Oxide on metals

Surface analysis has made enormous contributions to the field of adhesion science. It enabled investigators to probe fundamental aspects of adhesion such as the composition of anodic oxides on metals, the surface composition of polymers that have been pretreated by etching, the nature of reactions occurring at the interface between a primer and a substrate or between a primer and an adhesive, and the orientation of molecules adsorbed onto substrates. Surface analysis has also enabled adhesion scientists to determine the mechanisms responsible for failure of adhesive bonds, especially after exposure to aggressive environments. The objective of this chapter is to review the principals of surface analysis techniques including attenuated total reflection (ATR) and reflection-absorption (RAIR) infrared spectroscopy. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) and to present examples of the application of each technique to important problems in adhesion science. 

Since the paper by Pilling and Bedworth in 1923 much has been written about the mechanism and laws of growth of oxides on metals. These studies have greatly assisted the understanding of high-temperature oxidation, and the mathematical rate laws deduced in some cases make possible useful quantitative predictions. With alloy steels the oxide scales have a complex structure chromium steels owe much of their oxidation resistance to the presence of chromium oxide in the inner scale layer. Other elements can act in the same way, but it is their chromium content which in the main establishes the oxidation resistance of most heat-resisting steels. 

When studying the electrochemical promotion behaviour of catalytic oxidations on metals deposited on YSZ, one always makes the same observation Positive currents, i.e. O2 supply to the catalyst, cause NEMCA (electrophobic behaviour) only for high 02 to fuel (Pa/Pd) ratios in the gas phase. How can we explain this, at a first glance, counterintuitive but general observation ... 

Gong X-Q, Liu Z-P, Raval R, Hu P. 2003. A systematic study of CO oxidation on metals and metal oxides Density Functional Theory calculations. J Am Chem Soc 126 8-9. 

In summary, in situ STM studies of CO titration on the oxygen precovered metal surfaces have demonstrated atomic details of CO oxidation on metal surfaces and have shown excellent agreement with macroscopic kinetic measurements. Moreover, in situ studies have revealed an interesting but not well-understood, nonlinear behavior of reaction kinetics. The accelerated reaction rate observed takes place only when surface oxygen islands, either compressed oxygen islands or surface oxide islands, are reduced to the nanometer size. The nonlinear reactivity of these nanoislands is in stark contrast with the large adsorbate layer and requires further investigations. 

Mn(II) oxidation on metal oxides. The rate of oxidation of Mn(II) in the presence of y-FeOOH can be described by the following equation (26) ... 

In the studies described above the experimental conditions were chosen for experimental convenience, so they may differ greatly from those found in natural waters. To try to identify the factors that might influence Mn(II) oxidation on metal oxides surfaces in natural waters, the surface equilibria and kinetic models developed above can been used to predict the time scales for Mn(II) oxidation in these waters. 

A special problem can be the passivation of the electrode surface by insulating layers, for example, formation of oxides on metals at a too high anodic potential or precipitation of polymers in aprotic solvents from olefinic or aromatic compounds by anodic oxidation. As a result, the effective surface and the activity of the... 

It is surprising that the adsorption of Co2+ is anomalous when compared with other transition metal ions in that Co(II) and Ni(II) and to a lesser extent Cu(II) are very similar chemically. It is known (8) that certain metal ions can be catalytically oxidized on metal electrodes. It may therefore be possible for Co2+ in the present system to be oxidized to Co8+ in the region of the Mn02-water interface. Although this suggestion has... 

Mention has already been made of the uciion of oxygen and oxidants on metal. It should be noted that metals react with sulfides, such as hydrogen sulfide, and are subsequently subject to additional slow attack by oxygen and oxidants. Thus, copper reacts to form sulfide and then the basic copper sulfate. 

Similar to the catalyst of the catalytic thermometry sensor, the catalytic activity of the CTL-based sensor depends not only on the kind of catalyst material and the surface-to-volume ratio of the powder but also on the preparation procedure of the powder. In considering these conditions, a detailed comparison of the CTL catalytic activity has not been reported so far. The present authors and coworkers observed the CTL emission by ethanol vapor on y-aluminum oxide, barium sulfate, calcium carbonate, and zirconium oxide at a few hundred degrees. On the other hand, CTL emission is not observed during the catalytic oxidation on metal and semiconductive materials, e.g., tin oxide, zinc oxide, and copper oxide. 

Rust has been recognized for millennia and films of oxides on metals since the 1800s. However, for about 150 years, a tantalizing phenomenon remained unexplained. Some metals, suitably treated, enter a state expressively known as passive. Their normal reactivity to outside stimuli (contact with dissolving acids, for example) is quelled. A reason for this was hard to find for more than 150 years. None of the methods generally available before about 1950 detected anything on the metal, and yet its character had changed dramatically. 

Gallezot, P. and Besson, M., Carbohydrate oxidation on metal catalysts, Carbohydrate Eur., 13, 5-11, 1995. 

New experimental methods have been developed to growth well defined films of oxides on metal supports in UHV conditions. This approach allows in principle to overcome some difficulties connected to the use of electron spectroscopies for the study of insulating materials, as most of the oxides are. Recently, some very good review articles have been published on this subject [3-10]. It is no surprise that the increasing experimental activity has stimulated a parallel computational activity based on high-quality first principle calculations. 

The thermochemical cycle in Scheme 4 can be used to estimate the effect of one-electron oxidation on metal-hydride acidities. The method is analogous to one that has been extensively used to investigate organic cation radicals [10c]. Eq. 29 shows that measurements of °ox(MH) and °ox(M ) provide relative p a data for metal hydrides and their cation radicals. Absolute values for p a(MH +) are obtained if the acidities of the neutral hydrides are known. The oxidation potentials of 18-electron hydrides can be readily obtained by cyclic voltammetry. In our experience, the waves that are obtained are frequently chemically irreversible, even at rather high scan rates. Consequently, the oxidation peak potentials will be kinetically shifted and represent minimum values for the true °ox(MH) data, the estimates for p a(MH +) represent maximum values, and calculated Ap a are minimum values. 

Aerobic oxidations on metal macrocycles encapsulated in zeolites... 

The adsorption of alcohols, aldehydes, and carbon oxides on metal electrocatalysts has been extensively studied because of the significance of their oxidation reactions for electrochemical energy generation (7,9,81,195). Particular attention has been payed to the surface intermediates of methanol oxidation on platinum. At least two adsorption states have been assigned to methanol, a weak one possibly associated with physisorption (196) and one or more states arising from dissociative strong adsorption of the reactant (797, 198). Breiter (799) proposed a parallel scheme for methanol oxidation... 

The metal-ceramic interface constitutes a class of materials with extremely relevant properties which are crucial to a large series of technological applications such as anticorrosion protection, microelectronics and also in the chemical industry where they are commonly employed as catalysts. For obvious reasons, the preparation for these different applications depends on the final use of the material and both metals on oxides or oxides on metals can be prepared. 

The corrosion rate of metals may be controlled by either the anodic reaction or the cathodic reaction. In most cases of metallic corrosion, the cathodic hydrogen reaction controls the corrosion rate in acidic solution, while in neutral solution the cathodic oxygen reaction preferentially controls the corrosion rate of metals. Generally, the presence of corrosion precipitates, such as metal oxides and hydroxides, exerts a considerable influence on the corrosion of metals in neutral solutions. The effects of surface oxides on metallic corrosion will be discussed in the following section. 

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