In recent years, the popularity of metal hydrides has increased considerably for hydrogen storage and their applications in hydrogen fuel cells. Their potential applications for clean energy are ...promissory. However, the temperatures required for adsorption and desorption are extremely high, which range between 500 and 700 K, making their use impractical. To overcome these difficulties, the following work considers using three hydride alloys: magnesium-aluminum (MgAl), magnesium-nickel (MgNi), and magnesium-zinc (MgZn). The Mg concentrations were set to be between 80 and 100 wt% in order to reduce the temperatures of adsorption and desorption in contrast with the temperatures of pure magnesium. The chemisorption and repulsion energies of the hydrogen molecule on the surface (110) of the different metallic alloys were studied at 0, 200, 400, 600, and 700 K, respectively. The study was based on the density functional theory (DFT), with the module DMol
3
of the molecular simulation program Materials Studio, which was used to obtain these energy values. The results confirm that adding aluminum, nickel, or zinc into magnesium matrix increases the chemisorption and decreases the energy repulsion values on surfaces of the metallic alloys, improving the effectiveness of the hydrogen storage.
One difficult aspect to be overcome within technology of hydrogen and fuel cells is hydrogen storage in solid phase materials. Theoretical studies are indispensable support to guide the ...experimentalist in the development of synthesis or characterization of new materials. DFT (density functional theory) was used to optimize the geometry, and at same time, to obtain final enthalpy of bulk alloys of Mg1−xAlx (0 ≤ x ≤ 0.10) and later it was possible to cleave bulk alloy in the direction of the plane (110) to obtain surface effects. Finally, hydrogen molecules were added at the surface of MgAl in the direction (110) and optimized their geometry in order to obtain their final enthalpies of each one of these alloys. Values of chemisorption energy and repulsion of those alloys were obtained, as well as aluminum optimum concentration for adsorption of hydrogen. The value of binding energy for H2 molecule on magnesium surface is about 0.5 eV.
•The enthalpy of MgAl alloy as a function of composition of aluminum is calculated.•The electronic density of states as a function of composition of aluminum are obtained.•Enthalpies of bulk unit cell and supercell of Mg1−xAlx alloy are decreased when concentration of aluminum are increased.•The binding energy of H2 molecule on the Mg1−xAlx alloy is comparable with experimental results.
In this study, we present results of the electronic density of states (DOS) and bulk magnetic moment of iron (Fe), cobalt (Co) and their alloys (Fe
x
Co
1–
x
;
x
= 1.0, 0.95, …, 0.0). Density ...functional theory with the generalized gradient approximation was applied to obtain geometric and electronic properties. The methodology uses virtual crystal approximation, in conjunction with CASTEP module and the functionals PBE and PBESol of the molecular simulation program Material Studio. We optimized the geometry of the bulk (obtaining their lattice parameters), which the structure was used to determine the bulk magnetic moments. To determine the magnetic moment, we calculated the difference of the electronic DOS of the electrons with spin up and spin down. The geometric optimization and magnetic moment obtained in the present study are very similar to the experimental results, with a maximum error of 8%, which makes the present article interesting.
In this paper, we present calculations for two second-order phase transitions in (110) Fe0.5Co0.5 thin films with 11, 15, and 19 monoatomic layers. The lattice and magnetic transitions are based on ...thermodynamic equilibrium considerations of the magnetic alloy. The procedure proposed by Valenta and Sukiennicki was applied to calculate the composition x(i), the lattice order parameter t(i), and the magnetic order parameter σ(i) as a function of temperature T. We confirmed that both phase transitions, lattice and magnetic, are of the second order, in accordance with experimental results in the literature. The obtained behavior of these parameters indicates their inhomogeneity due to the boundary conditions on the surfaces of the thin film.
In this work we calculate heat capacity of alloy thin films of FeCo on the surface of the plane (110), using three parameters, the concentration x(i), the lattice long range order parameter t(i) and ...the magnetic order parameter σ(i), being i the number of layers of the thin film. The formulations reported by Hill 1 in the context of small particles and Valenta's model 2 can be applied to the film structure when we treat a thin film as a system divided into subsystems equivalent to two-dimensional parallel layers. The FeCo bulk alloy is completely homogeneous while a thin film have spatial discontinuities in their surfaces. We consider three ferromagnetic thin films formed by 11, 15 and 19 layers in the Helmholtz's free energy, which is minimized applying their first partial derivatives with respect to chemical composition, long range order parameter and magnetic order parameter. We calculate internal energy and heat capacity as a function of temperature and we verify that have two jumps as are reported in literature for the bulk; there are many results of bulk or surface effects of FeCo, but no enough results about ferromagnetic FeCo thin films and this fact does this work interesting.
•Heat capacity as a function of temperature for 11, 15 and 19 atomic layers of FeCo thin films are determined.•Curie temperature for Fe0.5Co0.5 thin films with 11, 15 and 19 are obtained.•Bulk and thin films heat capacity of Fe0.5Co0.5 have a similar behavior.•Discontinuity in heat capacity of thin films are similar to to bulk Fe0.5Co0.5.
In this paper, we present calculations for two second-order phase transitions in (110) Fe0.5Co0.5 thin films with 11, 15, and 19 monoatomic layers. The lattice and magnetic transitions are based on ...thermodynamic equilibrium considerations of the magnetic alloy. The procedure proposed by Valenta and Sukiennicki was applied to calculate the composition x(i), the lattice order parameter t(i), and the magnetic order parameter σ(i) as a function of temperature T. We confirmed that both phase transitions, lattice and magnetic, are of the second order, in accordance with experimental results in the literature. The obtained behavior of these parameters indicates their inhomogeneity due to the boundary conditions on the surfaces of the thin film.
In recent years, the popularity of metal hydrides has increased considerably for hydrogen storage and their applications in hydrogen fuel cells. Their potential applications for clean energy are ...promissory. However, the temperatures required for adsorption and desorption are extremely high, which range between 500 and 700 K, making their use impractical. To overcome these difficulties, the following work considers using three hydride alloys: magnesium-aluminum (MgAl), magnesium-nickel (MgNi), and magnesium-zinc (MgZn). The Mg concentrations were set to be between 80 and 100 wt% in order to reduce the temperatures of adsorption and desorption in contrast with the temperatures of pure magnesium. The chemisorption and repulsion energies of the hydrogen molecule on the surface (110) of the different metallic alloys were studied at 0, 200, 400, 600, and 700 K, respectively. The study was based on the density functional theory (DFT), with the module DMol3 of the molecular simulation program Materials Studio, which was used to obtain these energy values. The results confirm that adding aluminum, nickel, or zinc into magnesium matrix increases the chemisorption and decreases the energy repulsion values on surfaces of the metallic alloys, improving the effectiveness of the hydrogen storage.
Carotenoids are essential in human diet, so that the development of programs toward carotenoid enhancement has been promoted in several crops. The cereal tritordeum, the amphiploid derived from the ...cross between
Roem. et Schulz. and durum wheat has a remarkable carotenoid content in the endosperm. Besides, a high proportion of these carotenoids are esterified with fatty acids. The identification of the gene(s) responsible for xanthophyll esterification would be useful for breeding as esterified carotenoids show an increased ability to accumulate within plant cells and have a higher stability during post-harvest storage. In this work, we analyzed five genes identified as candidates for coding the xanthophyll acyltransferase (XAT) enzyme responsible for lutein esterification in
genome. All these genes were expressed during grain development in tritordeum, but only HORCH7HG021460 was highly upregulated. Sequence analysis of HORCH7HG021460 revealed a G-to-T transversion, causing a Glycine to Cysteine substitution in the protein of H290 (the only accession not producing quantifiable amounts of lutein esters, hereinafter referred as zero-ester) of
compared to the esterifying genotypes. An allele-specific marker was designed for the SNP detection in the
diversity panel. From the 93 accessions, only H290 showed the T allele and the zero-ester phenotype. Furthermore, HORCH7HG021460 is the orthologue of XAT-7D, which encodes a XAT enzyme responsible for carotenoid esterification in wheat. Thus, HORCH7HG021460 (XAT-7Hch) is a strong candidate for lutein esterification in
and tritordeum, suggesting a common mechanism of carotenoid esterification in Triticeae species. The transference of XAT-7Hch to wheat may be useful for the enhancement of lutein esters in biofortification programs.
•Esterification increases carotenoid retention during storage of durum wheat grains.•Esterification would be useful in durum wheat breeding programs.•F2-bulks contrasting for esterification give a ...better picture of carotenoid esterification potential than single lines.
Carotenoid esterification is a common mechanism for carotenoid sequestration, accumulation and storage in plants. Carotenoids are responsible for the bright yellow colour of pasta. Therefore, carotenoid retention during storage is of great importance in the durum wheat food chain.
In this work, we investigated the role of carotenoid esterification on carotenoid retention in durum wheat using two consecutive storage experiments. Firstly, we compared two landraces and two durum wheat varieties as a preliminary work. We then compared individuals derived from the BGE047535בAthoris’ cross contrasting for esterification ability.
Our results show that carotenoid esterification leads to a higher carotenoid retention during storage in durum wheat. Thus, the use of the carotenoid esterification would be useful as an extra strategy to ongoing efforts to improve carotenoid retention in the durum wheat food chain.
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