Narrow Results

With a first-principles method based on density functional theory, the effect of the alloying element titanium (Ti) on the thermodynamic stability and electronic structure of hydrogen (H) in pure vanadium (V) is investigated. The interactions between H and the vacancy and the defect solution energies in a dilute V–Ti binary alloy are calculated. The results show that: (i) a single H atom prefers to reside in a tetrahedral interstitial site in dilute V–Ti binary alloy systems; (ii) H atoms tend to bond at the vacancy sites; a mono-vacancy is shown to be capable of trapping three H atoms; and (iii) the presence of Ti in pure V can increase the H trapping energy and reduce the H trapping capability of the vacancy defects. This indicates that doping with Ti to form dilute V–Ti binary alloys can inhibit the solution for H, and thus suppress the retention of H. These results provide useful insight into V-based alloys as a candidate structural material in fusion reactors.

By using the first-principles calculations, we studied the effect of carbon (C) on the behaviors of helium (He) in vanadium (V). The results show that C can effectively reduce the solubility of He in bulk V. Compared with defect-free V bulk, the C-vac complex reduces the charge density around it, which makes it act as a trapping center and promotes He nucleation. The maximum number of He atoms trapped by the C-vac complex is five. Furthermore, the interaction between He and the C-vac complex is slightly stronger than that in a C-free vacancy, which indicates that C could increase the trapping ability of vacancy to He atom. Based on the above results, we conclude that C has a certain influence on the dissolution and the trapping behaviors of He in V.

We have investigated the effect of impurity X (X = C and O) atoms on the behavior of hydrogen in vanadium, which is an ideal structural material for nuclear fusion reactors, by first-principles calculations. We found that (1) in bulk V, the interaction between an interstitial H atom and an X atom is repulsive, and the interaction with O is much stronger than that with C. (2) The X–vacancy (vac) cluster can act as a center for capturing H in V. The C-vac cluster can trap as many as two H atoms, while the O–vac cluster can capture up to four H atoms. (3) C and O impurities can effectively decrease the trapping energy of a single H atom in a vacancy. The H-trapping energies in the C–vac and O–vac complexes are 0.88 eV and 0.46 eV, respectively, both of which are lower than those in the X-free vacancy. (4) Both H–X and X-metal interactions affect the H solubility in V. The above results provide important information for application of vanadium as a structural material for nuclear fusion tokamaks.

The electronic and magnetic structures of a hydrogenated and hydrogen free superlattice of three iron monolayers and nine vanadium monolayers are studied using the first principle full-potential augmented-plane-wave method as implemented in WIEN2k package. The average and the local magnetic moments of the system are studied versus the hydrogen positions at the octahedral sites within the superlattice and also versus the filling of the vanadium octahedral location by hydrogen atoms. The local Fe magnetic moment and the average magnetic moment per iron atom are found to increase as the H position moves towards the Fe–V interface. On the other hand, the average magnetic moment per Fe atom is found to initially decrease up to filling by three H atoms and then increases afterwards. To our knowledge, this is the first reporting on the increase in the computed magnetic moment with hydrogenation. These trends of magnetic moments are attributed to the volume changes resulting from hydrogenation and not to electronic hydrogen–metal interaction.

The technique of X-ray photoelectron spectroscopy has been used to investigate the chemical reactivity at the metal/CuO interfaces. Thin films of the metallic overlayer (0.5 nm, 1.0 nm and 2.0 nm thickness) were deposited on copper oxide substrates at room temperature. In situ characterization of the interfaces has been performed. The 2p core level regions of the metals have been investigated. The spectral features show considerable reactivity at the interfaces. The core level peaks of the metal are observed to be shifted to the high BE energy side with the appearance of satellites. The spectral data confirm the formation of the metallic oxide at the interface. The satellite structure in the copper region is observed to disappear and the spectral features are found to approach those of elemental copper. The room temperature deposition of the metal on copper oxide therefore results in the reduction of copper oxide to elemental copper followed by the oxidation of the metal. The interface is found to consist of a mixture of metal oxide and elemental copper. The 2.0 nm samples were annealed. These samples show the diffusion of copper oxide through the overlayer. The metal reacts with this diffusing oxide to form metallic oxide. The interface is found to consist of a mixture of unreacted metal, the metal oxide, and elemental copper. The amount of the unreacted metal varied between 0% and 40% and can be controlled by the processing conditions. The investigation shows room temperature chemical reactivity at the metal/CuO interface and provides a new method of preparing sub-nano-oxide films.

To design an ideal hydrogen (H) storage material, the understanding of the interaction between a host material and hydrogen is essential. The strength of the interaction determines the enthalpy and activation energy for H hopping. To obtain those physical quantities by utilizing first principle method, the crystal structure should be elucidated. We focused on Vanadium (V) as a representative of BCC (body-centered-cubic) type of hydrogen storage materials. The feature of BCC type storage material is characterized by the existence of β phase. We investigated the crystal and electronic structural changes with various H concentration in V. Without taking vibrational contribution into account, H atoms prefer to locate at tetrahedral sites. While taking the contribution into account, β phase can be the stable structure at VH composition.

Using a Morse type pair potential, molecular-dynamics simulations have been performed to investigate the atomic geometries, growing patterns, structural stabilities, energetics and magic sizes of Ti_n, V_n and Cr_n (n = 2-50) clusters. Following rearrangement collision of the atom–cluster system in fusion process, and absorbing their energies step by step down to 0 K, possible optimal equilibrium geometries of the clusters have been generated to tackle the structural determination problem. This approach serves an efficient alternative to the growing path identification and the optimization techniques. It has been found that titanium, vanadium and chromium clusters prefer to form three-dimensional compact structures in the determined configurations and the appearances of medium sizes are, in general, five-fold symmetry on the spherical clusters. Moreover, relevant relations between atomic arrangements in the clusters and the magic sizes have been observed.

Three lanthanide-vanadium porphyrins, [LnV(TPPS)H₂O]_n (Ln = Tb(1), Dy(2), Er(3); H₆TPPS = tetra(4-sulfonatophenyl)porphyrin), have been prepared from hydrothermal reactions and their structures were characterized by single crystal X-ray diffraction technique. The macrocyclic ring of H₆TPPS is coplanar and the center is occupied by the vanadium(III) ion. The lanthanide(III) ions are bound by eight oxygen atoms to yield a distorted square anti-prism geometry. They are characteristic of a three-dimensional (3-D) open framework with a void space of around 210 ų. Fluorescence studies reveal that compounds 1–3 exhibit an emission band in the red region with the quantum yields being of 2.0%, 1.4% and 5.0%, respectively. CV/DPV results discover one quasi-reversible wave (1), one reductive peak (2) and two reductive peaks (3). Compounds 1–3 show largely different photophysical and electrochemical properties, although their structures only show tiny difference in lanthanide metal ions. This is due to metal-induced properties variation.

The catalytic functionalization of C–H, C–OH and C–C bonds belongs to the most important processes in nature and the industry. In nature, this process occurs via involvement of enzymes, effectively and selectively, usually with very high turnover numbers. The pivotal role in enzymatic activity is played by the metal center cofactors, which involve several bioavailable transition metals, such as, iron, copper, manganese and zinc. In the industry, bond functionalization requires the presence of metal catalysts; therefore, a bio-inspired design of metal catalysts is a challenging approach. The recent advances in the catalysis of industrially important reactions, namely the oxidation and hydrocarboxylation of alkanes, the oxidation of alcohols and C–C coupling are reported. Convenient, environmentally friendly methods are presented, and the role and efficacy of the various transition-metal (iron, copper, zinc, manganese, nickel, vanadium, palladium and cobalt) catalysts are explored.

The aim of this work was to evaluate the effects of five V2O5 medium concentrations ranging from 0.5 to 2.0 mM on cell viability, redox status and antioxidants enzymes of wine yeast S. cerevisiae UE-ME3. A slightly decrease of yeast cells growth rate for 0.5 and 1.0 mM, and a significantly decrease for 1.5 and 2.0 mM were observed. Conversely, a significantly increase of G6PD activity and GSH/GSSG ratio for 0.5 mM V2O5, and a significantly decrease of GR and CAT T activities for 0.5 and 1.0 mM also occurs. Furthermore, for V2O5, ranging between 1.0 and 2.0 mM, we observed a significantly decrease of G6PD and GSH/GSSG ratio, occurring, at the same conditions a reverse effect on GR and CAT T activities, with a significant increase of GR for 1.5 and 2.0 mM. We suppose that bimodal response of S. cerevisiae to vanadium pentoxide, eventually mediated by NADPH and GSH level, rule cell death.

Recent development of hot press forming technique shows successful application of quenching and partitioning (Q&P) hot stamping process to improve the mechanical properties (tensile ductility and crash toughness) of hot stamped steel components. The present project investigated the Q&P hot stamping process of a vanadium bearing ultra-high strength boron steel with medium silicon content in order to reveal the effects of vanadium on the partitioning stage by comparing the corresponding mechanical properties of vanadium free steel. Typical Q&P parameters, such as partition time, were studied. Our results show that compared with the V free steel, the total elongation initially decreased faster during partitioning from 15 s to 35 s and then increased slowly from 35 s to 65 s for the V bearing steel, which resulted from the complicated interactions between several metallurgical factors, which will be discussed and verified experimentally in detail in the present project. Finally, our results show that the boron steels alloyed with vanadium are stronger than those without vanadium addition under all the studied Q&P processing.