The present situation of research on atmospheric corrosion of copper and its alloys and the relevant corrosion mechanism were summarized. The main influence factors, several common research methods of atmospheric corrosion of copper and its alloys were reviewed. Meanwhile, prospective points in the future for the study in this field were brought forward.
In this article, experimental methods and numerical simulations for research of erosion-corrosion were intensively summarized. Furthermore, the main problems related with the experimental test and the numerical simulation were analyzed. Based on the current work, further development trend was also proposed.
A variety of inorganic and organic materials commonly used for surface modification of aluminum pigments was firstly summarized. While the main methods for surface modification of aluminum pigments, including sol-gel encapsulation, in-situ polymerization, emulsion polymerization, plasma polymerization and dispersion polymerization etc. were then introduced. The influence of materials and measures of surface modification on the performance of the modified aluminum pigments was also illustrated. Finally, the development trend in this field was prospected as well.
The correlation between the intergranular corrosion (IGC) behavior and the aging temper (including T6 aging at 150 and 175 ℃, T8 aging at 150 ℃) of 2099 Al-Li alloy was investigated. Then a diagram was established to describe the relation of IGC with the aging procedure. According to the aging resulted corrosion morphology of the alloy, the aging process might be divided into four stages: i.e. stage I is the initial aging stage, stage II the under-aging stage, stage III the near-optimal aging stage and stage IV the over-aging stage. The aged alloy showed different modes corrosion after aged by different stages: i.e. pitting corrosion or local intergranular corrosion (LIGC) for stage I; general intergranular corrosion (GIGC) for stage II; LIGC for stage III; and pitting corrosion without IGC for stage IV. In the under-aged alloy, a great number of very fine precipitates preferentially deposited along grain boundaries, which seem like a continuous chain, hence resulting in the highest susceptibility to IGC for the alloy. In the over-aged alloy, the precipitates were coarsened and the inter-precipitate spacing became larger, so that the susceptibility to IGC may be suppressed. In general, with the rising of aging temperature, the grain boundary precipitates grew coarse and the spacing between the precipitates became larger, while a proper pre-deformation of the alloy might facilitate the uniform nucleation of precipitates and suppress the formation of precipitate-free zone (PFZ) along grain boundary. These two factors shortened or even eliminated the Stage II and Stage III, therewith increasing the resistance to IGC of the alloy.
The evolution of corrosion process of hot-dip galvanized steel in a simulated acid rain atmospheric environment as a function of time was investigated by corrosion mass loss test, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and electrochemical techniques.<br>Consequently, corrosion kinetics, the surface and cross-sectional morphology and composition as well as electrochemical characters of corrosion products were acquired. The influence of the rust layers on the atmospheric corrosion of hot-dip galvanized steel was studied. According to the corrosion kinetics the rust layers can well protect the hot-dip galvanized steel from corrosion. The results of electrochemical measurement further illustrate that the protective effect of the rust layers is firstly enhanced, and then weakened as the corrosion time increases.
The sliding wear-corrosion of AISI 316 stainless steel against alumina in artificial seawater was investigated by means of weight loss test, electrochemical measurement and microstructure examination. The result shows that in the presence of wear the corrosion rate of AISI 316 stainless steel is obviously enhanced; the weight loss of the steel caused by corrosion-wear is higher than that under cathodic protection; the weight loss due to merely mechanical wear amounts to ca 76%~88% of the total weight loss of the wear-corrosion, which shows that the pure mechanical wear is the main factor in corrosion-wear process; however it may not be ignored that the weight loss corresponding to the synergistic effect between corrosion and wear amounts to ca 12%~24% of the total weight loss of the wear-corrosion.
Erosion-corrosion morphology of Cr13 stainless steel induced by jet flow of hydrochloric acid solution was characterized by means of SEM. Round-shaped pits was observed on the surface site corresponding to the center of impingement area of the jet flow. Around the center area, there exist radial patterns of comet-like grooves. The density of pits and grooves increases with increasing corrosion time. SEM micrographs reveal that the comet-like grooves composed of a pit as its head and a swallow-like groove as its tail, of which the head is initiated on the inclusion MnS particles; however, the tail is mainly laid on site of the martensite, while no obvious corrosion occurs on the δ-Ferrite zone of the steel.
The influence of main parameters on the measurement results of electrochemical frequency modulation (EFM) and the deviation of causality factors from their theoretical values were analyzed. Then the accuracy of corrosion rate measured by EFM for Q235 steel in NaCl solution was comparatively checked by means of measurements with EIS, linear-potentiodynamic technique and weight-loss method. The results show that great error will be introduced when the base frequency is too high; 0.01 Hz is a proper base frequency for Q235 steel in NaCl solution. Causality factor CF2 is much reliable than CF3 for checking the accuracy of EFM measurement. Rp value measured by EFM is much accurate than that by linear-potentiodynamic technique; in comparison with weight-loss method, EFM is a rapid and accurate method for measuring corrosion rate.
The water-line area corrosion of carbon steel in 3.5%NaCl solution was studied by me- ans of wire beam electrode (WBE) technique. The corrosion current distribution was regularly measured over a period of 40 d. In the initial stage, it was found that, down from the waterline, the anodic current increased gradually. This indicated that an oxygen concentration cell had been formed already. But the cathode region and anode region were mixed up in this stage. With the progress of the corrosion process, the cathode region was located near the waterline and the anode region was located beneath the cathode region. As the cathodic reaction above the waterline was speeding up, the corrosion region extended from the lower portion of the electrode upward to the waterline and thus the corrosion rate of whole electrode increased. In the smooth stage of corrosion, the main cathode region was located above the waterline and the corrosion rate became stable. This work confirms the applicability of the WBE method for the study of water-line corrosion. This method can especially provide information concerning the evolution of the corrosion current distribution of the electrode, which can not be acquired by the traditional technique with a bulk electrode of long steel strip.
The corrosion behavior of copper beneath a droplet of 0.6 mol/L NaCl solution was studied by means of wire beam electrode technique combined with electrochemical impedance spectroscopy (EIS). The results show that the distribution of galvanic current remains negative at the center and positive at the periphery of copper surface covered by the droplet at the initial stage. And the polarity reversed with the extension of time, i.e. the positive one at the center and the negative one at the periphery. To study more comprehensively, the EIS measurement was conducted at an interval of 2 h for two copper wires selected separately at the center and the periphery, and the change of the local impedances was found consistent with that of the current distributions. Meanwhile, the surface morphology of the electrode and the composition of the corrosion products were also examined by using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). At the beginning, reddish brown oxide products formed much quickly and earlier at the periphery rather than at the center. Then, with the extension of time, the electrode surface was totally covered by corrosion products from the periphery to the center. But, the corrosion products film at the center was severely damaged and replaced by malachite green products, while that remained less destructed relatively at the edge. Further, the corrosion mechanism of copper beneath the droplet was explored that it was the formation and transformation of the corrosion products dominated the changes of the distribution of the corrosion current.
The corrosion behavior for carbon steel Q235 and weathering steel 09CuPCrNi-A has been studied by alternative field exposure in a site of urban atmosphere and a site of petrochemical environment at Wuhan metropolis for 180 d and then the steel samples were examined by means of SEM, EDS, XRD and electrochemistry measurement. The results show that the surface of the rust layer is non-uniform with many cracks and pores for the steels exposed both in Wuhan urban atmosphere and Wuhan petrochemical environment; the rust layer formed in the early stage will have an impact on that in the later stage; and the changes in the environment will affect the evolution of the rust layer. The corrosion kinetics and polarization curve results show that the free corrosion current densities of the steels measured after exposure may exist a ranking as follows: Isuccessionally exposure in Wuhan urban atmosphere<Iexposure in Wuhan urban atmosphere/Wuhan petrochemical environment<Iexposure in Wuhan petrochemical environment/Wuhan urban atmosphere<Isuccessionally exposure in Wuhan petrochemical environment.
Corrosion of X80 pipeline steel in an acidic red soil slurry was studied by means of electrochemical impedance spectroscopy (EIS) and polarization technique. The results show that in a water-saturated red soil, the EIS of X80 steel contains a capacitive arc at high frequency and a capacitive arc from the interface process in frequency region of 10-2~104 Hz as well as an inductive loop appears at low frequency exhibiting processes related with adsorption or pitting nucleation; the electrode process was controlled by diffusion process after 30 d exposure; iron oxides residing in the soil tend to enhance the corrosion process of the steel, correspondingly a corrosion mechanism has been proposed.
A phosphate coating was prepared on AZ31B Mg alloy by chemical conversion process in a phosphorizing bath with additives Mn(NO3)2 and/or Na2MoO4, respectively. The effect of the additives on surface micromorphology and corrosion performance of the coatings were investigated by scanning electron microscope (SEM), electrochemical workstation and CuSO4 spot test. The results show that grain size of the films firstly decreases and then increases with of the increasing Mn(NO3)2 amount in a range of 0~2 g/L, correspondingly the corrosion resistance of the coatings becomes better and then worse; the grain size of the coating significantly reduces and then increases with the increasing Na2MoO4 amount in a range of 0~0.5 g/L, while the corrosion resistance of the coating rises up substantially; the surface morphology and corrosion resistance of the coatings can also be improved by simultaneously adding Mn(NO3)2 and Na2MoO4, but of which the effectiveness is inferior to that by merely adding Na2MoO4 in the phosphorizing bath. Through the above analysis, it follows that Mn(NO3)2 may play a weak role in enhancing the corrosion performance of the coatings; but it is interesting to note that by adding only 0.25 g/L Mn(NO3)2 to the phosphorizing bath the prepared coatings become much denser with better corrosion resistance.
