Recent exciting experimental studies on the structures and phase transitions of metal surfaces are presented in this review. Atom-resolved images are shown with techniques of Scanning Tunneling Microscopy and Transmission Electron Microscopy. The natures of structural phase transitions at surfaces are discussed referring to those of bulk metals.
Recent progress in dynamical approach to the activated adsorption and its reverse process over well-defined metal surfaces has been reviewed. Experiments monitoring the threshold for the dissociative adsorption and the extent as a function of the incident energy have been made. And this provided information on the height and orientation of the activation barrier as well as the presence of quantum mechanical tunneling through the barrier. The angular distribution of desorbing molecules and the velocity distribution yield a wealth of information on the interaction between the molecules and surfaces. State specific measurements of desorbing molecules are briefly summarized.
The Pt and Ir surfaces are known to provide charactersitic superstructures by changing the atomic arrangement although these metals have only one crystalline form in the bulk. So far, such structural rearrangement has been accepted as a two dimensional phase change. In this review, it is discussed from a view of morphological change of the crystal. Metal surface has a potentiality for the synthesis of novel compounds, and in fact some novel compounds have been prepared on these metal surfaces by performing catalytic reactions. Surface nitride on Pd (100) is an example of a novel compound which is prepared by a catalytic reaction of NO and H2. The nitride has a c (2×2) strucrture and is a reactive intermediate giving ammonia. A hexagonal OH overlayer grown on Ni (100) surface during the reaction of H2 and O2 is also a novel compound, which is an intermediate for water formation reaction. These are the first examples showing that the intermediates have ordered structures, and this fact might contradict the reaction mechanisms based on random reaction of adsorbed species.
Experimental and theoretical efforts toward the unde standing of the chemical properties of heterometallic junctions are reviewed. The main focus is b ought onto the valence electronic structure of interfaces and its relevance to the adsorption of carbon monoxide. Examples such as Cu/Ru (001), Fe/Ru (001), Pd/Ta (110), Pd/Al (111) and Pd/Au (111) are presented and models describing dominant interaction in these systems are outlined to discuss the nature and origin of unique properties of the heterometallic junction.
Low temperature operation of an impregnated cathode has been achieved by introducing Sc atoms into a mono-atomic-order layer on the cathode surface. The mechanism of electron emission enhancement of the Sc type impregnated cathode has been clarified by Auger electron spectroscopy as well as X ray diffraction. It is found that the electron emission is enhanced by the presence of the surface mono-atomic-order layer composed of Ba, Sc and O, that reduces the cathode work function. Among all, formation mechanism of atomic Sc plays the most important role. The following reaction to produce Sc atoms is proposed. Sc2W3O12+3Ba=2Sc+3BaWO4 Based on the mechanism of electron enhancement, a (W-Sc2W3O12) coated impregnated cathode is proposed. This cathode is found to be more stable, i.e. more reproducible, than the previously proposed (W-Sc2O3O3) coated impregnated cathode. Improved stability is seen both in obtaining a good electron emission current and in fabricating coated films of designed properties.
Precious metal catalysts have been used in various commercial processes. In this review, some industrial processes using metal catalysts such as the three-way catalysts for the treatment of automobile exhaust and bifunctional catalysts for reforming process are described. As important factors for the catalytic activity and selectivity, the size and microstructure of metal particles and the formation of bimetal are reviewed. On Ni/SiO2, formation of benzene from cyclohexane is favorable on large particles, but selectivity to alcohol from aldehyde is high on small particles. Recent EXAFS results showed that the structure of the fine particles on supports changed readily and reversibly by the adsorption of O2 and CO. The addition of the second metal to form bimetal is an indispensable method for some industrial catalysts. The addition effects are generally explained by the ensemble and ligand effects.The structures of the bimetallic particles as well as the surface composition are stated. The new methods of preparation of supported bimetallic catalysts are introduced.
The growth process of transient oxide films in the initial stages of moderate temperatures alloy oxidation is discussed. The effect of the bulk alloy composition, starting oxidation procedures compositional change in the oxide films, epitaxy, the initial surface segregation, are surveyed. Schematic diagrams and the surface oxide map are used shown to illustrate the morphology and structure of the films, as revealed by the combined surface analysis techniques. The following topics are included. (1) The transient oxidation of Fe-18 Cr alloy. (2) The early stage of oxidation of Fe and surface segregation effects.
This review describes a recent advanced knowledge of the thermodynamics of Fe-Cr-O system in such low oxygen potential atmospheres as that in bright annealing. More attention is paid to the redox reactions of Fe-Cr-O system, especially the reaction of chromiun in a ferrous alloy with the water vapor in BA atmospheres having low dew points to form Cr2O3 and FeCr2O4. An outline of the surface characteristics of Fe-Cr alloy as bright annealed is given together with a discussion of the crystal structure of oxide films and their effect on the behavior of corrosion.
The all-aluminum alloy vacuum system was applied for TRISTAN vacuum system, molecular beam epitaxy and chemical vapor deposition processes, and other general purpose ultrahigh vacuum systems. The extremely high vacuum (XHV) of the order of 10-13 Torr has been obtained. One of the basic technologies of the aluminum alloy ultrahigh vacuum system is the surface control of the aluminum alloys with regard oxide layers. Extrusion, machining, and heating in oxygen and argon atmosphere provide a thin, stable and high density oxide layers on the aluminum alloys, and extremely low outgassing rate after 150°C baking procedure was achieved. The oxide layer was characterized by SEM, AES, IMA, and TENT. A high purity aluminum with low internal gas content has superior performance for the thermal desorption, adsorption, and dynamic desorption. A clad material of the high purity aluminum and high strength aluminum alloys are described.
The importance of in-Situ analysis has been increasing in the study of corrosion protection mechanism of surface films on corrosion resistant metals and alloys. The necessity, merits, and possible subjects of in-Situ analysis are discussed and the methods of analysis are reviewed. Typical results obtained using these methods are given and, finally, problems in these methods are pointed out.
From the viewpoint of electrochemistry and corrosion science, recent applications of the ellipsometric method are briefly reviewed. Lateral variation in the thickness of passivated films on alloy steels due to microstructure (grains and their orientation) is measured by a microscopic ellipsometer. Underfilm corrosion on a painted steel surface is analyzed by a conventional ellipsometer as well. The analysis indicates that the dissolution of oxide layers on the steel surface, which are formed by oxygen reduction reaction with high alkaline, is primarily responsible for the paint delamination. Both techniques can be expected as useful in-situ methods to develop a new field in corrosion science.
Structures of typical oxide films formed on aluminum, and the structural changes with a combination of treatments are reviewed. Oxide films on Al are classified into four typical groups by structure : porous oxide films, barrier oxide films, thermal oxide films, and hydroxide films. The porous oxide films are formed anodically in acid solutions and barrier oxide films in neutral solution and the thermal oxide films are formed by heat treatments and hydroxide film by hydrothermal treatments. The morphology and formation behavior of these oxide films are described briefly. Three characteristic phenomena observed with the combination of treatments are described : pore-filling, sealing, and formation of composite oxide films. Pore-filling, where pores of porous oxide films are filled with new oxides, takes place by anodizing porous oxide-covered Al in a neutral solution, and is useful for determining the porosity of the oxide film. Sealing of pores in oxide films is attained by hydration of oxide exposed to hot water, and the dissolution rate of the sealed oxide film is much lower than that of unsealed film. Composite oxide films are formed by anodizing hydroxide-covered Al in neutral solutions, and the growth of the oxide film proceeds by dehydration of hydroxide at the hydroxide/oxide interphase and formation of oxide at the oxide/metal interphase.
This report reviews topics on new function of anodic oxide films on aluminum with cylindrical parallel pores. At present, the porous films are utilized for various uses. The fact is mainly based on fundamental properties of films such as durability, abrasion resistance, electrical insulation and dielectrical property. Wide application are now expected, but the actual uses are limited. Recently, unique characteristics on cell structure between pore and pore, and on condition of distribution of anion and adsorbed water in cell, are found by using highly efficient instruments. Functional materials are deposited in pores of the films and new uses of the films are developing for products such as diaphragm, separate film, catalyst film, chemical sensor, electrical devices and photo functional device.
As has been well known since Kramer's findings, exoelectron emission correlates closely to tribological damages and adsorption of gas species. Technological applications of exoelectron emission to the monitoring of tribological processes have been culminated in a number of research papers. Recent research efforts appear to be centered on the mechanism of exoelectron emission. This paper describes exoelectron emission stimulated by ultraviolet light, electric field, and tribological inputs. The trap level of exoelectrons for Al was found at 3.55eV below the vacuum level. The experimental evidences of field stimulated exoelectron emission from pure Al and of tribostimulated exoelectron emission from graphite are introduced.
Friction is defined as the shearing force of contacting surfaces. However, the friction behavior depends not only on mechanical properties but also on physical and chemical properties of the metal surfaces, since the contacting area is sensitively affected by the contaminats of adsorped molecules or chemical compounds formed on the surfaces. In this paper, the effects of surface properties on the friction of metals are discussed in the following points; (1) effects of chemisorption of gas molecules, (2) effects of lubricants including a Langmuir-Blodgett film lubrication, (3) effects of adhesion force in the contacting area between the two metals, and (4) effects of wear process in the friction behavior.
Chemical analysis of a small amount of rust was taken from the blade part of a halberd excavated in an old tomb has revealed that magnetile ores were used as the starting raw material. The carbon content of the steel of the blade was estimated to be about 0.5 to 0.6% by the examination of microstructure of rust. The composition of non-metallic inclusions in the steel suggests that fluxes mixed with CaO-containing materials were utilized in the steelmaking process. Method for manufucturing the halberd is also discussed.