Acknowledgements 1. Introduction 2. Electromagnetic wave propagation 3. The absorption of light 4. Specular reflection 5. Single particle scattering: perfect spheres 6. Single particle scattering: irregular particles 7. Propagation in a nonuniform medium: the equation of radiative transfer 8. The bidirectional reflectance of a semi-infinite medium 9. The opposition effect 10. A miscellany of bidirectional reflectances and related quantities 11. Integrated reflectances and planetary photometry 12. Photometric effects of large scale roughness 13. Polarization 14. Reflectance spectroscopy 15. Thermal emission and emittance spectroscopy 16. Simultaneous transport of energy by radiation and conduction Appendix A. A brief review of vector calculus Appendix B. Functions of a complex variable Appendix C. The wave equation in spherical coordinates Appendix D. Fraunhoffer diffraction by a circular hole Appendix E. Table of symbols Bibliography Index.

Theory of Reflectance and Emittance Spectroscopy

Electrochemical corrosion of unalloyed copper in chloride media––a critical review

Low-temperature oxidation is a reaction, occurring at or below room temperature, between a solid and a gas. It usually involves the combination of oxygen with metals, and it has the greatest commercial impact in the presence of moisture, as in corrosion. Cabrera and Mott put forward a theory of low-temperature oxidation, based on the assumption that cation migration occurs under the influence of a potential built up across the growing oxide film. Recent experimental results require that this theory be expanded to explain recent observations such as anion migration during oxide growth and the transition from the initial chemisorbed monolayer to a bulk, threedimensional oxide. The additional ideas put forward in the present paper may be summarized as follows. Low-temperature oxidation is controlled by the nature of the oxide; whether it is a network former or a modifier. A period of fast, linear oxidation is followed by a slow logarithmic reaction whose rate, in turn, can increase if the oxide film crystallizes to form grain boundaries. The initial fast oxidation is a continuation of the chemisorption process. Place exchange (anions and cations interchanging positions) occurs when the energy due to the image force of an oxygen ion is greater than the bond energy holding the ion in place. A stable film forms when this bond energy is greater than the image force energy. The oxygen ions formed on the oxide surface then set up a potential across the film. This potential provides the driving force for continued reaction. Oxide growth during this later stage is a slow, logarithmic process. A barrier to ion transport exists at the gas-oxide interface in the case of anion migration and at the metal-oxide interface in the case of cation migration. In both cases, the field built up across the oxide lowers the barrier sufficiently so that ion migration can occur. Network modifiers allow cation migration. The reaction rate is sensitive to crystallographic orientation of the metal, but not to oxygen pressure. A constant voltage is maintained across the film, so that the Cabrera-Mott theory explains the logarithmic kinetics. Network-forming oxides allow onion migration. The number of anions, and hence, the rate of reaction, is sensitive to oxygen pressure, but not crystallographic orientation of the metal substrate. Since the potential is a result of the mobile anions, the film tends to grow under constant field. The logarithmic kinetics then must be explained by an increasing activation energy for ion transport, as proposed by Eley and Wilkinson. The logarithmic growth rate can be increased by the presence of water vapor if the water introduces “dangling” bonds into an oxide network structure. Crystallization of the oxide film also increases its rate of growth and results in the formation of oxide islands.

Low-temperature oxidation

Corrosion inhibition by Justicia gendarussa plant extract in hydrochloric acid solution

NEXAFS investigations of transition metal oxides, nitrides, carbides, sulfides and other interstitial compounds

Ellipsometric‐Potentiostatic Studies of Iron Passivity I . Anodic Film Growth in Slightly Basic Solutions

The optical constants of clean iron single-crystal surfaces maintained in an ultrahigh vacuum were determined. An ellipsometric technique was used to determine values of the optical constants as a function of wavelength in the region of 3600–7000 A. A maximum at 4900 A in the conductivity versus wavelength curve indicates the presence of an interband transition.

Optical Constants of Iron in the Visible Region

The oxidation at 300° K of high purity iron surfaces prepared under ultra-high-vacuum conditions was studied using ellipsometry to measure film thickness. By working at low oxygen pressures (between 10−7 and 10−4 torr) it was found that the early stages of the oxidation process followed a linear growth law with rate being proportional to the pressure. This behavior is in agreement with a picture proposed by Cabrera. The sticking probability of oxygen in the pressure range studied was of the order of 5 × 10−3 Traces of water vapor lowered the limiting film thickness approached in the latter, nonlinear, oxidation stage to 18 A from the 26 A found at all pressures for dry oxygen.

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Room Temperature Oxidation of Iron at Low Pressures

Studies of passive film breakdown by detection and analysis of electrochemical noise

Polarized light was used to measure the thickness and optical properties of passive films as they were forming while simultaneous electrochemical measurements were being made. The film formation studies showed that a change in film thickness of 15–20Aa was associated with the onset of a passive potential. A direct, logarithmic‐type law governed the growth of a semiconductor film with crystallographic orientation of the substrate having little effect.When iron surfaces prepared in an ultrahigh vacuum (a vacuum of the 10−9 Torr order of magnitude), were passivated a 20Aa film formed instantaneously on the introduction of an air‐saturated . This film then dissolved and a new film commenced to grow. A passive potential coincided with a film 15Aa thick. No such initial dissolution occurred when the solution contained only dissolved oxygen, the instantaneously formed film continuing to grow and a passive potential occurring after the growth of around 40Aa. When the solution contained no dissolved gases, the instantaneous film did not form.Film breakdown studies revealed that only the 20–30Aa film next to the metal was responsible for passivity even if thicker films were initially present. Studies of the sites of film breakdown showed that the number of sites was highest for films on {110} iron surfaces and that these sites were not related to points where dislocations intersected the surface. These studies support the oxide film theory of passivity.

Jerome Kruger

Papers

Ellipsometric‐Potentiostatic Studies of Iron Passivity I . Anodic Film Growth in Slightly Basic Solutions

Optical Constants of Iron in the Visible Region

Room Temperature Oxidation of Iron at Low Pressures

Studies of passive film breakdown by detection and analysis of electrochemical noise

Optical Studies of the Formation and Breakdown of Passive Films Formed on Iron Single Crystal Surfaces in Inorganic Inhibitor Solutions