Preparation of ultrathin two-dimensional polymer films on iron by modification of alkanethiol and alkylamine self-assembled monolayers with silane coupling agents is reviewed. These films are protective against aqueous and indoor atmospheric corrosion of iron, though iron oxide forms in the films during preparation and modification of the monolayers. Novel modifications of an alkanethiol self-assembled monolayer on copper are also described.
Electron microscopes have been playing leading roles in recent development of nano-technologies. Among various microscopes, transmission electron microscopes (TEM) in particular have unique characteristics and capabilities which include atomic order of resolution, analysis from localized nano-areas, etc. In this article, we report recent trends of hardware and software associated with TEMs. In response to materials science applications, higher voltage microscopes such as 300kV TEMs have been made available. These TEMs will be standard instruments for transmission electron microscopy for materials science in the future. Analytical functions including EDX, EELS, etc. have been significantly improved over the years both in hardware and software. With the development of field emission (FE) electron sources for TEMs analytical performance has been greatly improved. For specimen preparation, FIB systems have been successfully applied for transmission electron microscopy. Many materials which have been difficult with conventional techniques can now be prepared and examined using TEMs mach more efficiently than in the past. In this article, we have shown some typical applications for related with corrosion engineering.
Si diffusion layers on SUS 310 steel surfaces were formed by halide-activated pack cementation, and their high temperature corrosion resistance was evaluated. The Si diffusion layers formed in the sample surfaces consisted of an inner layer and an outer layer. The inner layer contained 11-12 mass% Si was uniform and adhesive to the substrate metal. It was found from XRD analysis that the inner layer consisted of two phases of α-Fe and Cr3Ni5Si2. The thickness of the inner layer increased with an increase in the treatment time and a rise in the treatment temperature. The inner layers of 60-80μm thickness were obtained by the treatments for more than 28.8ks at 1223K. The results of high temperature corrosion experiments showed that the corrosion resistance of the sample having Si diffusion layer was greatly improved by the formation of a protective inner scale consisting of SiO2.
The stress corrosion cracking (SCC) susceptibility of copper alloys in dilute NaNO2 has been investigated using slow strain rate test (SSRT), constant load test and electrochemical measurement. The SCC susceptibility examination in ammonia environment was also performed. As a result, aluminum brass showed high SCC susceptibility in low concentration of NaNO2 about 100ppm. The addition of the ammonium ion, which was reported to enhance SCC susceptibility, revealed to reduce the SCC susceptibility. The cause of increase in SCC susceptibility was attributed to the characteristics of nitrite ion. Addition of benzotriazole (BTA), which is widely used to reduce general corrosion, was studied to find the effectiveness of BTA as an inhibitor of SCC in NaNO2 solutions. The formation of protective film, which controls an anode reaction, was attributed to the inhibition of the SCC.
Real information on the corrosion resistance for such big structures as water gates could not be expected from tests using small plate coupons free from any one of crevice geometry. Specimens chosen for this test were two box like models mainly made of type 316 steel or type 304 steel. The first was a larger one with a size of 1340×1000×500 in mm, and the second was a smaller one with a size of 400×400×200 in mm, both of which were designed to simulate real configuration of the water gates in terms of shape and welds. These specimens were exposed for 503 days to a natural river site 9km upstream from the sea. For specimens positioned at a level between low and high tide, there occurred hardly any kind of corrosion. On the other hand, for all specimens immersed deep into the water, there occurred several forms of corrosion, for example, inside the rubber/metal crevice and under deposits, as well as dezincification from brass bearing.
The aim of this paper is to investigate fundamental damage behaviour of metallic materials such as aluminum, carbon steel and titanium, which have typically different crystal structures, by the single impact from low velocity to hypervelocity. Impact tests by a WC ball were performed on the three metallic materials at various impact velocities and at normal angle. Both two-stage light gas gun and ordinary air gas gun were used in this study. Indentation shapes on a cross-sectional surface and the ratios of crater diameter and depth to the diameter of the WC ball were examined. Three modes were recognized in indentation configurations independent of the type of materials. Average contact pressure, which was obtained by the impact energy divided by indentation volume, showed not only a mechanical property of the target material during the impact process but also fracture strength of the projectile. A single particle impact test at a shallow impact angle and at a hypervelocity showed huge material removal even if its single impact and suggested the difference in mechanism of the material removal between subsonic and hypervelocity impacts.