In this work, the effects of stray alternating current (AC) on the corrosion of coated X70 pipeline steel and the delamination of 3-layer polyethylene (3PE) coatings with defects were investigated using COMSOL Multiphysics simulation, electrochemical impedance spectroscopy and three-dimensional (3D) digital microscope techniques. The results showed that under the same level of AC interference, pits with deeper maximum pit depth were observed at the smaller defect areas than those at larger defect areas. It was consistent with the simulation results that a greater corrosion current density was accompanied on samples with smaller defects. According to 3D digital images, the larger delamination of 3PE coatings was found on samples with smaller defects. With the increase of current density, the impedance of samples with small defects decreased, while that of samples with large defects increased. Additionally, with the same defect size, the maximum pit depth became deeper and the corrosion was more severe.
The soil mechanic course acts as a professional basic course of civil engineering. In recent years, we have made a better teaching effect by enriching teaching contents constantly and improving the teaching methods and means, but under the new situation there still exists certain shortage and weakness that need to strengthen. Based on the experience in teaching the author has putted forward the main problems existing in the teaching of soil mechanics course. What’s more, the specific suggestions on teaching reformation and practice have been suggested.
The Cu-based friction material with Ni coated nanometer SiO2 (Ni/n-SiO2) particles was prepared by the powder metallurgy technology. Friction properties of the friction materials were evaluated by a friction tester. The microstructure and worn morphology were characterized by optical microscope (OM) and scanning electric microscope (SEM). The results indicate that the microstructure is uniform. The Ni/n-SiO2 particles can enhance the wear ability of Cu-based friction materials. The wear rate of the friction material with Ni/n-SiO2 is 6.58 times of that without Ni/n-SiO2. The main wear mechanisms are abrasive wear and adhesive wear, and Ni/n-SiO2 particles can reduce the abrasive wear and adhesive wear.
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