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The interaction between four-hydrogen atoms and a FCC FeNi-based alloy ideal structure having a vacancy (V) was studied using a cluster model and a semi-empirical theoretical method. The energy of the system was calculated by the atom superposition and electron delocalisation molecular orbital (ASED-MO) method. The electronic structure was studied using the concept of density of states (DOS) and crystal orbital overlap population (COOP) curves. After a sequential absorption, the hydrogen atoms are finally positioned at their energy minima configurations, near to the vacancy. The energy difference for H agglomeration was also computed. The vacancy-Hn complexes become less stable for n > 3. The changes in the electronic structure of Fe and Ni atoms near to the vacancy were also analysed. The interactions mainly involve Fe and Ni, 4s and 4p atomic orbitals. The contribution of 3d orbitals is much less important. The Fe-Fe, Fe-Ni and Ni-Ni bonds are weakened as new Fe-H, Ni-H and H-H pairs are formed. The effect of the H atoms is limited to its first neighbours. The detrimental effect of H atoms on the metallic bonds can be related to the decohesion mechanism for H embrittlement. [ABSTRACT FROM AUTHOR]

The Fe–C–H interaction near defects in iron structures was studied using qualitative structure calculations in the framework of the atom superposition and electron delocalization molecular orbital. Calculations were performed using three Fe clusters to simulate an edge dislocation, a divacancy; both in bcc iron and a stacking fault in an fcc iron structure. In all cases, the most stable location for C atom inside the clusters was determined. Therefore, H atom was approximated to a minimum energy region where the C atom resides. The total energy of the cluster decreases when the C atom is located near the defects zone. In addition, the presence of C in the defects zone makes no favorable H accumulation. The C acts as an expeller of H in a way that reduces the hydrogen Fe–Fe bonds weakening. [ABSTRACT FROM AUTHOR]

The interaction of hydrogen with a platinum (111) cluster using the atom superposition and electron delocalization–higher binding ASED-TB quantum calculation method was studied. The metal surface was represented by a Pt cluster of seven layers. The effect of hydrogen on this metal substrate was studied by the analysis of density of states and crystal orbital overlap populations curves. The energy surface plots allow us to find a possible diffusion path through the cluster from one side to the other. The Pt–Pt metal bond is weakened during H adsorption and diffusion. The main components in the Pt–H bond are the Pt 6s (31%), 6p (26%), and 5 dxz (16%) orbitals. [ABSTRACT FROM AUTHOR]

The electronic structure of S adsorption on goethite (110) surface has been studied by ASED-MO cluster calculations. For S location, the most exposed surface atoms of goethite surface were selected. The calculations show that the surface offers several places for S adsorption. The most energetically stable system corresponds to S location above H atom. We studied in detail the configurations that correspond to the higher OP values. For these configurations, the H-S and Fe-S computed distances are 2.1 and 3.7 Å, respectively. The H-S and Fe-S are mainly bonding interaction with OP values of 0.156 and 0.034, respectively. The Fe-S interaction mainly involves Fe 3dx2-y2 atomic orbitals with lesser participation of Fe 4py and Fe 3dyz atomic orbitals. The O-S interaction shows the same bonding and antibonding contributions giving a small OP value. The O-S interaction involves O 2p orbitals. There is an electron transfer to the Fe atom from the S atom. On the other hand, there is an electron transfer to S atom from the H and O atoms, respectively. [ABSTRACT FROM AUTHOR]

Hydrogen adsorption on Fe(100) was analyzed using a semiempirical theoretical method. Calculations were performed using a Fe[sub 130] cluster. Adsorption sites for one and two hydrogen atoms on the surface correspond to local energy minima configurations. Changes in the electronic structure of surface Fe atoms were analyzed for the system without hydrogen and with one and two adsorbed hydrogen atoms. Fe atoms close to H weaken their metallic bond. This is due to the formation of H–Fe bonds. Hydrogen influences only its nearest neighbor Fe atoms. The H–H interaction was also analyzed and our results show that H–Fe interaction is much stronger than any possible H–H interaction. No additional decohesion is observed in the Fe–Fe bonds; however, more Fe–Fe bonds are affected. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Li adsorption on the (8,0) SWCNT is stronger nearby a single C vacancy. • Li induces a magnetic moment, a band gap energy reduction and transfers electron density to the CNT. • O2 and H2 molecules dissociates on the CNT while CO adsorbs molecularly. • CO adsorption changes Li+(8,0)SWCNT from magnetic to non magnetic and reduces its band gap. • Li+(8,0)SWCNT becomes non magnetic and shows a metallic behavior after O2 interaction. • After H2 adsorption there is an increase in the band gap energy. Abstract This work presents a theoretical study, based on DFT calculations, about the changes induced when diatomic molecules (CO, O 2 and H 2) are adsorbed on defective (8,0) SWCNT doped with a Li atom. The adsorption of one Lithium atom is tested inside and outside of the nanotube containing a single vacancy. The Li atom induces a magnetic moment on the nanotube and an important reduction in its the band gap (E g). The adsorption energy values (E ads) for CO, O 2 and H 2 when Li is located inside, are higher than when Li is outside. The H 2 adsorption does not change the magnetic nature of the system. However, the CO and O 2 molecules reduce the magnetic moment from 1.0 µ B to 0.0 µ B. The band gap energy is reduced for CO and O 2 , while increases in the case of H adsorption. The work function (WF) value is reduced in the cases of CO and H 2 ; whereas for O 2 we observed an opposite behavior, then the final charge state of this molecule is negative. Based on our results, the system Li + defective (8,0) SWCNT can be proposed as possible candidate as gas sensor of CO,O 2 and H 2. [ABSTRACT FROM AUTHOR]

Abstract: The interaction of two-hydrogen atoms in a zone of γ-Fe55Cr25Ni20 alloy having a vacancy (V) was studied by the atom superposition and electron delocalization molecular orbital (ASED-MO) method. The impurities are located aligned both along [1–10] direction and with the vacancy, in the (111) plane. This behavior can be related with a lineal hydrogen–vacancy clusterization, as a precursor to crack initiation. The electronic structure of the Fe, Cr and Ni atoms near the vacancy, changes after hydrogen''s location. The interactions mainly involve Fe 4p x and Cr 4p y atomic orbitals. The and 3d xz metallic orbitals also have participation in the hydrogen–alloy interactions. An electron transfer to the H atoms from the Fe, Cr and Ni nearest neighbor atoms contributes to form the new H–metal bonds. The metal–metal bonds weakened as the new H–Fe, H–Cr, and H–Ni pairs were formed. The Cr atoms have an important role in the embrittlent process; the strengths of the Cr–Fe, Cr–Cr and Cr–Ni bonds are the most affected while the H–Cr interaction has the highest overlap population. Same H–H interaction is observed and could be associated with the precursor of hydrogen bubble but it is far away to a typical H2 chemical bond. All the cited physical and chemical processes play a key role in subsequent localized corrosion nucleation such as the initiation of stress corrosion cracking. [Copyright &y& Elsevier]

Abstract: Fuel cell vehicles have been identified as the personal transportation technology of the future because of their high efficiency and very low emissions. To achieve the goal of road-ready fuel cell vehicles, great strides must be made in the development of fuel cells, hydrogen production and hydrogen storage technologies, that includes metal–H interaction studies and safety considerations. The interaction between two-hydrogen atoms and a γ-Fe structure containing a vacancy has been studied using a cluster model and a theoretical method. For the study of the sequential absorption, the hydrogen atoms were positioned in their energy minima configurations, near the vacancy. The interactions mainly involve Fe 4s–H 1s atomic orbitals. The contribution of Fe 4p and Fe 3d orbitals is much less important. The Fe–Fe bond is weakened as new Fe–H–H and H–H pairs were formed. The effect of H atoms is limited to its first Fe neighbors. The Fe–Fe bond strength decreases with the introduction of the H atoms. Fe–H bonding is achieved at expense of weakening the metal–metal nearest bonds. There is not a real bond between the H atoms but some H–H interaction is observed. The detrimental effect of H atoms on the Fe–Fe bonds can be related to one of the aspect of embrittlement in γ-Fe. [Copyright &y& Elsevier]

Abstract: We studied one of the aspects of iron embrittlement in an FCC lattice with a vacancy in the presence of hydrogen as an impurity. The energy calculations were performed using the ASED method (Atom Superposition and Electron Delocalization). The electronic structures were analyzed by the YAeHMOP program (extended Hückel Molecular Orbital Package). H in bulk FCC iron prefers octahedral sites while in the presence of a vacancy it is located near the defect in a position shifted from the center of the hole. The formed Fe–H bond makes the Fe–Fe bonds first neighbors to the vacancy 28% weaker with respect to the H-free structure. [Copyright &y& Elsevier]

Abstract: Steel exposed to high temperatures and stress in a corrosive environment suffers detriment in the mechanical properties and finally embrittlement. The objective of this work is to study the mechanical properties of steels of different chemical compositions under hydrogen attack (HA). The influence of chromium and vanadium in the mechanical resistance was analyzed. The 1.25Cr1Mo0.25V and 2.25Cr1Mo ferritic steels previously hydrogenated are studied at different temperatures and loads. The temperature, electric charge density and electrolyte concentration were modified during the electrochemical charge in order to find the optimum hydrogen income to the material. The metal test conditions were characterized by scanning electron microscopy. The material remains in stationary state for a period of time and the residual damage was evaluated. The steels were subject to torsion creep tests while the temperature and the load were maintained constant along the experience. We studied the relationship between the strain rate at the secondary stage and both the stress and temperature. The stress exponent and the activation energy were also determined. A comparison with the same steel samples without hydrogen charge was also performed. The microstructural mechanics during the tests and the embrittlement degree were also discussed. [Copyright &y& Elsevier]

Abstract: The location of a carbon and two hydrogen atoms in a -Fe divacancy is analysed using a tight-binding theoretical method. Calculations were performed using a cluster. Absorption sites for the impurities near the divacancy correspond to local energy minima configurations. Fe atoms first neighbours to H atoms weaken their metallic bonds. The decohesion of Fe–Fe bonds could be associated to H embrittlement. The C atoms almost do not affect the Fe–Fe bond strength. Fe–C and Fe–H bonds are formed mainly with Fe 4s orbitals. There is no bonding between C and H atoms but some H–H interaction is observed. [Copyright &y& Elsevier]

The Fe–C–H interaction in a dislocated bcc structure was studied using qualitative structure calculations in the framework of the atom superposition and electron delocalisation molecular orbital (ASED-MO) theory. Calculations were performed using Fe85 cluster to simulate a dislocated bcc structure. The cluster geometry and atomic parameters were optimised to make a better approximation to the repulsive energy terms. The most stable position for C atom inside the cluster was determined. Therefore, and H atom was approximated to the minimum energy region where the C atom was previously located. The total energy of the cluster decreases with the C atom near the dislocation core. The a/2[1 1¯ 1] dislocation creates an energetically favourable zone for accumulation of C. The presence of C in the dislocation core make no favourable H accumulation. The C acts such as an expeller of H and could reduce the weakening of Fe–Fe bonds. In addition, a sort of Fe–C–Fe “bridge” could prevent dislocation displacement if a shear stress would be applied. [Copyright &y& Elsevier]

Abstract: In this work, we present a density functional theory (DFT) study of hydrogen interaction with Pt on a B2 FeTi (110) metallic surface. DFT is used to trace relevant orbital interactions and to discuss the electronic consequences of incorporating H on Fe–Ti bonding. We determined the optimal location for Pt and, then, for adsorbed hydrogen. In addition, we followed the density of states and changes in chemical bonding both in the surface and the adsorbates. The overlap population analysis reveals metal–metal bond breaking after hydrogen adsorption, thus being the inter-metallic bond the most affected one. [Copyright &y& Elsevier]

Abstract: The electronic structure and bonding in a B2 FeAl alloy with and without hydrogen interaction with a Fe antisite were computed using a density functional theoretical method. The hydrogen absorption turns out to be a favorable process. The hydrogen was found close to an octahedral site where one of its Al capped is replaced by a Fe antisite. The Fe–H distance is of 1.45Å same as the Al–H distance. The density of states (DOS) curves show several peaks below the d metal band which is made up mostly of hydrogen based states (>50% H1s) while the metal contribution in this region includes mainly s and p orbitals. An electron transfer of nearby 0.21e− comes from the metal to the H. The overlap population values reveal metal–metal bond breaking, the intermetallic bond being the most affected. The H bond mainly with the Al atom and the reported Fe–H overlap population is much lower than that corresponding to FePd alloys and BCC Fe. The changes in the overlap population show the Fe–Al bond is weakened nearly 41.5% after H absorption, while the Fe–Fe bond is only weakened 34.5%. H also develops a stronger bond with the Al atoms. The main bond is developed with Al being twice stronger than Fe–H. [Copyright &y& Elsevier]

Abstract: The interaction between 10 hydrogen atoms and a α-Fe structure having a vacancy (V) has been studied using a cluster model and a semi-empirical theoretical method. The energy of the system was calculated by the atom superposition and electron delocalization molecular orbital method. The electronic structure was studied using the concept of density of states and crystal orbital overlap population curves. For the study of a sequential absorption, the hydrogen atoms were positioned in their energy minima configurations, near to the tetrahedral sites neighboring the vacancy, except the last H atom that was located far from the vacancy. The energy difference for H agglomeration was also computed. The vacancy-H n complexes become less stable than VH species for more than three hydrogen''s. The changes in the electronic structure of Fe atoms near the vacancy were also analyzed. The interactions mainly involve Fe 3d and 4s atomic orbitals. The contribution of Fe p orbitals is much less important. The Fe–Fe bond weakened as new Fe–H and H–H pairs were formed. The effect of H atoms is limited to its first Fe neighbors. The detrimental effect of H atoms on the Fe–Fe bonds can be related to the mechanism for embrittlement in α-Fe. [Copyright &y& Elsevier]

The H–C–Fe interaction has been investigated in γ-Fe with a stacking fault using a cluster model. The energy of the system was calculated by the atom superposition and electron delocalization molecular orbital method. The electronic structure was studied using the concept of density of states and crystal orbital overlap population curves. By modifying the geometrical positions of the impurity within the cluster we have found that C occupies nearly octahedral sites on the stacking fault plane. The H does not reside in the vicinity of the C. The presence of C could reduce the detrimental effect of H on the Fe–Fe bonds.The present paper provides detailed energy mapping for C–Fe and H–C–Fe subsystems in the fault region. C–Fe and H–C equilibrium distances are reported and the orbital contributions to the bonding are also addressed. [Copyright &y& Elsevier]