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METAL-GAS INTERACTIONS

METAL-GAS INTERACTIONS. Gases in metals and alloys: -contanimantions (arising from technology or from environment) - Alloy component. The metal-gas systems. At low concntration : at high (extended) concentration

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METAL-GAS INTERACTIONS

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  1. METAL-GAS INTERACTIONS Gases in metals and alloys: -contanimantions (arising from technology or from environment) - Alloy component

  2. The metal-gas systems • At low concntration: at high (extended) concentration • Me-H solid solutionsMe-hydrides • Me-O solid solitionsMe-oxides • Me-N solid solutions Me-nitrides • Me- semimetal (metalloid) systems analogy to the metal-gas systems) • at low concentration at high concentration • Me-C solid solutions Me-Carbides • Me-B solidsolutions Me-borides • Me-Si(?) solid solutions Me silicides

  3. The first process of interaction between metals and gases: adsorption • The significance of gas-adsorption in various technological phenomena, processes: outstanding ! • welding, (wettability), brazing (wettability) (slag-formming compounds!) • heat treatments,(corrosion: oxide layer formation on the surface at • high temperatures) • surface treatments decorative or, corrosion resistant layers on the • metal surfaces • W lding The central phenomenon of wetting between contacting liquid and solid phases: The question is: how the adsorbed gasous atoms can influence the surface tension (surface eneergy) →

  4. How the adsorbed gas atoms (molecules) influence the surface energy of the solidor molten metal (or alloy) a: total quantity, C: surface concentration of adsorbed gas The quantity of adsorbed atoms (or molecules) versus the ambient pressure (non-reactive partners!) The change of surface energy versus the concentration of solute atoms decreases, when α > 0 í.e. solute atoms can be capillar active, or inactive

  5. The measurement of surrounding gas content on the wetting Temperature: 1100 ͦC Ag molten drop, graphite substrate O2 O2 O2 O2 O2 O2 O2 O2 O2 High O2 (pO2) concentration in the surrouning atmosphere Low pO2 5/27

  6. THE ABSORPTIONThe mechanism of gas-absorption ( the energetic analyses of H-absorption) • The elementary process of gas adsorption-absorption

  7. The thermodynamic aspects of H-solution, the valence state of H in metallic matrix • During the H solution both the electronic and crystal structure can change • The simultaneous change of both is not necessary! • Solid solution formation: without change in the crystal structure • Compound (hydride) formatikon: lattice type and symmetry changeare involved • H-absorption can be performed: • from electrolites • from gas phase

  8. The valence state of H in metallic matrix • H solubility under isoterm conditions (pressure dependence) (T=const.) • An example: H2 dissolution Me (Sieverts)

  9. Most of the gases (O,N,H) are reactive:however, the reactivity depends on the metallic partnerslow concentration: dissolved statehigh concentrations:oxides, nitrides, hydrides The relation between solubility and compound formation : THE STANDARD HEAT OF FOMATION of compounds (oxides hydrides or nitrides) Higher heat of formation of bulk oxide, Increasing tendency of adsorption on the surfaces, increasing reactivity DG = RTln c C ≈ p(gas)

  10. Exotherm, and endoterm type of H-solution • More detailed informations about the H-solubility: exotherm and endotherm systems • The relation between the electronic structure of metal and the „metalloid” element:(C,N,H O,

  11. The mechanism of hydride phase formation • Temperature and pressure –dependence of H-content

  12. The hydride phase formation

  13. Exotherm type of hydrogen solution interaction between the H atoms and the conductivity band of the host metal

  14. Metal Hydride StorageAn essential feature of reversibility of cycling: to find a physical properties for the control of reversibility The relative resistivity change R/R0 . The correlation between H-content during the repeated H-charging in NiZr glass R/R0 in Ni61Zr33Cu6.glassy alloy

  15. Corrosion: definition and corrosion types Corrosion: in wider sense: degradation of materials by its environments (metals ceramics, polimers, composites) Classical corrosion: degradation of metals and alloys by electrochemical, or chemical environmental interactions Spontaneous process: under normal atmospheric circumstances, and room temperature A the direction of corrosion process (as chemical reaction) is opposite to that of metallurgical process directing to metal production During chemical corrosion: without ion formation!

  16. The normal potential of common metals in the indicated electrode processes

  17. The difference between chemical and electrochemical corrosion • Chemical corrosion: without ion formation • pl.:Fe→FeO, Al→Al2O3 • Electrochemical corrosion: the existence of metal (or alloy) contact with electrolite in which the dissolution is taking place: • The scheme:  • Driving force:

  18. THE IMPACT OF METAL-GAS INTERACTION IN THE DEVELOPMENT OF GLOBAL PROBLEMS (a short philosophy) • WORLD-WIDE PROBLEM ARE: • - ENVIRONMENTAL POLLUTION • -metal and alloy degradation in atmospheric circumstances(corrosion) • - TECHNOLOGICAL PROBLEMS ( CRISIS ARISING FROM THE ENERGY CONSUMPTION

  19. Do the global problems really exist? • Many people think so: • Symtoms: world-wide communication crises • international firms and monetary system • International press : not always transfer, but creates the news! • -environmental pollution • Over-population (global! but locally is not necessarily true: • Afrika→ over-population, Philipen→over pop. • But: Europe, USA: fall in population • Nort-South Europa: result: migration! • Stress evolution • between different cultural identities→terrorism

  20. Technically: the energy consumption and the environmental pollution are the central problems. The history and distribution of the energy consumption The significance of alternative energy sources is dramatically increases The importance of H2 is perspectivic 2H2 +O2 =2H2O + Q(heat)

  21. The energetic properties of the main energy carriers

  22. THE IMPACT OF METAL-GAS INTERACTION IN THE DEVELOPMENT OF GLOBAL PROBLEMS (a short philosophy) • WORLD-WIDE PROBLEM ARE: • - ENVIRONMENTAL POLLUTION • -metal and alloy degradation in atmospheric circumstances(corrosion) • - TECHNOLOGICAL PROBLEMS ( CRISIS ARISING FROM THE ENERGY CONSUMPTION

  23. Global environmental problems • Local air quality concerns • Energy security and supply issues • Sustainable development issues • Technological innovation Factors promoting a hydrogen economy Barriers to a hydrogen economy • Fuel cell viability/cost • Fuel cell vehicle reliability/durability • Logistic investment • Combustion engine improvements • Fossil fuel dependence H-storage as a part of an integrated energetic system Not primary energy source, storage only! The mode of storage: • High pressure tanks • Cryo-storage • Storage in the form of metal hydrides

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