| 其他摘要 | Steels as important structural materials have been widely used in buildings, machines, vehicles, etc. These equipments are mainly operated under atmospheric environment. Particles and dust in the air often induce corrosion of the steels and significantly influence their service lives. In industrial environments, SO2 is one of the most important factors that facilitate the corrosion of steels. It is important that research corrosion of steels in industrial atmosphere. In this work, the corrosion tests of the carbon steel and weathering steel were carried out in industrial urban atmosphere and indoor acceleration atmosphere. The rusts were characterized by scanning electron microscopy, electron probe micro analyzer, X-ray diffraction, infrared transmission spectroscopy and X-ray photoelectron spectroscopy. The corrosion process and mechanism in polluted atmosphere were investigated. The following conclusions were drawn:
1. The variation of the initial urban atmospheric corrosion rate of carbon steel could be divided into three segments and the initial atmospheric corrosion of carbon steel in industrial atmosphere is observed to follow the cubic equation. The multiple regression analysis of environmental factors were carried out in order to obtain the best regression model. According to the model, temperature, rainfall time, sunshine time, SO2, and infusible dust are the most important factors. According to the phases present in the corrosion products, the rusts were composed of γ-FeOOH on the beginning of the exposure period, Fe3O4 and α-FeOOH were detected with time going on. When α-FeOOH happened in the rust, the corrosion rate decreased. When Shenyang enters into heating time, the corrosion rate of carbon steel increased sharply again. The contents of α-FeOOH and Fe3O4 in the skyward rust were more than the contents in the earthward rust and the contents of Fe2O3 were less than the contents in the earthward rust. α-FeOOH and Fe3O4 in the inner rusts more than the contents in the outer rust and the contents of Fe2O3 were on the way round.
2. The corrosion rate of carbon steel in twelve months were contrasted, the corrosion rate in August was the maximum. In the polluted winter, due to low temperature and lack of rainfall, the corrosion rate was low. Grey relational analysis of the corrosion rate of carbon steel in twelve months and environmental factors. Sunshine, relative humidity, infusible dust and water-soluble dust were the most important factors affecting the short-term corrosion of carbon steel. The rusts of carbon steel in different seasons were different and the corrosion products were alike, including γ-FeOOH and Fe3O4, but the contents of the rust were different.
3. In the contrast of corrosion of carbon steel and weathering steel in the Shenyang and Changbai Mountain atmosphere, the two steels corrosion rate reached the max after one year. In the polluted atmosphere, the contents of S in the rust increased with time going on. Cr in weathering steel could be detected in the interface of rusts/substrate. In the unpolluted atmosphere, Cr in weathering steel didn’t enrich in the interface. The corrosion products were γ-FeOOH and Fe3O4. In the polluted atmosphere, the corrosion products were γ-FeOOH, α-FeOOH and sulfate. The acidic pollutants stimulated formation of α-FeOOH. In the unpolluted atmosphere, the formation of the dense and stabilized rust on the weathering steel took a rather long time, In the short-term, protective ability of the rust on weathering steel resembled carbon steel. However, the acidic pollutants in the polluted atmosphere stimulated the formation of protective rust on the weathering steel and exhibited the excellent corrosion resistance of weathering steel.
4. The individual effect of SO2 on the behaviours of the industrial atmospheric corrosion for carbon steel was studied with self-made simulated atmospheric corrosion system. The influence of the different concentration of SO2 on the initial atmospheric corrosion of carbon steel was investigated. The corrosion kinetics of carbon steel Q235 in different condition was researched .The variation of thickness loss of Q235 in different concentration of SO2 made a great difference. When the concentration of SO2 was low, sulfate was detected. When the concentration of SO2 was high, γ-FeOOH, δ-FeOOH and sulfite was detected and sulfate disappeared. Increasing the concentration of SO2 could not affect the content of S elements in rust, but promoted the formation of oxide. When the concentration of SO2 was 0.05%, there were a lot of micro-cells on the surface of carbon steel. As the exposure time prolong, many rust nests were formed and the elements content of the inner and outer of nests were different. A probable mechanism is presented to explain the formation of nests. |
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