碳钢大气腐蚀时表面结露行为的某些影响因素

利用作者建立的能直接观察和记录金属表面结露过程的实验室装置,进一步考察了表面划痕,各种尘埃、盐玷污等多种因素对于碳钢表面上结露行为的影响,以加深对金属大气腐蚀初期过程的认识。     

Applicability of constant dew point corrosion tests for evaluating atmospheric corrosion of aluminium alloys

Field exposure tests of aluminium alloys were conducted at three sites in Japan. Meteorological data indicated that the dew point of the ambient atmosphere and aluminium panels remained constant for the short-term. Constant dew point corrosion tests were employed to reproduce atmospheric corrosion of aluminium alloys in the laboratory. The corrosion rates, corrosion morphology and corrosion product composition after 7 days of tests in the laboratory were similar to those formed after 3 months of exposure at coastal sites. Not only did the constant dew point corrosion test effectively reproduce the atmospheric corrosion of aluminium alloys, it also accelerated it.     

Corrosion simulation of carbon steels in atmospheric environment

Atmospheric corrosion simulation of carbon steels has been performed in order to clarify the atmospheric corrosion mechanism of carbon steel. The corrosion simulation was conducted in a chamber by controlling the environmental factors such as temperature, relative humidity and temperature of carbon steels. When the corrosion simulation was conducted using only the data of temperature and relative humidity, although the carbon steel in the corrosion simulation showed almost the same corrosion behavior as that in outdoor environment, the corroded area of the former was smaller than that of the latter. In order to simulate dew condensation, the temperature of carbon steel was controlled by a cooling-system. As a result of the corrosion simulation, both the corrosion behavior and the corroded area were almost the same as those in outdoor environment. It was concluded that the initial atmospheric corrosion of carbon steel in the shielded environment could be simulated in the chamber by controlling the temperature, the relative humidity and the temperature of materials.     

Artificial neural network corrosion modeling for metals in an equatorial climate

The majority of the metals used in the distribution and transmission electric energy lines, such as cables, towers and accessories are susceptible to the corrosion degradation process. For that reason, studying the factors that influence the atmospheric corrosion is an important issue. In this paper, an artificial neural network model was developed with linear and sigmoidal functions, aiming to predict low-carbon steel, copper and aluminum corrosion rates according to environmental parameters in the area of São Luis – Maranhão, Brazil. The area along the “702 – São Luis II –Presidente Dutra” 500 kV transmission line, located in an equatorial region, is employed for this purpose. A specific methodology was developed to determine the local corrosivity rate for these metals. Five atmospheric corrosion stations (ACS) were installed along the 702 transmission line in an extension of 200 km. Along with the meteorological data, local pollutants were collected and analyzed during a period of two years. In the same period, specimens were exposed to this atmosphere and periodically collected for corrosion evaluation. The obtained results indicate that the neural network can be used as a good corrosion estimator.     

Corrosion product formation during NaCl induced atmospheric corrosion of magnesium alloy AZ91D

Magnesium alloy AZ91D was exposed in humid air at 95% relative humidity (RH) with a deposition of 70 μg/cm⁻² NaCl. The corrosion products formed and the surface electrolyte were analysed after different exposure times using ex situ and in situ FTIR spectroscopy, X-ray diffraction and Ion Chromatography. The results show that magnesium carbonates are the main solid corrosion products formed under these conditions. The corrosion products identified were the magnesium carbonates hydromagnesite (Mg₅ (CO₃)₄ (OH)₂4H₂O) and nesquehonite (MgCO₃ 3H₂O). The corrosion attack starts with the formation of magnesite at locations with higher NaCl contents. At 95% RH, a sequence of reactions was observed with the initial formation of magnesite, which transformed into nesquehonite after 2-3 days. Long exposures result in the formation of pits containing brucite (Mg(OH₂)) covered with hydromagnesite crusts. The hydromagnesite crusts restrict the transport of CO₂ and O₂ to the magnesium surface and thereby favour the formation of brucite. Analysis of the surface electrolyte showed that the NaCl applied on the surface at the beginning was essentially preserved during the initial corrosion process. Since the applied salt was not bound in sparingly soluble corrosion products a layer of NaCl electrolyte was present on the surface during the whole exposure. Thus, Na⁺ and Cl⁻ ions can participate in the corrosion process during the whole time and the availability of these species will not restrict the atmospheric corrosion of AZ91D under these conditions. It is suggested that the corrosion behaviour of AZ91D is rather controlled by factors related to the microstructure of the alloy and formation of solid carbonate containing corrosion products blocking active corrosion sites on the surface.     

Electrochemical noise monitoring of the atmospheric corrosion of steels: identifying corrosion form using wavelet analysis

The early stage atmospheric corrosion of T91 and Q235B steels exposed to Tianjin’s urban atmosphere over 20 days was studied using two electrochemical probes via an electrochemical noise (EN) technique. To identify the corrosion process and the corrosion form of the two steels, EN data were analysed by statistics and wavelet transform. The results revealed that the wavelet energy of decomposed EN mainly located at high-frequency level for Q235B steel, whereas it mainly located at the low-frequency level for T91 steel. Analyses of surface images confirmed that Q235B steel underwent uniform corrosion whereas T91 steel suffered from localised corrosion. The obtained noise resistance correlated well with weight loss data.     

Indoor atmospheric corrosion of electronic materials in tropical-mountain environments

Indoor corrosion rate during one year exposure for carbon steel, copper, nickel, and tin was determined in three different atmospheres in Colombia. In addition, pollutants deposition rates and environmental parameters were also measured during indoor-outdoor conditions. The results show higher pollutant deposition in outdoor conditions, while inside metallic boxes the pollutant deposition significantly diminishes. No difference for relative humidity values was found between inside and outside measurements. For all samples, except nickel, the corrosion rate decrease with exposure time. The nature of corrosion products was found to be related to the exposure conditions.     

Long-term atmospheric corrosion of zinc

A great deal of information is available on the short- and mid-term atmospheric corrosion of zinc: corrosion rate data as a function of atmosphere type, corrosion mechanisms, effect of environmental variables, effect of surface orientation, damage functions, etc. However, very little information has been published on the atmospheric corrosion of zinc over long time periods (10-20 years), despite its great usefulness. On the other hand, many studies have analyzed the nature of corrosion products formed on zinc in a wide range of atmospheric environments, using different experimental techniques, but few have focused on the morphology of corrosion product layers. This paper reports the characteristics—mainly composition and morphology—of corrosion products formed on zinc panels after long-term exposure (13-16 years) in various types of atmospheres in Spain: rural, urban, industrial, mild marine and severe marine.     

Long-term monitoring of atmospheric corrosion at weathering steel bridges by an electrochemical impedance method

Weathering steel corrosion was monitored for one to two years under natural atmosphere by an electrochemical impedance technique. Two identical comb-shape weathering steel sheets embedded in epoxy resin were used as monitoring probe electrodes at two different bridges in Japan. Impedances at 10 kHz (Z_10kHz) and 10 mHz (Z_10mHz) were automatically measured every hour. Coupons (50 × 50 × 2 mm³) prepared from the same steel sheets were exposed together to measure the corrosion mass loss. The average (Z_10mHz)⁻¹ value for half to one year exposure correlated well with the average corrosion rate determined from the corrosion mass loss.     

Discovering key meteorological variables in atmospheric corrosion through an artificial neural network model

This paper presents a deterministic model for the damage function of carbon steel, expressed in μm of corrosion penetration as a function of cumulated values of environmental variables. Instead of the traditional linear model, we designed an Artificial Neural Network (ANN) to fit the data. The ANN numerical model shows good results regarding goodness of fit and residual distributions. It achieves a RMSE value of 0.8 μm and a R² of 0.9988 while the classical linear regression model produces 2.6 μm and 0.9805 respectively. Besides, F_LOF for the ANN model were next to the critical value.The improved accuracy provides a chance to identify the most relevant variables of the problem. The procedure was to add/remove one after the other the variables and perform from scratch the corresponding training of the ANN. After some trial and error as well as phenomenological arguments, we were able to show that some popular meteorological variables like mean relative humidity and mean temperature shown no relevance while the results were clearly improved by including the hours with RH < 40%. The results as such might be valid for a limited geographical region, but the procedure is completely general and applicable to other regions.     

EIS monitoring study of atmospheric corrosion under variable relative humidity

Electrochemical impedance spectroscopy (EIS) technique was used to investigate atmospheric corrosion in laboratory simulated environments with variable relative humidity (RH) and fixed Cl⁻ content. The results show the suitability of EIS for analyzing electrochemical corrosion behaviour at 5-100% RH. At 5-30% RH, EIS spectra reflected the character of the electrode, whereas at 40-100% RH, the model of EIS spectra was established with the help of surface analysis. From 70% RH, the film resistance (R_r) reflects the degree of corrosion and the charge transfer resistance (R_t) provides quantitative representation of the corrosion rate, which were verified by weight loss tests.     

A mechanistic study of initial atmospheric corrosion kinetics using electrical resistance sensors

This paper describes a novel experimental approach to the study of atmospheric corrosion of iron and zinc, utilising electrical resistance sensors that are sensitive to corrosion losses of the order of one atomic monolayer. Using such devices, a mechanistic study of the initial stages in the atmospheric corrosion of iron and zinc was performed in a rectangular flow cell using controlled relative humidity (RH), temperature and gas flow rate. Additionally, the effects of SO₂ contamination in the gas phase and prior NaCl contamination of the metal surface were studied. It was found that the initial corrosion kinetics of iron and zinc are, not unexpectedly, dominated by the development of surface corrosion product films, but that the growth kinetics vary with metal, humidity, etc. Specifically, in the presence of gas-phase SO₂, activation energies and kinetic and chemical rate orders were consistent with control of the atmospheric corrosion process by solution-phase oxidation of sulphite–sulphate ion. For iron, this implies that the well-known sulphate-nest theory is inoperative at least during the early stages of atmospheric corrosion. In contrast, for chloride–contaminated zinc, the data were consistent with a rate-controlled diffusion of a species, probably water vapour or oxygen, through a thickening corrosion product film. Finally, the kinetic and chemical rate orders for corrosion of chloride–contaminated iron precluded a diffusion-controlled mechanism, but were consistent with a rate-controlling process involving some regeneration of chloride: e.g. as in metal–ion hydrolysis in a pit or similar localised corrosion events.     

Influence of atmospheric pollution on corrosion of materials in Saudi Arabia

Research has been carried out for 7 years in eight marine atmospheres with annual average chloride deposition rates of 63–704?mg Cl^?/m² day and sulphur dioxide deposition rates of 6.851–10.887?mg SO₂/m² day. A study of environmental parameters: temperature, relative humidity, airborne chloride and SO₂ on the site have been accomplished. Apart from this, the paper also considers the corrosion rates of carbon steel, stainless steel (AISI 304) and galvanised steel and the resulting corrosion products and layers, and their dependence of atmospheric salinity of the site. X-ray diffraction analyses were carried out in order to understand the lepidocrocite and goethite, high akaganeite and magnetite contents of corrosion products. Corrosion rates were determined by weight loss. The aggressive classification was made as per the ISO 9223. Moreover, a technique for calculation of coefficients in the power-linear function for long-term prediction of metal corrosion losses of exposed metals and alloy are presented.     

The atmospheric corrosion of copper by hydrogen sulphide in underground conditions

The atmospheric corrosion of copper by hydrogen sulphide has been followed during field tests using different sulphide concentrations, for 77 days, and during exposure to a well-defined synthetic atmosphere in a test chamber. The main components formed at the surface of the samples are copper oxides and sulphide. We show that exposure tests performed for short times in synthetic atmospheres cannot be extrapolated to long time exposure in real conditions, since three successive phases of film growth are observed. The mechanism of film growth is discussed, assuming that cationic diffusion through the cuprous oxides and sulphide is the rate-determining step.     

Indoor atmospheric corrosion of copper and steel under heat trap conditions in Cuban tropical climate

Abstract

Corrosion behaviour of copper and steel under heat trap conditions in Cuban tropical climate is reported. Temperature and humidity reach higher values than those reported for traditional outdoor and indoor conditions. Annual calculated time of wetness is in the range corresponding to outdoor or ventilated sheds. This behaviour is not reported for other indoor conditions. Sulphur compounds deposition rate is higher than chloride deposition rate at all corrosion stations. Main corrosion products formed on steel and copper are goethite and brochantite respectively. No significant differences in the statistical influence of exposure time and time of wetness on atmospheric corrosion process of copper and steel under heat trap conditions are determined.     

The atmospheric corrosion of copper at two sites in Portugal: a comparative study

This paper presents a comparative study on the atmospheric corrosion of copper, at two sites, in Portugal, with exposures started in two different seasons (summer and winter). Particular attention is devoted to the initial stages of the corrosion process.The levels of pollutants, namely of SO₂ and chlorides, in both atmospheres, have been measured, over the periods from August 1999 to July 2000 and from November 2000 until July 2001. Climatic data for both sites and both periods has been collected and analysed.Kinetics of the corrosion process (weight losses) have shown to be described by: Δm=kt^0.6 and Δm=kt^0.4, with k equal to 3.4 (g m⁻² month^−0.6) and 17 (g m⁻² month^−0.4), for the one year exposures, started in summer, at the urban and maritime atmospheres, respectively. Exposures started in winter, at the urban atmosphere, have lead to kinetics described by Δm=kt^0.7 with k=5.0 (g m⁻² month^−0.7).The chemical composition and the morphology of the copper patinas, corresponding to exposures of 2 and 12 months, at the two sites, are compared as well as the morphology of the corroded surfaces.     

Degradation of galvanised iron roofing material in Tanzania by atmospheric corrosion

Abstract

Galvanised iron is popular in many applications, particular as a roofing material. However, just like other materials, especially metallic ones, it is prone to degradation by corrosion. In this particular study, the degradation of galvanised roof sheets was investigated at a coastal, urban and rural site in Tanzania, Africa. Samples were exposed to various outdoor environments over a period of 3 years. In addition, some accelerated laboratory investigations were conducted in different simulated air pollution environments in an artificial corrosion chamber constructed for this purpose to supplement the outdoor exposure tests. It was found that the combination of the tropical climate and increasing air pollution due to industrial development in the capital Dar-es-Salaam resulted in substantial atmospheric corrosion of the roof sheets, which eventually leads to failure and the necessity for replacement. The rural site had the lowest degree of atmospheric corrosion as expected. A combination of different corrosion products was identified as a result of the atmospheric corrosion by Raman and EDX analyses. The information gained from this investigation could be utilised to construct more durable structures requiring less frequent replacement and maintenance in future.     

Hydrogen entry into steel during atmospheric corrosion process

Hydrogen entry and permeation into iron were measured by an electrochemical method during atmospheric corrosion reaction. The hydrogen permeation was enhanced on passive films because the hydrogen adsorption increased by the hydrogen evolution mechanism which is different from that on a bear iron surface. The permeation rate during a wet and dry corrosion cycle showed a maximum in the drying process depending upon the surface pH and the corrosion potential. The pollutant such as Na₂SO₃ which decreases the pH and the corrosion potential causes an increase in the permeation rate. The mechanism of the change in the permeation rate during the wet and dry cycles is explained by the polarization diagram of the electrode covered by thin water layer.     

Advances in understanding atmospheric corrosion of iron. I. Rust characterisation of ancient ferrous artefacts exposed to indoor atmospheric corrosion

Metallic substrates and rust layers of several hundred year old (y.o.) ferrous artefacts were characterised. Composition, structure and porosity of the rust were analysed by different methods: OM, SEM, EDS, EPMA, XRD, μXRD, SAXS, BET and mercury porosimetry.Several important parameters to describe an old rust layer were determined and measured. These parameters will be used for the modelling of long-term indoor atmospheric corrosion.