Publications

我々は，これまでの研究において，クロロベンゼンを反応阻害溶媒として用いることにより，液体修復剤を内包するポリウレタンカプセルを形成できることを見出すとともに，これを分散させたポリウレタン樹脂塗料をアルミニウム板上に塗布した後，外的損傷を加えると塗膜が自己修復作用を示すことを報告している．本研究ではカプセル合成の際に添加する阻害溶媒の種類と量に着目し，作成した塗膜の自己修復能を調査した．特にトルエンおよびキシレンは阻害効果が高く，これを用いて作成したカプセルは多くの修復剤を内包し，これらを分散させた塗膜の自己修復能が非常に高いことが明らかとなった．

A Dynamic Electrolyte Film Corrosion (DEFC) model is presented that integrates a model for uniform film condensation/evaporation in presence of salts with a simple model of iron corrosion. The focus is on the role of the film thickness. A limited number of measurements confirms that it is unavoidable to consider the hygroscopic effects. The model is used to simulate the role of sample thickness, heat transfer and changing rates of temperature and relative humidity in well defined climate chamber conditions. Obtained film thicknesses and corrosion rates are simulated using identical input data in absence of salt and for two salts (NaCl and a seawater-like mixture of 90%NaCl-10%MgCl2). The large indirect influence of salts on the corrosion is discussed. Also one-week simulations are performed based on recorded and averaged meteorological data. They show that averaged meteorologic data will lead to incorrect results.

In this research, a novel governing mechanism has been proposed for the formation of conversion coating on the thermal oxide film of Advanced High Strength Stainless Steels (AHSSS). These new lightweight and engineered materials are being designed to impart emission reduction and solid performance. This coating has been characterized using advanced surface analysis such as HAADF-STEM, GDOES, and ToF-SIMS. The results showed that the conversion components can be found not only on the surface but also at the oxide/metal interface. This deposition in the depth happens preferentially in the Si-poor regions and with the penetration of the conversion components into depth. It was indicated that fluoride ions play an important role to facilitate this penetration by dissolving the less stable components in the oxide film. Dissolution of the Fe in the Fe-Cr solid solution structure results in the formation of a mixed chemical structure containing Cr and P. This novel mechanism brings a new insight into the field of conversion coating when a thick oxide film is present on the top surface.

No abstract is provided for this article.

Lithium salts have been proposed as promising environmentally friendly alternatives to carcinogenic hexavalent chromium-based inhibitors for the corrosion protection of aerospace aluminium alloys (AAs). Incorporated into organic coatings, lithium salts are released at damaged locations to establish a conversion layer in which distinct sublayers have different barrier characteristics. Thus, detailed knowledge on the sequence of formation events from the early stages of nucleation towards the final multi-layered arrangement is essential for developing and optimising lithium-leaching technology for protective coatings. Here, liquid-phase-transmission electron microscopy (LP-TEM) is employed to observe nanoscopic morphological evolutions in situ during the lithium-based conversion process of AA2024-T3. Thanks to dedicated preparation of delicate sandwiched TEM specimens allowing us to explore the events cross-sectionally, we provide real-time direct mechanistic information on the conversion process from the initiation to an advanced growth stage. In parallel, we perform supplementary ex situ SEM and TEM investigations to support and validate the LP-TEM findings. The unprecedented experimental approach developed and executed in this study provides an inspiring base for studying also other complicated surface conversion processes in situ and at the nanoscopic scale.

ZnO films have increasingly been in the spotlight due to their largely varied electro-physical and optical properties. For several applications, porous anisotropic nanocrystalline layers are especially interesting. To study the growth kinetics of such films during different fabrication processes, a powerful non-destructive in-situ technique is required. In this work, both ex-situ and in-situ spectroscopic ellipsometry are used along with advanced modelling techniques that are able to take both the anisotropy and the porosity of the films into account. Scanning electron microscopy, along with nitrogen absorption methods for measuring porosity, validated the ellipsometric data and proposed model. The film, grown by chemical bath deposition, was monitored from around 700 to 1800 nm in thickness. This same principle can now be used to monitor any other porous and/or anisotropic structure in an effective in-situ manner, e.g., growth of porous anodic aluminium oxides, nano-porous silica films, etc.

The protective film formed in a defect by leaching of lithium oxalate from model organic coatings during neutral salt spray exposure has been investigated. A scribed area of about 1 mm width was introduced on the coated AA2024‐T3 aluminium alloy. The scribed area was examined before and after exposure in neutral salt spray environment for 4, 8, 24 and 168 h by scanning and transmission electron microscopies. It was found that the lithium oxalate was able to leach from the organic coating during neutral salt spray exposure and it promoted the formation of a film that provided effective corrosion protection to the alloy. The typical film morphology consists of three different layers, including a relatively compact layer near the alloy substrate, a porous middle layer and a columnar outer layer. Variation of the film morphology was also observed at different locations of the scribed alloy surface, which may be related to the difference of local concentration of lithium species. Electron energy loss spectroscopy detected lithium, aluminium and oxygen in the film. Although the film showed the varied morphologies in different regions of the scribed area, the alloy substrate was protected from corrosion when the film was formed. Copyright © 2016 John Wiley & Sons, Ltd.

The knowledge of the composition and structure of hydrated films on aluminium is important for the bonding between aluminium and polymers. Native surface layers on aluminium consist of an anhydrous inner layer of amorphous A1203 and a hydrated outer layer, where the outer layer determines the adhesion properties. On the one hand the pseudoboehmite oxyhydroxide surface can be seen as a model for the chemistry found at the surface of the air-formed film after ambient exposure of the aluminium metal. On the other hand pseudoboehmite layers are promising for improving the adhesion between polymers and aluminium. Spectroscopic Ellipsometry in the visible (VISSE) and IR (IRSE) are powerful tools for the morphological (thickness and refractive index) and chemical characterisation of oxides formed on aluminium. Both optical techniques are used to study anodizing and hydration under boiling water conditions of aluminium. The growth in thickness and the chemical composition of the oxide formed is shown. The porosity of the layer together with the chemical composition is obtained and the changes as a function of boiling time are presented. In addition the above type of hydration is applied on the anodically formed barrier oxide film. IRSE shows that the hydration of this type of film by immersion in boiling water results in the conversion of aluminium oxide to pseudoboehmite. Finally the further oxidation of a native oxide film on aluminium is measured; the results are compared with the growth of the hydrated layers.

This study investigates the Volta potentials of the differently treated zinc surfaces and the interface dipole moments after adsorption of carboxylic acid and anhydride molecules on zinc surfaces by means of scanning Kelvin probe (SKP). The interfacial bonding properties of carbonaceous contamination as well as adsorbed succinic acid, myristic acid, and succinic anhydride molecules with zinc substrates have been investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The variation of the Volta potential due to the treatments applied on zinc was evaluated by means of SKP. Moreover, the dipole moments of adsorbed carboxylic acid and anhydride molecules were measured and correlated to surface hydroxyl fractions and oxide electronic properties. The results clearly showed that the zinc Volta potential varies with the oxide composition, resistance, and the configuration of the molecules adsorbed.