Changes In Corrosion Rate Research Articles

Using polymers to minimize corrosion of steel in concrete

Efforts to restrict chloride transport can lead to changes in the corrosion rate of steel in cement-based materials, such as concrete. Two potential methods have been examined for several years. They include: the addition of polymer fibers to the concrete at the time of mixing; and the encapsulation of previously contaminated concrete using polymer resin or polymer composites. It has been reported that the first method could minimize initial chloride intrusion and that the latter method could prevent additional chloride intrusion if concrete is already salt-contaminated. The effectiveness of these methods in minimizing corrosion was evaluated based on changes in corrosion rates determined using polarization resistance measurements. The results, which have been observed over a period of several years, will be reported. Limitations of polarization resistance measurements to evaluate the effectiveness of these methods as means of minimizing corrosion will also be discussed.

Stability of thin-walled high-pressure vessels subjected to uniform corrosion

The stressed state in real metal constructions changes in the process of operation even under permanent external loading. It takes place due to changes in the cross-sections of the loaded elements, resulting from the surface corrosion. This paper proposes a method for determining the critical time of stability loss in thin-walled high-pressure vessels subjected to uniform corrosion from the inside. The method is based upon the model of a thin elastic cylindrical shell. It is shown that this critical time can be established if the solution of the respective problem of the static stability loss for the vessel, not subjected to corrosion, and the law of corrosion rate change are known. Several special cases of the law of corrosion rate are examined.

Gravity Effect on Copper Corrosion

With a new gravity electrode by means of centrifugal force, gravity effect on copper corrosion in nitric acid was examined. The electrode system could control the gravity field up to 350 g by changing rotation speed. The experiments were performed in three different configuration modes of copper electrode; parallel, upward- vertical and downward-vertical to the gravity. After immersing copper electrode into 3 moldm -3 HNO 3 solution, under given gravity, corrosion currents and weight losses of the electrodes were measured. Consequently, it became obvious that copper corrosion is drastically protected in high gravity field. As long as the gravity is not so high, the upward-vertical mode indicated the most drastic change in corrosion rate with increasing gravity. In high gravity field, the corrosion rates in all modes converged to negligibly small values. On the contrary, in the solution with 0.01 moldm -3 HNO 3 + 3 moldm -3 NaNO 3 , the corrosion rate increased with increasing gravity. All these results was attributed to the facts that the convection flow induced by gravity affects the corrosion processes in different two ways; one is the blocking effect on copper dissolution and another the promoting effect on nitric-acid decomposition.

アルカリ溶液中における５０８３アルミニウム合金の腐食速度と圧延残留応力との関係

The corrosion rate of 5083 aluminum alloy cold rolled by a constant reduction rate (10% per pass) or a constant reduction amount (10% of original thickness per pass) method was measured in a 0.5mol/l-NaOH solution at 40°C. The changes in corrosion rate with the total reduction correspond very well to the changes in residual stress of the samples. For the sheets rolled by the constant rate method, the corrosion rate and the residual stress show the maximum at about 50% total reduction. In the case of constant amount rolling, both show two maxima at 30% and 80%, and show a minimum at 50% total reduction. These tendencies can be understood from the fact that the deformation process, which has the characteristic of the development of shearing band in the case of 5083 alloy, differs in the two rolling methods.

An investigation of galvanostatic transient methods used to monitor the corrosion rate of steel in concrete

The sensitivity of the time constants describing galvanostatically induced potential-time transients to corrosion rate changes was examined on steel embedded in concrete. While it was noted that the shape of the transients changed significantly with changes in corrosion rate, the decay was not an exponential function which would be expected if it were determined by activation controlled reactions. Indeed the time constants resulting from an assumed exponential decay were insensitive to corrosion rate changes. However, a proposed empirical function, which fitted the transients more accurately, produced time constants that were inversely proportional to the corrosion rate of active steel. It may be noted that potential- time transients are expected to be insensitive to specimen area and this may prove to be an advantage when monitoring the corrosion rate of an unknown or variable steel area.

Radionuclide Decay Effects on Waste Glass Corrosion

ABSTRACTThe release of glass components into solution, including radionuclides, may be influenced by the presence of radiolytically produced nitric acid, carboxylic acid, and transient water dissociation products such as ·OH and O2-. Under batch test conditions, glass corrosion has been shown to increase up to a maximum of three-to five-fold in irradiated tests relative to nonirradiated tests, while in other studies the presence of radiolytic products has actually decreased glass corrosion rates. Bicarbonate groundwaters will buffer against pH decreases and changes in corrosion rates. Under high surface area-to-solution volume (S/V) conditions, the bicarbonate buffering reservoir may be quickly overwhelmed by radiolytic acids that are concentrated in the thin films of water contacting the samples. Glass reaction rates have been shown to increase up to 10-to-15-fold due to radiation exposure under high S/V conditions.Radiation damage to solid glass materials results in bond damage and atomic displacements. This type of damage has been shown to increase the release rates of glass components up to four-fold during subsequent corrosion tests, although under actual disposal conditions, glass annealing processes may negate the solid radiation damage effects.

アルカリ溶液中での純アルミニウムの腐食速度に及ぼす冷間圧延の影響

The corrosion rate of 99.99mass% aluminum cold-rolled by a constant reduction rate (10% per pass) or a constant reduction amount (10% of original thickness per pass)method were measured in a 0.5mol/l-NaOH solution at 40°C. The changes in corrosion rate with the total reduction 0-90% corresponded very well to the changes in residual stress of the samples. For the sheets rolled by the constant rate method, the corrosion rate and the residual stress showed the maxima at 30% and 80%, and showed the minimum at 50% total reduction. In the case of constant amount rolling, both showed the maximum only at 30% total reduction. Both properties remained almost constant independently of total reduction after the recovery treatment at 100°C for 3h. These behaviors mean that the residual stress induced by rolling is a controlling factor in corrosion. Effects of pass programs, surface contamination and damage were also examined.

Effect of Temperature and Dissolved Oxygen on the Corrosion Behavior of Carbon Steel in High-Temperature Water

Abstract The corrosion behavior of carbon steel in high-temperature water, and the structure and composition of the oxide film were examined as functions of dissolved oxygen concentration (DO), temperature (T), and corrosion time (t). The total amount of iron corroded (WT) was differentiated into the amounts of iron ions in the oxide (WF) and dissolved into the water (WD). The total rate of corrosion (rT), the rate of iron dissolution (rD), and the rate of accumulation of iron in the oxide (rF) were obtained by differentiating the time variations in WT, WF, and WD. The structure and composition of the oxide film were examined by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and transmission and scanning electron microscopy. In general, rT increases with increasing DO and T, rD shows T- and DO-dependent minimum, and there is serious localized corrosion at high DO above 500 ppb. Oxide films consist of magnetite except at T=60°C, DO=50 to 200 ppb where a thin layer of hydrous ferric oxide is formed. At DO=500 ppb , the outermost part of the magnetite changes into γ-Fe2O3, and above DO=1.0 ppm, appreciable amounts of α-Fe2O3 cover the magnetite oxide layer. The rT and rD values are not related to the presence of αFe2O3 or Fe3O4 in the surface structure of the oxide, but clearly decrease as the OH−/Fe mole ratio at the oxide surface increases. The mechanism determining the corrosion rate changes is discussed.

Factors affecting the corrosion rate of steel in carbonated mortars

The corrosion of steel in carbonated mortar has been investigated by monitoring polarization resistance, corrosion potential and mortar resistivity. The results suggest that factors such as relative humidity and chloride contamination affect the corrosion rate via their influence on mortar resistivity. To account for the observed electrochemical relationships, most notably the linear correlation between corrosion rate and conductivity, and the exponential increase in corrosion rate with fall in corrosion potential, it is proposed that the corrosion kinetics of steel in carbonated mortar are subject to anodic control with the anodic reaction rate being limited by the resistance of the mortar. In this model, termed anodic resistance control, resistivity is viewed as a factor which may limit a half reaction rate in a similar way to diffusion and activation polarization. It is also shown that, when such a model is operating, the use of polarization resistance to monitor corrosion rate changes may still be justified provided the cathodic reaction rate is an exponential function of potential.

Corrosion rate determination using57Fe Mössbauer spectra of corrosion products of steel

Goethite and lepidocrocite are reported as main corrosion products of steel formed in Cuban wet tropical atmosphere. Corrosion rate changes exponentially with time. It was determined that area ratio between lepidocrocite paramagnetic doublet lines and goethite sextet has the same exponential behavior, that is why this method can be proposed for studing atmospheric corrosion kinetics.

Density dependence of the electrochemical characteristics of carbon overcoated thin film media

The effectiveness of carbon overcoats as a corrosion barrier for thin film media has been studied. The sputtering pressure and power used during the deposition of the carbon overcoat has a direct influence on its density, and thus upon its corrosion protection characteristics for the underlying metal media. Corrosion rates of the carbon overcoated metal media were measured both electrochemically and by exposing disks to conditions of elevated temperature and humidity. Corrosion measurements show that the corrosion rate of the magnetic media, (sputtered at a constant pressure and power), increases with increased deposition pressure (1–30 mTorr) and decreased sputtering power (2.8–0.3 kW) of the carbon film. The increased corrosion rate is caused by a decrease in density of the carbon film. In another experiment, sputtering pressure was varied in both the magnetic and overcoat layers. Corrosion measurements reveal a relatively small change in corrosion rate for sputtering pressure in the range of 1 to 6 mTorr of Ar, but a significant increase at 30 mTorr. This sharp increase was attributed to an increase in surface area of the magnetic layer believed to be generated by the the formation of rough porous films at high pressure. In this study carbon and magnetic films sputtered at high power and low pressure yield media with the lowest corrosion rate.

The episodic nature of the atmospheric rusting of steel

Sensitive corrosion monitors developed at these Laboratories have been used to measure the atmospheric corrosion rates of mild steel twice weekly. The time-of-year dependence of the corrosion behaviour was investigated by deploying one or more of these monitors each month for a year at Leatherhead. The results show that corrosion rates are very strongly influenced by specific ‘events’ which occur perhaps five or six times a year and alter the corrosion kinetics. This study details the significant corrosion rate changes that occurred as a result of a major event which was characterized by long range inland transport of sea salt.

Effect of some inorganic anions on corrosion of tin in nitric acid solutions

AbstractThe electrochemical corrosion of tin in various concentrations of nitric acid has been studied. The change in corrosion rates with nitric acid concentration has revealed the occurrence of four distinct corrosion processes. The corrosion of tin was found to be maximum at 4·5M HNO3, and at 14·4M HNO3 the metal is passivated. The effect of various inorganic anions was investigated: it wasfound that some of these inhibit corrosion while others accelerate it. The anions added were NO2−, NO3−, Cl−, CrO42−, SO42−, S2O52−, HPO42−, H2PO−4, IO3−, and B4O72−. Of these, Cl− and CrO42− were studied in some detail. Acetate ions were also found to inhibit the corrosion of tin in nitric acid.

Study of influence of manganese additions on electrochemical corrosion behaviour of austenitic spheroidal graphite iron

The effect of the progressive replacementof nickel by manganese on the electrochemical corrosion behaviour of austenitic spheroidal graphite iron has been investigated in 5% solutions of NaCl, NaOH, and H2SO4 using potentiodynamic polarization and metallographic studies. The change in corrosion rate in the substituted alloys depends significantly on the corrosion medium. The results indicate that up to 15%Ni can be effectively replaced by ∼ 8%Mn+2%Cr with relatively small sacrifice of corrosion resistance in 5%NaCl and 5%NaOH media. however, there is a significant loss of corrosion resistance in 5%H2SO4 when manganese is added. The addition of 1,2,3 benzotriazole inhibitor improved the corrosion resistance in the acid medium. The role of microstructure on electrochemical corrosion is discussed using metallographic observations and polarization results.

Intergranular Corrosion in High Purity Ferritic Stainless Steels: Isothermal Time-Temperature Sensitization Measurements

Abstract Iosthermal sensitization heat treatments have been carried out on a high purity ferritic stainless steel (Fe-26% Cr) and the development of susceptibility to intergranular corrosion determined by means of the Huey test. It has been found that exposure to temperatures above 600 C (1110 F) does not cause a significant change in corrosion rates. Below this temperature, susceptibility to intergranular corrosion begins to develop. This sensitization increases in severity and reaches a maximum at longer times as the temperature is lowered. Isocorrosion (TTS) curves which are constructed on temperature versus log time graphs from the experimental data are analogous to those reported for austenitic stainless steels. This is discussed in terms of a common chromium depletion theory for the two classes of alloys. The sensitization which is found to develop after long times at temperatures near 475 C (885 F) is believed to be due to chromium depletion adjacent to the grain boundaries, rather than being assoc...

The Use Of Pulsed Applied Voltage in the Derivation of Corrosion Rates From Polarisation Resistance Measurement

Abstract An experimental technique has been developed for the rapid determination of changes in corrosion rates using the well established Stern–Geary equation. The value of the technique was demonstrated for the corrosion rates of aluminium brass in seawater and in seawater containing 0·01% sodium dimethyl dithiocarbamate for which the corrosion characteristics had been established previously. An instrument based on these principles could be developed for a variety of corrosion measurement application.

Linear Polarization Measurements In the Study of Corrosion Inhibition

Abstract A reliable and accurate method of determining metal dissolution rates in a relatively short time is much needed in studies of corrosion inhibition. Weight-loss determinations on specimens supply only average rate data over the interval of the test. Rate determinations by chemical analysis of the corrosive environment are also subject to this limitation. Both of these methods are subject to errors arising from intermittent removal of the sample from the environment. Knowledge of corrosion rate changes during the period of exposure is valuable to understanding of the mechanism of the reaction involved. The linear polarization method has been found very rapid and convenient for studying rate changes and evaluating corrosion inhibitors. It has also made possbile observations of the synergistic effects that may exist between inhibitor and environment.

Corrosion of Iron in an H2S-CO2-H2O System

Abstract Corrosion studies of iron in an H2S-CO2-H2O System were made under static and dynamic conditions. The data indicated that there existed a certain hydrogen sulfide partial pressure, approximately 0.02 psia, above which hydrogen blistering occurred. Similar results with sulfide stress cracking were obtained. The hydrogen sulfide partial pressure at onset of cracking was 0.150 psia. Hydrogen sulfide became the controlling factor at very low partial pressures causing an initial drop in the corrosion rate. Apparently, the type of corrosion film formed controlled the corrosion rate. Changes in these films were observed to take place coincident with changes in corrosion rate and prevalence of hydrogen blisters. The relationship of these phenomena is discussed. 6.2.2, 8.4.3, 3.2.2, 3.5.8

空気を含む水溶液中におけるニッケルの自己不働態化

The corrosion rate of nickel was measured in aerated sulfate solutions of various pH. An abrupt change of corrosion rate was found at aboult pH 5. In acidic region, the corrosion rate was nearly equal to the diffusion rate of dissolved oxygen and the spontaneous potential was less noble than the Flade potential. In alkaline solution, on the other hand, the corrosion rate was undetectablly small and the spontaneous potential was in the passive region. The polarization curve of nickel in acidic solution (pH=3.77) showed that the maximum dissolution current of iMmax in the active state, which can be measured in the solution saturated with pure nitrogen gas, was larger than the reduction current of dissolved oxygen iO. While, in neutral solution (pH=7.53), iMmax was smaller than iO. The critical state of iMmax=iO was found to be at about pH=5. It could be explained from the electrochemical standpoint that nickel is passivated by the reduction current of dissolved oxygen (O2+2H++4e→2OH−) only when |iMmax|<|iO|.

A Method For Determining Corrosion Rates From Linear Polarization Data

Abstract A method for determining corrosion rate from electrochemical polarization data obtained in the region of the corrosion potential is described. The technique has foundation in theory, is supported by experimental evidence, and appears to have widespread application. The advantages and limitations of the method are discussed. It would appear that the use of linear polarization measurements can supply valuable information regarding: (1.) Studies of the effect of environment variables on corrosion rate. These include changes in composition, velocity, and temperature, (2.) Evaluations of inhibitors in controlling corrosion, (3.) Comparison of the corrosion rates of various alloys of similar composition in a given environment, and (4.) Determination of changes in corrosion rate with time, including studies of underground structures as well as materials in aqueous solutions. It also may be possible to use this method in evaluating the condition of coatings in service which cannot be inspected by visual ...