Weak Bond Energy Research Articles

The effect of indium additive on the structural relaxation of Se–Sb–Sn semiconducting glasses

Differential scanning calorimetry (DSC) has been used to study the kinetics of structural relaxation in the glass transition region of Se80Sb12Sn8−yIny (y=0, 0.5, and 1) chalcogenide glasses, which were previously annealed at 394K below the glass transition temperature. Based on the Kovacs–Aklonis–Hutchinson–Ramos model, the dependence of the endothermic peak temperature (Tp) on heating rate has been used to evaluate the relaxation parameter. From the knowledge of this parameter the structural relaxation activation energy (Δh) has been obtained. The shift in Tp with heating rate and annealing time (ta) has been used to calculate the structural parameter, which controls the contribution of temperature and structure to the relaxation time. Results reveal that Δh decreases with In content due to the replacement of some SnSe4/2 structural units of strong bond energy by Se3In2 of weak bond energy. This reduces the cross-linking energy as well as the overall mean bond energy of the studied glasses as predicted by the chemical bond approach. The values of Δh were used to estimate the fragility index which is found to be in the range 29.7–31.7 indicating that the glasses under investigation were obtained from strong glass-forming liquids. The excess enthalpy (δH) has also been calculated, for different annealing times ta, from the knowledge of the excess specific heat. The values of δH were plotted as a function of ln(ta) and exhibit a linear behavior which indicates that the studied glasses were not completely relaxed.

Large electron correlation effect leading to Be─Be bond

The bonding of the beryllium diatomic molecule (Be2) in the ground state is exclusively made from the electron correlation effect. Unlike the ordinary van der Waals bond, where the electron correlation of the dispersion type makes weak bond energy (De) at large bond distance (Re), the BeBe bond is surprisingly strong with De = 830 cm−1 and Re = 245 pm. This paper presents in an analytical way the different electron correlation effects with the corresponding spectroscopic data.

Influence of Micro-Addition Chromium on the Valence Electron Structure and Toughness of Fe<sub>2</sub>B Phase

Fe2B is a kind of typical intermetallic compound, which has good corrosion resistance in molten zinc. However, the fatal intrinsic brittleness limits its further application in the Hot-Dip Galvanizing Industry. Therefore, it is worthwhile to improve the toughness of Fe2B phase. In this study, the fracture toughness property of Fe2B phase with and without micro-addition chromium is investigated. In comparison with pure Fe2B phase, the intrinsic brittleness of Fe2B phase with chromium is lower. In addition, the valence electron structure of Fe2B containing various chromium content is calculated by the method of bond length difference (BLD). The results show that, in the (Fe1-x Crx)2B phase, the number of covalent electron pairs and the weaker bond energy are increased by the substituting atom-Cr. The calculated results are in good agreement with experimental observations.

Partial atomic volume and partial molar enthalpy of formation of the 3d metals in the palladium-based solid solutions

The composition dependence of the average atomic volume, as well as of the enthalpy of formation, was investigated for the palladium-containing binary systems with the 3d metals. The partial atomic volume and the partial molar enthalpy of formation of the 3d metals were determined for the palladium-based solid solutions (Pearson symbol cF4, space group $$Fm\bar 3m$$ , Cu type). The 3d early transition metals (scandium, titanium, and vanadium) as well as the 3d104s2 … 3d104s24p metals (zinc and gallium) show (1) the partial atomic volume for the palladium-based solid solutions smaller than is their atomic volume in the nonbonded state and (2) significantly large (negative) values of the partial molar enthalpy of formation indicating a strong bond energy between atoms of palladium and those of the 3d early transition metals (as well as a strong bond energy between atoms of palladium and zinc or gallium atoms). The 3d late transition metals (and chromium) show (1) the partial atomic volume for the palladium-based solid solutions larger than is their atomic volume in the nonbonded state and (2) low (negative) values of the partial molar enthalpy of formation indicating weak bond energy between atoms of palladium and those of the 3d late transition metals.

Hydrogen insertion in metals: the mechanism and effect of recombination of ad-atoms

The model for hydrogen evolution reaction via a Volmer–Tafel mechanism has been considered, in which a recombination stage was represented as a set of successive and contemporary reactions. The solution of the respective kinetic equation has been obtained for the steady-state regime, which enables us to analyze the balance of the surface processes affecting the metal hydrogenation. It is demonstrated that the diffusing hydrogen flux into the metal bulk is weaker in the case of surfaces with greater concentration of adsorption centres and weaker bond energy between the active centres and hydrogen atoms.

Mechanical properties of Fe-amorphous wires after hydrogen-charging and discharging

Tensile tests of Fe 77.5Si 15B 7.5 metallic glasses electrolytically charged with hydrogen are presented. The results show that pronounced irreversible changes in plastic behavior are produced which leads us to conclude the existence of at least two different hydrogen-trapping sites in the metallic glass with weak and strong bond energy. The deeper trapping site is associated with the same defects that are responsible for the plastic behavior of the metallic glass.

The chemical bonding in the lowest 5Σ −u and 1Σ +g states of Sc 2

The lowest 5Σ − u and 1Σ + g states of Sc 2 are calculated using a non-empirical HF Pseudopotential and a multi-reference single-and-double CI. The weak bond energy relative to the ground-state dissociation of the former state and the short equilibrium internuclear distance of the latter state are analyzed, and their bonding natures are explained.

Halothane Hepatotoxicity and the Reduced Derivative, 1,1,1-Trifluoro-2-chloroethane

Halothane (1,1,1-trifluoro-2-bromo-2-chloroethane) is a safe, clinically useful inhalation anesthetic. Rare, unpredictable cases of liver necrosis have been reported following its use. Although the mechanism of this reaction in man is unknown the most plausible is biotransformation to reactive intermediates compounds. The oxidative metabolism of halothane appears to be benign. There is early evidence that reductive (nonoxygen dependent) may be harmful. Since the bromine atom of halothane appears to possess weak bond energy, the reduced, debrominated derivative of halothane, 1,1,1-trifluoro-2-chloroethane, was synthesized and tested for hepatotoxicity in the rat. The derivative is unstable and thus was prepared anaerobically and trapped in propylene glycol solvent. Injection of small amounts of this compound into the portal vein of rats produces extensive liver necrosis. It is postulated that biotransformation of halothane via a reductive pathway could produce this reactive intermediate metabolite.

Halothane hepatotoxicity and the reduced derivative, 1,1,1-trifluoro-2-chloroethane.

Halothane (1,1,1-trifluoro-2-bromo-2-chloroethane) is a safe, clinically useful inhalation anesthetic. Rare, unpredictable cases of liver necrosis have been reported following its use. Although the mechanism of this reaction in man is unknown the most plausible is biotransformation to reactive intermediates compounds. The oxidative metabolism of halothane appears to be benign. There is early evidence that reductive (nonoxygen dependent) may be harmful. Since the bromine atom of halothane appears to possess weak bond energy, the reduced, debrominated derivative of halothane, 1,1,1-trifluoro-2-chloroethane, was synthesized and tested for hepatotoxicity in the rat. The derivative is unstable and thus was prepared anaerobically and trapped in propylene glycol solvent. Injection of small amounts of this compound into the portal vein of rats produces extensive liver necrosis. It is postulated that biotransformation of halothane via a reductive pathway could produce this reactive intermediate metabolite.

Comparison of the activation energies of the processes of thermal degradation and mechanical fracture of polymethyl methacrylate

On the basis of a comparison of the activation energies of the processes of thermal degradation and mechanical fracture of PMM with various additives it is concluded that in the presence of a "pole shift effect" it is more correct to calculate the activation energy U2 of the mechanical fracture process on the assumption that τ0 = const and γ=f(σ, T). The energy U02 is then correlated with the weak-bond rupture energy. In the general case, the activation energy U01, calculated on the assumption that τ0=f(σ, T) ≠ const, i. e., from the slopes of the lg τ -1/T graphs, cannot be identified with the interatomic-bond rupture energy.

Theoretical Considerations on the Possibility of Enhancing the Effect of Temperature upon the Melt Viscosity of Linear Polymers by the Incorporation of Weak Bonds in the Chains. I. Thermodynamic Arguments

Abstract A basic limitation in the processing of thermoplastics lies in the high viscosity of their melts. Since high viscosity is largely a consequence of high average molecular weight, this problem would be solved if a polymer could be provided in the form of polymer blocks which are essentially independent at elevated temperatures and which bond together reversibly at ambient temperatures. The theoretical possibility of achieving such a system is considered from the point of view of thermodynamic arguments as applied to an idealized system of monodisperse polymer blocks linearly connected by weak chemical bonds. Average molecular weights are expressed in terms of a molar Gibbs function contribution associated with a weak bond in the polymer. Assuming a requirement for substantial decomposition at 500°K, arguments are presented for an entropy contribution of ca. 200 J °K−1 mole−1 for such bonds, and on this basis an optimum weak bond energy of 60 ± 20 kJ mole−1 is indicated. Possible block terminations ...