]. The diffraction analysis was performed at scan speed of 5.0 • /min and sampling pitch of 0.0143 • with an exposure time of 42.97 s. To obtain the structural parameters of the Zr/Nb NMC, XRD patterns were studied by Rietveld analysis, where accuracy factors were ~8 for R p and ~11 for R wp .…”

Section: Experimental Methodsmentioning

confidence: 99%

First-Principles Calculations and Experimental Study of H+-Irradiated Zr/Nb Nanoscale Multilayer System

Laptev

Svyatkin

Krotkevich

et al. 2021

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Nanoscale multilayer coating (NMC) based on Zr/Nb layers (100/100 nm) before and after H+ irradiation was investigated by combining experimental techniques with first-principles calculations. Detailed studies of structural and phase state and defect structure of Zr/Nb NMC were performed using methods of transmission electron microscopy, X-ray structural analysis, glow discharge optical emission spectrometry, and the Doppler broadening spectroscopy using variable energy positron beam. The first-principles calculations of binding energies for hydrogen in metal Zr/Nb layers was carried out by the pseudopotential method within the density functional theory framework. First-principles calculations and experimental data indicate the presence of macro- and microstrains predominantly in the zirconium layers of Zr/Nb NMC. The main feature of the studied Zr/Nb NMC is the predominant hydrogen localization in Zr layers near the interfaces. The annihilation of positrons is shown to occur mainly in the Zr layers in the vicinity of the interface.

“…The binding energy of hydrogen atoms with surrounding lattice atoms was determined by the Kissinger method [31]. Structural phase analysis was performed on a Shimadzu XRD-7000S diffractometer [32], morphology was determined using a TESCAN VEGA 3 SBU scanning electron microscope, and thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC) was performed on an STA 449 F3 Jupiter analyzer. The synthesis of MgH 2 -SWCNT composites was carried out using an AGO-2 planetary mill in an argon atmosphere.…”

Section: Methodsmentioning

confidence: 99%

The Effect of High-Energy Ball Milling Conditions on Microstructure and Hydrogen Desorption Properties of Magnesium Hydride and Single-Walled Carbon Nanotubes

Kudiiarov

Elman

Kurdyumov

2021

Magnesium hydride is considered to be one of the most promising hydrogen storage materials, although it nevertheless has some problems, such as the high value of the activation energy of hydrogen desorption. To solve this problem, some scientists have proposed adding nanocarbon materials, in particular carbon nanotubes, to magnesium hydride. Currently, a detailed understanding of the mechanisms of obtaining composites based on magnesium hydride and carbon nanotubes is lacking, as is our understanding of the effect of nanocarbon additives on the activation energy and temperature of hydrogen desorption depending on the parameters of the composite synthesis. In addition, the data obtained at various values of milling parameters are very different, and in some works the effect of carbon nanomaterials on the hydrogen properties of magnesium hydride was not confirmed at all. Thus, it is important to determine the effect of nanocarbon additives on the properties of hydrogen storage of magnesium hydride under various milling parameters. This work is devoted to the study of the effect of nanocarbon additives on magnesium hydride and the determination of the dependences of the hydrogen desorption temperature and activation energy on the synthesis parameters. Composite powders containing MgH2 with 5 wt.% single-walled carbon nanotubes (SWCNT) were prepared using a planetary ball mill. The milling was carried out at various milling speeds, namely 300, 660, and 900 rpm. Results suggested that the structure of the nanotubes is preserved with prolonged grinding of magnesium hydride and SWCNT in a ball mill for 180 min at a relatively low grinding speed of 300 rpm. The composite obtained with these parameters has the lowest temperature of hydrogen desorption and an activation energy of H2 desorption of 162 ± 1 kJ/mol H2, which is 15% lower than that of the magnesium hydride MgH2 (189 ± 1 kJ/mol H2).