Following the review article, “Action of Corrosion Inhibitors (Part 1)” published in Zairyo-to-Kankyo, 56, 243 (2007), oxidation-type and precipitation-type inhibitors are reviewed. Inhibition of the anodic process and stimulation of the cathodic process by oxidation-type inhibitors and suppression of corrosion in acid and oxygenated neutral solutions by precipitation-type inhibitors are described here.
Flat healds (13Cr stainless steel, 340 mml×2 mmw×0.3 mmt) used in a water jet loom (WJL) suffer from crevice corrosion in the tap water. In the present work, a repassivation method for determining the critical concentration of chloride ion, Cl−, for the growth of crevice corrosion, CR, CREV, was measured using the metal/metal-crevice of heald in NaCl solutions containing less than 40 mg/L Cl−. Optimum conditions of potential and current to grow crevice corrosion in the initiation stage (S1) and the growing stage (S2) before the repassivation stage (S3) were examined. A heald was cut into two pieces and then a metal/metal-crevice was formed by overlapping the two pieces. Crevice corrosion was initiated in the solution containing 500 mg/L Cl− by a potentiokinetic method in S1. When crevice corrosion was grown at 200 mV vs. SCE in S2 by a potentiostatic method, corrosion area expanded, and then the specimen with two pieces did not work as a creviced one. Then, crevice corrosion in S2 was grown using a galvanostatic method with a current of 200 μA. Before changing to S3, the potential of specimen was raised up to a potential that was 50 mV lower than the holding potential in S3 by diluting test solution. Increases in current were observed after two times of dilution of the test solution in S3. CR, CREV was determined as the highest Cl− concentration in diluted test solutions in which no increase in current was observed. Use of galvanostatic method for growing crevice corrosion was desirable in the repassivation method of determination of the CR, CREV, because the quantity of electricity was controlled easily by time. The determined CR, CREV vs. potential relationship coincided well with the extrapolation line of the reported ER, CREV (repassivation potential for crevice corrosion) vs. Cl− concentration relationship in the tap water.
Structure of thin corrosion products film (CPF) on hot-dip Zn-Al alloy coated steel sheets were investigated by means of photoemission spectroscopy using synchrotron radiation of 160 eV and μ-FT-IR method, and were compared with those on Zn and Al pure metal sheets. CPF was prepared by 1 h and 16 h exposure in air saturated with water vapor at 323 K under the presence of NaCl particles. As a result, the dominant component of the CPF on the Zn-0.2%Al coating changed from Zn(OH)2 to 2ZnCO3·3Zn(OH)2, while the CPF of Zn-55%Al alloy coating was consisted mainly of ZnCl2·4Zn(OH)2. And it was found that the structure near the surface of CPF, which was composed mainly of Al oxide, was transformed into the surface structure covered with Al chloride by humid exposure under the presence of NaCl.
Research aims to study the AE activities of the rusts produced by soil corrosion of underground steel pipes. Author compared the AE activities of three types of the rust produced by atmospheric corrosion and soil corrosion by two methods. These are the monitoring of passive AEs under natural drying and active AEs under external turbulence such as forced heat cycles and mechanical loading. The soil-corrosion rust emitted AEs much more than the atmospheric rust did when they were submitted to mechanical deformation at lower strains. AE activities of the soil-produced rusts under cyclic heating (wet-and-dry) are, however, not so high compared to those of the atmospheric rusts. The rust produced on the steel pipe by soil corrosion for 20 years produced weak and few cylinder wave AEs under natural drying, and found to be detected only by AE sensors with resonant frequencies lower than 100 kHz for short distances of few hundred mm. This rust produced a number of AE at some period under cyclic heating, but the prediction of the timing for the rapid AE generation is difficult. Thus long term AE monitoring with highly sensitive AE sensors is needed for the corrosion monitoring of underground steel structures.