Effect of Thiosulfate on Pitting Corrosion of Ni-Cr-Fe Alloys in Chloride Solutions

CORROSION ◽  
10.5006/2923 ◽  
2018 ◽  
Vol 74 (11) ◽  
pp. 1214-1228 ◽  
Author(s):  
Abraham A. Becerra Araneda ◽  
Mariano A. Kappes ◽  
Martín A. Rodríguez ◽  
Ricardo M. Carranza
Keyword(s):  
Pitting Corrosion ◽  
Chromium Content ◽  
High Potential ◽  
Anodic Peak ◽  
Nacl Solution ◽  
Potentiodynamic Curves ◽  
Maximum Current ◽  
Fe Alloys ◽  
Stable Passivity ◽  
Pit Initiation

Pitting corrosion of Alloys 600, 690, and 800 (UNS N06600, N06690, and N08800) was studied in 1 M NaCl solution with different concentrations of thiosulfate (). Alloys exhibited vastly different electrochemical behavior, depending on the concentration and chromium content of the alloy. Alloy 600 exhibited a breakdown and repassivation potential that decreased with decreasing concentration, in the range from 1 M to 10−4 M. Breakdown and repassivation potentials decreased about 300 mV and 600 mV, respectively, when 10−4 M was added to a 1 M NaCl solution. For Alloys 690 and 800, additions of in the range of 1 M to 0.01 M caused a decrease in the breakdown and repassivation potentials. Dilute solutions were more aggressive, and a 0.01 M addition of to a 1 M NaCl solution caused a decrease in breakdown and repassivation potentials of about 300 mV. In a solution containing 0.001 M Na2S2O3 + 1 M NaCl, Alloys 690 and 800 showed two different submodes of pitting, each one of them existing at a different range of potential. Chloride pitting corrosion was observed at high potentials and was characterized by pits with a lacy cover. The stable pit initiation potential associated with this process in both alloys was near 300 mVAg/AgCl and was preceded by frequent metastable events. Chloride plus pitting was observed at low potentials (near −225 mVAg/AgCl) and was characterized by hemispherical pits. In potentiodynamic curves, this submode of pitting showed a characteristic anodic peak of approximately 120 mV width and a maximum current density of 10 μA/cm2 for both alloys. Potentiostatic tests at potentials within this anodic peak led to stable pit growth. Those pits could be repassivated by scanning the potential either in noble or active directions. Low-potential and high-potential pitting submodes were separated by a stable passivity range, as determined by potentiodynamic curves. Upon a further decrease in concentration down to 10−4 M, only high-potential pitting corrosion was observed, with pitting and repassivation potentials similar than those in 1 M NaCl solution.

Effect of Cr Content On Pitting Behavior of Fe-Cr Alloys

CORROSION ◽  
1966 ◽  
Vol 22 (4) ◽  
pp. 107-112 ◽  
Author(s):  
R. F. STEIGERWALD
Keyword(s):  
Mild Steel ◽  
Pitting Corrosion ◽  
Room Temperature ◽  
Chromium Content ◽  
Immersion Test ◽  
Applied Current ◽  
Polarization Measurements ◽  
Cr Content ◽  
The Relationship ◽  
Pit Initiation

Abstract Immersion and applied current studies are used to investigate the pitting behavior of binary Fe-Cr alloys formed both by conventional melting techniques and by diffusion of chromium into mild steel (chromizing). Experiments on both sets of materials show that a chromium content of 28–30 percent is critical for elimination of room-temperature pitting corrosion. It is proposed that chromium acts to improve the pitting resistance of Fe-Cr alloys by stabilizing passivity, thus reducing pit initiation and slowing pit growth. The relationship between polarization measurements and pitting is discussed. It is shown that in a simple immersion test pitting occurs at potentials quite different from the “critical” potentials predicted by polarization measurements.

scholarly journals Effects of Alloying Elements on the Corrosion Behavior of Sputter–deposited Zr–(12–21)Cr–W Alloys in 0.5 M NaCl Solution

1970 ◽  
Vol 25 ◽  
pp. 75-82
Author(s):  
Basu Ram Aryal ◽  
Jagadeesh Bhattarai
Keyword(s):  
Corrosion Test ◽  
Open Circuit Potential ◽  
Chemical Society ◽  
Open Circuit ◽  
Sputter Deposition ◽  
Nacl Solution ◽  
Corrosion Rates ◽  
Sputter Deposited ◽  
Stable Passivity ◽  
Zirconium Metal

The synergistic effect of the simultaneous additions of tungsten and zirconium in thesputter-deposited amorphous or nanocrystalline Zr-(12-21)Cr-W alloys is studied in 0.5 MNaCl solution open to air at 25°C using corrosion tests and open circuit potentialmeasurements. Corrosion rates of the sputter-deposited Zr-(12-21)Cr-W alloys containing10-80 at % tungsten (that is, 0.95-1.85 x 10-2 mm.y-1) are more than one order of magnitudelower than that of the sputter-deposited tungsten and even lower than those of zirconium aswell as chromium in 0.5 M NaCl solution. The addition of 8-73 at % zirconium content inthe sputter-deposited binary W-(12-21)Cr alloys seems to be more effective to improve thecorrosion-resistant properties of the sputter-deposited ternary Zr-Cr-W alloys containing12-21 at % chromium in 0.5 M NaCl solution. The sputter-deposited Zr-(17-21)Cr-W alloyscontaining an adequate amounts of zirconium metal showed the more stable passivity andshowed higher corrosion resistance than those of alloy-constituting elements in 0.5 M NaClsolution open to air at 25°C.Keywords: Zr-(12-21)Cr-W alloys, sputter deposition, corrosion test, open circuit potential,0.5 M NaCl.DOI:  10.3126/jncs.v25i0.3305Journal of Nepal Chemical Society Volume 25, 2010 pp 75-82

scholarly journals Pitting Corrosion Resistance and Repassivation Behavior of C-Bearing Duplex Stainless Steel

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 930 ◽  
Author(s):  
Hanme Yoon ◽  
Heon-Young Ha ◽  
Tae-Ho Lee ◽  
Sung-Dae Kim ◽  
Jae Hoon Jang ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Pitting Corrosion ◽  
Galvanic Corrosion ◽  
Dual Phase ◽  
Corrosion Resistant ◽  
Grain Sizes ◽  
Α Phase ◽  
Pitting Corrosion Resistance ◽  
Corrosion Pits ◽  
Pit Initiation

The effects of C-substitution for part of the N content, on the pitting corrosion resistance and repassivation tendencies of duplex stainless steels (DSSs) were investigated. For this investigation, normal UNS S32205 containing N only (DSS-N) and the C-substituted DSS (DSS-NC) were fabricated. Microstructural analyses confirmed that the two DSSs had dual-phase microstructures without precipitates, and they possessed similar initial microstructure, including their grain sizes and phase fractions. Polarization and immersion tests performed in concentrated chloride solutions revealed that the DSS-NC was more resistant against stable pitting corrosion and possessed a higher repassivation tendency than the DSS-N. Furthermore, the corrosion pits initiated and propagated to a less corrosion resistant α phase. Polarization tests and corrosion depth measurements conducted in an HCl solution indicated that the DSS-NC exhibited lower galvanic corrosion rate between the α and γ phases than the DSS-N. Therefore, the growth rate of pit embryo was lowered in the DSS-NC, which shifted the potentials for the stable pit initiation and the pit extinction to the higher values.

Low Potential Pitting Corrosion of Ni-Cr-Fe Alloys in Chloride Plus Thiosulfate Solutions: Determination of Potential and Concentration Boundaries

CORROSION ◽  
10.5006/3562 ◽  
2020 ◽  
Vol 76 (8) ◽  
pp. 786-795
Author(s):  
Abraham A. Becerra Araneda ◽  
Mariano A. Kappes ◽  
Martín A. Rodríguez ◽  
Ricardo M. Carranza
Keyword(s):  
Pitting Corrosion ◽  
Chloride Ions ◽  
Aged Alloy ◽  
Electrochemical Tests ◽  
Alloy 800 ◽  
Chloride Threshold ◽  
Alloy 690 ◽  
Fe Alloys ◽  
Thiosulfate Concentration

Low potential pitting corrosion (LPPC) of Alloys 690 and 800 (UNS N06690 and N08800) was studied in neutral solutions, containing chloride ions from 0.1 M to 1 M and thiosulfate ions from 5 × 10−5 M to 10−3 M. LPPC occurred close to the corrosion potential (–0.25 VAg/AgCl) by a synergic effect of the chloride and thiosulfate ions. The threshold concentrations of aggressive species for LPPC occurrence were identified by potentiostatic tests with mechanical scratching of the surface, which yielded more conservative estimations compared to other electrochemical tests. The ranges of potential and concentration of chloride and thiosulfate where LPPC occurred and where it merged with the conventional chloride pitting were determined. The lowest threshold concentrations were measured in Alloy 800, with a lower Cr content than Alloy 690. Thermally-aged Alloys 800 and 690 had lower resistance to LPPC than the corresponding solution-annealed material. In 1 M chloride-based solutions, for aged Alloy 800, LPPC occurred at a thiosulfate concentration as low as 5 × 10−5 M; in 10−3 M thiosulfate-based solutions, the chloride threshold was 0.1 M. For thermally-aged alloys, pits propagated intergranulary in some experiments. In solutions with chloride and thiosulfate concentrations close to the threshold required for pitting, repassivation of LPPC was observed after a sustained period of pit growth, originally initiated by scratching the surface. Such a repassivation has not been reported before in the literature in chloride and thiosulfate solutions. Two possible explanations were presented for this phenomenon.

scholarly journals Studies on Pitting Corrosion of Al-Cu-Li Alloys Part II: Breakdown Potential and Pit Initiation

Materials ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 1786 ◽  
Author(s):  
Elmira Ghanbari ◽  
Alireza Saatchi ◽  
Xiaowei Lei ◽  
Digby D. Macdonald
Keyword(s):  
Barrier Layer ◽  
Pitting Corrosion ◽  
Mean Diffusivity ◽  
Corrosion Damage ◽  
Critical Parameters ◽  
Breakdown Potential ◽  
Linear Relationships ◽  
Aluminum Lithium ◽  
Ph Optimization ◽  
Pit Initiation

Prediction of the accumulated pitting corrosion damage in aluminum-lithium (Al-Li) is of great importance due to the wide application of these alloys in the aerospace industry. The Point Defect Model (PDM) is arguably one of the most well-developed techniques for evaluating the electrochemical behavior of passive metals. In this paper, the passivity breakdown and pitting corrosion performance of AA 2098-T851 was investigated using the PDM with the potentiodynamic polarization (PDP) technique in NaCl solutions at different scan rates, Cl− concentrations and pH. Both the PDM predictions and experiments reveal linear relationships between the critical breakdown potential (Ec) of the alloy and various independent variables, such as a C l − and pH. Optimization of the PDM of the near-normally distributed Ec as measured in at least 20 replicate experiments under each set of conditions, allowing for the estimation of some of the critical parameters on barrier layer generation and dissolution, such as the critical areal concentration of condensed cation vacancies (ξ) at the metal/barrier layer interface and the mean diffusivity of the cation vacancy in the barrier layer (D). With these values obtained—using PDM optimization—in one set of conditions, the Ec distribution can be predicted for any other set of conditions (combinations of a Cl − , pH and T). The PDM predictions and experimental observations in this work are in close agreement.

scholarly journals The Corrosion Behavior of Sputter-Deposited Nanocrystalline W-Cr Alloys in Nacl and NaohaSolutions

1970 ◽  
Vol 25 ◽  
pp. 53-61
Author(s):  
Minu Basnet ◽  
Jagadeesh Bhattarai
Keyword(s):  
Corrosion Resistance ◽  
Corrosion Rate ◽  
Corrosion Behavior ◽  
Chromium Content ◽  
Open Circuit ◽  
Nacl Solution ◽  
Corrosion Rates ◽  
Naoh Solution ◽  
Order Of Magnitude ◽  
Sputter Deposited

The corrosion behavior of the sputter-deposited nanocrystalline W-Cr alloys wasstudied in 0.5 M NaCl and alkaline 1 M NaOH solutions at 25°C, open to air usingimmersion tests and electrochemical measurements. Chromium metal acts synergisticallywith tungsten in enhancing the corrosion resistance of the sputter-deposited W-Cr alloys soas to show higher corrosion resistance than those of alloy-constituting elements in both 0.5M NaCl and 1 M NaOH solutions. In particular, the nanocrystalline W-Cr alloys containing25-91 at% chromium showed about one order of magnitude lower corrosion rates (that is,about 1-2 × 10-3 mm.y-1) than those of tungsten and chromium metals even for prolongedimmersion in 0.5 M NaCl solution at 25°C. On the other hand, the corrosion rate of thesputter-deposited W-Cr alloys containing 25-75 at % chromium was decreased significantlywith increasing chromium content and showed lowest corrosion rates (that is, 1.5-2.0 × 10-3 mm.y-1) after immersed for prolonged immersion in 1 M NaOH solution. The corrosion ratesof these nanocrystalline W-(25-75)Cr alloys are nearly two orders of magnitude lower thanthat of tungsten and more than one order of magnitude lower corrosion rate than that ofsputter-deposited chromium metal in 1 M NaOH solution. The corrosion-resistant of all theexamined sputter-deposited W-Cr alloys in 0.5 M NaCl solution is higher than in alkaline 1M NaOH solution at 25°C. Open circuit potentials of all the examined W-Cr alloys areshifted to more noble direction with increasing the chromium content in the alloys afterimmersion for 72 h in both 0.5 M NaCl and 1 M NaOH solutions at 25°C, open to air.Keywords: Sputter deposition, nanocrystalline W-Cr alloys, corrosion test, electrochemicalmeasurement, NaCl and NaOH solutions.DOI:  10.3126/jncs.v25i0.3300Journal of Nepal Chemical Society Volume 25, 2010 pp 53-61

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