High-pressure solid solutions of molecular hydrogen in amorphous magnesium silicates

High-pressure solid solutions of molecular hydrogen in amorphous magnesium silicates

New amorphous solutions MgySiO2+y-XH2 with the magnesium concentration varying from y = 0 to y = 0.88 were synthesized at a hydrogen pressure of 75 kbar and a temperature of 250 °C, followed by quenching to the temperature of liquid nitrogen. The quenched samples were studied by thermal desorption,...

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Bibliographic Details
Published in:Journal of alloys and compounds Vol. 770; pp. 229 - 235
Main Authors: Efimchenko, Vadim S., Barkovskii, Nikolay V., Fedotov, Vladimir K., Meletov, Konstantin P., Simonov, Sergey V., Khasanov, Salavat S., Khryapin, Kirill I.
Format: Journal Article
Language:English
Published: Lausanne Elsevier B.V 05-01-2019
Elsevier BV
Subjects:
Amorphous materials
Depolymerization
Desorption
High-pressure
Hydrogen
Hydrogen absorbing materials
Hydrogen storage
Liquid nitrogen
Magnesium silicates
Quenching
Raman spectroscopy
Silica glass
Silicates
Silicon dioxide
Solid solutions
Spectrum analysis
Thermal stability
X ray spectra
X-ray diffraction
Amorphous materials
Hydrogen absorbing materials
Raman spectroscopy
High-pressure
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Summary:New amorphous solutions MgySiO2+y-XH2 with the magnesium concentration varying from y = 0 to y = 0.88 were synthesized at a hydrogen pressure of 75 kbar and a temperature of 250 °C, followed by quenching to the temperature of liquid nitrogen. The quenched samples were studied by thermal desorption, X-ray diffraction and Raman spectroscopy. The X-ray diffraction study showed that all hydrogenated samples preserved the amorphous state and had no crystalline inclusions. At the same time, the positions of the first sharp diffraction peak (FSDP) of the samples with y = 0.32 and 0.6 were shifted by ΔQ = 0.14 Å−1 after the hydrogenation thus signaling on changes in the amorphous network and even its small depolymerization. According to the thermal desorption analysis, the hydrogen content X of the quenched MgySiO2+y-XH2 samples nonlinearly decreased with increasing concentration y of the magnesium ions Mg2+ from X = 0.600(3) at y = 0 to X = 0.259(3) at y = 0.88. The samples with y ≥ 0.49 evolved a significant portion of the dissolved hydrogen on heating in vacuum above 0 °C therefore showing a higher thermal stability than the hydrogenated silica and silicates with low magnesium concentrations. Raman spectroscopy demonstrated that hydrogen was dissolved in all samples in the form of H2 molecules, and the width of the H2 stretching line narrowed approximately four-fold with increasing magnesium concentration. Both this effect and the changes in the H2 desorption kinetics presumably resulted from the decreasing dispersion in the size of silicate cavities in the amorphous matrix, which changes from the silica glass structure at y ≤ 0.32–0.49 to the close-packed enstatite glass structure at higher magnesium concentrations. •Amorphous silicates MgySiO2+y are loaded with hydrogen at a H2 pressure of 75 kbar and T = 250 °C.•Hydrogen is dissolved in the silicates in the form of H2 molecules.•H2 content of the obtained solid solutions MgySiO2+y-XH2 varies from X = 0.6 at y = 0 to X = 0.3 at y = 0.88.•The hydrogenated magnesium silicates remain amorphous, but undergo an irreversible densification.•The silica glass structure of the silicates changes to a much denser enstatite glass structure at y ≥ 0.49.
ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2018.08.111