Effects of Temperature and Potential on the Inhibitive Action of Oxoacid Salts for Pitting in High-Temperature Chloride Solutions

Yashiro, Hitoshi; Oyama, A.; Tanno, Kazuo

doi:10.5006/1.3280470

Cited by 22 publications

(25 citation statements)

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“…Moreover, according to the previous report, it was concluded that pit initiation due to C1-ion action becomes facilitated with increasing T~ in an SO, 2-ion-free chloride solution (temperature-sensitive), while the inhibitive action of the SO, 2-ion is not sensitive to the change of Ts in an SO, 2-ion-containing chloride solution (temperature-insen- sitive) [13]. Thus, it can be concluded that as T~ increases, the metal dissolution rate markedly increases due mainly to the many tunnels formed by an SO42-ion attack on the bare metal surface at the pre-existing pit bottom, extended by the temperature-sensitive C1-ion action at potentials above Epl,.…”

Section: Resultsmentioning

confidence: 99%

Effects of applied potential and solution temperature on the pitting corrosion of pure aluminium in sulphate ion-containing chloride solution

Kim

Lee

Pyun

et al. 1999

Metals and Materials

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Effects of applied potential and solution temperature T. on the pitting corrosion of pure aluminium (AI) were investigated in 0.01 M NaCI solutions containing various sulphate (SO, 2-) ion concentrations using a potentiodynamic polarisation experiment, the potentiostatic current transient technique, ac impedance spectroscopy and atomic force microscopy (AFM). The potentiodynamic polarisation curves showed a rise in the pitting potential E,, values and a simultaneous increase in anodic current density at potentials much higher than the Ep,, value as the SO42-ion concentration increases. This implies that SO,"-ions impede pit initiation at potentials below Ep, but enhance pit growth above Ep,,. This was confirmed from the larger pit growth rate parameter b values of pure A1 exposed to SO4 ~ ion-containing chloride solutions during the abrading action than those exposed to SO42-ion-free chloride solution. Furthermore, at E=25~ the charge density Q values for the A1 metal dissolution in the presence of SO42-ions were smaller than the value in its absence. By contrast, as validated by the capacitance values and the AFM images of the re-anodized specimens, an enhanced metal dissolution was observed in SO42-ion-containing chloride solutions at T,=60 ~ and 80~ From the experimental findings, it is suggested that SO42-ions act as inhibitors of pitting corrosion on pure AI below E~,, and at T,=25~ whereas they act as promoters at T,=60 ~ and 80~ This originates from the accelerated dissolution of the bare metal extensively exposed to the temperature-sensitive C1-ion attack, which occurs at potentials above E,,,,.

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Section: Resultsmentioning

confidence: 99%

Effects of applied potential and solution temperature on the pitting corrosion of pure aluminium in sulphate ion-containing chloride solution

Kim

Lee

Pyun

et al. 1999

Metals and Materials

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“…∼800 mV vs. Ag-AgCl). 13 In compar- ison, in this work all that may be required to inhibit corrosion is the raising of the pitting potential above that able to be supplied by the droplet. As such the upper values given in Table VIII may be overestimates for a droplet system.…”

Section: 41mentioning

confidence: 99%

“…In particular, anions such as nitrate and sulfate, which are likely to be present in amounts comparable to chlorides in waste stores, 3 have been shown to inhibit corrosion processes in bulk solutions above specific critical ratios to the chloride ion. [7][8][9][10][11][12][13][14][15][16][17] The concentration of MgCl 2 in equilibrium with an ambient RH of 90% is ∼1.5 M, and increases with decreasing humidity. 18 Inhi- * Electrochemical Society Member.…”

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confidence: 99%

Effect of Nitrate and Sulfate on Atmospheric Corrosion of 304L and 316L Stainless Steels

Cook

Padovani

Davenport

2017

J. Electrochem. Soc.

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The effects of nitrate and sulfate salts on the chloride-induced atmospheric pitting corrosion of 304L and 316L stainless steel was investigated through automated deposition of droplets of magnesium and calcium salts. Nitrate was found to inhibit pitting under magnesium salt droplets when the ratio between the deposition density of nitrate anions and chloride anions was above a critical value, which was the same for both 304L and 316L. This critical ratio was found to decrease with increasing humidity. Sulfate was also observed to inhibit pitting for MgCl 2 + MgSO 4 mixtures, but only at higher humidities. Sulfate did not show any inhibition for CaCl 2 + CaSO 4 mixtures, an effect attributed to the low solubility of CaSO 4 . At low relative humidities, precipitation of the inhibiting salt was observed, leading in some cases to crevice-like corrosion under salt crystals. The pitting behavior was explained in terms of the thermodynamic behavior of concentrated solutions. In the UK, stainless steel is used to package intermediate level radioactive waste, ILW, which is characterized by relatively large volumes and variable levels of radioactivity.1 Whatever the strategic approach to its management c , most ILW has been packaged in thinwalled containers (2.3-6 mm thick, typically grades 304L or 316L, UNS S304003 and UNS S316003, respectively) and will undergo long periods of exposure to atmospheric conditions, either in surface or underground facilities prior to permanent disposal.During these periods, waste containers will be exposed to regimes of varying temperature and relative humidity (RH), as well as to chloride-containing salts arising from aerosol deposition. As a result, it is important to identify suitable storage conditions to ensure durability of waste containers, in particular to avoid conditions associated with the development of pitting and, even more importantly, atmospherically-induced stress corrosion cracking (AISCC). 2,3Monitoring of ILW storage facilities and other indoor locations considered broadly representative of ILW stores suggests that temperature and relative humidity, which are key parameters in the development of atmospheric corrosion, are expected to vary between ∼0-30• C and ∼30-100% RH, respectively. 3 Ionic chemical species deposited on surfaces after relatively long periods of indoor storage found in swab tests in a variety of real storage facilities include calcium, magnesium, sodium, potassium, chloride, nitrate and sulfate ions. Inside the storage buildings surveyed, chloride deposition densities were found to be below ∼20 μg/cm 2 , with deposition rates of the order of 1 μg/cm 2 per year estimated. 3 With such a deposition rate, the chloride deposition density could increase to ∼100 μg/cm 2 over the next century.In atmospheric conditions relevant to this work, a number of tests have been carried out to evaluate the atmospheric pitting corrosion of stainless steel in the presence of chloride deposits (e.g., Refs. 2, 4-6) but none of these have been carried out in the presence of...

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“…As known widely, 20) nitrate retards pitting effectively but the mechanism is not clear enough in terms of potential dependency for inhibition. 21,22) In Fig. 4, anodic polarization curves for 310 steel in 3 mol dm Ϫ3 NaCl solution containing 0.3 mol dm Ϫ3 NaNO 3 are shown as a function of temperature.…”

Section: Effect Of Nitratementioning

confidence: 99%

“…The weaker effect of nitrogen at relatively less noble potential region as appeared at high temperatures could be made up for by the addition of molybdenum. Because the effect of molybdenum becomes more pronounced at higher temperatures, 22) the combination of nitrogen and molybdenum would provide a desirable pitting resistivity over a wide range of potential and temperature.…”

Section: Role Of Nitrogenmentioning

confidence: 99%

Effect of Nitrogen Alloying on the Pitting of Type 310 Stainless Steel.

Yashiro¹,

Hirayasu²,

Kumagai³

2002

ISIJ International

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The effect of nitrogen alloying on the pitting behavior of type 310 stainless steel has been investigated through measurements of pitting potential (E ' pit ) as a function of temperature and concentration of NaCl (C NaCl ). Nitrogen was effective to shift E ' pit to nobler direction especially at temperatures below critical one. The critical pitting temperature was defined as the temperature below which the usual linear relationship between E ' pit and logarithm of C NaCl did not stand. Alloying the stainless steel with nitrogen increased the critical pitting temperature. Below the critical temperature where E ' pit did not follow the usual dependency on C NaCl , pitting was retarded most effectively by nitrogen except when C NaCl was so high that E ' pit lay below ca. 400 mV. Although the whole mechanism of nitrogen is not still clear, nitrogen is most likely to suppress acidification of pitting site through formation of ammonium ion. Nitrogen in a metal matrix and nitrate in a solution seemed to have a common feature with respect to the potential dependency of inhibition efficiency. The fact that nobler potentials were more favorable for both nitrogen in metal matrix and nitrate in a solution for inhibition seemed to indicate that oxidation of nitrogen to nitrate might also be involved in the inhibition mechanism.KEY WORDS: nitrogen; stainless steel; pitting; chloride; nitrate; temperature. Table 1. Chemical composition of the stainless steels investigated (mass%).

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Effects of Temperature and Potential on the Inhibitive Action of Oxoacid Salts for Pitting in High-Temperature Chloride Solutions

Cited by 22 publications

References 0 publications

Effects of applied potential and solution temperature on the pitting corrosion of pure aluminium in sulphate ion-containing chloride solution

Effects of applied potential and solution temperature on the pitting corrosion of pure aluminium in sulphate ion-containing chloride solution

Effect of Nitrate and Sulfate on Atmospheric Corrosion of 304L and 316L Stainless Steels

Effect of Nitrogen Alloying on the Pitting of Type 310 Stainless Steel.

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