It is well known that corrosion protection of pure Al is enormously improved by the formation of porous anodic oxide films and by pore sealing treatment. However, the effects of anodizing and pore sealing on corrosion protection for Al alloys are unclear, because the alloying elements included in Al alloys affect the structure of anodic oxide films. In the present study, porous anodic oxide films are formed on pure Al, 1050-, 3003- and 5052-Al alloys, and pore sealing was carried out in boiling water. Changes in the structure and corrosion protection ability of porous anodic oxide films on pure Al and the Al alloys by pore sealing, were examined by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). SEM observation showed that anodic oxide films formed on pure Al have a smooth surface after pore sealing, and that cracks are formed in anodic oxide films on 1050-, 3003- and 5052-aluminum alloys, after pore sealing. Corrosion protection after pore sealing increased with anodizing time on pure Al, but only slightly increased with anodizing time on the Al alloys.

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A liquid-phase ion gun (LPIG) was used to create a local H2S enriched environment near Cr-containing steel surface in Na2S solutions in an attempt to induce sulfide stress cracking on the specimen surface. In a 1.5 mM Na2S solution, anodic polarization of an LPIG Pt microelectrode at a potential of 1.90 V vs. SHE resulted in the local solution becoming successfully acidified to below pH 4, a pseudo-sour environment. When Cr-containing steel specimens were potentiostatically polarized under this pseudo-sour environment by LPIG, sulfides were formed on the specimen surface depending on Cr-concentration, specimen potential, and chloride ion in solution. When LPIG was operated on Cr-containing specimens subjected to tensile stress using a four-point bending tester, cracks were formed on the specimen surface.

Coating is one of the most useful techniques for corrosion protection of metallic materials, however, if coating is damaged, local corrosion will occur. It is important to repair the damaged area of coating soon, however it needs much cost. From these, our research group develop the coating with self-healing property, called by self-healing coating. In this coating capsules containing healing-agent of coating are dispersed. If the coating is damaged, capsules will be broken at the same time. The healing-agent containing in capsules will flow out. The healing-agent reacts with the water vapor in the air to form a healing-structure and cover the damaged area of coating. The capsules contained healing-agent are produced as follows. First, the prepolymer, this is precursor of shell of capsules, drip into the aqueous solution dissolved glycerol, it hardly dissolves in the aqueous solution since the prepolymer is the oil phase. A mixture of oil droplets dispersed in the aqueous solution is formed. When this mixture is agitated with high speed, the oil droplets become micro spheres and emulsion forms. Furthermore, the reaction between prepolymer and glycerol occurs only at this interface between oil phase and water phase, spherical shaped capsules contained a healing-agent in a polyurethane shell can be produced. From our previous study, the coating with these spherical capsules has a self-healing property, because healing-structure could be observed at the damaged area of coating, but this structure covered damaged area, incompletely. It is necessary to improve self-healing property of coating. From the self-healing mechanism of the coating, the self-healing property of the coating will be strongly depended on the amount of healing-agent flowing to the damaged area. Therefore, we start the development of the coating with capsules with other shape such as fiber shape are dispersed in order to develop an advanced self-healing coating with higher healing property. Considering the procedure of capsule formation, the shape of capsules can be controlled by the agitation speed and viscosity of prepolymer solution. The shape of capsules will be related to the amount of healing-agent flow from capsules to the damaged area of coating, when coating is damaged. e.g. more amount of healing-agent will flow from fiber shaped capsules than that from spherical shaped capsules, because fiber capsules will be arranged horizontally to the metal substrate due to the flow during the formation of coating, and the more capsules will be broken, when vertical damage was formed in the coating. In this paper, the shape of capsules produced from prepolymer solution with high viscosity and self-healing property of coating dispersed with these capsules were discussed. The procedure synthesizing capsules is follows. The prepolymer prepared by reaction between TDI and glycerol in cyclohexanone as a solvent under 75 ℃, 600 rpm. In order to increase the prepolymer concentration and viscosity of solution, the heat treatment of prepolymer solution were performed under 140 ℃, 8 min. After heat treatment, IPDI as a healing-agent, and xylene as inhibiter solidification inside of capsules were added. First, this prepolymer solution drip into the sodium dodecyl sulfate and glycerol aqueous solution with low agitation speed (200 rpm). The prepolymer solution was not dissolved in the aqueous solution and small oil droplets were dispersed in the aqueous solution. The shape of some of droplets will be changed from spherical to long spheroidal or fiber by agitation of solution. Furthermore, the shell formation reaction take place only at the interface between oil and water phases, the spherical, spheroidal and fiber shaped capsules could be formed. For comparison, the capsules produced under high agitation speed (600 rpm) and those from prepolymer solution without heat treatment were also prepared. These capsules were observed by a scanning electron microscope SEM. Fig. 1-a show the shape of capsules prepared from prepolymer solution without heat treatment under high agitation speed, 600 rpm. From this image, only spherical with 20 - 60 µm of diameter can be observed. The shape of capsules from same prepolymer under low agitation speed, 200 rpm, also only spherical however the size of capsules is bit larger, the maximum diameter is about 80 µm, as shown in Fig. 1-b. The shape of the capsule the produced from prepolymer with heat treatment with high agitation speed, shown in Fig. 1-c, are similar to that without heat treatment. In contrast to these, the capsules produced from prepolymer with heat treatment under low agitation speed have some kinds of shape, such as spherical, spheroidal and long fiber. The coating dispersed with these shaped capsules will be also discussed. Figure 1

Al and Al alloys are used for many purposes, e.g. automobiles, heat exchanger, electronics, because of their good properties such as lightness, high heat conductivity, good processability, hardness, and so on. However, corrosion protection of these materials are not so high, corrosion of Al, such as pitting corrosion and atmospheric corrosion, will occur during operation. From this, some kinds of surface treatments are needed for improvement of corrosion protection of Al used for long-term. A polymeric coating is one of popular technique to improve the corrosion protection of substrate metal. However, corrosion protection of substrate covered by polymeric coating will easily lose by mechanical damage of the coating, leading to exposure of substrate metal to surroundings and to the local corrosion of substrate under damaged area of coating. From above, new surface treatment techniques for Al substrate to keep high corrosion protection, even the surface was damaged, are developed in our research group. This is a coating, with self-healing property by dispersion of micro-capsules containing the healing agent of coating. When the coating is damaged, the healing agent flow out to the damaged area of coating and react with water vapor to form the self-healing structure and this can be covered to the damaged area of coating. However, the procedure of synthesis of micro-capsule containing healing agent is too complex and yield of this is too low to synthesize the capsules with low cost. From above, we start to develop the new type of self-healing coating. This coating can be formed on Al alloy anodized. As you know by anodic oxidation of Al alloy, electrochemically in some kind of acidic solution, porous type of anodic oxide film can be formed on Al alloy, which have many small pores arranged regularity. Pores of porous film are used as a container of healing agent of coating. Firstly, the pores in porous film formed on Al alloy were filled by healing agent. And then, this sample was covered by polyurethane coating. If this coating was damaged, mechanically, healing agent contained in pores of porous film, flow out to the damaged area and reaction with water to form polyurea as a self-healing structure and cover to the exposed Al substrate. In this study, healing property of this type of self-healing coating is investigated by observation of the surface of specimen with scratchin. #1050 Al alloy (size : 20 mm × 20 mm × 1.5 mmt) were electro-polished in CH3COOH / HClO4solution. And then anodic oxide films were formed on pretreated specimens by anodizing in (COOH)2 solution with a constant current density of 200 Am-2 for 1 hr. The anodized specimens immersed in IPDI for 100 min with ultrasonic bath, in order to promote that IPDI soln. to penetrate to pores of the porous film. After wiping the surface of the specimen by soft tissue, then a mixed solution of ethylene glycol and prepolymer of polyurethane coating was purged to specimen surface and leave for 24 h to form the polyurethane coating on anodized Al alloy surface. The prepolymer was synthesized by using the mixture of TDI, glycerol and cyclohexanone. Mixture was agitated under 600 rpm of stirring rate for 24 h. In order to remove the water dissolved in this mixture, the first 1 h of agitation, the mixture was bubbled by passing pure N2 gas. During the agitation, TDI reacts with glycerol to form the precursor of polyurethane. After specimen damaged by scratching with 7 N of load and ageing, corrosion protection of damaged Al alloy specimens with polyurethane coating were evaluated by immersion tests. The coated specimens were immersed to CuSO4 / KCl solution kept at room temperature for 1 day. After the immersion tests, to remove the coating, the specimens were immersed to the coating remover solution. And then, specimens were immersed to H3PO4 / K2CrO4 solution. Surfaces after immersion tests and removing of surface layer were observed by scanning electron microscopy (SEM). From the SEM observation for damaged specimen covered with porous film and normal coating, as shown in Fig. 1-a, sharp and deep scar can be seen at the canter of image of specimen surface. The scar can be seen on the image of damaged specimen with self-healing coating on anodized specimen, however, unique structure also can be observed at the bottom of scar, shown in Fig .1-b. This structure may be formed by the reaction between water in air and IPDI contained in the pore of porous film on Al alloy, thus, this coating has a self-healing property. Figure 1