Papers by Keyword: Formation Enthalpy

Abstract: A wide range of intermetallic compounds of the Al-Ti, Al-Ni, Al-Zr, Al-Cr, Al-Fe, Al-V systems has been examined. The enthalpy of formation of intermetallic compounds in a wide temperature range has been calculated. The obtained values are attributed to one mole of the chemical compound. The dependences of the obtained values on the stoichiometric composition of chemical compounds with regard to their position on the state diagram are established. A comparative assessment of the stability of intermetallic compounds for each system has been conducted. A method of approximate calculation of the enthalpy of intermetallic compounds has been proposed.

Abstract: First-principles calculations were conducted to investigate the effects of Zn on the structure of β″ phase. The effects of Cu, which was often added in the alloy, were also taken into consideration. Firstly, single Zn or Cu atom was doped on different sites of the β″ phase. Then the formation enthalpies and lattice constants of doped β″ phases were calculated. The results showed that it was more energetically favorable for single Zn or Cu atom to occupy Si3/Al sites than other sites. Furthermore, different quantities of Zn or Cu atoms were doped on Si3/Al sites. With the amounts of doping atoms increasing, the formation enthalpies of β″ phases doped by Zn were lower than which doped by Cu, indicating that it was more preferential for Zn to enter the β″ phase when Zn content was higher than Cu. Additionally, the doping of Zn could reduce the formation enthalpies of the β″ phase, which promoted the formation of the β″ phases. As a result, the aging hardening response of the alloy was improved. High angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) characterization was also conducted on a peak-aging Zn added Al-Mg-Si-Cu alloy. The HAADF-STEM image of β″ phase showed that the occupancies of Zn atoms were just on the Si3/Al sites and substituted all the Al atoms, which was consistent with the results of first-principles calculations.

Abstract: Inertial Confinement Fusion (ICF) is an effective way to achieve nuclear fusion. In ICF, boron carbide ceramics are a crucial material to prepare targets due to its high neutron capture section, high hardness, and thermal stability. A common way to prepare boron carbide is the precursor transformation method, which can overcome the difficulty in the shaping of ceramics. Decaborane and olefins are reaction materials to prepare the precursor. However, the mechanism of the reaction is not clear now, and few studies on computational chemistry have been published in this area. In this research, the semi-empirical method of quantum mechanics and Molecular Dynamics in Hyperchem8.0 were used to optimize molecules in geometry. Formation enthalpy, bond energy, bond length and angle were calculated to explain experimental patterns. The optimized data is consistent with some typical phenomena in hydroboration and ring-opening metathesis polymerization. It demonstrates that those computational methods in Hyperchem8.0 can be applied to interpret and predict relevant reactions. In addition, this explanation provides a theoretical foundation for future synthesis on polyborane precursor.

Abstract: The hydrogen storage properties of Li₄BN₃H₁₀ doped by Cl anion are investigated by using first-principles method based on density functional theory. According to the calculated results of formation enthalpy and substitution enthalpy, Cl^- doping may result in the substitution of H by Cl^- in the hydride lattice and accordingly, a favorable thermodynamics modification. The electronic structure analysis indicates that the main peak of H-1s moves close to Fermi level when substituting H^- by Cl^-. The stability of hydrogen in the doped hydride is lowered compared with that in the hydride without doping, which improves the hydrogen desorption properties of the hydride.

Abstract: The elastic constants of FeP with orthorhombic structure were calculated by using the density-functional theory method. The formation enthalpy, electronic density of states, bulk modulus, and lattice parameters of orthorhombic FeP were also calculated. All of the results are in good agreement with the experimental data and theoretical results available. The results indicate that orthorhombic FeP intermetallic compound is brittleness.

Abstract: A method to estimate the thermodynamic properties of Multi- component white gold alloys from those of constitutive binary alloys was proposed. The Miedema's theory and Chou model. were used to calculate the formation enthalpies of Au–Cu–Ag-Zn-RE alloys. The agreement between the calculation and experiment is reasonable. Formation enthalpies of Au–Cu–Ni-Zn-RE and relative stability of their intermetallic compounds were predicted with present method.

Abstract: An elabrate study on the structrural and mechanical properties of the five-element FeNiCrCuCo high-entropy alloys is carried out by first-principles calculation within the density-functional theory. The combination application of plane-wave pseudopotentials and alchemical pseudoatom methods is realized to imitate the random elemental lattice occupation in the alloys. The dependence of composition variation to the crystallographic and thermodynamic properties of FeNiCrCuCo alloys in simple BCC and FCC lattices are investigated. The key role of chromium in strengthening the inter-atomic cohesion and stabilizing the lattice structure of HEAs is suggested.

Abstract: A method to estimate the thermodynamic properties of Multi- component white gold alloys from those of constitutive binary alloys was proposed. The Miedema's theory and Chou model. were used to calculate the formation enthalpies of Au–Cu–Ni-Zn-RE alloys. The agreement between the calculation and experiment is reasonable. Formation enthalpies of Au–Cu–Ni-Zn-RE and relative stability of their intermetallic compounds were predicted with present method.

Abstract: An analytic embedded-atom potentials was developed. It was applied to calculating mono-vacancy formation energy, divacancy binding energy, elastic constants, energy difference of different structures, the surface energy, and the phonon spectra of iron and europium. The formation enthalpies of Fe-Eu binary alloy were also calculated. The calculated physical properties are in agreement with the experiments available or other theoretical results. The formation enthalpies are in good agreement with the results obtained by Miedema’s theory.

Abstract: Mg2Sn is a well known anode material used in rechargeable lithium batteries, and a principal component of low melting tin-based alloys. In order to improve its anodic as well as anti corrosion performance, alloying of selected metals like aluminum into Mg2Sn was recommended in the literature. In this research,phase stability of a series of tin based (MgxAl1-x)2Sn alloys was studied by DFT calculations. Structural and thermodynamic properties of Al in Mg2Sn was disclosed, which may be of interest to the design of new anode materials or low melting alloys for industrial applications