Corrosion behavior of carbon steel in chloride aqueous solutions under a low dose rate was investigated by corrosion test using chloride aqueous solutions with different chloride concentration at a dose rate of 500 Gy/h. The corrosion rate of carbon steel increased by the irradiation, and the corrosion rate had the maximum value at a certain concentration. The oxidants produced by radiolysis of chloride aqueous solution enhanced the corrosion of carbon steel. The main oxidants were oxygen and hydrogen peroxide, and the diffusion process of oxidants controlled the corrosion of carbon steel under irradiation. There was a positive correlation between the dependence of corrosion rate and chloride concentration and the dependence of oxidant concentration and chloride concentration.
Galvanic corrosion induced by carbon fiber reinforced plastics (CFRP) coupled to a pure aluminum 1050 has been investigated by an electrochemical measurement. The galvanic current measurement was made between the 1050 specimen and the CFRP laminate connected through a zero resistance ammeter in 3.5 wt% NaCl solution at room temperature for 7 days. The galvanic current flew from the CFRP to the 1050 specimen was about from 2500 to 3500 μA/cm2 for the experimental period. The weight loss of the 1050 specimen connected with the CFRP was 207 mg/cm2, while the weight loss of the 1050 specimen out of contact with the CFRP was practically zero after the galvanic current measurement. After 84 days of immersion in 3.5 wt% NaCl solution, the weight loss of the 1050 plates contacted directly with the CFRP prepreg was about 60 times that of the 1050 plates contacted with the 1050 specimen. These results indicate that the corrosion rate of the pure aluminum 1050 in NaCl solution is accelerated by contact with the CFRP.
An effect of phosphoric acid on pitting attacks of aluminum A1050 in a formic acid solution has been investigated. Surface observation after corrosion test revealed that the pitting attacks with 10~20 μm diameter occurred when H3PO4 concentration was higher than 100 ppm and temperature was 333 K or more. The anodic and cathodic reactions for the corrosion reaction were thermodynamically determined from E-pH diagrams.
To clarify the corrosion mechanism of steel bars in concrete poles (CPs), the corrosion state of a steel bar that had been taken out of a discarded CP and a new steel bar that had been immersed in a quasi-concrete-environment (weak alkaline) solution were compared. The formation of rust was observed beneath the scale that covered the surface of the steel bar removed from the CP. A similar rust compound was observed in the bar immersed in the weak alkaline solution, which shows that the corrosion of a steel bar in a CP environment can be experimentally reproduced.
To simulate the atmospheric corrosion of weathering steel, artificial Schwertmannite (Fe8O8(OH)6(SO4)) rust particles were synthesized by aerial oxidation of aqueous FeSO4 solution in the presence of metal ions such as Cr(III), Cu(II) and Ni(II), and the transformation behavior of metal-doped Schwertmannite into α-FeOOH was examined at different pH. No remarkable change in crystallinity of Schwertmannite was recognized by addition of Cr(III), Cu(II) and Ni(II). The Schwertmannite prepared without adding metal ions was needle-like particles with a length of ca. 265 nm. The added Cr(III) would be incorporated by substituting for Fe(III) in Schwertmannite crystal, leading to the reduction of particle size of this material. The Cu(II) and Ni(II) in the solution were less easily incorporated in the particles than Fe(III), although growth of the Schwertmannite particles was slightly suppressed by Cu(II). The Schwertmannite particles were transformed into α-FeOOH at pH=3－11. Incorporation of metal ions into Schwertmannite suppressed the transformation into α-FeOOH. Especially, added Cr(III) strongly inhibited the transformation over the whole pH ranges. These results allow us to infer that metals alloying with weathering steel strongly affect the formation of α-FeOOH rust from Schwertmannite and the effect is in order of Cr(III)＞＞Cu(II)＞Ni(II).
Rigid Media Tube Filters (RMF) bonded to coarse-grained alumina by aluminum borate reaction bond layer (9Al2O3・2B2O3; 9A2B) are used to remove solid impurities from the molten aluminum. Molten aluminum corrodes the 9A2B bond layer. To improve corrosion resistance of the RMF, we examined yttrium titanate (Y2Ti2O7; YT) coating using YT aqueous precur sorsolution. As results of the corrosion resistance evaluation of the filters in the molten aluminum, 9A2B bond layer of the coarse alumina was corroded about 2 weeks, but that 5 coats of YT remained for over 4 weeks.
1400-MPa class high-strength PC wires are used for pre-stressed concrete structures. One of trusted hydrogen embrittlement tests for steel is a testing method that is provided in the FIP Report1) and defined in JSCE S 12013) for a test procedure. This test includes a constant load test in a 20% NH4SCN at 50ºC for up to 200 hours to measure the rupture time. The test examined corrosion behavior in the early stage of the test when hydrogen concentration in steel would show a rapid increase. It was recognized that dissolved oxygen accelerated a corrosion reaction in pure oxygen atmosphere, but a 6-hour immersion test showed no notable difference in corrosion rate and corrosion potential in air and deaerated atmosphere. Polarization measurements suggested that a cathodic reaction independent of dissolved oxygen exerted a profound effect on a corrosion reaction. The analysis of corrosion products and iron ion led to a presumption that the iron-sulfide and iron oxide would precipitate concurrently in the early stage of immersion in 20% NH4SCN.
The behavior of under-film corrosion was investigated by Raman imaging using multivariate analysis of corrosion products, which were generated by CCT and SST. Effect of the conversion coatings on the corrosion under the wetdry cyclic conditions was considered by comparing between zinc phosphate conversion coating and zirconium oxide conversion coating covered by cation electrodeposited coatings. The following findings were obtained. Under the zinc phosphate conversion coating, β-FeOOH was formed near the corrosion tip because corrosion products were deposited just under the scratch and macrocell corrosion was caused. Under the zirconium oxide conversion coating, β-FeOOH was not formed. It was considered that macrocell corrosion was not induced because of the smaller amount of corrosion products under the scratch and the higher anti-corrosion properties of the coating. It was confirmed that Raman imaging using multivariate analysis was useful for the analysis of under-film corrosion.