The influence of potential on surface fatigue crack growth retardation of mild steel in sea water was investigated at different applied potentials ranged from -770mV to -650mV (SCE) in terms of the rate of crack growth and from the fractographic observation of the fractured surface of specimens. Sinusoidal load at stress ratio of 0.32 was applied with frequencies of 0.17Hz at which crack arrest occurred because of crack tip blunting caused by dissolution and of 0.33Hz at which crack grew steadily under the freely corroding condition in sea water. Crack arrest reoccurred at potentials of -760mV and -750mV (SCE), which were near the free corrosion potential of unloaded specimen in sea water, in this case∼-760 mV (SCE), at both the frequencies, but this tendency for the crack arrest was less at 0.33Hz than at 0.17Hz. When testing at more positive potentials ranged from -740mV to -650mV (SCE), the crack grew steadily and the rate of crack growth was accelerated as compared with that in air at both the frequencies. The acceleration factor, (dl/dN)cf/(dl/dN)air, increased with increasing positive polarization, and was 2.4 for 0.33Hz and 1.9 for 0.17Hz at -720mV (SCE) and more positive potentials at a ΔK of 5.5MN/m3/2.
To investigate the plowing phenomenon of barnacles crust on the paint coating, steel test plates were separately coated with each of 4 types of paint varying in tar epoxy resin contents and were suspended in the sea. During 30 months of suspension, change in Vicker's hardness of coating was measured and attachment of barnacles and the plowing on coatings were observed. No plowing of barnacle was observed on the coating containing more than 40% v/v resin. The hardness of such coating was 1.6MHV, before suspension, but increased to 2.0MHV after 30 months. However, a high degree and frequency of plowings was observed on coating having 25% v/v resin with an initial and final hardness of 0.8 and 0.9MHV, respectively. Balanus trigonus and Megabalanus rose were observed as dominant glowers on the coatings. Especially, the latter is a more dangerous species with regard to plowing. Serious plowing was observed mostly on individuals larger than 20mm in crust diameter.
The effect of pinhole-ratio and film conductivity on corrosion behavior of carbon steel covered with ceramic films formed by plasma CVD and ion plating (it was called inorganic-coating steels) was investigated in synthetic seawater. Pinhole-ratio of inorganic-coating steels was estimated on the basis of charge transfer resistance Rct obtained in the impedance measurement in H2SO4 solution. Corrosion rate of inorganic-coating steels in synthetic seawater increased with increasing pinhole-ratio. This relationship on insulating film-coating steels was clearer than that on conductive film-coating steels. The results of polarization curve and scanning vibrating electrode measurement indicate that conductive films and carbon steel constitute galvanic couple in synthetic seawater. So corrosion rate of conductive film-coating steel is about ten times as large as that of insulating film-coating steel at the same pinhole-ratio. In conductive film-coating steels, maximum pit depth and pit number is characterized by film species after immersion test.
The relationship between inhibition abilities and characteristics of the polymers having carboxylic acid-side chains on the corrosion of mild steel in a cooling water system was investigated by physicochemical methods. In a low concentrated solution, the inhibition efficiency (η) of these polymers depended on (1) the number average molecular weight (Mn), (2) the content of maleic (MA) and acrylic acid (AA) units and (4) the concentration of these polymers in comparison with (3) the kind of MA and AA units. It was found for the condition of polymers having higher η value that (1) the Mn was 1000 to 3000, (2) the content of MA and AA units was about 50% and (4) the concentration of polymer was 100 to 200ppm. In a high concentrated solution, the η somewhat tended to rest on (2) the content and (3) the kind of MA and AA units and (4) the concentration of these polymers relative to (1) the Mn. It was found for the best condition of polymer in inhibition that (2) (& (3)) the content of AA was about 100% and (4) the concentration of polymer was more than 500ppm. The was also related to the degree of gelation of these polymers and calcium ions in a high concentrated solution. It is thought that these anionic polymers adsorbed on the surface of mild steel to form the layer and depressed the corrosion of mild steel under the condition of low and high concentrated solutions not to cause a scale-inhibition and a gelation.
The instruments, principles, measurement techniques and applications of infrared spectroscopy (IR) were reviewed. The instruments are classified to two types, conventional dispersive type and Fourier-transform type. The latter type shows a relative importance in practical use. The characteristics and principles of several techniques for surface analysis, such as “reflection spectroscopy”, “attenuated total reflection spectroscopy”, and “reflection absorption spectroscopy” were described. Examples of applications of these techniques to study the growth of inhibitor film, the degradation of polymeric materials, the structural change of lubricant film, and the orientation of organic molecule etc. were also shown briefly.
The durability of reinforced concrete is dependent on the degree of corrosion of reinforcement in concrete. In this article, the causes of corrosion, and the current technology of corrosion prevention of reinforcement in concrete are described. Carbonation of concrete and chloride attack which are the main causes of its corrosion are especially discussed. Furthermore, the rehabilitation methods of deteriorated concrete structures are also described briefly.