CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

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Chapter 6 Conc. Substrate condition E corr mV vs Ag/AgCl I pass µA/cm 2 I corr µA/cm 2 E transpass mV vs Ag/AgCl 1 M Uncoated 250 1.1 × 10 2 10 ×10 0 1100 1 M Ti coated 330 5.5 × 10 1 4.5 ×10 0 1146 8 M Uncoated 340 1.2 × 10 3 7 ×10 1 1025 8 M Ti coated 385 1.1 ×10 3 5.1 × 10 1 1051 Table. 6.2: Average value of polarization parameters for uncoated and Ti coated 304L SS in 1 M and 8 M HNO 3 . In both the concentrations of test solutions, Ti coated 304L SS specimens showed nobler corrosion potential (E corr ) as compared to uncoated condition indicating formation of protective oxide film in the oxidizing medium of nitric acid. Noticeable improvement in passive current density (I pass ) and corrosion current density (I corr ) was observed for Ti coated specimen in 1 M nitric acid, however improvement was marginal in 8 M nitric acid compared to uncoated condition (Table. 6.2). The improvement in transpassive potential for Ti coated specimens (E transpassive = E coated - E uncoated ) in 1 M nitric acid was 46 mV (vs. Ag/AgCl), and 26 mV (vs. Ag/AgCl) in 8 M nitric acid, respectively. Overall, from Table.6.2 it is clear that at lower concentration (1 M HNO 3 ), lower passive current density and higher transpassive potential, and at higher concentration (8 M HNO 3 ) higher passive current density and lower transpassive potential was observed. Thus, the polarization parameters indicate that passive film formed on Ti coated specimens at higher concentration dissolves faster. The protection efficiency calculated using Eq. 13 was 52 % in 1 M nitric acid, and 27 % in 8 M nitric acid, respectively as compared to uncoated condition. The protecting ability of the coated surface depends mainly on the physico-chemical properties of the developing oxide film as well as structural heterogeneities on the surface. Titanium readily forms titanium oxide in acidic solutions due to its strong affinity towards oxygen,
Chapter 6 but the kind of film formed, and its enthalpy of formation decides the stability of the oxide layer. The mechanism of passivation initiates with the formation of Ti 3+ ions, which consequently forms certain metastable oxides which further oxidizes to TiO 2 [197]. However, the composition of oxide layer depends upon the oxidizing power of the solution, and generally consists a mixture of anatase with certain quantity of rutile phase [197]. Various oxide layers that develops in acidic solution when titanium undergoes passivation are Ti 3 O 5 (H f = - 2459.15 kJ/mole), Ti 2 O 3 (H f = - 1520.84 KJ/mole), TiO 2 (H f = - 944.75 KJ/mole), respectively. The non-stoichiometric oxides are having low enthalpy of formation, and are generally porous in nature [200]. The perfect stoichiometric oxides are compact and have high enthalpy of formation. The non-stoichiometric oxides are stable in low concentration, and forms good passive film but dissolve in strong acid solution due to low oxide density as well as increase in aggressivity in the exposed area of the pores [196-198]. Apart from this, the electrochemical environment at structural heterogeneities such as pinholes, flaws, and inter-columnar boundaries is more aggressive as compared to that of matrix due to accumulation of solution, and passive film formed in these regions is thinner. Thus, the protective oxide film formed electrochemically offers less resistance to corrosive medium and fails usually in the depth of the pores at higher concentration. Moreover, galvanic potentials do exist at pinholes, and inter-columnar boundaries and these regions prevent passive oxide layer formation and lead to enhanced corrosion of base material. Once initiated, corrosion proceeds at the boundaries between the coating and substrate, and the protection of base material is lost. Apart from this, accelerated corrosion reduces the coating bond strength, and uniform dissolution of the coated surface occur leading to peeling up of the coating. 6.2.1.5 Morphological investigation after potentiodynamic polarization study The results for surface morphological study for uncoated and Ti coated 304L SS specimens after potentiodynamic polarization in both the concentration of test solution are shown in Fig.
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2.3 Effect of alloying elements on
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6.2.3.2 Open circuit potential vs.
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eprocessing can be recovered, and c
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The ex-situ study of passive film w
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Fig.3.10: Schematic of electrical e
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Fig.6.11: Polarization study of unc
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AISI: American Institute of Steel I
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Chapter 1 C H A P T E R 1 Spent Nuc
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Chapter 1 1.3 Challenges in spent n
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Chapter 1 corrosion resistance. The
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Chapter 1 choice of zirconium is du
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C H A P T E R2
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Chapter 2 temperature, (c) higher i
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Chapter 2 Chromium in excess of 12
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Chapter 2 2. 3 Effect of alloying e
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Chapter 2 The twins are identified
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Chapter 2 and at temperature around
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Chapter 2 of adsorption of oxygen o
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Chapter 2 transpassive dissolution
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Chapter 2 healing chromium oxide fi
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Chapter 2 their segregation to the
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Chapter 2 is intimately related to
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Chapter 2 in nature because the dis
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C H A P T E R3
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Chapter 3 3.1.1.2 Specimen preparat
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Chapter 3 ionized. However, differe
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Chapter 3 various industrial applic
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Chapter 3 In the present investigat
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Chapter 3 3.1.3.2 Atomic force micr
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Chapter 3 present on the surface fo
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Chapter 3 necessary condition is th
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Chapter 3 Y m is the sputter yield.
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Chapter 3 Fig. 3.7: Schematic of X-
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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
Page 96 and 97: Chapter 4 nitric acid is that the b
Page 98 and 99: Chapter 4 Potential (V) Vs Ag/AgCl
Page 100 and 101: Chapter 4 4.2.3 In-situ electrochem
Page 102 and 103: Chapter 4 The surface morphologies
Page 104 and 105: Chapter 4 a b c d Opening up of gra
Page 106 and 107: Chapter 4 Intensity (Arbitrary unit
Page 108 and 109: Chapter 4 The chromium, and oxygen
Page 110 and 111: Chapter 4 Intensity (Arbitrary unit
Page 112 and 113: C H A P T E R5
Page 114 and 115: Chapter 5 elements, and often impar
Page 116 and 117: Chapter 5 5.2 Results and discussi
Page 118 and 119: Chapter 5 Presence of oxygen is due
Page 120 and 121: Chapter 5 was an increase in marten
Page 122 and 123: Chapter 5 formation of Cr 2 N was a
Page 124 and 125: Chapter 5 electrochemical environme
Page 126 and 127: Chapter 5 N + Dose E corr (mV vs. A
Page 128 and 129: Chapter 5 layer capacitance (C dl )
Page 130 and 131: Chapter 5 correlation between surfa
Page 132 and 133: Chapter 5 boundary dissolution was
Page 134 and 135: Chapter 6 C H A P T E R 6
Page 136 and 137: Chapter 6 193]. As a single phase c
Page 138 and 139: Chapter 6 particles range from 8×1
Page 140 and 141: Chapter 6 Results revealed that in
Page 142 and 143: Chapter 6 The change over from capa
Page 144 and 145: Chapter 6 The impedance parameters
Page 148 and 149: Chapter 6 6.6a-d. The uncoated spec
Page 150 and 151: Chapter 6 (55.18°) respectively, w
Page 152 and 153: Chapter 6 OCP shifted in noble dire
Page 154 and 155: Chapter 6 The high phase angle over
Page 156 and 157: Chapter 6 Fig. 6.10d: Log f vs. Log
Page 158 and 159: Chapter 6 Fig. 6.11b: Polarization
Page 160 and 161: Chapter 6 Covalent aspect of lattic
Page 162 and 163: Chapter 6 As compared to uncoated s
Page 164 and 165: Chapter 6 6.2.3.2 Open circuit pote
Page 166 and 167: Chapter 6 Similarly, the plots for
Page 168 and 169: Chapter 6 for the duplex coating, a
Page 170 and 171: Chapter 6 Fig.6.16b: Polarization s
Page 172 and 173: Chapter 6 6.2.3.5 Morphological exa
Page 174 and 175: Chapter 7 C H A P T E R 7 The cha
Page 176 and 177: Chapter 7 1. Surface morphology exa
Page 178 and 179: Chapter 7 6 Duplex Ti-TiO 2 coated
Page 180 and 181: Chapter 7 EC-SPM study on effect
Page 183 and 184: [1] Baldev Raj, U. Kamachi Mudali,
Page 185 and 186: [37] G. Okamoto, T. Shibata, Corros
Page 187 and 188: [79] M. Moens, M. Van Craen, F.C. A
Page 189 and 190: [117] R.E.Williford, C.F.Windisch J
Page 191 and 192: [157] N. Mottu, M. Vayer, R. Erre,
Page 193: [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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