| 1. |
- Jayamani, Jayaraj, et al.
(author)
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Corrosion behavior and surface film characterization of TaNbHfZrTi high entropy alloy in aggressive nitric acid medium
- 2017
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In: Intermetallics (Barking). - : Elsevier BV. - 0966-9795 .- 1879-0216. ; 89, s. 123-132
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Journal article (peer-reviewed)abstract
- Corrosion behavior of TaNbHfZrTi high-entropy alloy (HEA) was investigated in nitric and fluorinated nitric acid at ambient (27 °C) and boiling (120 °C) conditions. The alloy passivated spontaneously during potentiodynamic polarization in 11.5 M HNO3 at ambient condition. The corrosion rate was negligible in boiling 11.5 M HNO3, exposed for 240 h. Scanning electron microscopic (SEM) studies did not show any significant corrosion attack. The high corrosion resistance of TaNbHfZrTi HEA was attributed to its single phase bcc structure. X-ray photoelectron spectroscopic (XPS) analysis revealed that the protective passive film formed in boiling nitric acid was predominantly composed of Ta2O5, in contrast to the presence of ZrO2 and HfO2 in air-formed native film. Potentiodynamic polarization studies indicated a pseudo-passivation behavior of the HEA in 11.5 M HNO3 + 0.05 M NaF at ambient condition. In boiling fluorinated nitric acid, SEM images of TaNbHfZrTi HEA displayed a severely corroded morphology indicating the instability of the metal-oxides of the alloying elements. XPS investigations confirmed the presence of ZrF4, ZrOF2 and HfF4 along with un-protective oxides of Ta, Nb and Ti on the film, resulting in decreased corrosion resistance of TaNbHfZrTi HEA in fluorinated nitric acid.
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| 2. |
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| 3. |
- Jayamani, Jayaraj, et al.
(author)
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Corrosion investigations on zircaloy-4 and titanium dissolver materials for MOX fuel dissolution in concentrated nitric acid containing fluoride ions
- 2016
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 473, s. 157-166
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Journal article (peer-reviewed)abstract
- Aqueous reprocessing of plutonium-rich mixed oxide fuels require fluoride as a dissolution catalyst in boiling nitric acid for an effective dissolution of the spent fuel. High corrosion rates were obtained for the candidate dissolver materials zircaloy-4 (Zr-4) and commercial pure titanium (CP-Ti grade 2) in boiling 11.5 M HNO3 + 0.05 M NaF. Complexing the fluoride ions either with Al(NO3)3 or ZrO(NO3)2 aided in decreasing the corrosion rates of Zr-4 and CP-Ti. From the obtained corrosion rates it is concluded that CP-Ti is a better dissolver material than Zr-4 for extended service life in boiling 11.5 M HNO3+0.05 M NaF, when complexed with 0.15 M ZrO(NO3)2. XPS analysis confirmed the presence of TiO2 and absence of fluoride on the surface of CP-Ti samples, indicating that effective complexation had occurred in solution leading to passivation of the metal and imparting high corrosion resistance.
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| 4. |
- Jayamani, Jayaraj, et al.
(author)
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Electrochemical Activity at the Interface of Dissimilar Explosive Joint of Stainless Steel with Zircaloy by Scanning Electrochemical Microscopy
- 2012
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In: Journal of Advanced Microscopy Research. - : American Scientific Publishers. - 2156-7573 .- 2156-7581. ; 7:3, s. 214-217
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Journal article (peer-reviewed)abstract
- Electrochemical activity at the interface of dissimilar explosive joint of stainless steel with Zircaloy has been studied in 11.5 M nitric acid using scanning electrochemical microscopy. The reduction of nitric acid and oxidation of nitrous acid in the tip-substrate gap is proposed as a mechanism for the electron transfer reaction. Due to this reaction increase in tip current was observed, indicating that the positive feedback mode of SECM is under operation. The difference in tip current was correlated with the microstructure and the electrochemical activity of the dissimilar weld interface.
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| 5. |
- Jayamani, Jayaraj, et al.
(author)
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Electrochemical and passive characterization of a beta type Ti45Zr38Al17 cast rod in nitric acid medium
- 2012
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In: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 85, s. 210-219
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Journal article (peer-reviewed)abstract
- Electrochemical behavior of the recently developed beta-type Ti–38at% Zr–17at% Al (TZA) alloy has been studied in nitric acid medium for applications in nuclear reprocessing plant. Potentiodynamic polarization and electrochemical impedance studies revealed that the passive film formed on the TZA alloy was highly protective in nature. Mott–Schottky analysis of the passive film formed on TZA alloy showed n-type semiconducting properties. The electrochemical data confirmed the superior corrosion resistance of TZA alloy as the passive film formed exhibited better properties than that of the commercial pure Ti. XPS analyses confirmed that the stable passivity of TZA alloy in nitric acid was due to the formation of thick and protective passive layer, predominantly of ZrO2 with TiO2.
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| 6. |
- Jayamani, Jayaraj, et al.
(author)
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Electrochemical Studies and XPS Analysis of the Surface of Zirconium-702 in Concentrated Nitric Acid With and Without Fluoride Ions
- 2018
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In: Transactions of the Indian Institute of Metals. - : Springer Science and Business Media LLC. - 0972-2815 .- 0975-1645. ; 71:3, s. 521-531
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Journal article (peer-reviewed)abstract
- Zirconium exhibited pseudo-passive behavior in fluorinated nitric acid (11.5 M HNO3 + 0.05 M NaF) as the current density measured from the electrochemical studies was several orders higher than the value in fluoride free nitric acid. Impedance studies on zirconium sample exposed in 11.5 M HNO3 for 240 h confirmed the formation of the passive film with high polarization resistance value and the calculated thickness of the film based on the capacitance value was about ~4.5 nm. On the other hand, in fluorinated nitric acid, the charge transfer resistance value associated with the zirconium dissolution process was dominant when compared to that of the film formation. Results of X-ray photoelectron spectroscopic investigations upheld the presence of ZrOF2 and ZrF4 and indicated that the protective oxide layer growth was restricted by the presence of fluoride ions.
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| 7. |
- Jayamani, Jayaraj, et al.
(author)
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Microstructure and Corrosion Behavior of Hf-40 Wt Pct Ti Alloy in Nitric Acid Medium for Reprocessing Applications
- 2016
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In: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 47:9, s. 4393-4403
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Journal article (peer-reviewed)abstract
- The Hf-40 wt pct Ti (Hf-Ti) alloy was developed for neutron poison application in the spent nuclear fuel reprocessing plant. The furnace-cooled Hf-Ti sample exhibited the microstructure comprising equiaxed-α, lamellar-α, and feathery-α. The water-quenched Hf-Ti sample confirmed the presence of lath and internally twinned martensite. In comparison to the furnace-cooled sample, low corrosion current density and passivation current density values obtained for the water-quenched Hf-Ti in 6 M HNO3 at 298 K (25 °C) indicated better passivation ability. The martensitic structure exhibited high hardness (660 HV) and negligible corrosion rate in 6 M nitric acid at 298 K (25 °C). X-ray photoelectron spectroscopic (XPS) analysis confirmed that passivation behavior of this alloy was due to the protective passive film composed of TiO2 and HfO2.
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| 8. |
- Jayamani, Jayaraj, et al.
(author)
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Passive film properties and corrosion behavior of Ni–Nb and Ni–Nb–Ta amorphous ribbons in nitric acid and fluorinated nitric acid environments
- 2015
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In: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 151, s. 318-329
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Journal article (peer-reviewed)abstract
- Potentiodynamic polarization and electrochemical impedance studies revealed the passivation ability and corrosion resistance of Ni60Nb40 and Ni60Nb30Ta10 amorphous ribbons in 11.5 M HNO3 and 11.5 M HNO3 + 0.05 M NaF media at room temperature. Mott–Schottky analysis indicated the formation of n-type semiconducting passive film on these amorphous ribbon samples. Electrochemical parameters such as corrosion current density, passivation current density and donor density confirmed the passive film property of Ni60Nb30Ta10 amorphous ribbon to be superior to that of Ni60Nb40 amorphous ribbon. Weight loss was insignificant in Ni60Nb30Ta10 ribbon exposed to boiling 11.5 M HNO3 for 240 h. XPS analysis revealed that the origin of passivity of Ni60Nb40 and Ni60Nb30Ta10 amorphous ribbons in boiling 11.5 M HNO3 was due to the formation of a relatively thick passive film of ≈3 nm enriched with Nb2O5 and a thin passive film of ≈1.5 nm enriched with both Nb2O5 and Ta2O5 on the respective ribbon's surface. In boiling fluorinated nitric acid, Ni60Nb40 ribbon underwent severe dissolution owing to the instability of Nb-oxide passive film and the oxide/metal interface.
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| 9. |
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| 10. |
- Kamachi Mudali, U., et al.
(author)
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Corrosion : An Overview of Types, Mechanism, and Requisites of Evaluation
- 2019
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In: Non‐Destructive Evaluation of Corrosion and Corrosion‐assisted Cracking. - Hoboken, NJ, USA : John Wiley & Sons. - 9781118350058 - 9781118987735
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Book chapter (peer-reviewed)abstract
- Corrosion of metals and alloys in an aqueous environment is generally an electrochemical process that requires four essential components: an aqueous electrolyte, an anode, a cathode, and a current carrying pathway (i.e. circuit). In electrochemical corrosion, the anodic oxidation reaction should be compensated by the reduction reaction at cathode. The basis for the types of corrosion is their appearance and propagation mode. The eight well-known forms of corrosion are uniform or general corrosion, galvanic corrosion, pitting corrosion, crevice corrosion, intergranular corrosion, dealloying or selective leaching, erosion corrosion, and environmentally assisted cracking. Apart from these eight forms, the microbiologically influenced corrosion is also considered as one of the important corrosion forms. Nondestructive technique plays a vital role for damage assessment and life extension of the component as it is suitable in detection of the early stages of corrosion so that corrective measures can be taken before damage becomes severe.
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