Thermodynamic properties of hydrogen at pressures up to 1 Mbar and temperatures between 100 and 1000K

Hemmes, Herman K.; Driessen, A.; Griessen, R.

doi:10.1088/0022-3719/19/19/013

Cited by 182 publications

(130 citation statements)

References 16 publications

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“…16 These conditions correspond to µ H =−0.49 eV and µ H =−0.31 eV, respectively. 42 Two different sets of experimental conditions will be analyzed. µ H =−0.49 eV corresponds to the dehydrogenation process and is therefore appropriate for analysis of defects in LiNH 2 .…”

Section: Chemical Potentialsmentioning

confidence: 99%

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

2012

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Reversible reaction involving Li amide (LiNH2) and Li imide (Li2NH) is a potential mechanism for hydrogen storage. Recent synchrotron x-ray diffraction experiments [W. I. David et al., J. Am. Chem. Soc. 129, 1594] suggest that the transformation between LiNH2 and Li2NH is a bulk reaction that occurs through non-stoichiometric processes and involves the migration of Li + and H + ions. In order to understand the atomistic mechanisms behind these processes, we carry out comprehensive first-principles studies of native point defects and defect complexes in the two compounds. We find that both LiNH2 and Li2NH are prone to Frenkel disorder on the Li sublattice. Lithium interstitials and vacancies have low formation energies and are highly mobile, and therefore play an important role in mass transport and ionic conduction. Hydrogen interstitials and vacancies, on the other hand, are responsible for forming and breaking N−H bonds, which is essential in the Li amide/imide reaction. Based on the structure, energetics, and migration of hydrogen-, lithium-, and nitrogen-related defects, we propose that LiNH2 decomposes into Li2NH and NH3 according to two competing mechanisms with different activation energies: one mechanism involves the formation of native defects in the interior of the material, the other at the surface. As a result, the prevailing mechanism and hence the effective activation energy for decomposition depend on the surface-tovolume ratio or the specific surface area, which changes with particle size during ball milling. These mechanisms also provide an explanation for the dehydrogenation of LiNH2+LiH mixtures.

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Section: Chemical Potentialsmentioning

confidence: 99%

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

2012

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“…In the pressure range of interest, the non-ideal contribution of pressure to the Gibbs energy for the gases is very small. In fact, to account for the non-ideal contribution of hydrogen gas, Hemmes et al [51] calculated the equation of state of hydrogen and other thermodynamic quantities in the range p B 100 GPa and 100 B T B 1000 K. Numerical values of Gibbs energy and other quantities given in [51] have been used in this work to extrapolate the Gibbs free energy versus temperature of hydrogen gas at 100 bar and used in the calculations for comparison with the ideal gas model. A difference in temperatures of less than 3 K (at 100 bar) has been found.…”

Section: Gas Phasementioning

confidence: 99%

Understanding the hydrogen storage behavior of promising Al–Mg–Na compositions using thermodynamic modeling

Abdessameud

Medraj

2016

Mater Renew Sustain Energy

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Thermodynamic modeling of the Al-Mg-Na-H system is performed in this work to understand the phase relationships and reaction mechanisms in this system. The Al-Na system is reassessed using the modified quasichemical model for the liquid phase. All the terminal solid solutions were remodeled using the compound energy formalism. The thermodynamic properties of the ternary systems are estimated from the models of the binary systems and the ternary compound using the CALPHAD method. The reaction pathways for the systems MgH 2 / AlH 3 , MgH 2 /NaAlH 4 , and MgH 2 /Na 3 AlH 6 are calculated and compared to the experimental data from the literature. Details about the reaction mechanisms and temperatures, the amount of the products, and their composition are revealed and discussed in this work. The calculations show that in the composites MgH 2 /NaAlH 4 and MgH 2 /Na 3 AlH 6 , the components spontaneously destabilize mutually in specific relative amounts by forming NaMgH 3 , which may play only a catalytic role on the decomposition of (MgH 2 ? Al) mixture, NaAlH 4 , or Na 3 AlH 6 . Also, Al destabilizes MgH 2 and NaMgH 3 by forming b phase and reducing the decomposition temperatures of these hydrides by more than 50°C. The constructed database is successfully used to reproduce the pressure-composition isotherms (PCIs) for Mg-10 at% Al and Mg-4 at% Al alloys at 350°C. The results provide a better understanding of the reaction mechanisms in the PCIs found in the literature concerning the number of plateau pressures and their sloping. It is shown that the first plateau pressure observed during the PCIs of Al-Mg alloys depends on Al content and is higher than that of pure Mg. This difference is due to Al solubility in hcp-Mg.

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“…There are numerous models and empirical relationships that account for the nonideal behavior of gases, however these are often complicated transcendental equations that cannot be easily manipulated analytically [1][2][3][4][5]. The Abel-Noble equation of state, on the other hand, is a single parameter relationship of the form…”

Section: Equation Of State: Gasesmentioning

confidence: 99%

“…The simplicity of this relationship is notable when compared to other equations of states for real gases, such as virial equations, which may include upwards of ten parameters, many of which are themselves functions of temperature [1][2][3]. At pressures of general engineering significance (< 200 MPa) and temperatures near ambient the Abel-Noble equation tracks the compressibility factor,…”

Section: Equation Of State: Gasesmentioning

confidence: 99%

10.2172/918137

2000

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Thermodynamic properties of hydrogen at pressures up to 1 Mbar and temperatures between 100 and 1000K

Cited by 182 publications

References 16 publications

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

Understanding the hydrogen storage behavior of promising Al–Mg–Na compositions using thermodynamic modeling

10.2172/918137

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