CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

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Chapter 1 corrosion resistance. The corrosion resistance of austenitic stainless steel depends on the concentration of nitric acid, for lower concentration (< 50 %) corrosion susceptibility is determined by chromium content in the alloy, and for higher concentration containing Cr 6+ ions it is determined by impurity elements in the alloy. Mainly, AISI type 304L SS (18 % Cr-8 % Ni- 0.03% C) finds large scale application because of good passivity, corrosion resistance, and appropriate practical aspects such as working, welding, cost competitiveness etc. Despite many beneficial effects, type 304L SS fails in the oxidizing environment of nitric acid leading to intergranular corrosion, end-grain attack, transpassivity etc [2]. To overcome these problems different grades of austenitic stainless steels have been evolved over time. Fe-18Cr-15Ni-4Si- 0.01C austenitic stainless steel was developed to keep the intergranular and uniform corrosion low in the process environment of hot nitric acid. The addition of titanium and niobium to these alloys gives still improved property, however due to high silicon, and low carbon content these materials tend to form crack in the welded region. Similarly, special nitric acid grade (NAG) austenitic stainless steel such as URANS-16 (18 Cr-12 Ni) and URANS-65 (25 Cr-20 Ni) are designed with sharp control of carbon, silicon, sulphur and phosphorus. Because of high chromium content and tighter control of impurities, nitric acid grade stainless steel performs satisfactorily up to 65 % concentration in boiling condition. Nevertheless, these materials fail in nitric acid solution containing hexavalent chromium (Cr 6+ ) at elevated temperature due to transpassivity [3]. Thus, use of these materials in these extreme conditions is restricted. Moreover, large scale use is also not possible due to extra cost in the manufacturing process because of controlling the impurity level. 1.4.2 Titanium Titanium is a unique material, as strong as stainless steel with less than 60 % of its density, and possessing excellent corrosion resistance. Titanium is used in critical components such as spent nuclear fuel dissolvers handling hot concentrated nitric acid where austenitic stainless steel
Chapter 1 experiences intergranular corrosion. Higher resistance of titanium to corrosion is due to the formation of titanium dioxide (TiO 2 ) film on the surface due to formation of Ti 4+ ions [1]. However, the composition of oxide film depends upon the film formation conditions such as electrolyte composition, hydro-dynamic flow, and temperature etc. The oxide film formed on titanium is more protective than that of austenitic stainless steel, and often performs better in oxidizing environment of nitric acid. In boiling condition titanium corrosion resistance is very sensitive to nitric acid purity, and higher the metallic ion content in the acid, the better titanium performs. This is in contrast to austenitic stainless steel which is often adversely affected by the acid contaminants. This is because, titanium corrosion product (Ti 4+ ) is highly inhibitive, and titanium exhibits superb performance in recycled nitric acid streams such as reboiler loops. Despite many advantages, the use of titanium in spent nuclear fuel reprocessing plant is limited. One of the factors to this is the high cost relative to austenitic stainless steel. Moreover, even if titanium is having excellent corrosion resistance, it is not cure-for all corrosion problems. Failures in acid condensers and evaporators have been observed in spent nuclear fuel reprocessing plant [1]. Under these vapour and condensate conditions semi-protective oxide films forms on the surface which do not fully retard the oxidizing action of nitric acid. The presence of iron greater than 0.05 % in titanium enhances the corrosion rate due to formation, and segregation of iron rich ilmenite (FeTiO 3 ) intermetallic particles. In such situations advanced alloys such as Ti-5% Ta- 1.8% Nb were recommended which is titanium alloyed with more noble metals like tantalum and niobium which have similar size to that of titanium. The oxide film formed on such alloys shows low solubility and high stability in nitric acid medium. 1.4.3 Zirconium Zirconium is an important constructional material for spent fuel dissolver, and for many other critical applications in nuclear fuel reprocessing plant in highly oxidizing condition. The
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Page 8 and 9: 2.3 Effect of alloying elements on
Page 10 and 11: 4 C H A P T E R 4 73 # $%&' 4.1 In
Page 12 and 13: 6.2.3.2 Open circuit potential vs.
Page 14 and 15: eprocessing can be recovered, and c
Page 16 and 17: The ex-situ study of passive film w
Page 18 and 19: Fig.3.10: Schematic of electrical e
Page 20 and 21: Fig.6.11: Polarization study of unc
Page 22 and 23: AISI: American Institute of Steel I
Page 24 and 25: Chapter 1 C H A P T E R 1 Spent Nuc
Page 26 and 27: Chapter 1 1.3 Challenges in spent n
Page 30 and 31: Chapter 1 choice of zirconium is du
Page 32 and 33: C H A P T E R2
Page 34 and 35: Chapter 2 temperature, (c) higher i
Page 36 and 37: Chapter 2 Chromium in excess of 12
Page 38 and 39: Chapter 2 2. 3 Effect of alloying e
Page 40 and 41: Chapter 2 The twins are identified
Page 42 and 43: Chapter 2 and at temperature around
Page 44 and 45: Chapter 2 of adsorption of oxygen o
Page 46 and 47: Chapter 2 transpassive dissolution
Page 48 and 49: Chapter 2 healing chromium oxide fi
Page 50 and 51: Chapter 2 their segregation to the
Page 52 and 53: Chapter 2 is intimately related to
Page 54 and 55: Chapter 2 in nature because the dis
Page 56 and 57: C H A P T E R3
Page 58 and 59: Chapter 3 3.1.1.2 Specimen preparat
Page 60 and 61: Chapter 3 ionized. However, differe
Page 62 and 63: Chapter 3 various industrial applic
Page 64 and 65: Chapter 3 In the present investigat
Page 66 and 67: Chapter 3 3.1.3.2 Atomic force micr
Page 68 and 69: Chapter 3 present on the surface fo
Page 70 and 71: Chapter 3 necessary condition is th
Page 72 and 73: Chapter 3 Y m is the sputter yield.
Page 74 and 75: Chapter 3 Fig. 3.7: Schematic of X-
Page 76 and 77: Chapter 3 rate of 10Å/min using 5
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Chapter 3 different doses of nitrog
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Chapter 3 The modulus of electroche
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Chapter 3 equivalent circuit as sho
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Chapter 3 reference electrode with
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Chapter 3 for understanding the pas
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C H A P T E R4
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Chapter 4 encountered by all materi
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Chapter 4 pitting, and intergranula
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Chapter 4 The ridged structure, and
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Chapter 4 nitric acid is that the b
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Chapter 4 Potential (V) Vs Ag/AgCl
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Chapter 4 4.2.3 In-situ electrochem
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Chapter 4 The surface morphologies
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Chapter 4 a b c d Opening up of gra
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Chapter 4 Intensity (Arbitrary unit
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Chapter 4 The chromium, and oxygen
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Chapter 4 Intensity (Arbitrary unit
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C H A P T E R5
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Chapter 5 elements, and often impar
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Chapter 5 5.2 Results and discussi
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Chapter 5 Presence of oxygen is due
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Chapter 5 was an increase in marten
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Chapter 5 formation of Cr 2 N was a
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Chapter 5 electrochemical environme
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Chapter 5 N + Dose E corr (mV vs. A
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Chapter 5 layer capacitance (C dl )
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Chapter 5 correlation between surfa
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Chapter 5 boundary dissolution was
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Chapter 6 C H A P T E R 6
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Chapter 6 193]. As a single phase c
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Chapter 6 particles range from 8×1
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Chapter 6 Results revealed that in
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Chapter 6 The change over from capa
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Chapter 6 The impedance parameters
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Chapter 6 Conc. Substrate condition
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Chapter 6 6.6a-d. The uncoated spec
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Chapter 6 (55.18°) respectively, w
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Chapter 6 OCP shifted in noble dire
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Chapter 6 The high phase angle over
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Chapter 6 Fig. 6.10d: Log f vs. Log
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Chapter 6 Fig. 6.11b: Polarization
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Chapter 6 Covalent aspect of lattic
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Chapter 6 As compared to uncoated s
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Chapter 6 6.2.3.2 Open circuit pote
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Chapter 6 Similarly, the plots for
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Chapter 6 for the duplex coating, a
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Chapter 6 Fig.6.16b: Polarization s
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Chapter 6 6.2.3.5 Morphological exa
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Chapter 7 C H A P T E R 7 The cha
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Chapter 7 1. Surface morphology exa
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Chapter 7 6 Duplex Ti-TiO 2 coated
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Chapter 7 EC-SPM study on effect
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[1] Baldev Raj, U. Kamachi Mudali,
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[37] G. Okamoto, T. Shibata, Corros
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[79] M. Moens, M. Van Craen, F.C. A
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[117] R.E.Williford, C.F.Windisch J
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[157] N. Mottu, M. Vayer, R. Erre,
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[197] M. Metikos Hukovic, M. Ceraj
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[19] H. H. Uhlig, Corros Sci, 19 (1
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[57] J. F. Ziegler, J. P. Biersack,
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[97] I. Betova, M. Bojinov, V. Kara
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[139] V. Ashworth, R. P. M. Procter
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[176] G. Frankel, G. Grundmeier, H.
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List of publications 1. Referred
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CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

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