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.
Short heat waves (SHW), defined as periods of several consecutive days with high temperatures above the developmental optimum, will become more frequent due to climate change. The impact of SHW on ...yield and yield-related parameters has received considerable interest, but their effects on grain quality remain poorly understood. We employed a simulation approach to investigate the impact of SHW on durum wheat quality over a 7 day period, starting 1 week after anthesis. During the SHW treatment, carried out using portable polyethylene tents, the temperature in the treated plots increased by 10-15 °C during daily hours. The SHW treatment reduced the number of grains per spike, thousand kernel weight, and total carotenoid content in grains in stressed plants in comparison to control plants. However, no differences in the protein content or percentage of vitreous grains were observed. The behavior of individual carotenoids in response to SHW appears to differ, suggesting a differential change in the balance between β,ε- and β,β-branches of the carotenoid biosynthetic pathway as a consequence of SHW-induced stress. The present study highlights the importance of developing efficient breeding strategies for reduced sensitivities to heat stress. Such strategies should not only prioritize yield but also encompass grain quality.Short heat waves (SHW), defined as periods of several consecutive days with high temperatures above the developmental optimum, will become more frequent due to climate change. The impact of SHW on yield and yield-related parameters has received considerable interest, but their effects on grain quality remain poorly understood. We employed a simulation approach to investigate the impact of SHW on durum wheat quality over a 7 day period, starting 1 week after anthesis. During the SHW treatment, carried out using portable polyethylene tents, the temperature in the treated plots increased by 10-15 °C during daily hours. The SHW treatment reduced the number of grains per spike, thousand kernel weight, and total carotenoid content in grains in stressed plants in comparison to control plants. However, no differences in the protein content or percentage of vitreous grains were observed. The behavior of individual carotenoids in response to SHW appears to differ, suggesting a differential change in the balance between β,ε- and β,β-branches of the carotenoid biosynthetic pathway as a consequence of SHW-induced stress. The present study highlights the importance of developing efficient breeding strategies for reduced sensitivities to heat stress. Such strategies should not only prioritize yield but also encompass grain quality.
