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Corrosion of 4043-Al alloy was examined by repeated wet–dry cycle tests with NaCl solutions at 323 K, and compared with immersion test corrosion in 0.2–5.5 kmol/m3 NaCl solutions. The Al alloy specimens after the immersion tests for 86.4 ks (1 day) or 604.8 ks (7 days) showed preferential dissolution of the aluminum matrix around Si-phase compounds, and the dissolution was more remarkable at lower NaCl concentrations. Mass loss of the specimens after the 604.8-ks immersion was also higher at lower NaCl concentrations. In the repeated wet–dry cycle tests, a 20 mm3 droplet of 0.2–5.5 kmol/m3 NaCl solution was initially dripped on the specimens, and left for 690 s to allow the drying up of the droplet, resulting in solid NaCl precipitation. Then, the dissolution and precipitation of NaCl were repeated a further 149 times by dripping 20-mm3 pure water at 690-s intervals. The specimens after the 150 cycles showed different corrosion modes at the center and edge of the droplets. At the edge, 40–80 × 10−6 pits/m2 of 20–50 µm diameter had formed, showing more corrosion with higher NaCl concentration droplets, and at the droplet center, the corrosion showed preferential dissolution of the aluminum matrix around the Si-phases, similar to the situation in the immersion tests. Copyright © 2015 John Wiley & Sons, Ltd.

In a previous study, self-healing polyurethane coatings with microcapsules containing healing agents have been developed for the protection of metal from corrosion. At the initial stage of the development of these coatings, we synthesized the microcapsules containing healing agents by adding organic solvents to inhibit the solidification of the whole capsule. In this study, the structure of the capsules formed with different solvents, such as chlorobenzene, toluene and xylene was examined. We also evaluated the self-healing ability of coatings with these capsules after damaging the coating by scratching. The amount of healing agents contained in capsules depends on the kind and the amount of solvents added. In the capsule formed with 20 or 50 wt%-chlorobenzene, there is almost no healing agent of liquid phase, while in the capsule formed with 70 wt%-chlorobenzen healing agents are contained. Toluene and xylene are more effective inhibitors than chlorobenzene. The capsule formed with 70 wt%-toluene or xylene contains much more amounts of the healing agent of liquid phase than that formed with 70 %-chlorobenzene, and the coatings with the former capsules have an appreciable self-healing ability.

Austenite formation on the surface of pure iron during nitriding in a mixture of NH3 and H2 gases and surface hardening due to formation of iron-nitrogen martensite by subsequent quenching were investigated. In nitriding at 973 K at a partial pressure of NH3(fNH3) of 5% and 10%, austenite layer is formed at the surface while double-layered structures consisting e-Fe2~3N and austenite are developed at fNH3 of 20%. In addition, at these high fNH3, voids are formed in e-Fe2~3N nitride as well as austenite with high nitrogen content. At fNH3 of 5% and 10%, the growth rates of austenite accords with parabolic growth law and become faster with increasing fNH3. On the other hand, after prolonged treatment at fNH3 of 20%, thickness of the nitrided zone is less than that for 10% due to substantial formation of voids and resultant emission of nitrogen from the surface. The hardness of the nitrided zone is nearly the constant at 800HV in the specimen nitrided at fNH3 of 5% whereas softening near the surface occurs in the specimens nitrided at fNH3 of 10% and 20% due to formation of the retained austenite and the voids.

In the novel hydrosilylation curing system, derived from an α,ω-bis(2,4,6,8-tetramethylcyclotetrasiloxan-2-yl) carbon chain crosslinker 1 and allyl-group-end-blocked oligomer 2, effervescence phenomena during curing were examined. We found that the main component of the gas formed was propylene when 1 and 2 were heated in the presence of H2PtCl6 for cure and that the amount of the gas was largely dependent on the structure of allyl functionality; in the system with allyl carbonate or allyl ester gas genaration was very distinctive and propylene formation was dominant well over the normal hydrosilylation.

We describe here the preparation and properties of a novel curing system, which has been derived from an SiH-containing organic oligomer 1 and an allyloxy end-blocked organic oligomer 2. The composition of these oligomers could be crosslinked via a platinum-catalyzed hydrosilylation reaction, that is, the addition reaction of the SiH bonds of 1 to the allyl functionality of 2, above 100°C, yields a rubbery material in a short period of time. The compatibility of the SiH-containing oligomer 1 with the allyloxy end-blocked oligomer 2 was governed by the oligomer main chain employed. Hence the SiH-containing oligomer 1 was completely miscible with 2, having the same main chain and, thus, the system yielded a homogeneously cured material. The poly(propylene oxide) curing system 1a/2a was systematically investigated in detail to manifest its curing behavior and crosslink structure. © 1993 John Wiley & Sons, Inc.

Several organic oligomers (Mw = 103–104 order) containing SiH bonds of the general formula 1 have been successfully synthesized by platinum-catalyzed partial hydrosilylation reaction of an allyloxy (or an allyl carbonate) end-blocked linear organic oligomer 2 with 2,4,6,8-tetramethylcyclotetrasiloxane, [CH3(H)SiO]4 (3) (hereafter called hydrocyclotetrasiloxane). 1H-NMR spectroscopy confirmed the introduction of hydrocyclotetrasiloxane moiety into the oligomers through SiC linkage by hydrosilylation reaction. 13C-NMR analysis revealed that the cyclic structure of the starting hydrocyclotetrasiloxane 3 was retained intact in product 1. As the precursor for 1, allyloxy (or allyl carbonate) end-blocked oligomers 2 could be prepared from hydroxyl-terminated oligomers 4. The storage stability of product 1 was significantly influenced by the platinum catalyst still remaining in it. The poor stability was improved by decreasing the amount of the platinum catalyst and/or by adding coordinating compounds. As a result, an excellent stability of product 1 was obtained. © 1993 John Wiley & Sons, Inc.

Synthesis of New Organic Crosslinking Reagents Containing SiH Bonds and Curing System Thereof

In situ (as kept at 0.25 V vs. SHE in solution) and ex situ (in air) nanoscratching tests were performed to the iron single crystal (110) and (100) surfaces passivated at 0.25 V (SHE) in pH 8.4 borate solution to evaluatethe correlated mechanical and electrochemical properties, i.e., mechanoelectrochemical properties of the passive surfaces. The friction coefficient of the passive iron (100) surface was larger than that of the passive iron (110) surface, irrespective of in situ or ex situ nanoscratching. The friction coefficient obtained with in situ nanoscratching for both the passive iron (110) and (100) surfaces were significantly larger than that obtained with ex situ nanoscratching. The increase in the friction coefficient due to in situ nanoscratching is explained in terms of a series of mechanoelectrochemical reactions taking place at the moving front of the indenter, such as active dissolution from the film rupture sites followed by renassivation.