Transcript Slide 1

TEM-based techniques as a powerful tool in
development of ceramics materials
Yingda Yu, Inger-Lise Tangen, Tor Grande, Ragnvald Høier and Mari-Ann Einarsrud
IMT & Fysikk, NTNU
SUP Seminar on High Performance Ceramics and Heterogeneous Materials
13.06.2003 Trondheim
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0.27 nm
X 6 000 000
Which type information can be obtained from a TEM
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TEM can provide both of materials morphology and microstructure
information at the same time.

TEM is a powerful tool to reveal materials phenomena at atomic
level with extremely higher resolution ability,
ability. together with
chemical composition information.

TEM only checked a small part of samples, i.e. a poor sampling
instrument. (►interdiscipline cooperation)
Microstructure Characterization of Epitaxial Grown Thin Film
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The epitaxial growth
relationship can be
identified according
to HRTEM and SAED
results, and the
misfit parameter can
be calculated as
3.47% between the
epitaxial grown
LaFeO3 thin film and
LaAlO3 substrate.
Interface dislocations
Microstructure characterization related with AlN thermal conductivity
In this SUP subproject, searching for possible application AlN as sidelining
materials in aluminium electrolysis, it is important to understand the relation
between the sintered microstructure and its thermal conductivity.
Aase Marie Hundere PhD Thesis NTH 1995
Properties of AlN
High
High thermal
thermal conductivity
conductivity
Electrical isolator
High Hardness and strength
Excellent corrosion resistance
Good oxidation resistance
High thermal stability
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SEM and TEM micrographs
show the different
distributions of secondary
phases in the samples.
Experimental details and selected properties of AlN samples
Sample
code
Wt %
Y2O3
Sintering
time (h)
Sintering
condition
Thermal
Con. (W/mK)
Lattice
oxygen (wt %)
80F
82F
84F
86F
81F
83F
85F
87F
90
91
92
93
94
95
96
97
0.8
2.3
3.9
7.7
0.8
2.3
3.9
7.7
0.8
0.8
2.3
2.3
3.9
3.9
7.7
7.7
2
2
2
2
2
2
2
2
2
6
2
6
2
6
2
6
A
A
A
A
B
B
B
B
C
C
C
C
C
C
C
C
91
130
144
148
101
142
148
144
105
119
145
163
154
180
160
192
0.56
0.43
0.63
0.84
0.55
0.43
0.43
0.97
0.53
0.28
0.39
0.19
0.52
0.20
0.49
0.15
The presence of secondary phases
along AlN grain boundaries
disrupts the connections between
high thermal conductivity AlN
grains. In addition, the thin
amorphous layer between the
secondary phase and the AlN grin
will further reduce the thermal
conductivity .
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Microstructure characterization related with AlN thermal conductivity
Microstructural changes were found to disrupt the connectivity of the AlN grains,
resulting in a decrease in the thermal conductivity of the materials.
From GB
Inside Grain
O Ka
Al
EDS spectra obtained using
0.6 nm probe from AlN grain
boundary (GB) and inside
grain in FEG-TEM.
Representative HRTEM
images of vertical AlN GBs,
with AlN grains close to low
index planes.
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No substantial differences
SEM and TEM micrographs
were
seen between grain
show the different
boundaries
(GBs)
in the two
distributions of
secondary
phases
in the samples.
representative
samples
N Ka
Ka
Al
Ka
Y Ka
TEM Characterization of Pressureless Sintered AlN(CaO) Ceramics
To search new and improved materials to apply in Hall-Héroult aluminium electrolysis cells as
alternative side linings materials, which demands more cheap AlN materials.
In the investigation, the low cost additive (Calcium aluminates C12A7, 12CaO-7Al2O3) and lowtemperature sinter route to form dense material are explored.
Eirik Haugen PhD Thesis NTNU 2000
TEM results confirmed that the high
densification (>95%) AlN material
was obtained by using 8 wt% C12A7
sintering additive with AlN fine
staring powders at 1650C.
Crystallized secondary phases are
located at the triple junctions and
are determined as CA (CaAl2O3)
phase through serise SAED
patterns from large angle tilt.
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HRTEM image reveal that the AlN
grains are connected with a relative
clean grain boundaries (GBs),
which is important to have a higher
corrosion resistance towards
cryolite (anti-intergranualar
corrosion IGC).
CA6
CA2
CA
C12A7
C3A
TEM Characterization of Pressureless Sintered AlN(CaO) Ceramics
For further study the chemistry of the secondary phases in CaO-Al2O3 system, the sample
was prepared in an inner Mo crucible with a Mo lid sintered for 24 h in a graphite furnace
under a slight N2 overpressure.
14 wt% C12A7 (Calcium aluminates C12A7, 12CaO-7Al2O3) used as sintering additive,
together with AlN coarse starting powder.
Considering the mass balance due to the Al2O3 on AlN powder surfaces, an Al2O3 contents of
~55 wt% is expected.
However, only small amounts
of crystalline CA secondary
phases are found by XRD
analysis.
TEM and EDX composition
results reveal that secondary
phases consist with the
crystallized CA phase (CaAl2O4)
and high Ca-containing
amorphous C12A7 phase.
CA6
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CA2
CA
C12A7
C3A
TEM Characterization of AlN-TiN Composite Ceramics
For understanding the relationships between microstructures and sintering conditions
to lead to improving AlN Composite mechanical properties. AlN-TiN samples are sintered
by means of the eutectic Y-Al-O reaction for lowing the sintering temperature.
Inger-Lise Tangen PhD Thesis NTNU 2002
The smaller (<1μm) TiN
particles are located at
intragranular positions while
large TiN particles are at
intergranular positions of AlN
matrix.
The local residual strain
contrasts cause by the
thermal expansion mismatch
between AlN and TiN.
HRTEM reveals the
amorphous grain boundary
between AlN and TiN,
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20vol%TiN/AlN composite
AlN matrix
Nano-pores (arrowed)
appeared as increasing
TiN to 20vol%
10vol%TiN/AlN
4 mm
TiN
5 nm
particle
AlN-SiC Solid Solution and AlN-SiC Composite Ceramics
For further improving AlN flexural strength and fracture toughness,
the in-situ formed SiC reinforced AlN materials are investigated.
AlN-SiC Solid Solution
formed as SiC content
below 10vol%.
As further increasing SiC
powders contents, the
average grain size
decreased from 5-8 down
to 3-5 mm.
The high density composite obtained under a
flowing nitrogen
atmosphere in a graphic
furnace at 1880 C
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AlN-SiC Solid Solution and AlN-SiC Composite Ceramics
For further improving AlN flexural strength and fracture toughness,
the in-situ formed SiC reinforced AlN materials are investigated.
Elongated SiC grains associated with SiC polytype
are formed along AlN matrix GBs during sintering.
EELS chemical mapping (from above white square
area) used to understand the chemistry of
secondary phase region.
HRTEM and Moiré fringe tech-niques can be
used to investigate SiC polytype details and SiC
re-nucleation in SiC/AlN composite.
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SiC Polytype is formed
by different stacking
sequences
AlN Polytype is modified
by different AlO6
octahedral layers.
Moiré fringe
Fine phase identification of the elongated AlN polytype ceramic
The elongated grown AlN polytype grains are prepared for improving AlN fracture
toughness by pressureless sintering with different Al2O3 additive contents 1950°C
The AlN polytype phase
development in a series of
sample with increasing Al2O3
contents in the system AlNAl2O3-Y2O3 has been
inverstigated.
HRTEM reveals the detailed
AlN polytype phase
information (such as here as
intergrowth with 24H, 33R
and 39R).
Two new AlN polytype
phases 39R and 24H were
identified for the first time in
the AlN-Al2O3 system.
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nR polytype, consists of
three rhombohedra related
sub-blocks.
nH polytype, consists of
two hexagonal related subblocks.
Fine phase identification of the elongated AlN polytype ceramic
The elongated grown AlN polytype grains are prepared for improving AlN fracture
toughness by pressureless sintering with different Al2O3 additive contents 1950°C
The polytype structures can be decribed as flat inversion domain boundary (IDB) complexes
consisting of an aluminium surrounding by six oxygen atoms (octahedron) to form along AlN
basal (001) planes.
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The new 24H AlN polytype phase was identified for the first time in the
AlN-Al2O3 system.
Microstructure Characterization of AlN Fiber
Amorphous
covered surface
Configuration
Fiber Tip
Aluminum nitride whisker was prepared by
nitridation of aluminium foil at 1500 C under
250 mbar N2 gas pressure for 5 hrs.
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Both of SAED pattern (streak lines) and HRTEM
provide the microstructure information of the
whisker-like growth relationship, with AlN (001)
perpendicular to the growth direction.
The possible growth mechanisms
L
S
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Growth direction: [001]
Growth direction: perpendicular to [001]
Conclusion Remarks
TEM-based techniques is an powerful tool in development of
ceramics materials, i.e. to understand the relationships between
structures and sintering conditions and lead to improve the material
mechanical property (material design).
TEMs used in this SUP project
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Philips CM30, operated at an accelerating voltage 300 kV
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JEOL FEG TEM, operated at an accelerating voltage 200kV
and 300 kV
Future work
TEM related techniques would be expected one of the most
effective tools to provide both microstructual infomation and
chemical composition in the new-funeded nanotechnology
projects,

FunMat

NanoMat
Acknowledgement
The sub-Sup project was fully supported by the Norwegian
Research Council.
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