Diffusion of hydrogen, carbon and oxygen in the presence of hydrogen coadsorbed onto iron surfaces

Density-functional theory calculations based on the GGA-PBE (generalized gradient approximation Perdew–Burke–Ernzerhof) exchange correlation functional were used to investigate the effect of hydrogen on the diffusion of adsorbed carbon, oxygen and hydrogen on the surface of Fe(100). The diffusion energy barrier was calculated for both clean surfaces and those with hydrogen, and it was found that hydrogen produced binding energies for carbon and oxygen. These bonds stabilized the binding of hydrogen with the Fe(100) surface. For all of the surface species studied here, the energy barrier was increased when hydrogen was coadsorbed, from 1.29 eV to 1.46 eV for C, from 0.33 eV to 0.53 eV for O and from 0.11 eV to 0.15 eV for H. An approximation of the diffusion coefficient was obtained from energy barrier calculations and a pre-exponential factor of diffusion was calculated. Carbon exhibited low diffusion at the surface under experimental temperatures, while oxygen diffusion was activated above 450 K and hydrogen was diffused in all the temperature ranges investigatedElsevie

Study of the incorporation of S in TiO2/SO42− Coatings produced by PEO process through XPS and DFT

TiO2 has been widely studied due to its wide range of applications. Various techniques have been used for its synthesis. Plasma Electrolytic Oxidation (PEO) has been a synthesis technique of great interest since it allows obtaining coatings and incorporating different ions at environmental conditions. In this work, the synthesis of TiO2/SO42− was carried out by means of PEO, characterized by Raman, XRD (X-Ray Diffraction) and XPS (X-Ray Photoelectrons Spectroscopy). The experimental results were used for DFT (Density Functional Theory) simulations. For the PEO process, 99% Ti sheets, 0.10 M H2SO4 and 6 min synthesis time were used with useful cycle variations of 2% and 50%. On the other hand, DFT calculations were carried out to demonstrate the formation of structural defects in TiO2/S systems from the experimental results. The Raman and the XRD results show the presence of anatase and rutile phase of TiO2 in both useful cycles. The XPS results showed the presence of S in the form of SO42−, both on the surface of the material and in the bulk. The calculations showed that the quantification of sulfate ions in the Ti site was energetically favorable with a formation energy value of −3.09 eV, slightly lower than that of the bulk without substitution, which was −3.21 eV. Additionally, the DOS (densities of state) and substitution energy were analyzed.Fil: Vargas Villanueva, Steven. Universidad Nacional de Colombia Manizales; ColombiaFil: Torres Ceron, Darwin Augusto. Universidad Nacional de Colombia Manizales; Colombia. Universidad Tecnológica de Pereira; ColombiaFil: Amaya Roncancio, S.. Universidad Nacional de Colombia Manizales; Colombia. Universidad de la Costa; ColombiaFil: Arellano-Ramírez, I.D.. Universidad Nacional de Colombia Manizales; Colombia. Universidad Tecnológica de Pereira; ColombiaFil: Riva, Julieta Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Restrepo Parra, Elisabeth. Universidad Nacional de Colombia Manizales; Colombi

Thermal history of the southern Central Cordillera and its exhumation record in the Cenozoic deposits of the Upper Magdalena Valley, Colombia

The roughly 600 km long Central Cordillera of Colombia shows a varied tectonic, magmatic, and exhumation history, despite the reasonably homogenous appearance concerning topography, outcropping lithologies, and strike. Here we show with new geo-thermochronological data the thermal evolution of the southern Central Cordillera since the Early Jurassic. Extensive Jurassic magmatism is recorded by U–Pb crystallization ages of arc plutons intruded by dike swarms and collateral volcaniclastic flows. Inverse modeling of zircon and apatite fission-track ages from Central Cordillera reveals a long period of slow cooling since the Early Cretaceous at rates of 2–3 °C/Myr, based on best-fit t-T path solutions. The Early Cretaceous phase is recorded by the cooling of Jurassic granitoids, most likely driven by slow erosional exhumation along the western flank of the Central Cordillera related to the collision and accretion of the Quebradagrande arc against the continental margin. The Late Cretaceous rapid exhumation event caused by the ~80-70 Ma collision and accretion of the Caribbean Large Igneous Province at the western margin of South America observed in other parts of the Central Cordillera, is not detectable in our study area. During the Eocene-Oligocene (ca. 45-31 Ma), the obtained time-temperature paths are compatible with slow cooling rates between 1 and 2 °C/Myr and slow exhumation at long-term average rates of about 0.1 km/Myr. The combination of geo-thermochronological data and petrology of clastic basin sediments presented in this study indicates that the unroofing of the southern Central Cordillera crystalline basement also occurred during the Eocene-Oligocene phase of the Andean Orogeny, as widely recognized by a major unconformity. The exhumation was coeval with the reactivation of crustal structures, such as the Plata-Chusma fault, as evidenced by the syn-tectonic deposits of the Gualanday Group