Kinetics of Metal-Gas Interactions at Low Temperatures is devoted to the formation of natural oxide films. These thin surface layers are produced instantaneously when oxygen or water vapor is present in the gas atmosphere. They are responsible for corrosion behavior, for wear and friction of metallic materials, and also for hydrogen embrittlement and poisoning of catalytic surface reactions. Oxidation is a hindrance in surface science and in modern thin-film manufacturing. It can be reliably avoided only with expensive ultra-high vacuum techniques. Despite the practical relevance of the topic, quantitative data are sparse and the few papers published on low-temperature oxidation provide mainly qualitative information. This monograph presents an introduction to the subject in a tutorial style. It demonstrates how complex metal-gas interactions can be analyzed by standard procedures of chemical kinetics, and simulated by reaction models. Typical features of metal-gas reactions observed at ambient and elevated temperatures are illustrated by experimental results. Possible reaction mechanisms are described both by approximations and by advanced models. Rate and time laws describe the limiting cases and the more realistic situation where, in an overall reaction, several crucial partial steps must be considered, namely, adsorption onto the surface and the diffusion of charged or uncharged defects in metallic or semiconducting surface layers.

Klappentext

This book presents experimental data and recent results of model calculations on the formation of natural oxide film on metal surfaces and of metal hydride formation. Such films are responsible for corrosion, friction, and wear of metallic materials. Describing mostly the authors own research, this monograph gives an overview of models suitable for metal-gas reactions and demonstrates how complex metal-gas interactions can be analyzed by standard procedures of chemical kinetics. The book, and the data and equations it contains, will be useful to researchers in surface science, condensed-matter physics, and materials science.

Inhalt

1 Introduction.- 2 Principles of Reaction Kinetics.- 2.1 Equilibria of Chemical Reactions.- 2.2 Structure of Reaction Models.- 2.2.1 Reaction Partial Steps.- 2.2.2 Rate Equations of Partial Reactions.- 2.2.3 Combining the Partial Steps.- 2.2.4 Mathematical Solution of the Problem.- 2.2.5 Steady-State Conception.- 2.2.6 Rate Determining Step.- 2.2.7 Concluding Remarks.- 2.3 Characteristics of Reaction Partial Steps.- 2.3.1 Molecular Adsorption or Physisorption.- 2.3.2 Chemisorption.- 2.3.3 Formation of Lattice Defects.- 2.3.4 Formation of the Reaction Product.- 2.3.5 Diffusion Processes.- 2.3.6 Electronic Currents.- 2.3.7 Ionic Fluxes.- 2.3.8 Initial Stage of Oxidation.- 3 Experimental Techniques.- 3.1 Initial State of Metal Surfaces and UHV Experiments.- 3.2 Volumetric and Manometric Methods.- 3.3 Quartz Crystal Microbalance.- 3.4 Ellipsometry.- 3.5 Energetic Ion Scattering.- 3.5.1 Rutherford Backscattering Spectroscopy.- 3.5.2 Elastic Recoil Detection Analysis.- 3.5.3 Nuclear Reaction Analysis.- 3.6 X-Ray Reflectivity.- 3.7 Surface-Analytical Methods.- 4 Hydrogen Reactions.- 4.1 Experimental Results.- 4.1.1 Metal-Hydrogen Systems.- 4.1.2 Hydrogen Solution in Metals.- 4.1.3 Hydride Formation.- 4.2 Hydrogen Solution in Metals.- 4.2.1 Reaction Mechanism, Partial Steps.- 4.2.2 Transport of H2 Molecules in the Gas Phase.- 4.2.3 Desorption of Physisorbed Molecules.- 4.2.4 Dissociation of Physisorbed H2 Molecules.- 4.2.5 Recombination and Desorption of Chemisorbed Hydrogen Atoms.- 4.2.6 Surface Penetration, Forward Reaction.- 4.2.7 Surface Penetration, Backward Reaction.- 4.2.8 Diffusion in the Metal Phase.- 4.3 Hydride Formation.- 4.3.1 Reaction Mechanism, Partial Steps.- 4.3.2 Physisorption and Chemisorption.- 4.3.3 Transition from Chemisorption to the Hydride Subsurface.- 4.3.4 Diffusion in the Hydride Phase.- 4.3.5 Formation of the Hydride Phase.- 4.4 Computer Simulation of Advanced Models.- 4.4.1 Structure of the Model.- 4.4.2 Procedure of the Numeric Solution.- 4.4.3 Discussion of Results for Absorption.- 4.4.4 Conclusions.- 4.4.5 Desorption.- 5 Low-Temperature Oxidation.- 5.1 Experimental Results.- 5.2 Rate Laws Proposed in the Literature.- 5.2.1 Parabolic Law.- 5.2.2 Inverse Logarithmic Law.- 5.2.3 Linear Law.- 5.2.4 Logarithmic Law.- 5.3 Partial Steps of the Oxidation Reaction.- 5.3.1 Reaction Mechanisms.- 5.3.2 Charge Distribution and Electric Fields.- 5.3.3 Reactions at the Metal/Oxide Interface.- 5.3.4 Reactions at the Oxide Surface.- 5.4 Relations and Constants Used in Model Calculations.- 5.4.1 Equation of Continuity.- 5.4.2 Steady-State Condition.- 5.4.3 Principle of Coupled Currents.- 5.4.4 Structure of the Models.- 5.4.5 Numerical Procedures.- 5.5 Example of a Model Considering Space Charges.- 5.5.1 Equilibria of the Interface Reactions.- 5.5.2 Ion Currents.- 5.5.3 Electronic Currents.- 5.5.4 Mathematical Treatment.- 5.6 Models Neglecting Space Charges.- 5.6.1 Ion Current in the Homogeneous Field.- 5.6.2 Electrostatic Phenomena.- 5.6.3 Surface Penetration.- 5.6.4 Configuration of the Models.- 5.7 Detailed Presentation of a Model with Metal Interstitials as Mobile Defects.- 5.7.1 Equilibrium and Rate Equations.- 5.7.2 Surface Charges.- 5.7.3 The Potential V Across the Layer.- 5.7.4 Calculation of Concentrations, Currents, and the Oxide Growth Curve.- 5.7.5 Standard Oxide Growth Curve.- 5.7.6 Concentration of Reacting Species and Partial Fluxes.- 5.8 Results of Model Calculations, Parameter Variations.- 5.8.1 Effective Charge of Metal Interstitials.- 5.8.2 Ion Current.- 5.8.3 Surface Penetration.- 5.8.4 Effective Electron Mass.- 5.8.5 Energy U of the Conduction Band Distance.- 5.8.6 Energy W of the Chemisorption Level.- 5.8.7 Equilibrium Constant of Physisorption.- 5.8.8 Oxygen Pressure.- 5.8.9 Temperature.- 5.9 Effects of the Defect Structure of the Oxide.- 5.9.1 Models with Oxygen Interstitials, Space Charge Effects.- 5.9.2 Effect of the Oxygen Pressure.- 5.9.3 Models with Oxygen Vacancies and Metal Vacancies.- 5.10 Simulation of Experiments with the Volumetric Method.- 5.10.1 Reaction Model.- 5.10.2 Results of Model Calculations.- 5.11 Reaction Mechanisms of Low-Temperature Oxidation.- 5.11.1 Fundamentals of the Mechanism.- 5.11.2 Physisorbed Oxygen.- 5.11.3 Defect Formation and Oxide Formation.- 5.11.4 Electronic Structure and Electronic Currents.- 5.11.5 Effects not Considered by the Models.- 5.11.6 Approximations for Estimated Oxidation Curves.- 5.11.7 Experimental Results and Model Calculations.- 5.11.8 Conclusions.- 6 Poisoning of Hydrogen Reactions.- 6.1 Experimental Results.- 6.1.1 Wire Samples.- 6.1.2 Film Samples.- 6.1.3 Powder Samples.- 6.1.4 General Trends.- 6.2 Stability of Oxide Layers at Elevated Temperatures.- 6.2.1 Structure of the Model.- 6.2.2 Results.- 6.2.3 Conclusions.- 6.3 Surface Layer of Constant Thickness.- 6.3.1 Absorption, Dissociation and Permeation Control.- 6.3.2 Discussion of the Mechanism.- 6.3.3 Desorption, Surface and Permeation Controlled.- 6.3.4 Absorption, Permeation and Diffusion Control.- 6.4 Contamination Layers Growing During Exposure.- 6.4.1 Poisoning by Chemisorption Layers.- 6.4.2 Poisoning by Oxide Layers.- 6.4.3 Hydrogen Absorption in H2/O2 Gas Mixtures.- 6.4.4 Estimate of Exposure Time and H2 Absorption Before Poisoning.- Appendices.- A Chemical Potentials and Standard States.- A.1 Chemical Potentials.- A.1.1 Definitions.- A.2 Standard States and Standard Reactions.- A.2.1 Elements.- A.2.3 Physisorption.- A.2.4 Molecular Chemisorption.- A.2.5 Atomic Chemisorption.- A.2.6 Metal Interstitials.- A.2.7 Metal Vacancy.- A.2.8 Oxygen Interstitials.- A.2.9 Oxygen Vacancy.- A.2.10Other Compounds.- B Equilibria of Charged Species.- B.1 Poisson Equation.- B.2 Dipole Layers.- B.3 Space Charges.- B.3.3 Conclusions.- B.4 Mott Potential.- B.4.1 Oxygen Molecules as Acceptors.- B.4.2 Oxygen Atoms as Accepto…