Papers by Keyword: Anodic Polarization

Abstract: Studies have been conducted to assess the possibility of refining a lead collector containing precious metals, with the aim of obtaining lead using an economically viable technology. Studied the patterns of anodic oxidation of lead and impurities in alkaline-water-glycerate electrolytes, depending on the concentration of sodium hydroxide and glycerol in the electrolyte, the potential sweep rate.

Abstract: The anodic polarization behavior of Sanicro 28 austenitic stainless steels has been established in the cold worked (10 to 80% reduction in thickness) samples in 1N HCl, 1M H₂SO₄+ 1.5N HCl and 3N HCl solutions at room temperature. The current oscillations during the potentiodynamic scans appeared in 3N HCl implying formation of meta stable pits and this solution more severe than 1N HCl and 1M H₂SO₄+ 1.5N HCl. Two anodic peaks were observed in as-received and the cold worked samples in 3N HCl. In as-received state, the first anodic peak appeared at-3.95 mV_SCE and the second anodic peak appeared at 116 mV_SCE. It was established that selective dissolution started from 18mV_SCE. The grains and grain boundaries were not attacked at the beginning of the first peak-168 mV_SCE and started revealing at 18 and 216 mV_SCE in the potentiodynamic polarization test. The fore-scatter detector (FSD) attached to FEI Quanta EBSD revealed the pitting morphology of the specimens. It is shown that pit dimensions, types, distribution, the shape of pits in all deformation conditions is hemispherical and number of pits did not depend on the microstructural features, irrespective of the plastic deformation and it may not be related to severity of plastic deformation.

Abstract: The influence of residual stress and sensitizing on the electrochemical and corrosion behavior of type SUS304 stainless steels weldment has been studied in the Freeze-Thaw condition. After immersion test at Freeze-Thaw cyclic condition the severe corrosion damage was detected in the vicinity of weld boundary more than isothermal condition. The corrosion damaged zone corresponds to the location in which there are high residual stress and sensitization. The influence of residual stress and sensitization was distinguished and its magnitude was evaluated by voltammetry method.

Abstract: Anodic polarization behavior of ternary alloy Pb-0.08%Ca-1%Sn is studied by potentiodynamic polarization measurements, corrosion rate, the products on electrode surface after polarization, and microstructure of anode mud after polarization in electrowinning cell. The results show that Pb-Ca-Sn anode is easy to be passivated in electrolyte for copper electrowinning, the maintaining passivity current density is 97.72 µA•cm^-2 and the corrosion products on the surface of Pb-Ca-Sn electrode present loose scaly, being composed of α-PbO₂, β- PbO₂ and PbSO₄ after polarization.

Abstract: Based on the fundamental theory of electrochemical anodic polarization, simulated concrete is doped with corrosion inhibitor to prevent corrosion by chloride ion in the marine environment. Thus, with reference to the potential-time curves obtained in different concrete environments and construction conditions, the early dynamic state of active transition of rebar passive films in concretes can be quickly characterized. According to the experiments, the characteristics of passive active transition are synchronous with rebar corrosion. This helps to systematically study the influence of different components of concrete and external media on the durability of the concrete structure. The strong alkaline environment of the concrete is useful in controlling corrosion rate of reinforcing bar. As one of the additional protective measures of the durability of the concrete structure, corrosion inhibitor’s long-term performance contains uncertainty.

Abstract: A method of EIS measure-polarization-relaxation was used to investigate the corrosion performance of different hot-dip coating layers of galvanized steel. The result showed that the corrosion of hot dip galvanized steel was divided into four phases, and the corrosion of each phase was corresponded to different layer respectively. The anti-corrosion difference of every layer was very distinct. The optimal anti-corrosion layer of hot dip galvanized steel was δ phase. This method could be used to detect coating corrosion quickly.

Abstract: Since the PbSCC(Lead stress corrosion cracking) of alloy 600 tubing materials was reported by Copson and Dean in 1965, the effect of lead on a corrosion film and cracking morphology have been continually debated. An electrochemical interaction of lead with the alloying elements of SG tubings was studied and the corrosion products were analyzed. It was found that lead enhanced the anodic dissolution of alloy 600 and alloy 690 in the electrochemical test. The lead preferentially dissolved the Cr from the corrosion film of alloy 600 and alloy 690 in alkaline water. The lead ion seemed to penetrate into the TG crack tip and react with the corrosion film. A selective Cr depletion was observed to weaken the stability of the passive film on the alloys. Whereas passivity of Ni became stable in lead containing solution, Cr and Fe passivity became unstable.

Abstract: In this study, an Al-7 wt% Si-1.5 wt% Cu alloy was subjected to severe plastic deformation (SPD) by an equal-channel angular pressing (ECAP) technique. The ECAP process was repetitively carried out up to 8 passes using a strain introduction method of route BC, at a temperature of 25 °C and a pressing rate of 0.33 mm s-1. Microstructures of the samples before and after ECAP were observed by a scanning electron microscopy (SEM). Electrochemical properties of the Al-Si-Cu alloy fabricated by ECAP have been investigated in a borate-boric acid buffer solution containing Cl¯ ions at pH 8.3 and 25 °C by potentiodynamic polarization test. Corrosion pits on the sample surface after anodic polarization were investigated by means of SEM. The anodic polarization showed that as-cast Al-Si-Cu alloy with plate-shaped Si particles has poor resistance against pitting corrosion comparing to quenched sample without ECAP. Pitting potentials of ECAPed Al-Si-Cu alloy samples were higher than that of the sample without ECAP. In the Al-Si-Cu alloy, the corrosion pits were found in the region of Si particles and the size of pits formed on the ECAPed samples became smaller than that without ECAP. It is considered that the improvement of the pitting resistance of ECAPed Al-Si-Cu alloy is due to homogenous distribution of spherical Si particles generated during ECAP process.

Abstract: FRP (fiber-reinforced polymer) ships used with small boats for fishing pose numerous problems related to both the environment and recycling. From this perspective, aluminum offers an environmentally friendly substitute for FRP that is easy to recycle and imparts a high added value to fishing boats, with a reduction in fuel demands. The current density of 7075 Al alloy increases linearly with an increase in potential during anodic polarization, which implies that no passivation of this alloy occurs. With 1050 and 5456 alloys, passive films form during anodic polarization but are destroyed by the Cl
in seawater, only to regrow as a result of the self-healing capacity of aluminum. A shift to more anodic or cathodic conditions in the potential range of –1.5 ~ –0.68 V resulted in a sudden increase in current density. Current densities in the high-strength 7075 Al alloy showed the greatest values. In contrast, the current densities of 5456 alloy, known to have excellent corrosion resistance in seawater, were the lowest in the range of –0.70 ~ –1.3 V, and we conclude that this potential range offers optimal protection.