Expansion under compression: The unit‐cell volume of graphite oxide pressurized in water media, continuously increases reaching a sharp maximum at ca. 1.3–1.5 GPa (see picture, squares). Expansion of ...the lattice to a maximum of about 28–30 % is because of gradual pressure‐induced water insertion into the interlayer space of graphite oxide. The effect is reversible (triangles), resulting in a unique “breathing” of the structure upon pressure variation.
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Graphite oxide (GO) immersed in an excess of methanol and ethanol media is found to undergo a phase transformation at about 0.2−0.8 GPa, with an expansion of the unit cell volume by ∼40%, due to ...pressure-induced insertion of solvent into interlayer space. The pressure at which the structural expansion occurs does not correlate with the solidification pressure of the alcohol, in contrast to the graphite oxide/water system. The expanded high-pressure phase of GO/ethanol could be quenched back to ambient pressure. Compression of graphite oxide with a 2:1 water/methanol medium revealed a complex anomaly with two steps attributed to insertion of methanol and water at different pressure points.
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High-pressure behavior of α-Mn(BH4)2 was studied up to 29.4 GPa in diamond anvil cells using powder X-ray diffraction combined with DFT calculations and Raman spectroscopy, and two new polymorphs ...were discovered. The first polymorph, δ-Mn(BH4)2, forms near 1 GPa and is isostructural to the magnesium analogue δ-Mg(BH4)2. This polymorph is stable upon decompression to ambient conditions and can also be obtained by compression of α-Mn(BH4)2 in a large-volume steel press as well as by high-energy ball milling. It shows a high volumetric density of hydrogen of 125 g H2/L at ambient conditions. δ-Mn(BH4)2 was refined in the space group I41/acd with the cell parameters a = 7.85245(6), c = 12.1456(2) Å, and V = 748.91(1) Å3 at ambient conditions; it can also be described in a stable P-4n2 superstructure. Its thermal stability was studied by in situ X-ray powder diffraction and thermal analysis coupled with mass-spectroscopy. δ-Mn(BH4)2 transforms back to α-Mn(BH4)2 upon heating in the temperature range of 67–109 °C in Ar (1 bar) or H2 (100 bar) atmosphere, and a decomposition is initiated at 130 °C with the release of hydrogen and some diborane. Mn(BH4)2 undergoes a second phase transition to δ′-Mn(BH4)2 in the pressure range of 8.6–11.8 GPa. δ′-phase is not isostructural to the second high-pressure phase of Mg(BH4)2, and its structure was determined in the √2a × c supercell compared to the δ-phase and refined in the space group Fddd with a = 9.205(17), b = 9.321(10), c = 12.638(15) Å, and V = 1084(3) Å3 at 11.8 GPa. Equations of state were determined for α- and δ-Mn(BH4)2.
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There is a significant number of decentralized energy sources in the energy system of the Tomsk region (Russia). Heat supply sources are represented by boiler houses on solid (coal, wood, chips) and ...liquid fuel (oil). Besides technical factors, such as high percentage of wear of equipment used for power supply, low efficiency of energy production, loss of heat energy in transfer, there are important economic problem in the decentralized energy producing in the Tomsk region. High cost of fuel transportation to remote settlements determines high tariffs for heat and electricity supply, which makes it necessary to provide subsidies for the population. A decision system has been developed to switch decentralized heat sources with low energy consumption to local and renewable fuels in the region. The scheme takes into account the practical use of long-term studies of local and renewable energy sources potential in the Tomsk region. Results of the work of scientists and the Administration of the Tomsk Region are presented in Geo-information system (2018). Pollutants emission into atmosphere (including greenhouse gas) are one of important indicators for energy and decision-making policy (Klemeš et al., 2017a). In this way, key objects for modernization and key types of fuel for new / modernized decentralized heat supply sources of low power are determined.
One of the most important scientific and technical tasks of the nuclear power industry is to assure the reactor equipment life and reliability under random temperature pulsations. High-intensity ...temperature pulsations appear during the process of mixing non-isothermal coolant flows. Coolant thermal pulsations cause corresponding, sometimes very significant, fluctuations in the temperature stresses of the heat-exchange surface metal, which, added to static loads, can lead to fatigue failure of equipment components.
The purpose of this work was to conduct an experimental study of the temperature and stress-strain states of a pipe sample under the influence of local stochastic thermal pulsations caused by the mixed single-phase heat coolant flows.
To solve the set problems, an experimental section was created, which made it possible to simulate the process of mixing non-isothermal coolant flows accompanied by significant temperature pulsations. The design of the experimental section allowed us to study the thermohydraulic and life characteristics of pipe samples made of austenite steel (60×5 mm). Some tools were developed for measuring the pipe sample stress-strain state and the coolant flow temperature field in the zone of mixed single-phase media with different temperatures. The measuring tools were equipped with microthermocouples and strain sensors.
As a result, we obtained experimental data on temperature pulsations, time-averaged temperature profiles of the coolant flow in the mixing zone as well as statistical and spectral-correlation characteristics of thermal pulsations. Based on the results of measuring the relative strains, the values of fatigue stresses in the mixing zone were calculated.
In addition, some devices and methods were elaborated to measure the temperature and stress-strain states of the pipe sample under the influence of local stochastic thermal pulsations. The developed experimental section provided thermal-stress loading of the metal surface at a high level of alternating stress amplitudes causing rapid damage accumulation rates. The results were included in the database to verify the method for assessing the fatigue life of structural materials for nuclear power plants as applied to austenite steel 12Cr18Ni10Ti under the influence of random thermal cyclic loads.
The pressure evolution of RbBH4 has been characterized by synchrotron powder X-ray diffraction and Raman spectroscopy up to 23 GPa. Diffraction experiments at ambient temperature reveal three phase ...transitions, at 3.0, 10.4, and 18 GPa (at 2.6, 7.8, and ∼20 GPa from Raman data), at which the space group symmetry changes in the order Fm-3m(Z=4) → P4/nmm(2) → C222(2) → I-42m(4). Crystal structures and equations of state are reported for all four phases. The three high-pressure structure types are new in the crystal chemistry of borohydrides. RbBH4 polymorphs reveal high coordination numbers (CNs) for cation and anion sites, increasing with pressure from 6 to 8, via an intermediate 4 + 4 coordination. Different arrangements of the tetrahedral BH4 group in the Rb environment define the crystal symmetries of the RbBH4 polymorphs. The structural evolution in the MBH4 series is determined by the cation’s size, as it differs drastically for M = Li (CNs = 4, 6), Na (CN = 6), and Rb. The only structure common to the whole MBH4 family is the cubic one. Its bulk modulus linearly decreases as the ionic radius of M increases, indicating that the compressibility of the material is mainly determined by the repulsive BH4···BH4 interactions.
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Current–voltage characteristics of nanostructured vanadium oxide bronze β-NaV6O15 obtained from oxalate solutions by ultrasonic spray pyrolysis (USP) under various conditions were ...studied. The conditions of USP synthesis significantly affected the particle morphology, specific surface area, defect structure and oxidizing ability of the compound.
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High-pressure behavior of alpha-Mn(BH4)(2) was studied up to 29.4 GPa in diamond anvil cells using powder Xray diffraction combined with DFT calculations and Raman spectroscopy, and two new ...polymorphs were discovered. The first polymorph, delta-Mn(BH4)(2), forms near 1 GPa and is isostructural to the magnesium analogue delta-Mg(BH4)(2). This polymorph is stable upon decompression to ambient conditions and can also be obtained by compression of alpha-Mn(BH4)(2) in a large-volume steel press as well as by high-energy ball milling. It shows a high volumetric density of hydrogen of 125 g H-2/L at ambient conditions. delta-Mn(BH4)(2) was refined in the space group I4(1)/acd with the cell parameters a = 7.85245(6), c = 12.1456(2) angstrom, and V = 748.91(1) angstrom(3) at ambient conditions; it can also be described in a stable P-4n2 superstructure. Its thermal stability was studied by in situ X-ray powder diffraction and thermal analysis coupled with mass-spectroscopy. delta-Mn(BH4)(2) transforms back to alpha-Mn(BH4)(2) upon heating in the temperature range of 67-109 degrees C in Ar (1 bar) or H-2 (100 bar) atmosphere, and a decomposition is initiated at 130 degrees C with the release of hydrogen and some diborane. Mn(BH4)(2) undergoes a second phase transition to delta'-Mn(BH4)(2) in the pressure range of 8.6-11.8 GPa. delta'-phase is not isostructural to the second high-pressure phase of Mg(BH4)(2), and its structure was determined in the root 2a X c supercell compared to the delta-phase and refined in the space group Fddd with a = 9.205(17), b = 9.321(10), c = 12.638(15) angstrom, and V = 1084(3) angstrom(3) at 11.8 GPa. Equations of state were determined for alpha- and delta-Mn(BH4)(2).
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Graphite oxide immersed in excess of basic or acidic water media was studied using synchrotron X-ray diffraction at high pressure using diamond anvil cells. The lattice spacing of graphite oxide in ...excess of NaOH solution increases by the enormous value of 85% at 1.6 GPa. In contrast, structure expansion of graphite oxide immersed in liquid water with added HCl is significantly less pronounced compared with compression in pure water. The point of media solidification correlated with a sharp decrease in graphite oxide layers separation because of partial withdrawal of water from the structure. Therefore, pressure-induced structural breathing of graphite oxide due to insertion/desertion of water into/from interlayer space is strongly enhanced in basic media and suppressed in acidic media. The magnitude of structural breathing also depends on relative amounts of graphite oxide powder and solution. Strongly diluted samples with low relative amount of graphite oxide powder in the suspension exhibited less pronounced high-pressure anomaly.
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The pressure evolution of RbBH 4 has been characterized by synchrotron powder X-ray diffraction and Raman spectroscopy up to 23 GPa. Diffraction experiments at ambient temperature reveal three phase ...transitions, at 3.0, 10.4, and 18 GPa (at 2.6, 7.8, and 20 GPa from Raman data), at which the space group symmetry changes in the order Fm-3m(Z=4) → P4/nmm(2) → C222(2) → I-42m(4). Crystal structures and equations of state are reported for all four phases. The three high-pressure structure types are new in the crystal chemistry of borohydrides. RbBH 4 polymorphs reveal high coordination numbers (CNs) for cation and anion sites, increasing with pressure from 6 to 8, via an intermediate 4 + 4 coordination. Different arrangements of the tetrahedral BH 4 group in the Rb environment define the crystal symmetries of the RbBH 4 polymorphs. The structural evolution in the MBH 4 series is determined by the cation’s size, as it differs drastically for M = Li (CNs = 4, 6), Na (CN = 6), and Rb. The only structure common to the whole MBH4 family is the cubic one. Its bulk modulus linearly decreases as the ionic radius of M increases, indicating that the compressibility of the material is mainly determined by the repulsive BH 4 ···BH 4 interactions.
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