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HIGH TEMPERATURE OXIDATION BEHAVIOUR OF NANOCRYSTALLINE
Fe80Cr20 ALLOYS AND FERRITIC STEEL IMPLANTED WITH
LANTHANUM AND TITANIUM
HENDI SARYANTO
A thesis submitted in
fulfillment of the requirement for the award of the
Degree of Master of Mechanical Engineering
Faculty of Mechanical and Manufacturing Engineering
Universiti Tun Hussein Onn Malaysia
October, 2011
v
ABSTRACT
Fe-Cr alloys and ferritic steel have received considerable attention as Solid Oxide
Fuel Cell (SOFC) interconnects material. However, the main problem with the use
of Fe-Cr alloys and ferritic steels as interconnect materials is their inadequate high
temperature oxidation resistance. Chromium dioxide as the protective layers
becomes non protective, due to formation of crack and volatile Cr2O3 upon exposure
at high temperature oxidation. The prepared Fe80Cr20 alloy with smallest crystallite
size expected to develop a protective film of Cr2O3 scales. On other hand, surface
treatment via ion implantation technique can improve the oxidation resistance of
alloys. Therefore, the purpose of this study is to investigate the oxidation resistance
of implanted and unimplanted Fe80Cr20 alloy and available commercial ferritic steel
in normal atmosphere over the temperature range of 1173-1373 K. Nanocrystalline
Fe80Cr20 alloys have been produced by mechanical alloying process followed by hot
compaction process. Lanthanum and titanium dopant were implanted into substrate
of specimens with ion doses of 1x1017
ions/cm2. Implanted and unimplanted of
specimens were subjected to oxidation at 1173 K, 1273 K, and 1373 K for 100 h.
Morphology characterization of oxide scales of specimens were investigated by X-
Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) coupled with
Energy Dispersive X-Ray analysis (EDX). The results shows that Fe80Cr20 60 h as
the smallest crystallite size exhibit better oxidation resistance. The results also
indicates that the implantation of lanthanum dopant effectively reduce the growth of
oxide scale as well as increases the oxidation resistance.
vi
ABSTRAK
Aloi Fe-Cr dan logam ferritic telah mendapat perhatian sewajarnya sebagai bahan
penyambung dikenali Solid Oxide Fuel Cell (SOFC). Namun, masalah utama dalam
penggunaan aloi Fe-Cr dan logam ferritic sebagai bahan penghubung ialah bahan
tidak mencukupi ketahan pengoksidaan suhu yang tinggi. Kromium dioksida yang
digunakan sebagai lapisan pelindung menjadi gagal bertindak sebagai pelindung
kerana pembentukan rekahan dan pemeruwapan Cr2O3 kerana terdedah kepada suhu
pengoksidaan yang tinggi. Tujuan kajian ini adalah untuk membangunkan struktur
nanocrystalline baru pada aloi Fe80Cr20 yang dibandingkan dengan logam ferritic
komersial, kemudian diteruskan dengan rawatan permukaan melalui teknik
pengimplanan ion bagi penerapan pada suhu yang tinggi. Nanocrystalline Fe80Cr20
telah di hasilkan melalui proses pengaloian mekanikal diikuti dengan proses
pemampatan. Dopan lanthanum dan titanium diimplan kepada substrat specimen
dengan dos ion 1x1017
ions/cm2. spesimen yang diimplan dan tidak diimplan
didedahkan kepada pengoksidaan pada 1173, 1273 dan 1373 K selama 100 h. Skala
oksida bagi karakter morfologi untuk specimen dikaji menggunakan X-Ray
Diffraction (XRD) dan Scanning Electron Microscope (SEM) bersama-sama dengan
analisis Energy Dispersive X-Ray (EDX). Hasil kajian menunjukan spesimen yang
mempunyai saiz nano yang lebih halus (Fe80Cr20 alloy dengan masa pengisaran 60
jam) menunjukan prestasi yang terbaik dalam memperbaiki rintangan suhu
pengoksidaan. Hasil kajian juga menunjukan implantasi lanthanum dopan berkesan
untuk mengurangkan pertumbuhan skala oksida dan memperbaiki rintangan suhu
pengoksidaan.
vii
CONTENTS
TITLE
i
DECLARATION
ii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
CONTENTS
vii
LIST OF TABLES
xiv
LIST OF FIGURES
xvi
LIST OF SYMBOLS AND ABBREVIATIONS
xxii
LIST OF APPENDICES xxiv
CHAPTER 1 INTRODUCTION 1
1.1 Research background
1
1.1.1 Types of fuel cells
2
1.1.2 Solid oxide fuel cells
3
1.1.3 SOFC interconnects
5
1.1.4 Potential Metallic alloys as interconnects 5
viii
1.2 Problem statement
6
1.3 Hyphothesis
7
1.4 The research aim
7
1.5 Research objectives
7
1.6 Scopes of study 7
CHAPTER 2 LITERATURE REVIEW 22
2.1 Introduction of solid oxide fuel cell
9
2.2 Operating principle of SOFC
11
2.3 SOFC components
11
2.3.1 Cathode
12
2.3.2 Anode
12
2.3.3 Electrolyte
13
2.3.4 Interconnect
13
2.4 SOFC interconnect materials
15
2.4.1 Ceramic interconnect
15
2.4.2 Metallic inteconnects 17
2.4.2.1 Chromium based alloys
18
2.4.2.2 Iron based alloys 19
ix
2.5 Fabrication process of metallic interconnects
20
2.5.1 Powder metallurgy route
21
2.5.2 Mechanical alloying
22
2.5.3 Development of nanocrystalline alloys by
mechanical alloying process
26
2.5.4 Metal powder compaction
28
2.5.4.1 Hot compaction
28
2.5.4.2 Compacting temperatures
30
2.6 Surface modification via ion implantation
technique
32
2.7 Effect of reactive elements upon oxidation 35
2.8 High temperature oxidation 37
2.8.1 Oxidation resistance 38
2.8.2 Oxidation resistance of metallic alloys
39
2.8.3 Oxidation resistance of nanocrystalline iron
chromium alloys
40
2.8.4 The Wagner’s oxidation theory 41
2.8.5 Thermodynamically stable of oxide phases
44
x
2.9 Summary of literature reviews
47
CHAPTER 3 METHODOLOGY 48
3.1 Preparation of ball milled Fe80Cr20 powders
48
3.2 Mechanical alloying process
49
3.3 Powder consolidation of ball milled powders
50
3.4 Microstructural characterization of unmilled and
ball milled powder
51
3.4.1 X-ray diffraction peaks profiling analysis of ball
milled powders
51
3.4.2 Morphology characterization of ball milled
powders
54
3.4.3 Phase analysis of ball milled powders
55
3.4.4 TEM observation of ball milled powders
56
3.5 Chemical composition analysis of commercial
ferritic steel
56
3.6 Surface treatment via ion implantation process 57
3.6.1 Preparation of ion implantation process 58
3.6.2 Ion implantation proses 59
3.6.3 Ion implantation depth distribution analysis 59
xi
3.7 Experimental procedures for high temperature
oxidation test
60
3.8 Evaluatiom of high temperature oxidation test
61
3.8.1 Oxidation kinetis 61
3.8.2 Surface morphology characterization of oxide
scale
62
3.8.3 Identification of oxide phases 62
3.8.4 Cross-section analysis of oxide scale 63
3.9 Flow chart 64
CHAPTER 4 RESULTS AND DISCUSSION 66
4.1 Synthesis characterization of unmilled powders (Fe
and Cr)
66
4.2 Synthesis characterization of ball milled Fe80Cr20
powders
67
4.2.1 Measuring crystallite size of unmilled and ball
milled powders
68
4.2.2 Morphology characterization of ball milled Fe80Cr20
powders
71
4.2.3 Validation of nanocrystalline structure of ball
milled Fe80Cr20 powders using TEM obsevation
72
xii
4.3 Phase analysis of ball milled Fe80Cr20 powders
74
4.4 Microstructural characterization of consolidated
Fe80Cr20 alloys compared to commercial ferritic
steel
77
4.5 Chemical composition analysis of commercial
ferritic steel
78
4.6 Measuring crystallite size of Fe80Cr20 alloys as
consolidated specimens compared to commercial
ferritic steel
79
4.7 Synthesis evaluation of lanthanum and titanium
implantation into substrate of the specimens
81
4.8 High temperature oxidation test
84
4.8.1 The effect of nanocrystalline structure on the
oxidation kinetic of Fe80Cr20 alloys and
commercial ferritic steel
84
4.8.2 Surface scale morphology of Fe80Cr20 alloys
compare to commercial ferritic steel after
oxidation at 1173, 1273 and 1373 K
89
4.8.3 The effect of lanthanum and titanium implantation
on the oxidation behavior of Fe80Cr20 alloys and
commercial ferritic steel
94
4.8.4 Surface scale morphology of implanted specimens
compare to unimplanted specimens after oxidation
at 1173, 1273 and 1373 K
99
xiii
4.9 Identification of oxide phase
104
4.10 Cross-sectional morphology of the oxide scale
109
4.10.1 Cross-sectional analysis of un-implanted and
implanted Fe80Cr20 alloy after oxidation in air at
1173 K for 100 hours
119
4.10.2 Cross-sectional analysis of un-implanted and
implanted Fe80Cr20 alloy after oxidation in air at
1273 K for 100 hours
112
4.10.3 Cross-sectional analysis of un-implanted and
implanted Fe80Cr20 alloy after oxidation in air at
1373 K for 100 hours
116
CHAPTER 5 CONCLUSIONS AND RECOMENDATIONS 119
5.1 Conclusion
119
5.2 Recomendation
120
REFERENCES 121
APPENDICES 133
VITA
xiv
LIST OF TABLES
1.1
2.1
3.1
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
The main characteristics of different types of fuel cells
Sintering temperature and time ranges of commonly used P/M
metals and alloys
Parameter of ball milled powders
Peak width and peak intensity of as starting powders (pure Fe
and Cr powders) and ball milled Fe80Cr20 powders
Evaluation of starting materials of Fe80Cr20 as the ball milled
powders
The lattice parameter of pure Fe and Cr powders as starting
materials
Lattice parameter calculations for the ball milled Fe80Cr20
The solubility Cr into Fe (Solid solubility)
Chemical composition of commercial ferritic steel obtained by
Glow discharge spectrometry (GDS)
Peaks width and peaks intensity of Fe80Cr20 alloys and ferritic
steel as consolidated and as received specimens
Crystallite size and strain of Fe80Cr20 alloys and ferritic steel as
consolidated and as received specimens
The projected range (Ion range Rp) and longitudinal straggle
σRpof lanthanum and titanium implantation in to substrate of
the specimens
The effect of nanocrystalline structure on the weight gains of
specimens after oxidation at 1173, 1273 and 1373 K in air for
100 h
Comparison parabolic rate constant (kp) of specimens after
oxidation at three various temperatures (1173, 1273 and 1373
K) for 100 h
2
31
50
68
70
74
74
75
78
80
80
83
88
88
xv
4.12
4.13
4.14
4.15
4.16
Composition of Cr2O3 and FeO on the surface scale of specimens
after oxidation at 1173, 1273 and 1373 K
Partial pressure (Po2) and Gibbs energy (∆G°) of oxide types
Composition of oxide scale on the surface of specimens at 1173 K
Composition of oxide scale on the surface of specimens at 1273 K
Composition of oxide scale on the surface of specimens at 1373 K
93
105
110
113
117
xvi
LIST OF FIGURES
1.1
1.2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
2.12
2.13
2.14
SOFC principles of operation
Planar and Tubular design of solid oxide fuel cell
Operating principle of solid oxide fuel cell
Design for solid oxide fuel cell
Ball-powder-ball collision of powder mixture during
mechanical alloying
Average grain size (filled symbols) and atomic-level strain
(open symbols) for NixAl100−x powders after 100 h of milling as
a function of composition
Average grain size obtained for Ni56Al54 and Ni60Al40 powders
after 100 h of ball milling and after addition of elemental Ni or
Al and subsequent mechanical alloying as a function of total
milling time
Schematic design of hot pressing unit
Schematic of hot compaction process
Binary Fe-Cr equilibrium phase diagram
Typical temperature-time profile for Powder Metallurgy steel
parts during sintering
Schematic of an ion implantation system
Schematic of the ion implantation process
Isothermal oxidizing mass gain curves of Co60Cr40 and La
implanted Co60Cr40
Oxidation kinetics of nanocrystalline and microcrystalline Fe-
10Cr alloys, oxidised at 300ºC (573 K): (a) weight-gain vs time
plots for 3120 minutes
Parabolic kinetics for microcrystalline alloy compared with
parabolic kinetics for nanocrystalline alloy
3
4
10
11
23
27
27
28
29
30
30
33
34
36
40
41
xvii
2.15
2.16
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
3.12
3.13
3.14
3.15
3.16
3.17
3.18
3.19
4.1
4.2
4.3
4.4
4.5
4.6
4.7
Diagram of scale formation according to Wagner’s model
Standard free energy of formation of selected oxides as a
function of temperature
Glove Box
Hardened steel vial
RETCH PM400 planetary ball mil
Cycle of consolidation process
A straight line with a slope of 4ε and an intercept of Kλ/D
FWHM of the standard reference material for LaB6
X-Ray powder diffraction-BRUKER D8 ADVANCE
Scanning Electron Microscope (SEM) JSM-6380LA
Transmission Electron Microscope-JEM-2100, 200kV
LECO Glow Discharge Spectrometry 850A
Cockcroft-Walton accelerator Type 200 keV/200 μA
Polishing machine
Apparatus for Archimedes test
CARBOLITE box furnace
Cyclic of oxidation tests of implanted and un-implanted
specimens among temperature of 1173, 1273 and 1373 K for
100 hours
Fe-Cr - p(O2) phase diagram for 1173 K
Fe-Cr - p(O2) phase diagram for 1273 K
Fe-Cr - p(O2) phase diagram for 1373 K
Flow chart
Diffraction peaks of pure Fe and Cr
Diffraction peaks of Fe80Cr20 system as milled powders
Crystallite size vs Milling time
SEM micrograph of ball-milled Fe80Cr20 powders in early stage
of milling times : (a) Fe80Cr20 7 h, (b) Fe80Cr20 15 h
SEM micrograph of ball-milled Fe80Cr20 powders: (a) Fe80Cr20
20 h, (b) Fe80Cr20 40 h, (c) Fe80Cr20 60 h and (d). Fe80Cr20 80 h
Plan view TEM micrographs of ball-milled Fe80Cr20 powders:
(a) Fe80Cr20 40 h and (b) Fe80Cr20 60 h
Variation of the lattice parameter of the ball milled Fe80Cr20
with different milling time
at 1173 K
42
46
48
49
49
50
53
53
54
54
55
57
57
58
58
60
60
62
63
63
65
66
67
69
70
70
73
75
xviii
4.9
4.10
4.11
4.12
4.13
4.14
4.15
4.16
4.17
4.18
4.19
4.20
4.21
4.24
Identification of phase alloy for the ball milled Fe80Cr20 60 h at
44.523°
One of the selected Fe80Cr20 alloys as consolidated specimens
Surface morphology characterization of Fe80Cr20 alloys and ferritic
steel as consolidated and as received specimens
Diffraction peaks of Fe80Cr20 alloys and ferritic steel as
consolidated and as received specimens
The projected range ( Rp) of lanthanum implantation into substrate
of: (a) Fe80Cr20 40 h, (b) Fe80Cr20 60 h, (c) Fe80Cr20 80 h and (d)
Ferritic steel
The projected range (Rp) of titanium implantation into substrate of::
(a) Fe80Cr20 40 h, (b) Fe80Cr20 60 h, (c) Fe80Cr20 80 h and (d)
Ferritic steel
The effect of crystallite size on the weight gains of Fe80Cr20 alloys
compared to commercial ferritic steel after oxidation at 1173 K in
air for 100 h
The effect of crystallite size on the weight gains of Fe80Cr20 alloys
compared to commercial ferritic steel after oxidation at 1273 K in
air for 100 h
The effect of crystallite size on the weight gains of Fe80Cr20 alloys
compared to commercial ferritic steel after oxidation at 1373 K in
air for 100 h
Parabolic rate constants (kp) of the Fe80Cr20 alloys compared to
commercial ferritic steel after oxidation at 1173 K in air for 100 h
Parabolic rate constants (kp) of the Fe80Cr20 alloys compared to
commercial ferritic steel after oxidation at 1273 K in air for 100 h
Parabolic rate constants (kp) of the Fe80Cr20 alloys compared to
commercial ferritic steel after oxidation at 1373 K in air for 100 h
Surface scale morphology of specimens at 1173 K after 100 h
exposed to air: (a) D = 53.32 nm (Fe80Cr20 40 h); (b) D = 38.51 nm
(Fe80Cr20 60 h); (c) D = 76.30 nm (Fe80Cr20 80 h) and (d) D =
77.30 nm (Commercial ferritic steel
76
77
78
79
81
82
71
84
72
85
85
86
87
87
89
xix
4.22
4.23
4.24
4.25
4.26
4.27
4.28
4.29
4.30
4.31
Surface scale morphology of specimens at 1273 K after 100 h
exposed to air: (a) D = 53.32 nm (Fe80Cr20 40 h); (b) D =
38.51 nm (Fe80Cr20 60 h); (c) D = 76.30 nm (Fe80Cr20 80 h)
and (d) D = 77.30 nm (Commercial ferritic steel)
Surface scale morphology of specimens at 1373 K after 100 h
exposed to air: (a) D = 53.32 nm (Fe80Cr20 40 h); (b) D =
38.51 nm (Fe80Cr20 60 h); (c) D = 76.30 nm (Fe80Cr20 80 h)
and (d) D = 77.30 nm (Commercial ferritic steel)
Effect of lanthanum and titanium implantation on weight gains
of specimens after oxidation in air for 100 h at 1173 K
compared to unimplanted specimens
Parabolic rate constant of the implanted specimens compared
to unimplanted specimens after oxidation in air for 100 h at
1173 K
Effect of lanthanum and titanium implantation on weight
gains of specimens after oxidation in air for 100 h at 1273 K
compared to unimplanted specimens
Parabolic rate constant of the implanted specimens compared
to unimplanted specimens after oxidation in air for 100 h at
1273 K
Effect of lanthanum and titanium implantation on weight gains
of specimens after oxidation in air for 100 h at 1373 K
compared to unimplanted specimens
Parabolic rate constant of the implanted specimens compared
to unimplanted specimens after oxidation in air for 100 h at
1373 K
SEM micrograph of the top scale surface that formed at 1173
K after 100 h exposed to air: (a) Unimplanted Fe80Cr20 alloy;
(b) Fe80Cr20 alloy implanted La and (c) Fe80Cr20 alloy
implanted Ti
SEM micrograph of the top scale surface that formed at 1173
K after 100 h exposed to air: (a) Unimplanted commercial
ferritic steel; (b) commercial ferritic steel implanted with La
and (c) commercial ferritic steel implanted with Ti
90
91
94
95
96
97
97
98
99
100
xx
4.32
4.33
4.34
4.35
4.36
4.37
4.38
4.39
4.40
4.41
4.42
4.43
4.44
SEM micrograph of the top scale surface that formed at 1273 K
after 100 h exposed to air: (a) Unimplanted Fe80Cr20 alloy; (b)
Fe80Cr20 alloy implanted La and (c) Fe80Cr20 alloy implanted Ti
SEM micrograph of the top scale surface that formed at 1273 K
after 100 h exposed to air: (a) Unimplanted commercial ferritic
steel; (b) commercial ferritic steel implanted La and (c)
commercial ferritic steel implanted Ti
SEM micrograph of the top scale surface that formed at 1373 K
after 100 h exposed to air: (a) Unimplanted Fe80Cr20 alloy; (b)
Fe80Cr20 alloy implanted La and (c) Fe80Cr20 alloy implanted Ti
SEM micrograph of the top scale surface that formed at 1373 K
after 100 h exposed to air: (a) Unimplanted commercial ferritic
steel; (b) commercial ferritic steel implanted La and (c)
commercial ferritic steel implanted Ti
XRD pattern of the oxide phase for implanted and unimplanted
Fe80Cr20 alloy compare to commercial ferritic steel at 1173 K
XRD pattern of the oxide phase for implanted and unimplanted
Fe80Cr20 alloy compare to commercial ferritic steel at 1273 K
XRD pattern of the oxide phase for implanted and unimplanted
Fe80Cr20 alloy compare to commercial ferritic steel at 1373 K
Cross-sectional morphology of specimens after oxidation in air
at 1173 K for 100 hours: (a) Fe80Cr20 alloy (un-implanted), (b)
Fe80Cr20 alloy implanted La and (c) Fe80Cr20 alloy implanted Ti
Elemental mapping cross-sectional of un-implanted Fe80Cr20
alloy after oxidation in air at 1173 K for 100 hours
Elemental mapping cross-sectional of Fe80Cr20 alloy implanted
La after oxidation in air at 1173 K for 100 hours
Elemental mapping cross-sectional of Fe80Cr20 alloy implanted
Ti after oxidation in air at 1173 K for 100 hours
Cross-sectional morphology of specimens after oxidation in air
at 1273 K for 100 hours: (a) Fe80Cr20 alloy (un-implanted), (b)
Fe80Cr20 alloy implanted La and (c) Fe80Cr20 alloy implanted Ti
Elemental mapping cross-sectional of un-implanted Fe80Cr20
alloy after oxidation in air at 1273 K for 100 hours
101
102
102
103
106
107
108
109
111
111
112
113
114
xxi
4.45
4.46
4.47
4.48
4.49
4.50
Elemental mapping cross-sectional of Fe80Cr20 alloy implanted
La after oxidation in air at 1273 K for 100 hours
Elemental mapping cross-sectional of Fe80Cr20 alloy implanted
Ti after oxidation in air at 1273 K for 100 hours
Cross-sectional morphology of specimens after oxidation in air
at 1373 K for 100 hours: (a) Fe80Cr20 alloy (unimplanted), (b)
Fe80Cr20 alloy implanted La and (c) Fe80Cr20 alloy implanted Ti
Elemental mapping cross-sectional of un-implanted Fe80Cr20 60
h after oxidation in air at 1373 K for 100 hours
Elemental mapping cross-sectional of Fe80Cr20 60 h implanted
La after oxidation in air at 1373 K for 100 hours
Elemental mapping cross-sectional of Fe80Cr20 60 h implanted
Ti after oxidation in air at 1373 K for 100 hours
115
115
116
117
118
118
xxiv
LIST OF APPENDICES
A
B
C
D
E
F
G
H
I
J
X-RAY DIFFRACTION PATTERN OF STARTING
MATERIALS
X-RAY DIFFRACTION ANALYSIS
VALIDATION OF NANOCRYSTALLINE STRUCTURE OF
THE BALL MILLED Fe80Cr20 POWDERS USING TEM
OBSERVATION
ION IMPLANTATION RESULTS
THE COMPARISON OF THE OXIDATION KINETICS OF
IMPLANTED SPECIMENS WITH UNIMPLANTED
SPECIMENS
SURFACE SCALE MORPHOLOGY OF UNIMPLANTED
AND IMPLANTED SPECIMENS
MEASURING OXYGEN PARTIAL PRESSURE (PO2) AND
GIBBS ENERGY (∆G°) OF OXIDE TYPES
IDENTIFICATION OF OXIDE PHASE
IDENTIFICATION OF OXIDE PHASE THAT FORMED ON
THE OXIDE SCALE OF SPECIMENS AFTER OXIDATION
AT THREE VARIOUS TEMPERATURES (1173, 1273 AND
1373 K)
PAPER PUBLICATION
131
144
157
159
166
174
193
196
196
200
210
xxii
LIST OF SYMBOLS AND ABBREVIATIONS
α - Alpha
γ - Gamma
λ - Wavelength
θ - Diffraction angle
ε - Strain
∆G - Gibbs energy
∆W - Mass gain change
σRp - Longitudinal straggling
A - Surface area
a1 - The lattice parameter of the pure solvent element
a2 - The lattice parameter of solute element
ass - The lattice parameter of solid solubulity and x is the solid
solubility
Bcorrected - The instrumental corrected full width at half maximum (FWHM)
Binst - FWHM of the standard reference materials
Bobserved - The full width at half maximum (FWHM) from diffraction peaks
of the specimens
Cr - Chromium
Cr2O3 - Chromium dioxide
CT - Cycle Time
D - Crystallite size
d - Interplanar spacing
EDX - Energy-dispersive X-ray spectroscopy
Fe - Iron
Fe2O3 - Iron oxide
Fe80Cr20 7 h - 80wt%Fe and 20wt%Cr with milling time 7 hours
Fe80Cr20 15 h - 80wt%Fe and 20wt%Cr with milling time 15 hours
xxiii
Fe80Cr20 20 h - 80wt%Fe and 20wt%Cr with milling time 20 hours
Fe80Cr20 40 h - 80wt%Fe and 20wt%Cr with milling time 40 hours
Fe80Cr20 60 h - 80wt%Fe and 20wt%Cr with milling time 60 hours
Fe80Cr20 80 h - 80wt%Fe and 20wt%Cr with milling time 80 hours
FWHM - Full width at half maximum
ICDD PDF-2 - International standard diffraction data
K - Scherrer constant
kp - Parabolic rate constant
La - Lanthanum
LaCrO3 - Lanthanum chromite
LaB6 - Lanthanum Hexaboride
MT - Milling time
pO2 - Oxygen partial pressure
PT - Pause time
Rp - Ion range
S - Time oxidation (hours)
SEM - Scanning Electron Microscope
SOFCs - Solid oxide fuel cells
t - Time
Ti - Titanium
UTHM - Universiti Tun Hussein Onn Malaysia
W0 - Mass before oxidation
Wt - Mass after oxidation
xi - The depth penetration of implanted ions
XRD - X-Ray Diffractometer
YSZ - Yttria stabilised zirconia
