Post on 25-Jan-2021
METHODS OF STUDYING THE
CORROSION PROCESS MECHANISM
http://home.agh.edu.pl/~grzesik
Methods of determining the contribution of individual
reagents in matter transport through the scale
• Marker method
• Two-stage oxidation method
• Determining self-diffusion coefficients
• Scratch method
• Pellet method
Schematic illustration of scale formation
according to Tammann (1920)
Metal Metal
OxidantOxidant
Scale12 2X Me MeX
Marker method – schematic illustration
of Pfeil’s classic experiment (1929)
Fe
Air
Scale
Fe
SiO2
SiO2
Air
Marker experiment in a Fe-O system
H. Engell, F. Wever, Acta Met. 5, 695-700 (1957)
Marker method – interpreting results
Oxidant
Metal
Marker
Scale
Oxidant
Metal
Marker Scale
Oxidant
Metal
Scale
Oxidant
Metal*
**
* reaction location: 12 2X Me MeX
*
Marker
Marker
Oxidant
Metal
Marker
Me1-yX
X2
Me
Marker
MeX1-y
X2
Me
Marker
Me1±yX1±z
X2
Me
MarkerMe1+yX MeX1+y
For temperatures above Tammann’s temperature
Marker method – interpreting results
in the case of predomiant lattice diffusion
Conditions for the correct
procedure of a marker experiment
• the surface of the examined metal or alloy is smooth
• the marker does not react with the metallic substrate, oxidant, or
with substances that are compounds constituting the scale
• before beginning the oxidation process, contact between
the marker and surface of examined material is maintained
• the formed scale is compact, single-phase and strictly adheres
to the metallic core
• oxidation time is selected so that the thickness of the scale
will be at least one order of magnitude larger than the marker
Methods of depositing markers
on metallic substrate surfaces
• even distribution of marker grains (Al2O3, SiO2, etc.)
• even distribution of a thin (10 mm) wire (Pt, Au)
with around 1 mm length
• welding a thin wire constituting a marker
• Depositing a marker (Pt, Au) through an appropriate mesh
(Cu – SEM; Al)
• electrolytic deposition of a marker layer
• decomposition of a noble metal salt, placed on the sample
surface
• photolytic method
• Covering the sample surface with diluted platinum paste
Examples of incorrectly using the marker methodusing a non-elastic wire around the metal
Me
Markers
Me
Me
MeX MeX
Markers
AA
A A
Me
MeX
Examples of incorrectly using the marker methodmarker does not adhere to the metal after deposition
Cross-section
Example of how a marker experiment can be
incorrectly interpreted due to the undercutting mechanism
Marker
Metal Metal Metal Metal
OxidantOxidantOxidantOxidant
Scale
Scale
Scale
Co
S9
8C
o
Pt
50 mm
Cross-section of a sulfide scale formed
on cobalt with an indicated marker location
Z. Grzesik, Ceramika, 87, 1-124 (2005).
T = 700 oC, p(S2) = 10-2 Pa
Co
Co
S4
3
Pt
50 mm
Z. Grzesik, Ceramika, 87, 1-124 (2005).
T = 860 oC, p(S2) = 10-1 Pa
Cross-section of a sulfide scale formed
on cobalt with an indicated marker location
Energia / MeV
0,0 0,5 1,0 1,5 2,00
2
4
6
8
10
12
Nb1,68MeV
Au1,84MeV
Lic
zb
a z
liczen / 1
03
Lic
zba z
licze
n / 1
03
0,0 0,5 1,0 1,5 2,00
5
10
15
20
25
Energia / MeV
Przed siarkowaniem
Po siarkowaniu
SNb/NbS2
SNbS /S2 2
NbNb/NbS2
NbNb/NbS
1,68 MeV2
Au1,48MeV
Z. Grzesik, K. Takahiro, S. Yamaguchi, K. Hashimoto and S. Mrowec, Corrosion Science, 37, 801-810 (1995)
RBS spectrum (4He - 2 MeV) of an Nb sample
marked with Au, before and after sulphidation
Before sulfidation
After sulfidation
Cross-section of an MoS2 scale formed on Mo
with an indicated marker location
correctly
performed
experiment
Z. Grzesik, M. Migdalska, S. Mrowec, High Temperature Materials and Processes, 26, 355-364 (2007)
incorrectly
performed
experiment
Cross-section of an MoS2 scale formed on Mo
with an indicated marker location
Cross-section of an TaS2 scale formed on Ta
with an indicated marker location
correctly
performed
experiment
metal
zewnętrznawarstwa zwarta
utleniacz
pośrednia warstwa porowatawewnętrzna warstwa porowata
X2
Me
e
+
-
MECHANIZM POWSTAWANIA TRÓJWARSTWOWEJ
ZGORZELINY W OBSZARZE POWIERZCHNI PŁASKICH
Marker
Cross-section of a triple-layer scale on a flat
surface with an indicated marker location
metal
External
compact layer
oxidant
Intermediate
porous layer
Internal porous layer
OBRAZ SZCZELIN DYSOCJACYJNYCH W ZGORZELINIE
SIARCZKOWEJ NA STOPIE Cu-9%Zn, UZYSKANEJ
W PROCESIE DWUETAPOWEGO SIARKOWANIA
Autoradiogram
S. Mrowec, An Introduction to the Theory of Metal Oxidation, National Bureau of Standards and National
Science Foundation, Washington D.C., 1982.
Picture of dissociation crevices in a sulfide scale
on Cu-9%Zn alloy, obtained in a two-stage
sulphidation process
Cross-section of a sulfide scale on copper,
obtained at 444 oC
reaction time: 25 s reaction time: 9 min
compact scale
layer
marker
porous scale
layer
Cu
S. Mrowec, An Introduction to the Theory of Metal Oxidation, National Bureau of Standards and National
Science Foundation, Washington D.C., 1982
Marker method in a system
with a ceramic substrate
a) „classic” results interpretation
b) point defect concentration in studied materials and the
result of the marker experiment
c) nuclei of the reaction product inside the substrate and
the result of the marker experiment
d) physical microdefects of the substrate and the result of
the marker experiment
Schematic illustration of using the marker method
in an oxide – oxidant system
X2
MeX
Markers
X2 diffusion Me diffusion Me and X2 diffusion
X2
MeX
MeX2
X2
MeX
MeX2
X2
MeX
MeX2
Marker experiment interpretation
in an oxide – oxidant system
X2
MeaXb
MecXdd
bMe X Me X
d a
bc Me n
d a
bc ea b c d
n
d a
bc Me
d a
bc n e
d d a b c
b cX
d a b c
b cMe Xn c d
2 2
Ratio of external thickness to the internal part of the MecXd oxide layer
d a b c
b c
Z. Grzesik, Termodynamika i kinetyka defektów w kryształach jonowych, WN Akapit, Kraków 2011
Methods of depositing markers on
the surfaces of ceramic substrates
• depositing a marker (Pt, Au) through an appropriate mesh
(Cu – SEM; Al)
• photolytic method
• covering the sample surface with a diluted platinum paste
Schematic illustration of the marker location
in Co3O4 resulting from CoO oxidation
Cation sublattice
of Co3O4 is defectedAnion sublattice
of Co3O4 is defected
4 3 4CoO Co O Co nen Co ne O Co On 23 2
13 3 4
CoO Co O3 4
Co+n
e-
25 %75 %
Markery Au
O2
Schematic illustration of marker location in Co3O4grown during CoO oxidation, in the case where the
cation sublattice of Co3O4 exhibits predominant disorder
Au markers
4 3 4CoO Co O Co nen
Co ne O Co On 23 213 3 4
Co3O4 scale cross-section grown CoO
with an indicated marker location
Au markers
Cu O2
CuO
Au-markers
50 mm
Cu O CuO Cu e22 2
Cu e O CuO 2 12 22
M. Migdalska, Z. Grzesik, S. Mrowec, Defect and Diffusion Forum, 289-292, 429-436 (2009)
Cross-section of CuO scale grown on Cu2O
with an indicated marker location
Au markers
Cu O2 CuO
Cu+2
e-
50 %50 %
Markery Au
O2
Cu O CuO Cu e22 2 Cu e O CuO 2 12 22
Schematic illustration of marker location in CuO grown
during oxidation of Cu2O, in the case where the cation
sublattice of CuO exhibits predominant disorder
Au markers
NiS2 scale cross-section grown during NiS sulphidation
with an indicated marker location
Au markers
Schematic illustration of marker location in NiS2grown during NiS sulphidation
disordered NiS2anion sublattice
disordered NiS2cation sublattice
Ratio of external thickness to the internal part of NiS2 equals
around 0,82
NiS2 scale cross-section grown during NiS sulphidation
with an indicated marker location
Au markers
Correlation between deviation from stoichiometry
in Ni1-yS and sulfur vapor pressure
10-1 100 101 102 103 104 10510-3
10-2
10-1
1073 K1023 K
973 K
923 K
873 K
Badania własne
H. Rau, 1975
1168 K
1110 K
1038 K
986 K
914 K
835 K
Ni1-y
S
y
pS
2 / Pa
ymax in Ni1-yS ≈ 0,09
Z. Grzesik, 2005
The experimentally determined ratio between external thickness and the internal
part of the NiS2 sulfide equal to 0,82 remains in accordance with the theoretical
value obtained under the assumption that deviation from stoichiometry is present in
Ni1-yS on the level of 0,91
e64,1Ni82,0NiSSNi2 2291,0
222 NiS82,0S82,0e64,1Ni82,0
NiS2 scale cross-section grown during NiS sulphidation
with an indicated marker location
Au markers
a
b
s
homogenization: 873 K, 10 Pa, 24 h
homogenization: 873 K, 200 Pa, 24 h
sulphidation: 873 K, 1000 Pa, 5 min
b
a
s
10-1 100 101 102 103 104 105 10610-3
10-2
10-1
H. Rau, 1975
1168 K
1110 K
1038 K986 K
914 K
835 K
Ni1-y
S
y
pS
2 / Pa
10 11 12 13100
101
102
103
104
1051073 1023 973 923 873 823 773 723
T-1.104 / K-1
NiS2
Ni1-y
S
T / K
pS
2 /
Pa
NiSh2VSNi Ni22
1xNi
Influence of NiS homogenization parameters
on marker location at the initial stage of NiS2 formation
Au markers
Ni coating Ni coating
Marker location after NiS homogenization
Au markers
Ni coating Ni coating
Influence of MeX homogenization parameters on
marker location at the initial stage of MeX2 formation
Au markers
Marker location after MeX homogenization in the case where
oxidant pressure is lower than MeX2 dissociation pressure
Au markers
Marker location after sulphidation
of CoS to CoS2 (SEI)
Au markers
CoS2
CoS
Au markers
Marker location after sulphidation
of CoS to CoS2 (BSE)
substrate
product
Au markers
Marker location at the initial stage of CoS2 formation
on the surface of CoS homogenized
at the CoS2 dissociation pressure
CoS cross-section sulphidized at a sulfur vapor pressure
that enables CoS2 formation
Interior of CoS sulphidized at a sulfur vapor pressure
that enables CoS2 formation
CoS
Co
Cross-section of a Co sample covered with CoS
CoS2
CoS
Initial stage of CoS2 formation inside CoS
CoS2
CoS
Au markers
Marker location in CoS sulphidized to CoS2
Possible marker locations in a CoS-CoS2 system
depending on the predominant direction
of reagent diffusion
Au markers
Schematic illustration of marker location
in CoS sulphidized to CoS2
neCoCoSCoS2 n2
22n CoSSneCo
Schematic illustration of marker location
in CoS sulphidized to CoS2
Interior of NiS sulphidized at a sulfur vapor pressure
that enables NiS2 formation
NiS2
NiS
20 mm
Interior of NiS sulphidized at a sulfur vapor pressure
that enables NiS2 formation
Co3O4
CoO
Cross-section of a CoO sample covered with Co3O4
Co3O4
CoO
Au markers
Marker location in Co3O4growing on CoO
Surface of CoO formed as a result of Co oxidation
at 900oC and at 1000 Pa oxygen pressure
Surface of NiS formed as a result of Ni sulphidation
at 700oC and at 1000 Pa sulfur vapor pressure
Surface of CoS formed as a result of Co sulphidation
at 700oC and at 1000 Pa sulfur vapor pressure
Marker location on a developed CoS surface
Marker method – oxidation of a high entropy oxide
(Mg, Co, Ni, Cu, Zn) O
O2
(Mg, Co, Ni, Cu, Zn) O
Markers
O2 diffusion Me diffusion Me and O2 diffusion
O2 O2 O2
(Mg, Co, Ni, Cu, Zn) O(Mg, Co, Ni, Cu, Zn) O (Mg, Co, Ni, Cu, Zn) O
Marker method – oxidation of a high entropy oxide
(Mg, Co, Ni, Cu, Zn) O
Presence of predominant disorder inside the cation sublattice
O2
(Mg, Co, Ni, Cu, Zn) O g2'
i
x
X
x
MX
2
1e2MXM
xX
''Mg2 Xh2VX
2
1
reaction location:h
mdAh
where:
h – thickness of the oxide formed on the marker layer
A – proportionality coefficient
d – oxide density
m – oxide mass change during oxidant pressure change
Marker method – oxidation of a high entropy oxide
(Mg, Co, Ni, Cu, Zn) O
h = 12 μm
Conclusion:
In the case where predominant disorder exists in the cation
sublattice, markers should be located 12 micrometers below the
oxide surface.
Necessary conditions for obtaining reliable
results using the modified marker method
• Before marker deposition the oxide sample must be heated at
oxygen pressure lower than that used during oxidation of the
sample covered with markers.
• The change in deviation from stoichiometry of the studied oxide
must be large (order of a few percent) during the marker
experiment.
• Sample thickness should exceed 1 mm.
• Reequilibration time of defect concentration during oxygen pressure
change should be many time greater than around 1 minute (which
means a small chemical diffusion coefficient for defects and/or a
large sample thickness).
Conclusion:
Complete interpretation of a modified marker experiment is possible
after finishing both marker studies, as well as point defect
concentration and mobility studies in a given oxide.
Marker experiment – summary
Obtaining reliable results during predominant disorder studies
using the marker method in ceramic systems, especially porous
systems, is a much more difficult task compared to metal-oxidant
systems. In order to interpret results, precise analysis of the reaction
product growth location in the substrate is necessary. In the case of
ceramic substrates with high point defect concentration, the
materials should be homogenized before the “marking” process at a
highest oxidant pressure, at which the chemical compound
constituting the substrate remains stable. In the case of compounds
exhibiting large deviation from stoichiometry, this should be taken
into account when writing the appropriate chemical reactions, on the
basis of which marker locations inside the reaction product can be
foreseen.
Two-stage oxidation method
Me MeX
C(*X)
OUTWARD LATTICE METAL DIFFUSION
Ideal case(X and *X atoms do not mix together)
Me MeX
C(*X)
Real case(X and *X atoms mix together)
C(*X) – concentration of the oxidant isotope (tracer)
Me MeX
C(*X)
INWARD OXIDANT DIFFUSION ALONG GRAIN BOUNDARIES
Ideal case(X and *X atoms do not mix together)
Me MeX
C(*X)
Real case(X and *X atoms mix together)
Two-stage oxidation method
C(*X) – concentration of the oxidant isotope (tracer)
SIMULTANEOUS DIFFUSION OF BOTH REAGENTS
Slow mixing together of X and *X atoms
Me MeX
C(*X)
Me MeX
C(*X)
Fast mixing together of X and *X atoms
Two-stage oxidation method
C(*X) – concentration of the oxidant isotope (tracer)
Cu, O16 and O18 concentration profiles inside a sample obtained
during Cu2O oxidation at 1273 K and 105 Pa oxygen pressure
0 500 1000 1500 2000 25000
10
20
30
40
50
60
70
Cu2O
concentr
ation
/
at.
%
Time / s
Cu
O16
O18
CuO
M. Migdalska, Z. Grzesik, S. Mrowec, Defect and Diffusion Forum, 289-292, 429-436 (2009)
O16 and O18 concentration profiles in an Ni-Cr sample
after two-stage oxidation at 1323 K
I stage: Ar-20%16O2; 0,5 h
II stage: Ar-20%18O2; 2 h
I stage: Ar-4%H2-2%H216O2; 0,5 h
II stage: Ar-4%H2-2%H218O2; 2 h
David J. Young, „High temperature oxidation
and corrosion of metals”, Elsevier, Sydney 2016
Cr, Fe, O16 and O18 concentration profiles
in 13CrMo4-4 steel after oxidation at 823 K
Ar / 1% 16O2 / 1% C18O2; 2 h
T. Olszewski, „Oxidation mechanisms of materials for heat exchanging components in CO2/H2O-containing
gases relevant to oxy-fuel environments”, Forschungszentrum Jülich GmbH, Jülich, 2012
Ar / 1% 16O2 / 2% H218O; 2 h
Concentration profile of elements in a P92 steel
sample after oxidation in Ar / 1% 16O2 / 1% C18O2
atmosphere at 923 K
T. Olszewski, „Oxidation mechanisms of materials for heat exchanging components in CO2/H2O-containing
gases relevant to oxy-fuel environments”, Forschungszentrum Jülich GmbH, Jülich, 2012
Concentration profile of elements in an INCONEL 617
sample after oxidation in Ar / 1% 16O2 / 2% H218O
atmosphere at 1173 K
T. Olszewski, „Oxidation mechanisms of materials for heat exchanging components in CO2/H2O-containing
gases relevant to oxy-fuel environments”, Forschungszentrum Jülich GmbH, Jülich, 2012
Self-diffusion coefficient studies
Distribution of the concentration of a tracer inserted into the near-
surface layer of a MeX crystal (lattice diffusion)
x x20 0
c ln c
cc
Dt
x
Dt
0
2
2 4exp ln lnc
c
Dt
x
Dt
0
2
2 4
c – tracer concentration at distance x from the crystal surface,
c0 – tracer concentration on the surface before beginning the heating process,
t – heating time
D – self-diffusion coefficient (tracer)
Distribution of the concentration of a tracer inserted into the near-
surface layer of a MeX crystal (intergranular diffusion)
x x0 0
c ln c
ln
/c
D D d
D tx const
V g
V
2
4
c – tracer concentration at distance x from the crystal surface,
t – heating time
DV – lattice diffusion coefficient
Dg – intergranular diffusion coefficient
Self-diffusion coefficient studies
Distribution of tracer concentration in a MeX crystal, when tracer
concentration on the crystal surface is constant (lattice diffusion)
x0
c
c c erfx
Dt
0 1
2
c – tracer concentration at distance x from the crystal surface,
c0 – tracer concentration on the surface before beginning the heating process,
t – heating time
D – self-diffusion coefficient (tracer)
Self-diffusion coefficient studies
Scratch method
Me
MeX
Me
MeX
Me
MeX
Me
MeX
Me
inward diffusion outward diffusion mutual diffusion
Wagner’s pellet method
H. Rickert, Z. Phys. Chem. Neue Folge, 23, 356 (1960)
The range
of metal
loss
S S
AgAg
pellet
pelletAg S2Ag S2
scale
Ag S2Ag+
e-
S
Ag S2
Ag
pellet
Ag S2
scale
Ag+
e-
S. Mrowec, An Introduction to the Theory of Metal Oxidation, National Bureau of Standards and National Science
Foundation, Washington D.C., 1982
Modified Wagner’s pellet method
S
Ag
pellet
Ag S2
Ag S2
Ag S2
S
Ag
pellet
Ag S2
35S
Ag
pellet
Ag S2
Ag S2
Ag S2
Ag S2 *
Ag S2 *
Ag S
stop Zr-Cu ZrC W WC
5 mm
temperature: 1400 oC
time: 1,5 h
Cross-section of a WC sample that reacted with Zr
Z. Grzesik, M. B. Dickerson, K. Sandhage, of Materials Research, 18, 2135-2140 (2003)
THE END