Noboru Masuko

A TEM investigation of naturally formed oxide films on pure magnesium

The morphology and structure of oxide films formed naturally on pure magnesium by exposure to humid air and water have been investigated by use of ultramicrotomed cross sections and TEM. The initial film formed immediately after exposing fresh surface by scratching in air is thin and dense, and it has an amorphous structure. In humid air, a hydrated layer forms between the metal and the initial layer as a result of water ingress through the initial layer and metal oxidation. The film formed in water contains an additional top layer with platelet-like morphology, formed by redeposition of sparingly soluble magnesium, which migrates outward also through the initial layer. The properties of these layers and their significance in determining the corrosion behavior of magnesium are discussed.

Morphology and Structure of Oxide Films Formed on Magnesium by Exposure to Air and Water

Oxide films formed naturally on pure Mg are investigated by the use of ultramicrotomed cross sections and transmission electron microscopy. The film formed in air immediately after scratching the metal surface is initially thin, dense, amorphous, and relatively dehydrated. Continuing exposure to humid air or exposure to water leads to the formation of a thicker hydrated film adjacent to the metal. The film formed in water contains an additional top layer characterized by a plateletlike morphology. The structure of these layers and their significance in corrosion protection are discussed. The changes occurring in these structures as a result of exposure to the electron beam are reported.

The duplex structure of cell walls of porous anodic films formed on aluminum

Abstract The depth and the amount of anion incorporation into the cell walls of porous anodic films formed in a phosphoric acid solution have been studied using TEM and EDX. Both increased with increasing forming voltage; however, a duplex structure could not confirmed for films formed at voltages below 10V.

Electrochemical properties of iron rust

Abstract In order to elucidate the electrochemical properties of iron rust, galvanostatic cathodic polarization of rusted steel and rust electrodes, prepared by fixing a piece of rust plate on an acrylic plate with conductive adhesive, was examined. The change in the amount of crystalline substances in the rust layer was observed by X-ray diffraction. The electrochemically active intermediate substances, could not be identified by X-ray diffraction, but their behaviour was distinguished from that of crystalline substances. The rest potential of the rust electrode was controlled by the equilibrium potential of intermediate substances. “An overlapping dual electrode” model is proposed for rusted steel in aqueous solution. Beneficial elements added to weathering steel inhibit the formation of crystalline magnetite in the cathodic reduction process of rust and increase the electrical resistance of the rust layer.

The high resolution observation of porous anodic films formed on aluminum in phosphoric acid solution

Abstract The structure of porous anodic films before and after transformation caused by electron beam irradiation was studied by high resolution electron microscopy. The structure of as-produced anodic films formed in phosphoric acid solution was amorphous. Lattice images obtained from the film after irradiation revealed that a cell wall consisted of three layers of different crystallinity: an outermost amorphous layer next to a pore wall, an intermediate incomplete crystalline layer and an inner highly crystallized layer. Structure difference between three layers was explained by the quantitative difference of incorporated anions and protons.

The observation of anodic oxide films on aluminum by high resolution electron microscopy

Abstract High resolution electron microscopy has been used for the study of internal structure of porous anodic films with relate to the incorporated species such as electrolyte anions and water. The observation of the crystallization process of ion thinned porous films under a strong electron beam with the change of diffraction patterns and lattice images revealed that the rate of crystallization decreased in the order of the films formed in chromic acid > phosphoric acid > sulfuric acid solutions, which was correlated to the electrolyte anion content in each films. Transformation from amorphous to crystalline oxide was observed in a few minutes for the film formed in chromic acid solution which contains little chromium. Incorporated species and water inhibit crystallization because they lower the regularity of the oxide structure. Furthermore, morphological changes suggested the substantial nature of the anodic oxide films.

Effect of high supersaturation at the initial stage on diamond nucleation phenomena

Abstract The surface of diamond film deposited by chemical vapor deposition is usually too rough for it to be used as optical coatings for UV or visible light. The surface roughness is due primarily to the low density of diamond nuclei. To enhance the nucleation density of diamond, we investigated the effect of high supersaturation during an initial stage of deposition on the diamond nucleation phenomena. The deposition process was performed in two sequential steps: first, carbonic material was deposited onto the substrate in a CH 4 H 2 plasma for a few minutes; second, diamond particles were grown in a CH 4 O 2 H 2 plasma for 30 min. The high CH 4 concentration in the initial stage increased the number density of diamond particles by nearly two orders of magnitude. When the high concentration treatment was limited to a few minutes, the deposition of other carbon allotropes was found to be suppressed.