The study of nanodispersed composite MgH2-Ti: experiment and theory

In order to obtain faster hydrogen sorption kinetics, MgH2-Ti nanocomposites were prepared by high-energy ball milling, under Ar using 10:1 ball to powder ratio and 10% of catalyst. Microstructural and morphological characterization, performed by XRD and optical microscopy analysis, show a correlation with thermal stability and hydrogen desorption properties investigated by DTA. In order to obtain deeper insight into bonding mechanisms of Ti in MgH2 fully relaxed structure, we have performed ab initio electronic structure calculations of MgH2 + Ti system, using Full Potential Linearized Augmented Plane Wave method, as implemented in WIEN2K code.Physical chemistry 2006 : 8th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-29 September 200

Electronic Principles of Hydrogen Incorporation and Dynamics in Metal Hydrides

An approach to various metal hydrides based on electronic principles is presented. The effective medium theory ( EMT) is used to illustrate fundamental aspects of metal-hydrogen interaction and clarify the most important processes taking place during the interaction. The elaboration is extended using the numerous existing results of experiment and calculations, as well as using some new material. In particular, the absorption/desorption of H in the Mg/MgH2 system is analyzed in detail, and all relevant initial structures and processes explained. Reasons for the high stability and slow sorption in this system are noted, and possible solutions proposed. The role of the transition-metal impurities in MgH2 is briefly discussed, and some interesting phenomena, observed in complex intermetallic compounds, are mentioned. The principle mechanism governing the Li-amide/imide transformation is also discussed. Latterly, some perspectives for the metal-hydrides investigation from the electronic point of view are elucidated

Near-surface hydrogen dynamics in titania

The hydrogen interaction with the TiO2 (110) surface has been investigated using pseudopotential and PAW methods with addition of U Hubbard term. The hydrogen diffusion behavior and thermodynamic properties were calculated by means of full relaxation of structure in every step of bulk diffusion. The results show the existence of potential barriers close to every atomic layer, the trends of barriers and overall system energy lowering away from surface and the occurrence of preferential H sites within each interlayer basin. These findings go in favor of previously experimental findings of TiO2 low surface H coverage and observed easy diffusion of hydrogen from reduced surface into the TiO2 bulk or at least in near surface region

Nature of Bonding in MgH2:TM Doped Systems

Ab initio electronic structure calculations of the Mg 15 TMH 32 (TM – transition metal) systems for the entire 3d TM series have been performed using full-potential (linearized) augmented plane waves method with addition of the local orbitals ). Details of bonding and th e mechanism of the TM impurities influence on stability of MgH2 were investigated by means of electronic structure change after the TM impurities insertion into MgH2 and using the “atoms in molecules” (AIM) Bader’s charge density topology analysis. Obtained trends show that nature of TM-H bonding along the series change in a sense of directional bonding contribution rise, with maximum effect for late 3d metals Co and Ni. The effect of charge redistribution is nevertheless local and it in general weakens Mg-H bonds and the surrounding MgH2 matrix

The Influence of Boron Doping Concentration on MgH2 Electronic Structure

We have performed ab initio electronic structure calculations of Mg1-xBxH2 compounds with different boron concentrations, ranging from x =0.0625 to 0.5. Full structural relaxation was performed in order to properly describe influence of dopant on host matrix. Results showed that there is a strong influence of boron concentration on structural and thermodynamic stability of compound. B-H bond length is substantially shorter then in Mg-H coordination polyhedron. Boron significantly contributes to density of states at Fermi level within energy gap. The width of boron electronic states heavily depends on boron concentration, causing reduction of energy gap of host MgH2, and leading to metallic nature of compound with highest boron concentration. The predicted thermodynamic instability of compounds with higher boron concentration is in agreement with experimental findings that under similar stoichiometry, boron with magnesium forms only complex hydride, Mg(BH4)(2). It is also shown that existence of stable hydrides with MgH2 rutile structure and small concentration of boron is possible in principle and that boron can be used to further destabilize MgH2 in order to enhance its hydrogen sorption-desorption kinetics.12th Annual YUCOMAT Conference, Sep 06-10, 2010, Herceg Novi, Montenegr

Impact of the geographic factors on the transport of lead and cadmium in the air

The aim of this study is to describe the effect of geographical varieties on the transport of lead and cadmium in the air. During period between 1997- 2006, the concentrations of lead in suspended in the air at 5 measuring sites in Serbia were measured. The minimal measured daily concentrations of lead ranged from 0,42 μg/m3 (2002.) in Kraljevo. The maximal measured daily concentrations of lead to 251,8 μg/m3 (2004.) in Belgrade. During the period between 1997-2006., the concentrations of cadmium in suspended in the air at 5 measuring sites in Serbia were measured. The minimal measured daily concentrations of cadmium ranged from 0,1 μg/m3 (1999) in Kraljevo. The maximal measured daily concentrations of lead to 42,0 μg/m3 (2000) in Belgrade. Results from our experiments demonstrated that when rapid infiltration conditions or a rainstorm exist, particle-facilitated transport of contaminants is likely to the dominant metal transport pathway influenced by acid rain.Physical chemistry 2008 : 9th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 200

Catalitic effect of Co on hydrogen desorption form nanostucturated magnesium hydride

To study the influence of 3d transition metal addition on desorption kinetics of MgH2 ball milling of MgH2-Co blends was performed under Ar. Microstructural and morphological characterization, performed by XRD and SEM, show a huge correlation with thermal stability and hydrogen desorption properties investigated by DSC. A complex desorption behavior is correlated with the dispersion of the metal additive particles on hydride matrix. The activation energy for H-2 desorption from MgH2-Co composite was calculated from both non-isothermal and isothermal methods to be 130 kJ/mol which means that mutually diffusion and nucleation and growth of new phase control the dehydration process.6th Conference of Young Researchers, Dec 24-26, 2007, Belgrade, Serbi

Hydrogen desorption from vacant MgH2

The hydrogen desorption properties of vacant MgH2 structure were investigated both experimentally and theoretically. Ion irradiation by Ar8+ and Xe8+ ions were used to induce structural changes in MgH2. Hydrogen desorption properties were investigated by temperature programmed desorption (TPD). To obtained deeper insight in structural changes during desorption theoretical calculations were performed using DFT approach within Abinit code. Results showed that there are several mechanisms involved in desorption process, which depend on defect concentration, their position and their interaction and ordering. It has been demonstrated that the changes in near-surface area play the crucial role in desorption kinetics

Physicochemical characterization of mechanochemically activated pyrophyllite/Ag composites

Nanocomposites synthesized by incorporating nanostructured materials within the interlayer spaces of clay minerals have gained tremendous interest lately, owing to their exceptional physicochemical properties and vast potential in various fields. This study focuses on the mechanochemical activation of pyrophyllite, a commonly used natural clay material, using AgNO3 at different concentrations (2, 5, and 10 wt%). The activation process involved grinding the materials for varying durations ranging from 20 to 320 minutes. The resulting samples were analyzed using FTIR, TGA, and DTA thermal analysis techniques, XRD, SEM with EDX as well as PSD method for particle size distribution analysis. The results have shown a homogeneous distribution of silver along the analyzed surface. The duration of grinding and the amount of added silver greatly influence the composite physicochemical properties.Twenty-First Young Researchers’ Conference - Materials Science and Engineering: Program and the Book of Abstracts; November 29 – December 1, 2023, Belgrade, Serbi