Morphology of Rust Phases Formed on Naturally Weathered Weathering Steels in Bridge Spans / Morphologie der unter natürlichem Witterungseinfluß auf „Weathering‘-Stählen gebildeten Rostphasen
“…After 6 h immersion, SEM morphologies at 1 and 30 ATO both show a structure of laminas resembling nets on which some white lumps cover, as shown in Figure 9(a,b). It is easily observed that the laminas at 1 ATO are much smaller than that at 30 ATO, which reveals that the corrosion films of low alloy steels formed at 1 ATO have more dense structure than that at 30 ATO [17–23]. This observation provides an evidence for the fact that the low-frequency part of Nyquist plots at 1 ATO has a larger deformation than that at high HP + DO.…”
Hydrostatic pressure (HP) and dissolved oxygen (DO) both change with the increase of ocean depth. In order to unmask the corrosion phenomena of metals in deep sea environment, studying their combined effect on corrosion is necessary. In this report, couple effect of HP and DO (HP + DO) on corrosion behaviour of low-alloy high strength steel in 3.5 wt-% NaCl solution was investigated by Electrochemical measurements, SEM observations, XPS characterisations and 3-D size measurements. The results show that the corrosion rate of low-alloy high strength steel increases with increasing HP + DO under each immersion period, appearing an exponential decay growth. As HP + DO increases to a critical value, 30 ATO, its acceleration to corrosion process becomes limited. Moreover, HP + DO remarkably increases the growth of corrosion film on steel surface and leads to more loose structure in corrosion film. Finally, HP + DO stimulates the propagation of corrosion pits in 3D direction.
“…After 6 h immersion, SEM morphologies at 1 and 30 ATO both show a structure of laminas resembling nets on which some white lumps cover, as shown in Figure 9(a,b). It is easily observed that the laminas at 1 ATO are much smaller than that at 30 ATO, which reveals that the corrosion films of low alloy steels formed at 1 ATO have more dense structure than that at 30 ATO [17–23]. This observation provides an evidence for the fact that the low-frequency part of Nyquist plots at 1 ATO has a larger deformation than that at high HP + DO.…”
Hydrostatic pressure (HP) and dissolved oxygen (DO) both change with the increase of ocean depth. In order to unmask the corrosion phenomena of metals in deep sea environment, studying their combined effect on corrosion is necessary. In this report, couple effect of HP and DO (HP + DO) on corrosion behaviour of low-alloy high strength steel in 3.5 wt-% NaCl solution was investigated by Electrochemical measurements, SEM observations, XPS characterisations and 3-D size measurements. The results show that the corrosion rate of low-alloy high strength steel increases with increasing HP + DO under each immersion period, appearing an exponential decay growth. As HP + DO increases to a critical value, 30 ATO, its acceleration to corrosion process becomes limited. Moreover, HP + DO remarkably increases the growth of corrosion film on steel surface and leads to more loose structure in corrosion film. Finally, HP + DO stimulates the propagation of corrosion pits in 3D direction.
“…When the steel is interfered with the DC electric field as shown in Figure 9(c), the more γ-FeOOH exist in the rust layer in the successive exposure, while the amount of α-FeOOH decreases in the rust. Herein, it has to state that γ-FeOOH is metastable with respect to the α-FeOOH and there are pores existing in the flower structure [16,28]. As for the corrosion process of steels in corresponding systems, it essentially consists of two electrochemical reactions on the metal/solution interface and can be expressed as followed: Figure 9 Illustration of corrosion rust on the steel surface with and without the DC electric field interference; (a) Initial corrosion rust, (b) Transformation of corrosion products in successive exposure, (c) Transformation of corrosion products in successive exposure with the DC electric field interference.…”
Section: Resultsmentioning
confidence: 99%
“…The microstructure of corrosion products formed on steels in different exposure stages was performed through the SEM tests, as shown in Figure 8. According to some studies [27][28][29][30], it is worth noting that the γ-FeOOH exists in the shape of fine plates in the initial stage and will accumulate into a flower structure with the process of corrosion. While the α-FeOOH normally exhibits as cotton balls, these cotton balls could connect with each other and further develop into a dense layer with a good corrosion resistance [38].…”
Section: Characterisation Of Corrosion Productsmentioning
confidence: 99%
“…When the steel is interfered with the DC electric field as shown in Figure 9(c), the more γ-FeOOH exist in the rust layer in the successive exposure, while the amount of α-FeOOH decreases in the rust. Herein, it has to state that γ-FeOOH is metastable with respect to the α-FeOOH and there are pores existing in the flower structure [16,28]. As for the corrosion process of steels in corresponding systems, it essentially consists of two electrochemical reactions on the metal/solution interface and can be expressed as followed:…”
Section: Characterisation Of Corrosion Productsmentioning
confidence: 99%
“…The types of corrosion products and their corresponding contents in rust layer are significantly based on the exposed environments or some typical ions in solution systems. Furthermore, the microstructure of the corrosion products in oxide layer has been characterised by many researchers [27][28][29][30][31]. γ-FeOOH is the main corrosion product in the initial process and normally displays as small crystalline globules (sandy crystals) or fine plates (flowery structures), which could be further generated and subsequently transformed into α-FeOOH.…”
The initial corrosion of steels exposed to the simulated industrial atmospheric environment with a direct current (DC) electric field for 30 days was investigated using weight loss, electrochemical and characterisation methods. The results show that the steel weight loss increased with the increase in DC electric field intensity. The steels exposed to the DC electric field interference exhibited a higher corrosion rate than the blank samples during the exposure. The microstructural studies reveal that the existence of the DC electric field favours the growth of the γ-FeOOH, while suppresses the transformation of γ-FeOOH into α-FeOOH during the 30 days' exposure, as a result of decreasing the protective ability and stable property of the rust layer. The amount of porous γ-FeOOH enhances the transmission of oxygen and conductivity of the whole rust layer. All these induce an accelerated effect of DC electric field on the initial steel corrosion in simulated industrial environment.
This paper describes the peculiarities of carbon steel corrosion in very severe marine atmospheres and points out a number of uncertainties that still need to be explained, such as the following: (a) Data on the evolution of carbon steel corrosion (C) with exposure time (t) obeys the power function C ¼ At n . The variables upon which n depends are not fully known, though the salinity of the atmosphere undoubtedly plays a prominent role. (b) In marine atmospheres, the presence of akaganeite and magnetite phases among the corrosion products is especially significant. In relation with these corrosion products, a number of important questions remain unanswered: What conditions are necessary for their formation? Where are they preferentially located? Is there a critical atmospheric salinity concentration below they are unlikely to form? It is also of great interest to know the typical surface microscopic morphologies resulting from the presence of akaganeite, where the confusion among researchers is well known. (c) In very severe marine atmospheres, the morphology of the corrosion layers formed on steel can be highly unusual, such as sheet-type or mound rust. There is a lack of basic knowledge on the formation mechanisms and internal microstructure of these rust types.
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