Experiment study on the corrosion resistance of the surface metamorphic layer of grinding

Workpiece will face corrosive problems during its application after the manufacturing process. As the common final process, grinding can generate special metamorphic layer on the surface of workpiece and change the initial corrosion resistance of workpiece. In order to study the corrosion resistance of workpiece after grinding process, the paper carries on combining experiment of grinding and electrochemical corrosion. The characteristic of corrosion resistance of grinding is revealed based on the association of grinding mechanism and electrochemical theory. The corrosion potential of workpiece after grinding is higher than matrix, which shows the grinding surface is difficult to begin to corrode. Electrochemical impedance spectroscopy (EIS) shows the grinding surface has large phase angle, impedance and capacitance characteristic because the metamorphic layer of grinding has good obstructive ability. They reveal that grinding improves the surface corrosion resistance of workpiece. Then the mechanism of the corrosion resistance of grinding is revealed. The special grain boundary formed in grinding with much C element, large clusters and complex shape prolongs the corrosion channel, which reduces the corrosive speed. While, the sensitive hardening structure generated in grinding hardening with much free energy is easy to form the corrosion cell, which will accelerate the corrosion.

EFFECT OF FLOW RATE AND TEMPERATURE ON CORROSION RATE OF CARBON STEEL PIPE IN CONDENSATE SOLUTION FROM GEOTHERMAL POWER PLANT

The research aims to study the effect of flow rate and temperature on corrosion rate of carbon steel pipe in condensate solution from geothermal power plant. The corrosion rate in this study highlighted by electrochemical measurement. Electrochemical measurement performed in two conditions i.e stagnant and dynamic conditions. There are three kinds of temperature used in this research : 30oC, 40oC, and 50oC. Modification of corrosion cell installed for dynamic condition with flow rate variations : 0.27 m/s; 0.6 m/s; 1 m/s; 1.5 m/s; and 1.9 m/s. It was found that corrosion rate boosts with temperature and fluid flow rate in condensate solution of geothermal power plant. The highest corrosion rate (38 mpy) obtained at 50oC and 1.9 m/s of flow rate.

Inhibition Effect of Fluoride Ion on Corrosion of 304 Stainless Steel in Occluded Cell Corrosion Stage in the Presence of Chloride Ion

The role of F− in the corrosion of stainless steel at the stage of occluded cell corrosion in a mixture of chloride, fluoride, and sulfate ions was investigated. A simulated occluded corrosion cell was designed using an elaborate simulated rust layer. Composite electrodes were used to monitor the variation of the concentration of ions, pH, and dissolved oxygen of the occluded solution. The results show that the influence of F− on the corrosion of 304 stainless steel, in the occluded cell corrosion stage, is concentration dependent. When the F−/Cl− ratio is higher than 2, the corrosion can be significantly suppressed. Analyses showed that the corrosion inhibition effect could be attributed to the migration of F− to the occluded cell, which can reduce the migration of Cl−, dampen the decrease in pH, and react with metal ions to form semi-soluble products. Meanwhile, the influence of F− on the corrosion process was also verified using drilled stainless steel specimens, demonstrating the practicality and validity of the simulated occluded cell corrosion model.

Research on the Metal Corrosion Process in the Sea Mud/Seawater/Atmosphere Interface Zone

Corrosion in the interface zone is a complicated local corrosion phenomenon. The conventional single-electrode method finds it difficult to obtain the kinetic information of corrosion occurrence and development process. In this paper, metal corrosion was studied by Wire Beam Electrode (WBE) technology on the interfaces of sea mud/seawater and seawater/atmosphere. The study found that the metal corrosion in the interface is a process of coupling a dual corrosion cell into a single corrosion cell. Initially, a corrosion cell is formed with the seawater/atmosphere interface acting as the cathode and the upper part of the metal in the seawater area as the anode. This is due to the oxygen concentration cell caused by the waterline effect. The cathode area is always enriched near the seawater/atmosphere interface. The lower part of the metal in the seawater area and the metal in the sea mud area are the anode and the cathode, respectively, of another corrosion cell. Along with the immersion time, the anodic area of the first corrosion cell gradually extends to the lower part of the metal in the seawater zone and finally the sea mud zone, resulting in the disappearance of the second corrosion cell. In the single corrosion cell stage, the seawater/atmosphere interface is the cathode area; the seawater area and the sea mud area are the anode areas, and the electrode adjacent to the cathode area becomes the anode area with the largest current density. During the whole experiment, the sea mud zone is a process of polarity transition from the cathode zone to the anode zone, and finally forms the anode zone of the whole electrode together with the anode zone in the sea zone.

Characterization of Impressed Current Technique to Model Corrosion of Reinforcement in Concrete

Corrosion of reinforcement is an important durability concern for the structures exposed to coastal regions. Since corrosion of reinforcement involves long periods of time, impressed current technique is usually used to accelerate the corrosion of reinforcement in laboratories. Characterization of impressed current technique was the main focus of this research,which involved determination of optimum chloride content and minimum immersion time of specimens for which the application of Faraday’s law could be efficient. To obtain optimum chloride content, the electrolytes in the corrosion cell were prepared similar to that of concrete pore solutions. Concrete prisms of 200 mm by 200 mm by 300 mm were used to determine the minimum immersion time for saturation. It was found that the optimum chloride content was 35 gm/L and the minimum immersion time for saturation was 140 hours. Accounting the results, a modified expression based on Faraday’s law was proposed to calculate weight loss due to corrosion. Journal of Engineering Science 11(1), 2020, 93-99

D.C. etching anode aluminum foil to form branch tunnels by electroless depositing Cu

Purpose The purpose of this study is to explore the mechanism of branch pits and tunnels formation and increase the specific surface area and capacitance of anode Al foil for high voltage electrolytic capacitor by D.C. etching in acidic solution and neutral. Design/methodology/approach Al foil was first D.C. etched in HCl-H2SO4 mixed acidic solution to form main tunnels perpendicular to the Al surface, and then D.C. etched in neutral NaCl solution including 0.5 per cent C6H8O7 and Cu(NO3)2 with different concentration to form branch tunnels normal to Al surface. Between two etching, Cu nuclei were electroless deposited on the interior surface of main tunnels by natural occluded corrosion cell effect to form micro Cu-Al galvanic local cells. The effects of electroless deposited Cu nuclei on cross-section etching morphologies and electrochemical behavior of Al foil was investigated with SEM, polarization curve and electrochemical impedance spectroscopy (EIS). Findings The results show that sub branch tunnels can form along the main tunnels owing to the formation of Cu-Al micro-batteries, in which Cu is cathode and Al is anode. With increase in Cu(NO3)2 concentration, more Cu nuclei can be electroless deposited and serve as the favorable sites for branch tunnel initiation along the whole length of main tunnels, leading to enhancement in specific capacitance of anode Al foil. Originality/value Cu nuclei were electroless deposited on the interior surface of main tunnels by natural occluded corrosion cell effect to form micro Cu-Al galvanic local cells, which can serve as the favorable sites for branch tunnel initiation along the main tunnels to enhance specific capacitance of anode Al foil.

Etching Anode Foil with Branch Tunnels for Aluminum Electrolytic Capacitors

Al foil for high-voltage aluminum electrolytic capacitor was first D.C. etched in HCl–H2SO4 mixed acidic solution to form main tunnels and then D.C. etched in natural NaCl solution containing 0.1% H2C2O4 and different trace amounts of Zn(NO3)2. Between the two etching processes, Zn nuclei were deposited on the interior surface of the main tunnels by the natural occluded corrosion cell effect to form micro Zn–Al galvanic local cells. The effects of Zn nuclei on the cross-section etching and electrochemical behavior of Al foil were investigated using scanning electron microscopy, polarization curve measurement, and electrochemical impedance spectroscopy. The sub-branch tunnels can form along the main tunnels owing to the formation of Zn–Al micro-batteries, in which Zn is the cathode and Al is the anode. Increasing Zn(NO3)2 concentration increases the number of Zn nuclei that can serve as sites for branch tunnel initiation along the main tunnels, thereby enhancing the specific capacitance of etched Al foil.