Materials and Corrosion-werkstoffe Und Korrosion最新文献

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Model sketch illustrating the zinc deposition in: a) an electrolyte containing no polymer and b) an electrolyte containing polyquarternium polymer (PQ).

More detailed information can be found in: Gastelle F. Tiétcha, Ingo Klüppel, Matthias Kogler, Markus Valtiner, Laura Mears, Visualising electrochemical zinc deposition and the role of a polymer additive in the crystal growth mechanism, Materials and Corrosion 2024, 75, 146.

Copper and steel are often electrically connected in industrial devices, which causes galvanic corrosion in environments. To ensure the safety of the devices, it is needed to assess the corrosion rate of galvanic couples. The galvanic current is often used to calculate the galvanic corrosion rate in theory, however, in the actual devices, the copper parts are generally coupled with the steel parts and it is difficult to separate them to measure the galvanic current between them, as well as to determine the galvanic corrosion rates for actual devices. In this paper, the galvanic couple mixed potential distribution and influencing factors including area ratios, polarization characteristics, and medium resistivity are studied by experiments and calculation. The mixed potential becomes stable with a certain distance from the surface of copper/steel couple and acts as remote earth mixed potential. Remote earth mixed potential is positively associated with galvanic corrosion rate. Based on the results of experiments and calculation, a method to estimate the galvanic corrosion rate of steel in copper/steel couple by using the remote earth mixed potential is proposed.

Corrosion under insulation (CUI) is a form of corrosion typically occurring on steel pipes and vessels covered with thermal insulation. CUI is a critical issue in petrochemical and refining industry leading to significant financial losses and severe environmental hazards. State-of-the art CUI monitoring system consisting of wireless loggers with flexible resistometric sensors is used to assess the effect of insulation material, position, and presence of a defect on the actual corrosivity toward carbon steel under alternating condensation conditions. All three considered factors together with the climatic parameters and presence of corrosion products are important for the CUI process. Most complex is the role of the insulation material as the properties inhibiting corrosion under intact insulation may be linked to a worse insulating ability. Because of the high sensitivity and immediate response of the sensors, the technique can be applied for timely CUI detection of insulated pipelines in both industrial facilities and laboratory studies.

In this study, the functionality of self-formulated carbon-based conductive coatings (CBCCs) with incorporation of graphite as the anode in an impressed current cathodic protection system is studied. The anode materials are tested and evaluated for long-term durability and performance by an accelerated durability test method. The results show that the functional time is highly dependent on the acceleration factor, and thus the charge passed through the material during testing, as well as the material composition. From the results, there are also indications that the addition of graphene into the CBCC matrix has a positive effect on the homogeneity of the material, but without any major influence on the conductivity and performance.

Samples of alloy 601, 602 CA and 602 MCA with different thickness and microstructure, all 600 grit laboratory ground, are compared. All samples are exposed to up to 5693 h at 600°C in a metal dusting producing atmosphere with a total pressure of 20 bar. A smaller sample thickness leads to an increased pit density for alloy 601 and an increased pit density, a longer incubation time and an increased pit depth growth rate for alloy 602 CA. This is attributed to lower stresses in the scale of the thinner samples. Grain size effects of the substrate are probably concealed by the deformed and recrystallized subsurface due to the 600 grit finish of the samples. If carbides are unavoidable in an alloy, they should be small, as they can serve as chromium suppliers during scale formation better than larger ones. They increase incubation time and pit depth growth rate.

Molten nitrates or nitrate–nitrite mixtures have been used as heat transfer fluid as well as thermal energy storage medium in concentrated solar power plants and other industrial applications. However, containment materials in contact with these molten salts are subjected to molten salt corrosion, which has been a concern over the years. In this investigation, the corrosion behavior of pure Ni, Fe, Cr, and Fe-5Cr alloy (in weight percent) has been examined at 400°C in molten nitrates using electrochemical impedance spectroscopy and gravimetric tests. It is shown that Ni, Fe, and Fe-5Cr exhibit mass gain, with the best corrosion resistance for Ni followed by Fe-5Cr and Fe, while pure Cr goes through fast dissolution, forming hexavalent chromium product K₃Na(CrO₄)₂. The increase of salt basicity from Solar Salt to Hitec could accelerate the dissolution of Cr. Nevertheless, the formation of an inner Cr-containing scale could still offer the alloy good protection because the external insoluble Ni or Fe oxides can protect it from dissolution.

The role of the oxide layer in the corrosion of aluminium in hydrochloric, sulphuric(VI) and orthophosphoric acid is studied at pH 1. The oxide layer is stable in hydrochloric and sulphuric acids. The corrosion rate of aluminium in these solutions is 0.2 and 0.3 mm/year, respectively. The oxide layer is unstable in orthophosphoric acid and the corrosion rate is higher, 1.75 mm/year. The corrosion process is studied using scanning electron microscopy, immersion and electrochemical techniques. The mechanism of corrosion of aluminium in the orthophosphoric acid solution is proposed. It includes the adsorption of a reaction intermediate on the surface of the corroding metal and the formation of the oxide layer at anodic potentials with respect to the open-circuit potential. It is also explained when the inductive loop appears on the electrochemical impedance spectra of aluminium corroding in orthophosphoric acid solution. The mechanism of aluminium corrosion in hydrochloric and sulphuric acid is more complex compared to orthophosphoric acid, and is not analysed in detail.

For aircraft serving in coastal environments, the aluminum alloy skin is exposed to high temperature, humidity, and salt environment for a long time. Pitting and exfoliation will affect its normal service life. In this article, static salt spray experiments and electrochemical tests were carried out on 2198-T8 Al–Li alloy in nine different corrosive environments. The effects of salt concentration, temperature, and humidity on the corrosion behavior were analyzed and compared. The relationship between corrosion environment parameters and pits was established. The results show that, under the same corrosion environment, the length, width, and depth of the pits all follow the log-normal distribution; compared with the salt concentration and humidity, the increase in temperature has the most obvious promotion on the corrosion rate. Based on the frequency statistics of pit size and electrochemical test results, the pit morphology was simplified to a semiellipsoid geometric model, and the pit size in different corrosive environments was predicted. The predicted size data all fall within the 1.5-fold dispersion region.

The corrosion behavior of Q345qDNH steel and Q420qENH steel under the industrial atmosphere containing PM_2.5, as well as the effect of PM_2.5 on the rust layer were studied by dry–wet alternating accelerated corrosion experiment. The results show that the corrosion rate of Q345qDNH is always less than that of Q420qENH, the Cr content of rust layer is higher than that of Q420qENH steel. After 30 days of corrosion, compared with Q420qENH steel, the self-corrosion potential of Q345qDNH is larger, the self-corrosion current density is smaller, and the rust resistance is 1.49 times of Q420qENH steel, the I_α-FeOOH/I_γ-FeOOH ratio is 1.29 times of Q420qENH, indicating that the protection of the rust layer of Q345qDNH is better than that of Q420qENH. This is due to the effect of microstructure factors in the early stage of corrosion and alloying elements in the late stage of corrosion. PM_2.5 with SiO₂ as the main component is easy to deposit at cracks and holes, which becomes the nucleation substrate for corrosion products, promotes the nonuniform nucleation of corrosion products, making the rust layer develop unevenly, leading to an increase in holes in the outer rust layer.