DISS. ETH No. 15190. Thin Film Deposition by Spray Pyrolysis and the.
Application in Solid Oxide Fuel Cells. A dissertation submitted to the. SWISS
FEDERAL ...
Research Collection
Doctoral Thesis
Thin film deposition by spray pyrolysis and the application in solid oxide fuel cells Author(s): Perednis, Dainius Publication Date: 2003 Permanent Link: https://doi.org/10.3929/ethz-a-004637544
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DISS. ETH No. 15190
Thin Film
Deposition by Spray Pyrolysis
Application
and the
in Solid Oxide Fuel Cells
A dissertation submitted to the
SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH
for the
degree
of
Doctor of Natural Sciences
presented by
DAINIUS PEREDNIS
Dipl. Phys. born
ETH
August 9,1973 Lithuania
accepted
on
Prof. LJ. Dr. K.
the recommendation of
Gauckler, examiner
Honegger, co-examiner
Zürich,
2003
This thesis is dedicated to my parents Aldona
(1952-2003)
andBolius Perednis
Acknowledgement This book is dedicated to my parents Aldona and Bolius Perednis for their full
confidence, constant
and
care
support during all these years
home
at
and
in
Switzerland.
Prof.
I would like to thank my advisor to realize
opportunity
this thesis in his
his institute I have learnt
him for the over
possibility
a
throughout
lot about ceramics in
he gave
me
this thesis.
general.
present my work
to
Gauckler for the
J.
In
managing
in
laboratory, for the freedom
for his encouragement and support
project,
Ludwig
Dr.
During
particular,
this
the stay at
I wish to thank
at international conferences all
the world.
Special
thanks to Dr.
Kaspar Honegger (Sulzer Innotec AG)
examiner of the thesis and also for The
quality of this manuscript
people, especially Prof. Michael
Jörger,
Dr.
to read the
patience
Inorganic Materials Wilhelm
droplets Prof
Dr.
me an
was
Gerhard
experimental
acting
as co-
assistance.
improved significantly by
the
help
of many
Bayer, Brandon Bürgler, Nicholas Grundy,
Claus Schüler. I
appreciate
their valuable
suggestions and
manuscript.
Furthermore,
Oliver
giving
for
I wish to thank all the
and many other
(The
people,
Particle
and discussions
on
spray
Dr. Sotiris E. Pratsinis
at the group of Nonmetallic
colleagues
in
particular: for
Technology Laboratory)
help
in
counting
pyrolysis.
(The
Particle
Technology Laboratory)
for
helpful
discussions. Dr. Petr Bohac and Dr. Martin Hruschka for introduction to the spray
pyrolysis
technique. Dr.
Helge Heinrich (Institute of Applied Physics)
electron
My
for his
support in transmission
microscopy.
students
Marc
Dusseiller, Laurent Feuz,
René Nussbaumer,
Fernanda
Rossetti, Claudio Vanoni, Simon Oertli for significant contributions to this thesis. Present and former members of the SOFC team: Daniel Beckel, Dr. Eva
Anja Bieberle,
Jud, Dr. Christoph Kleinlogel, Ulrich Mücke, Michel Prestat, Jennifer Rupp,
Dr. Julia Will.
Christoph Huwiler and Srdan Vasic for sharing H33
office.
"
Secretary Irene Urbanek for help in administrative stuff. Martin Borer
(Dega AG) for his support in all questions concerning spray guns.
Peter Kocher for his technical support. Jeol JSM 6400 and LEO 1530 for thousands of pictures. The financial support from the Swiss Federal
Office of Energy
is
gratefully
acknowledged. Special
thanks to my sister Asta, her husband Kestutis, and all my friends for
their support outside the office. I wish to express my sincere thanks to my wife leva for her
support throughout my studies.
patience,
care,
and
Table of contents
Table of contents
1
Summary
5
Zusammenfassung
7
11
1 Introduction
1.2
11
of the study
1.1 Aim
12
Strategy
2 State of the art: spray
13
pyrolysis
2.1 Introduction
14
2.2 Powder production
16
2.3 Thin film
deposition
18
and applications
2.3 A Films for solar cell
18
applications
19
2.3.2 Sensors
coatings
20
2.3.4 Solid oxide fuel cells
21
2.3.3 Metal oxide
applications
23
deposition by spray pyrolysis
25
2.3.5 Miscellaneous 2.4 Models forfilm
2.5
2.4.1 Atomization of precursor solution
25
2.4.2 Aerosol transport 2.4.3 Decomposition of precursor
27 29 33
Summary
34
2.6 References
3
Morphology
and
deposition
of thin metal oxide fîlms
using
spray
43
Spray generation
3.1.2 Influence of spray parameters 3.2
3.3
on
film
morphology
44 46
Experimental. 3.2.1
41
42
3.1 Introduction
3.1.1
pyrolysis
46
Set-up
3.2.2 Chemicals and substrates
48
3.2.3 Characterization
50
51
Spray parameters 3.3.1 Substrate surface temperature
51
3.3.2 Solution flow rate
53
Type of salt
54
3.3.3
1
59
3.3.4 Solvent 3.3.5
Deposition
60
time
3.3.6 Nozzle to substrate distance
61
3.3.7 Additives
62
3.3.8
Deposition
64
rate
3.4
Summary
66
3.5
References
67
4 A model for film
69
deposition by spray pyrolysis
70
4.1 Introduction 4.2
71
Experimental setup
73
4.3 Results 4.3.1 Pressurized
73
4.3.2
77
Spray Deposition Multi-jet mode of electrostatic spray deposition 4.3.3 Cone-jet mode of ESD 4.3.4 Comparison of PSD and ESD systems 4.4 Analysis 4.5
81 84 86
of the deposited films
89
Decomposition of the salt solutions
93
4.6 Film
growth model Summary of the spray parameter study 4.6.2 Model for film deposition
93
4.6.1
93
4.7 Conclusions
96
4.8
98
References
5 Thermal treatment of metal oxide spray
101
pyrolysis layer
5.1 Introduction
102
5.2
104
Experimental.
106
5.3 Results and discussion 5.3.1 Structural
106
properties
5.3.2 Influence of thermal treatment 5.3.3 Electrical
properties
of spray
film
topography deposited films on
Ill 113
5.4
Summary
116
5.5
References
117
6 Solid oxide fuel cells with
electrolytes prepared
pyrolysis
119 120
6.1 Introduction 6.2
via spray
123
Experimental. 6.2.1 Anode substrates
123
6.2.2
Electrolyte deposition 6.2.3 Cathode preparation
123
6.2.4 Fuel cell measurements
127
125
2
129
6.3 Results and Discussion
electrolyte single-layer electrolyte film Cells with composite electrolyte films
6.3.1 SOFC with
a
YSZ
film
129
6.3.2 Cell with bi-layer
133
6.3.3
138
6.4 Conclusions
142
6.5
144
References
7 General conclusions
147
8 Outlook
149
9
153
Appendix 9.1 Measurement 9.2 Forces
ofdroplet size distribution using PDA
153 154
acting on droplet
10 Abbreviations
155
11 Curriculum vitae
157
3
Seite Leer / Blank leaf
J
Summary Solid oxide fuel cell emission of
However,
because it converts chemical energy
pollutants
cost
reduction remains the main SOFC is based
high temperature
temperatures of 900-1000°C zirconia
offers efficient power
(SOFC) technology
are
objective of
thick
on
reformed fuel is used.
might lead
This
components, and place large demands
on
reduction of the
(Cr5FelY203). Therefore,
Aim of this
study
thin film oxides suitable
of the
deposition
as
with the
on
development
chosen
reliability.
and therefore to
of
to
achieving
the set
pyrolysis method
spray
thin
(0.1
to 10
is
strongly
Thin film zirconia-based
inexpensive manufacturing
an
produce
interconnectors
as
to 700-800°C
onto porous anode substrates. This is
potential
incomplete
the anodes when
operating temperature
electrolytes for SOFC. The
electrolyte
coating technology
the
was
specific ionic conductivity of
expensive materials
minimizing ohmic losses
contribute to
urn) zirconia electrolyte. Operating
deposition
desirable in order to reduce system costs and to enhance
electrolytes
State of the art
the interfacial solid state reactions of cell
to
the
electrical energy.
to
development.
SOFC
due to the low
required
in order to avoid carbon
electrolyte and
150
(about
directly
with low
generation
an
urn)
goal.
process for
was
chosen for
form of
inexpensive
and gas
tight ceramic
films. In
chapter
working principle chapter 3
the most
proposed
in
2
4.
spray
Chapter
deposited
thin
pyrolysis
technique and its application
important
chapter
deposition of
brief overview of spray
of this
microstructure of the to
a
pyrolysis parameters
5 focuses
film.
presented with respect
depositing
are
in
chapter 6,
growth
studied. A film
the
to
the
various thin films. In model is
the influence of thermal treatment
on
Finally,
to
is
application
of spray
on
the
pyrolysis
electrolyte films for SOFC is demonstrated and their performance
is
reported. A
(ESD)
comparison
of two spray
and Pressurized
pyrolysis techniques, Electrostatic Spray Deposition in the
Spray Deposition (PSD), is presented
techniques, the substrate morphology. Using ESD,
surface temperature is the main the surface
morphology
is
the influence of these parameters
Further
chapter
4.
insight
in to the
Droplet transport
on
film
working principle and
evaporization
strongly
influenced
5
morphology
of the spray is
3. For both
parameter that determines the film
of the precursor solution and deposition time. When the PSD
deposition,
chapter
by the composition
technique is not
is used for film
pronounced.
pyrolysis
investigated using
method is a
given in
phase doppler
SUMMARY
anemometer.
Droplets
smaller than 10
the volume distributions
droplet evaporation mechanism is
urn
dominated the number distributions and in contrast,
dominated
were
is observed at
a
distance of 1
model does not involve
Chapter
be
can
5 reports the structural
a mean
size of 12
grain
analysis
film thickness does not exceed 5.5
The
reduced while
layer
of
chapter
ohmic losses and
6.
a
buffer
operated using hydrogen 800°C and exhibited
treatment
on
with 600
nm
electrolytes Surprisingly, using
during
technique
are
sufficiently low can
was
when the
be concluded that the
films would sustain the SOFC
pyrolysis technique
in
layer
of ceria 10 mol%
to be
porous NiO-YSZ
as
fuel and air
high
as
voltage
density
power
oxidant at temperatures of 1.01 V at 720°C
of more than 750
450 urn
with low
films consisted of
(CYO).
The
hours
720°C
could be coated
indicating
mW/cm2
at 770°C. at
ranging
by
Cells with a
500
was
a
were
from 600°C to
dense and crack-
generated by
containing tolerable nm
a
electrolyte
self-supporting anode substrates. The cells
bi-layer electrolyte over
solid solution
prepared
was
oxide fuel cells to be
bi-layer electrolyte
yttria
technology
SOFC
thin
the
cells
bi-layer
degradation.
electrolyte
film
pyrolysis technique.
thin film can
by electrolyte
power output. The
operated for
Summarizing,
promising
investigated.
thermal treatment up to 800°C. It
From the above results it
spray
pores with sizes of up to 3
the spray
are
annealing temperature of
an
Spray pyrolysis allows thin electrolytes
thin YSZ/CYO
were
the surface
the film microstructure is
have been obtained at
nm
urn.
open circuit
an
film. A
electrolyte
to cracks
deposited by the spray pyrolysis
thereby allows the operating temperature of solid
bi-layer was deposited onto
free
the
maintaining high
of YSZ and
on
than the
of up to 800°C.
application
demonstrated in
particles
10
authors, the proposed film growth
yttria-stabilized-zirconia (YSZ)
8 mol%
operating temperature
films with
of the films
calculated that at 700°C the ohmic losses caused
deposited
higher
deposition temperatures lead
high, rough
700°C. No crack formation is observed
spray
large droplets (>
CVD process.
a
technique. The influence of thermal Films with
possible growth
this temperature should be
In contrast to most
produced.
Significant
um.
from the substrate. A
cm
Generally,
process.
in the films. When the temperature is too
powder
than 10
droplets larger
of the precursor. Too low
decomposition temperature
or
the
where the substrate surface temperature and the
proposed
|im) determine the deposition
deposited
by
be
it
can
be stated that the spray
deposition
pyrolysis technique
is
an
extremely
method. The results obtained in this thesis prove that this
successfully used
in SOFC
technology.
6
Zusammenfassung Festelektrolyt-Brennstoffzellen (SOFC) ermöglichen mit
Energie das
Emission
niedriger
der SOFC
Entwicklung. Zirkonoxid,
das meistverwendete
heutzutage
Sie wandeln direkt chemische in elektrische
Schadstoffen.
und sind nicht dem Carnot Gesetz unterworfen. Derzeit ist die Kostenreduktion
um
Hauptziel
Wegen
von
eine effiziente Stromerzeugung
Elektrolytmaterial
mit einer Dicke
Betriebstemperaturen
900°C bis 1000°C
von
150
um,
ist
Hochtemperatur SOFC Systemen.
in
niedrigen spezifischen Ionenleitfähigkeit
der
von
notwendig. Diese
hohen
sind
Elektrolyten
Zirkonoxid
von
Temperaturen können
Festphasen-Grenzflächenreaktion zwischen benachbarten Zellbestandteilen beschleunigen. Hohe
Stabilitätsforderungen
Materialien, wie
1000°C
von
und
Systemkosten reduziert
gestellt,
ist daher erstrebenswert.
700°C
zu
Langzeitstabilität
die
sowie die indem
Betriebstemperatur kann reduziert werden,
werden. Die aus
die Interkonnektoren
an
so
dass
nur
teure
Cr5FelY203 hierfür verwendet werden kann. Eine Reduktion der
z.B.
Betriebstemperatur
werden auch
Hierdurch können
Zuverlässigkeit
verbessert
Dünnschichtelektrolyten
man
Zirkonoxid einsetzt. Ziel dieser Arbeit
Abscheidung
von
sind. Für die
Potential 0.1 bis 10
um
Kapitel
2
dünne und
3 behandelt die
auf die Mikrostruktur der von
schliesslich in Ein
kostengünstige Beschichtungstechnologie
wird ein kurzer Überblick der
das Schichtwachstum wird in
Anwendung
Oxiden, welche als Elektrolyten für SOFC geeignet
gasdichte Oxidschichten
Technik
sowie
der
wichtigsten
Kapitel
4
Anwendung
Parameter der
vorgestellt.
abgeschiedenen
die
mit dem
abzuscheiden.
in
Bezug auf das
in
Sprühpyrolyse
Dünnschichtabscheidung
Sprühpyrolyse.
Ein Modell für
Der Einfluss der thermischen
Schicht steht im Fokus
gesprühten Dünnschichtelektrolyten in
Kapitel
Prozesses für die
Elektrolyte auf porösen Anodensubstraten wurde
Sie ist eine
dieser
präsentiert. Kapitel
von
solcher
Abscheidung
Funktionsprinzip
Entwicklung eines kostengünstigen
die
dünnen Schichten
Sprühpyrolyse gewählt.
In
war
von
Behandlung
Kapitel
5. Die
einer SOFC Brennstoffzelle wird
6 demonstriert.
Vergleich
von
zwei
Sprühpyrolysetechniken,
die
Elektrostatische
Spray-
Abscheidung (Electrostatic Spray Deposition (ESD)) und die Druckluft Spray-Abscheidung
(Pressurized
Spray
Oberflächentemperatur
Deposition des
wird
(PSD)),
Substrates
der
war
7
im
Kapitel
3
präsentiert.
Die
für
beide
wichtigste Prozessparameter
ZUSAMMENFASSUNG
Techniken, da das Gefüge der Schicht durch diesen Parameter ganz entscheidend bestimmt
Gefüge der Oberfläche auch stark
wird. Bei ESD ist das
von
der Abscheidezeit und der
Zusammensetzung der gesprühten Precursor-Lösung beeinflusst. Im Gegensatz hierzu sind diese Parameter bei der PSD Technik für die Ein weiterer Einblick in das
gegeben. Doppler
Tröpfchen-Transport
Der
Annemometer untersucht. Die
10
Tröpfchen grösser
den
einem Abstand für die
1
dass
10
um)
des
Abscheidungstemperatur
führt
rauen
Schichten oder
zu
zu
Die in
Kapitel
ohmschen
Pulver führt. Im
grossen
über der
Gegensatz
zu
zu
tiefe
zu
hohe
Temperatur
den meisten Autoren, der
Schichten keinen CVD Prozess einschliesst.
amorph und kristallisieren
der Schichten. Die
abgeschiedenen
Wärmebehandlung ohne
während eine
Kristallitgrösse
von
12
nm
Risse
zu
werden nach einer
700°C erhalten.
Anwendung der Sprühpyrolyse für die Elektrolyte für die SOFC Technologie wird
vorgestellt.
6
Verlust
Brennstoffzellen
Mittels
Zwischenschicht
von
Hier
und
YSZ
von
Luft betrieben und erreichten eine dass eine dichte und rissfreie 770°C
Elektrolytdoppelschicht tolerierbarer
Betriebstemperatur der Festelektrolyt-
die
wird
einer
10
mol%
Beibehaltung hoher Leistungen. Yttriumoxid
Leerlaufspannung
von
Elektrolytschicht vorliegt. wurde
erreicht.
Sprühpyrolyse
von
Zellen
Diese Zelle
von
Ceroxid
dotierten
abgeschieden.
Die
600°C bis 800°C mit Wasserstoff als Brennstoff gegen
mit
einem 500
8
1.01 V bei 720°C. Dies hat
Hohe
Leistungsdichten
einer
600
nm
nm
Poren mit Größen
dünner
von
dünnen
wurde bei 720°C über 450
Degeneration betrieben. Überraschend,
wurden mittels die
Dünnschichtelektrolyten mit niederen
wurden auf poröse NiO-YSZ Anodensubstrate
Temperaturen
mW/cm2 bei
wurden
1000°C auf 700°C reduziert unter
(CYO)
Zellen wurden bei
Sprühpyrolyse
hergestellt.
Elektrolytdoppelschichten
750
wohingegen eine
Rissen in der Schicht,
bilden. Schichten mit einer durchschnittlichen
Glühung bei
die
Eine
soll.
liegen
Precursor
gesprühten
Kapitel 5 konzentriert sich auf die Gefüge
Schichten sind
wurde ab
möglicher Wachstums-Mechanismus
Oberflächentemperatur des Substrates und
vorgeschlagene Wachstums-Model für die Das
von
Abscheidungsprozess bestimmen wird vorgeschlagen. Ausserdem
Zersetzungstemperatur
zu
Tröpfchenverdampfung
Bildung glatter Oxidschichten die Oberflächentemperatur
die
für
Gegensatz dazu wird die Volumen-Verteilungen
Substrat beobachtet. Ein
dem die
den
die kleiner als 10 (im sind dominieren die
Tröpfchen
Im
4
Substrat wurde mittels einen Phasen
zum
dominiert. Wesentliche
um
cm zum
Schichten bei
Tröpfchen (> folgt,
von
der Düse bis
Sprühpyrolyse wird in Kapitel
der
Funktionsprinzip
von
statistische-Verteilungen der Anzahl.
Schichtmorphologie von geringer Bedeutung.
von
gezeigt,
mehr als
YSZ/CYO
Stunden mit bis
zu
3
Elektrolytschicht abgedeckt.
um
ZUSAMMENFASSUNG
Zusammenfassend
kann
man
feststellen,
dass
vielversprechende Dünnschicht Abscheidungsmethode ist. Die
Ergebnisse
dieser Arbeit
zeigen,
die
Sprühpyrolyse
9
eine
für die dünne und dichte Metalloxide
dass diese Technik
Technologie angewendet werden kann.
Technik
erfolgreich
in der SOFC
ZUSAMMENFASSUNG
Seite Leer /
Blank leaf
X
1.1
Aim of the
Ceramic thin film
study
are
widely used
resistance, in optical applications,
thin and gas
pyrolysis sized
process is
a
as
tight
ceramic
simple
and low
spray
coatings cost
for the
processing
robust and when
at
a
temperatures
it
layers
on
(YSZ), AI2O3,
equipment
yields oxide films
homogeneous layers composition
precursor solution
for thin film
occurs
with
(about
problems
performance of
500°C. The spray
as
deposition
and
nm-
lot of advantages
a
simple,
quality
to
at
the method is
rather low costs.
including Y2O3
This process has the
potential
to
are
spray
produce
thin
heated, the formation of the oxide layers
the substrate surface on
by pyrolysis
the substrates
is determined
study
was
as
150
the
development
electrolytes
can
be
and very
expected.
The
solely by the composition of the
directly
such
SOFC.
as
of
an
inexpensive manufacturing
for Solid Oxide Fuel Cells
process
(SOFC). Solid oxide
into electrical energy. The state of the art SOFC is
conductivity
of
required. The high temperatures lead
to
um) zirconia electrolytes.
zirconia, operating temperatures of 900-1000°C material
of high
potential
only.
oxides, suitable
thick
on
deposited layers
fuel cells convert chemical energy on
directly
thermal barriers.
as
process,
good adhering interfaces
of the
The aim of this
based
MgO.
is rather
wear
coating
different substrates. As the substrates
from precursor solutions
cation
and
low
as
for ceramic thin film
Many coatings have already been prepared by the stabilized zirconia
well
coating technique that offers
of ceramic films. The process
properly controlled,
as
This method has the
pyrolysis.
technique
powder production. Spray pyrolysis is
for
protective layers against corrosion,
and electrical devices
as sensors
produced by
Ceramic thin films may be
produce
Introduction
are
Due to the low ionic
material inter-diffusion and chemical reactions
Therefore, reduction of
the
degrading the
operating temperature from 1000°C
to
700°C is desirable in order to avoid material interdiffusion and to reduce system costs. In order to lower the ohmic
losses,
one
option is
to thin down the zirconia
11
electrolyte.
INTRODUCTION
1.2 Strategy
In this
study
stabilized zirconia
we
(YSZ)
apply
and Y2O3
Spray pyrolysis consists of droplets, study
and
pyrolysis
includes
the
characterization of the
the spray
an
pyrolysis technique for the deposition of yttria
doped CeÜ2 films
atomization of
of the salt
on
identification
a
on
dense
as
well
salt-containing liquid,
critical
coating and characterization
films.
12
spray
process
porous substrates.
the transport of spray
the substrate to form the ceramic
of
as
coating.
The present
parameters,
of the microstructures of the
electrical
deposited
Zi D.
pyrolysis
State of the art: spray
Perednis, L.J. Gauckler (to be submitted
to Journal
ofElectroceramics)
Abstract
The spray
These films cells. The
were
pyrolysis technique
has been
applied
used in various devices such
properties
of
deposited
thin films
as
parameter spray
and
deposit
wide
a
variety of thin
films.
solar cells, sensors, and solid oxide fuel
depend highly
extensive review of the effects of spray parameters
importance
to
on
film
on
the
quality
preparation is
given
to
conditions. An
demonstrate the
of the process parameters. The substrate surface temperature is the most critical
as
it influences film
roughness, cracking, crystallinity,
pyrolysis technique, such
decomposition of the
as
precursor
atomization of the precursor solution, aerosol transport, are
discussed in this review.
mechanism of film formation have been modified CVD process
occurs
etc. Processes involved in
published
so
far.
Only rough models
about the
Many authors have suggested that
a
close to the substrate. However, many observations contradict
the involvement of CVD process
during
the spray
13
pyrolysis process.
STATE OF THE ART: SPRAY PYROLYSIS
2.1 Introduction
based
the nature of the
on
methods gas
deposition
process. The
deposition
can
be divided into two groups
physical methods include physical
vapour
ablation, molecular beam epitaxy, and sputtering. The chemical
laser
deposition (PVD),
for thin oxide film
employed
The methods
comprise gas phase deposition methods and solution techniques (Figure 2.1). The
phase methods
(ALE) [3], while
chemical vapour
are
deposition (CVD) [1,2] and atomic layer epitaxy and
pyrolysis [4], sol-gel [5], spin- [6]
spray
methods
dip-coating [7]
employ precursor solutions. CHEMICAL DEPOSITION PROCESSES x
X
Gas Phase
Solution X
X
Spin Coating
I Spray Pyrolysis
X
Figure 2.1 Chemical thin
film
Spray pyrolysis is ceramic
coatings,
represents
a
very
simple
and
Spray pyrolysis does
been
employed
for the
multi-layered
processing technique
a
cost.
Even
deposition methods.
pyrolysis has been used
spray
can
electrodes
pyrolysis equipment
air blast
(ultrasonic frequencies produce and electrostatic
(liquid
Various reviews and
Radding
is
(liquid
the short
exposed to
concerning
a
consists
specific
or
chemicals. The method has
of
exposed
electric
in solar cell
[9]. an
atomizer, precursor solution,
to a stream
of
are
usually
atomization) [11]
field) [12]. have been
pyrolysis method, properties (particularly CdS),
published. Mooney
of the
and device
deposited
films in
application [13].
preparation and the properties of sprayed films 14
used in
air) [10], ultrasonic
necessary for fine
pyrolysis techniques
films
Tomar and Garcia have discussed the
is
glass industry [8] and
following atomizers
wavelengths
high
spray
have reviewed the spray
relation to the conditions,
pyrolysis
method, especially regarding equipment
for several decades in the
pyrolysis technique:
spray
easily prepared using this versatile technique. Spray
be
substrate heater, and temperature controller. The spray
deposition techniques,
films, porous films, and for powder production.
of dense
production to deposit electrically conducting Typical
dense and porous oxide films,
require high quality substrates
deposition
films
cost-effective
relatively
not
to prepare
Unlike many other film
powders.
and
Dip Coating
Sol-Gel
ALE
CVD
as
well
STATE OF THE ART: SPRAY PYROLYSIS
as
their
Risbud
application presented
materials
a
in solar
review of the
deposited by
spray
solar cell materials
spraying
cells, anti-reflection coatings and gas
equipment, processing parameters
pyrolysis technique [15]. Pamplin as
technique [16]. Recently thin
well
as a
metal
bibliography
oxide and
pyrolysis and different atomization techniques
chalcogenide
were
of sprayed YSZ films
Powder
chapter.
The
synthesis
has
of references
reviewed
Gauckler have discussed the mechanism of chemical spray
examples
sensors
[14]. Albin and
and
optoelectronic
published on
films
review of
the spray
pyrolysis
deposited by
by Patil [17].
deposition
a
and
spray
Bohac and
presented
some
[18].
and film
deposition using
application of these thin films
in solar
pyrolysis
cells,
gas sensors, solid oxide fuel
and other devices will be described. The models for thin film will also be reviewed.
15
will be discussed in this
spray
deposition by
spray
cells,
pyrolysis
STATE OF THE ART: SPRAY PYROLYSIS
2.2 Powder production
concerning powder preparation via
The first patents
[19]. Since then
1950s
fine be
with
produced
atomized to
dryer,
homogeneous
droplets which
then the
thermolysis
are
droplets undergo solvent evaporation, in the
particle decomposes
particles
are
to
means
finally
a
by spraying
reviewed
Pratsinis
Messing
of
a
carrier gas flow
precipitation, forming
reactor
the precursor solution into
the solution is
through
a
a
and drying. The
a
diffusion
dryer,
dry precipitate
microporous particle.
powders
from the aerosols
flame. This
the
technology
These
can
also
recently
was
[20].
al. have reviewed the spray
et
spray
calcination furnace. In the diffusion
precursor
thermolysis
on
composition. During synthesis
then sintered in the calcination furnace. The
be obtained
by
high-purity, unagglomerated, nm-sized particles
chemical
and
date back to the
of
passed by
reactor
pyrolysis
pyrolysis processing
many studies have been conducted
because the method enables
powders
spray
pyrolysis techniques
in terms of process
parameters that control the formation of powders [21]. Spray pyrolysis results in particles with
morphologies
from solid, to hollow and porous, and
concluded that the
even
fibers
of the solution and the precursor
properties
can
can
be obtained. It
strongly
was
influence the
particle morphology.
O
Crystallization
Decomposition
Drying
(g) ® «=> o
.=>
Hollow
particle
Droplet
Figure 2.2 Powder production.
Submicron
have been
spherical particles
synthesized using
the spray
flame-assisted ultrasonic spray
particle-size the
distribution
synthesis
plastic
deformation
or
tetragonal
et
2 mol%
yttria-stabilized
pyrolysis technique [22].
pyrolysis technique
[23]. Zhang
of fine, solid
of
to prepare YSZ
is that the
melting during heating, because 16
(YSZ)
Yuan et al. have used the
al. have demonstrated that
spherical particles
zirconia
powders
an
with
important
precipitated salt does
a narrow
criterion for not
undergo
this leads to the formation of shells of
STATE OF THE ART: SPRAY PYROLYSIS
low
permeability [24]. Consequently,
the residual solvent is
drying droplet (see Figure 2.2) resulting
easily evaporate through
the shell.
high
salt
previously
solubility is
stated
Using
an
in the
core
of the
increase of pressure, because the solvent cannot
Therefore, the shell cracks producing secondary droplets
powders
and broken shell relics which leads to that
in
entrapped
not necessary
of irregular
shape.
The authors also concluded
for the formation of solid and uniform
particles
as
by others [25].
spray
pyrolysis
powders
which contained
powders
with 10 wt%
silver and mixed-oxide
a
large
Ag which
phases
claimed to favourable for
900°C, Gurav
at
number of
were
with
a
al.
synthesized (Bi, Pb)-Sr-Ca-Cu-0
nano-particles (
decomposition
visible. The strong exothermic
mass
zirconium
acetylacetonate decomposes
Further
loss is attributed to the loss of two
weight
TG
!
-
-80
|
S
-100
.90
200
400
600
800
10
Temperature [°C] Figure.
4.20.
decomposition
In
Thermal in air at
a
analysis
zirconium
acetylacetonate
Zr(CsH702)4
heating rate of 10°C/min.
nitrogen atmosphere,
stages and is complete
of
curves
at
much
the zirconium
acetylacetonate decomposition
higher temperature compared
90
to
the
involves
decomposition
more
under
an
A MODEL FOR FILM DEPOSITION BY SPRAY PYROLYSIS
oxidizing atmosphere [15]. The decomposition
of two
starts at 150-200°C with the release
C3H4 after the reaction:
Zr(C5H702)4
The
formed
Zr(CH3COO)2(C5H702)2
of zirconium acetate and
complex
ZrO(CH3COO)2
->
at 340°C. At
Finally,
at 800°C
the
decomposition
is
->
Z1OCO3
It follows
that, under
necessary to
ZrOC03
completed
-»
+
as
formed
and Z1O2 is formed:
Zr02
+
C02
to zirconium
deposition temperature
we
measured the
increasing temperature. Thermogravimetry
solvent mixture
(ethanol
acetylacetonate
at
and
butyl carbitol)
10°C/min in air
curves
to
at 75°C
atmosphere
are
shown in
and 175°C. The first process at 75°C
carbitol has the
below 200°C,
although
highest evaporation
the
zirconium
acetylacetonate
via three
weight loss
boiling point
Figure 4.21.
solvents start to evaporate at
attributed to the
peaking
slightly
at
can
loss of the
recorded for
of the pure
The
weight
curves
a
pure
butyl
and is
evaporation.
evaporated completely
carbitol is at 230°C. When
mixture, the precursor solution decomposes
58°C, 1170C and 163°C. This
means
lower temperatures. The process at 117°C
decomposition of Zr(C5H702)4,
91
indicate
loss processes
be attributed to ethanol
rate at 175°C
is added to the solvent
processes
weight
and the solvent mixture with dissolved zirconium
that the solvent mixture without dissolved salt evaporates via two
butyl
oxide, compared
are
in the air.
precursor solution with
The
to
follows:
nitrogen atmosphere, temperatures approximately 300°C higher
a
To estimate the minimum
peaking
decomposes
CH3COCH3
decompose the zirconium acetylacetonate
decomposition
2C3H4
acetylacetonate
450°C, ZrOC03 is formed
ZrO(CH3COO)2
+
which
seems
to be
that the can
completed at 200°C.
be
A MODEL FOR FILM DEPOSITION BY SPRAY PYROLYSIS
It
further
can
be concluded that
decomposition
in ethanol and
compared
route
acetylacetonates decompose via
depends
butyl carbitol mixture,
to the
the gas
on
it
atmosphere.
decomposes
to
a
When
Zr02
at a
melting phase and the
Zr(C5H702)4
is dissolved
much lower temperature
decomposition of solid Zr(C5H702)4-
•Zr(acac)4 -
100
200
EtOH
+
+
EtOH
+
Butyl Carbitol
Butyl Carbitol
300
400
500
Temperature, [°C] Figure. at a
4.21.
Thermogravimetry (TG)
of solvent and precursor solution
heating rate of 10°C/min.
92
decomposition
in air
A MODEL FOR FILM DEPOSITION BY SPRAY PYROLYSIS
4.6
Film
model
growth
4.6.1 Summary of the spray parameter study
The spray parameter
given
in order to derive
a
study
presented
model for the film
influence of a spray parameter In the case of the ESD
was
on
the film
temperature, the type of precursor salt, the
deposition
morphology
solvent in the
case
was
also influenced
of the PSD
It
was
suppressed
solvents with rather low
Using
cracking
boiling points
by
to very porous or
the
deposition
occurs
at
were
case
the
and the type of
deposition to
the
temperatures.
lower substrate temperature when
higher boiling points.
prepared only by spraying
of the PSD, dense films of
acetylacetonate
at
fractal like.
in contrast to the ESD, the
used instead of solvents with
are
quality films
zirconium
pyrolysis setup.
significant effect. Polymer additives
a
of films
precursor solution. In the
deposited not only using
influenced
somewhat crack formation at low substrate
the ESD setup, the best
acetylacetonate
the spray
deposition temperature
technique. However,
demonstrated that
observed that the
was
the substrate temperature. The number of
the
by
time and the type of precursor salt did not have precursor solution
short summary is
and the type of solvent. The main
highest deposition temperature, the film morphology changed The
on
a
increasing deposition temperature. Finally,
the surface increased with
on
was
deposition time, was
Here
process. It
morphology
parameter that determined the film morphology
particles
chapter 3.
morphology depends
film
technique, the
earlier in
precursor, but also
the zirconium
good quality
by spraying
were
zirconium
nitrate solution.
4.6.2 Model for film deposition
Spray pyrolysis involves sequentially.
The most
many
important of these
impact with consecutive spreading and and observations,
a
film
growth
processes are
aerosol
precursor
model will be
process into two stages: before and after
occurring either simultaneously
generation and transportation, droplet
decomposition. Based
proposed.
droplet impact
93
or
on
the above results
We will divide the spray
onto the substrate. In
pyrolysis
the first stage,
A MODEL FOR FILM DEPOSITION BY SPRAY PYROLYSIS
the processes
occurring during the droplet transport will be taken into
stage, film formation
on
the substrate surface will be considered.
In the first stage, the
Solvent that
evaporation is the
important 4.4 and
(Figures
at
from the nozzle to the heated substrate. this stage. PDA measurements indicated in the last 10
place predominantly The
4.11).
largest droplets (larger they contain
mm
before the substrate
the
large droplets evaporate
initial size
larger than
onto the substrate.
precipitation during than 3
u,m
the
20
urn
much slower
most of the precursor salt
Therefore, in the
case
is
droplet transportation
in diameter behave
compared change
in diameter do not
of large
to
the
the small
in size
significant
contributions to the
presence of many almost
dry droplets
of
growth
a
dense film
until or
they
solute
completely before
shown in
as
Droplets
with initial size smaller
reaching the substrate surface. Therefore, they will increase surface roughness make
(Figures
ones.
droplets, powder formation
improbable. Droplets
a more
large droplets.
significantly
Their solvent evaporates
differently.
urn) play
than 10
4.9). Therefore, deposition temperature should be optimized for
an
impact
transported
important process
takes
4.7 and
are
role than the small ones, because
Additionally, with
droplets
most
significant evaporation
is reached
the second
account. In
in the spray leads to porous and
and will not
Figure
rough films
4.16. The or
powder
only.
Stick
Rebound
Splash
Spread &
Spread
Contract
Figure. 4.22. Droplet impact
onto a
The first stage ends when results of
droplet impact
rebound, spread formation of
depends the
on
a
its
or
splash
are
on
dense film
heated substrate.
a
droplet impacts
shown in
the surface. The
or
to
rings. The
retarding thermophoretic
forces which
the substrate. The five
droplet hitting
A
spreading
of
are
are too
are
too
strongest close
viscous
or
droplet
small to
dry, they
fast, they will splash. If the droplets spread but the velocity is
94
possible
the surface may
impacted droplets
sequence after the
size, viscosity and velocity. If droplets
temperature gradient is largest. If they too
Figure 4.22.
onto
they
can
stick,
lead to the
has hit the surface
will rebound due to
the substrate, where the will stick and if
too
high, rings
are
they
are
formed.
A MODEL FOR FILM DEPOSITION BY SPRAY PYROLYSIS
Consequently, only
of
spreading
the
with not too
droplets
high
velocity
a
will lead to the
formation of a dense film. After chemical of the
the second stage of spray
droplet impact,
properties
of a precursor solution
impacted droplet,
the
evaporation
play
smooth films.
The substrate should
tensile
strength,
contains disk
stress
just
the film fractures
sufficient amount of
(Figures
4.21 and
less solvent. These
consequently Finally,
more
(Figures
can
on
to
the formation of
to
develop
for solvent due to
liquid
the surface leads to
a
and when the stress exceeds the local
4.18a and
the zirconium
spreading
When the
4.19a).
over
impacting droplet
the substrate surface and forms
acetylacetonate
melts and
decomposes
a
to
4.22). With increasing temperature, the impacting droplets contain
nearly dry droplets particles
will
droplet reached the substrate, and, It
spread droplet
solvent, it spreads
will stick
as
on
the film
occur on
high deposition temperatures,
at too
a
liquid but viscous film,
shaped splat. Simultaneously,
oxide
not the case, cracks will
drying. The contraction of
in the still
droplets leads
and
decomposition
heat and temperature
provide enough
evaporation and salt decomposition. If this is
of
of
physical
In this stage, the
of residual solvent and precursor
place simultaneously. Fast spreading
build-up
starts. Then the
important role.
an
the oxide take
film contraction upon
pyrolysis
the substrate without
as
shown in
the solvent of the
Figures
spreading,
and
4.19b and 4.19c.
droplets evaporates before
the
result, powder will be obtained.
be concluded that the crucial
points
in
our
model is to avoid
complete solvent
evaporation in the droplet during transportation, because this leads either to powder formation or
on
the
particular, acetylacetonates which melt during decomposition, improve
the
deposition of rough films,
substrate. In
spreading
behaviour of
a
spreading of impacted droplets
and to enhance the
droplet
on
the
substrate, and consequently enable the deposition of
smooth, dense films. Chen et al. it
was
proposed
a
model for the formation of a porous film
considered necessary that the wet
model for dense film
concentration
structure.
slow
the salt concentration
ring-shaped splat.
gradient
These three
were
necessary to obtain porous films. It
was
on
the substrate and
spreading droplet is
dimensionally cross-linked rings
suggested
most
important parameters
necessary to
form
a
porous
solution, and the for the
that the type of precursor salt have
95
model,
salt
droplets
within the
boiling point of the solvent were found to be the
our
a
of
The substrate surface temperature, the surface tension of the
of porous films. The authors also
As in
reach the substrate surface. In contrast to the
spreading
gradient within the obtained splat
suggested that obtain the
deposition,
droplets
[16].
deposition
an
influence
A MODEL FOR FILM DEPOSITION BY SPRAY PYROLYSIS
on
porous film
of acetates
as
formation, because the
are
was
not
obtained
models
growth
involving
the CVD process
that dense and smooth
assume
formed, when both the solvent and the precursor salt completely vaporize before
droplet reaches
the substrate
of
measurements
[4, 5, 17]. However, low deposition temperature and
droplet evaporation
in contradiction to
are
solvent is not
analysis
of salt
no
but not in air. In
nitrogen atmosphere
a
droplets
showed that the CVD model is
decomposition
temperatures and under observed
of
completely evaporated before the spreading
indication of a CVD process involvement in spray
our
a
PDA
CVD process. The PDA
a
measurements indicated that for formation of dense and smooth film it is
thermal
nitrates instead
using
precursors.
The film
films
porous structure
important
on
the surface. The
possible
our
that the
much
at
experiments,
higher
we
have
pyrolysis.
4.7 Conclusions
Droplet transport and evaporation in PDA. Similar
jet spraying
droplet size
mode. In both cases, the
smaller than 10 urn, and the 10
droplets larger than mm
on
the other
10 p.m.
in the
distance, i.e. 5 In the
mm
case
number distribution
the ESD
of spraying in the ESD
the temperature, the film
large droplets
dominated by
droplets
dominated
was
begins only
at
a
by
distance of
larger temperature
mode. Due to the
very
cone-jet mode,
and all of them
rapidly
containing
Therefore, the deposition temperature is the
large droplets (>
of solvent
multi-jet
many
droplets reaching the substrate should
on
was
hand, the droplet volume distribution
significant evaporation
the substrate. This resulted in films
Based
investigated using
of solvent starts at
even
smaller
from the substrate.
droplets evaporated
follows that
were
processes
obtained for the PSD system and the ESD multi-
droplet
case
of the PSD,
case
were
pyrolysis
Significant evaporation
from the substrate in the
gradient
These
distributions
spray
morphology can change
the present results, 10
um)
contain
of the precursor. The
most
are more
a
droplets
were
nm
important be
smaller than 1
sized
particles
30
mm
from
the surface. It
on
dense and smooth film.
a
important
parameter. By increasing
in film
a
spray
cracked to
on
growth
a
porous microstructure.
proposed.
was
than the small
The
droplets. These
the substrate and carry most of the
of acetylacetonates, which melt
96
urn
um.
be wet to obtain
from
spread
smaller than 7
were
plausible film growth mechanism
enough solvent to use
all
during decomposition,
mass
is beneficial
A MODEL FOR FILM DEPOSITION BY SPRAY PYROLYSIS
for the formation of a
smooth, dense film. The proposed film growth model does
CVD process.
97
not
involve
a
A MODEL FOR FILM DEPOSITION BY SPRAY PYROLYSIS
4.8
[I]
References
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International, 22(3),
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Will, A. Mitterdorfer, C. Kleinlogel, D. Perednis and L.J. Gauckler, "Fabrication of thin electrolytes for second-generation solid oxide fuel cells", Solid State Ionics, J.
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[3]
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Kodas, T. Pluym and
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KX.
Matsuzaki, M. Hishinuma and I. Yasuda, "Growth of yttria stabilized zirconia thin films by metallo-organic, ultrasonic spray pyrolysis", Thin Solid Films, 340(1-2), p. 72-76, 1999.
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Chen, E.M. Kelder, P.J.J.M. van der Put and J. Schoonman, "Morphology control of thin LiCoC>2 films fabricated using the electrostatic spray deposition (ESD) technique", Journal of Materials Chemistry, 6(5), p. 765-771, 1996.
[8]
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Segato and P.H. Duvigneaud, "Formation of MgO ultrasonic spray pyrolysis from beta- diketonate", Thin Solid Films, 283(1-2), O.
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H.B.
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V.V.
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CR.
YSZ thin films
Dyukov, S.A. Kuznetsova, L.P. Borilo and V.V. Kozik, "Film-forming capacity Zr(IV), and HfiTV) acetylacetonates", Russian Journal ofApplied Chemistry,
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[15]
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A MODEL FOR FILM DEPOSITION BY SPRAY PYROLYSIS
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"Unique porous LiCo02 thin layers deposition", Journal of Materials Science, 31(20), p.
CH. Chen, E.M. Kelder and J. Schoonman, electrostatic spray 1996.
Siefert, "Properties of Thin ln203 and Sn02 Films Prepared by Corona Spray Pyrolysis, and a Discussion of the Spray Pyrolysis Process", Thin Solid Films, 121(4), p. 275-282, 1984. W.
99
Seite Leer /
Blank leaf
100
3
Thermal treatment of metal oxide spray
pyrolysis layer D.
Perednis, L.J. Gauckler (to be submitted
to Solid State
Ionics)
Abstract
(SOFCs)
is
investigated.
conductivity
electrical
region
of 3-12
the spray
of
suitability
The
spray-deposited
YSZ films
obtained
pyrolysis technique.
on
presented.
No cracks
were
conductor
are
was
on
for solid oxide fuel cells
the film microstructure and
Dense films with
sapphire single crystals
SOFC
size in the
and Inconel 600 substrates
were
studied at temperatures
found that at 700°C the ohmic losses caused
sufficiently low for
grain
using
observed after thermal treatment at 800°C The
electrical conductivity of nanocrystalline thin films 700°C to 1000°C It
electrolytes
The influence of thermal treatment
of YSZ thin films is
nm were
as
applications
exceed 5.5 p.m.
101
by
ranging
from
the YSZ ionic
when the films thickness does not
THERMAL TREATMENT OF METAL OXIDE SPRAY PYROLYSIS LAYER
5.1 Introduction
Solid oxide fuel cells energy in
an
temperatures the
efficient
electrolyte
manner.
(>800°C).
is
can
be prepare
structure
pattern.
The
temperatures of up
to
were
600°C
deposition temperature
was
films and observed that the et al.
solid
and spray
simplicity,
pyrolysis
spray
on
following
the
deposited
on
the
was
nm
films
and
determination
of
the
peaks indicating nanocrystalline
Pyrosol
the
[2]. Choy
deposition temperature.
at
process et
al.
was
deposition
[7] found that the
The YSZ films
fully stabilized cubic zirconia
crystallite
characterized
evaluated very seldom from the XRD
to 30 nm
above 550°C. Ruiz et al.
were
deposited below
formed when the
[5] deposited nanocrystalline zirconia
size increased when the carrier gas
was
lighter. Nguyen
films [10] investigated the crystallinity of tetragonal 2 mol.% Y203-doped Zr02 thin
deposited by electrostatic flow rate
(2 ml/h)
at 400°C with spray
The
preparation by
from 20
ranged
size
grain
for
whereas
amorphous,
as
deposition (PVD)
vapor
identification
phase
for
size
crystallinity of a film depends 500°C
used
by various methods such as spin coating,
already been deposited by
(XRD)
grain
average
is
(YSZ)
alternative to the traditional methods because of its
observed. However, the
were
zirconia
structure. In many cases, wide diffraction
crystallographic
to reduce
[3], aluminium [4], steel [5], gadolinia-doped ceria [6], porous
Si
diffraction
x-ray
by high operating
limited
lowering the operating temperature is
La(Sr)Mn03 [7, 8], and La(Sr)Co03 cathodes [9].
using
are
production.
Thin YSZ films have
glass [1, 2],
for
deposition (CVD), physical
an
low cost and minimal waste
substrates:
SOFCs
Typically, yttria-stabilized
vapour
pyrolysis. Spray pyrolysis
the chemical energy of fuel into electrical
state of the art
However,
in SOFC. Thin YSZ films
sol-gel route, chemical
convert
possibility
One
thickness.
electrolyte
(SOFCs)
pyrolysis
a
at
deposition.
flow rate of 3.9 ml/h
are
Studies of
nanocrystalline
nanocrystalline
of up to 400°C
techniques
to
were
the
amorphous.
deposition
with
Films
films
a
low
deposited
deposited by
conditions. If not, the
amorphous
after thermal treatment.
materials
successfully
study
are
deposited
polycrystalline. Generally,
require
microscopy (TEM) and
may be
found that all films
was
under proper
nanocrystalline
Transmission electron
techniques which
It
deposition temperatures
structure transforms to
these two
spray
accurate
x-ray
grain
determination of the
diffraction
(XRD)
are
two
size.
major
used for structural characterization. We have used
grain growth in
102
YSZ films
deposited by
spray
pyrolysis.
THERMAL TREATMENT OF METAL OXIDE SPRAY PYROLYSIS LAYER
The aim of this work
was
to
study the properties of thin
thermal treatment.
103
YSZ films
as a
function of their
THERMAL TREATMENT OF METAL OXIDE SPRAY PYROLYSIS LAYER
5.2 Experimental
The details of the spray
conditions for YSZ thin films have been described on
and
used
to the
prepared according
an
aerosol
(Goodfellow) by
acetylacetonate (Fluka Chemie, Buchs, Switzerland)
and
precursor solution
was
of the
stoichiometry
by exposing
deposited
were
was
concentration of the salts in the solution to
deposition
(Fluka Chemie, Buchs, Switzerland)
The
(Aldrich Chemicals, Buchs, Switzerland).
chloride
yttrium
films
and Inconel 600 foils
ether
diethylene glycol monobutyl
solvent for zirconium
as
studies and the
(50:50 vol%) of ethanol (Fluka Chemie, Buchs,
precursor solutions. A mixture
Switzerland)
our
previously [11]. YSZ
sapphire single crystals (Stettler AG)
heated
spraying
used in
pyrolysis setups
was
it either to
required
0.1 mol/1. The precursor solution
stream of air
a
The total
(Zr02)o.92(Y203)o.os-
film
high voltage.
or
was
The
atomized
deposition
temperature ranged from 250°C to 350°C Film
topography and surface roughness
(AFM) (TOPOMETRIX Explorer). substrates air. The
(TEM)
were
heating
heat treated after and
cooling
deposition
of the films
crystallinity
and
X-ray diffraction (XRD).
were cut
case,
at
determined
on a
by
Philips CM30
The in situ a
For the TEM
was
studies, disks 100
um
sapphire
microscopy
thick and 3 were
mm
at 300 kV.
The
in
mechanically
The TEM studies
grain
were
size
was
imaging.
X-ray powder diffraction study of the deposited YSZ films
diffractometer
performed
on
electron
samples
with Ar ions.
microscope operating
chamber
In this case, the YSZ film
analyzed by
the
change
of
made
mean
grain
size
was
an
using X-ray
removed
X-ray powder diffractometer. The at
various temperatures
determined
by peak broadening
in steps of 0.02° and count times of 2
from 250 to 700°C The
was
(G.T.P. Engineering Co.) incorporated in
(Cu-K« radiation).
from the Inconel 600 substrate and then 2©-scan
deposited
investigated by transmission
was
electron
high temperature environmental
powder Scintag
the YSZ films
from the YSZ coated Inconel 600 foil. The
dark field
atomic force microscopy
500, 600°C, 700°C, and 800°C for 2 hours in
polished, dimple-grinded and finally ion milled
performed
analysed using
rates were set at 120 K/hour.
The
diameter
In this
were
was
s/step
measurements.
The surface
electron microscopy
morphology
of the
deposited films
(SEM) (LEO 1530).
104
was
characterized using scanning
THERMAL TREATMENT OF METAL OXIDE SPRAY PYROLYSIS LAYER
The dc
conductivity of the films deposited
using 4-point measurement
applying platinum paste out
using
a
as
and
Keithley digital
shown in
Figure
platinum wires
multimeter
on
sapphire single crystals
5.1. The four
on
parallel electrodes
was
were
the film surface. Measurements
(model 197A)
at
obtained made
were
carried
various temperatures in the range of
700-1000°Cinair.
YSZ film
Pt wires
Sapphire substrate
Figure
5.1. Sketch of experimental setup used for four
105
by
point conductivity measurement.
THERMAL TREATMENT OF METAL OXIDE SPRAY PYROLYSIS LAYER
5.3 Results
and discussion
5.3.1 Structural properties
The
crystallization
and
grain growth
in air of the YSZ films
were
X-ray powder diffraction. For this purpose, the YSZ film deposited 275°C
was
removed from the substrate. The
any influence of the substrate
on
film
separation of the film
studied using in situ Inconel 600 foil at
on
from the substrate avoids
crystallization.
»#'i'M«fiin>"n» *»>'*»*« 700°C *vM|ww. < >« inmw«"!»»! iw
600°C
500°C * 400°C 350°C
w»**ii»4«>
-
_
200
-
0 0
200
400
600
Cell Current
with
Current-voltage
6.13
Figure
800
1200
1000
[mA/cm2]
and current-power characteristics of
an
SOFC
anode-supported
sprayed electrolyte bi-layer (YSZ/CYO) (no.GSN76) and screen-printed LSCF cathode.
Additionally, YSZ/CYO
performance current
decreased at
loads,
protective
layer improved long
In contrast to the was
operated
was
term
720°C for
at
observed after 70 h of operation at
a current
rate
of -0.3 %/h. However,
for the power output loss
the LSCF cathode due to
are
mA/cm2
and 600
no
450 hours
degradation
mA/cm2.
protective
significant degradation
The cell with the
over
load of 240
load at 770°C, the power output of the cell without a
stability.
single layer electrolyte cells essentially
e.g. -0.02 %/h and -0.07 %/h at 360
reasons
(>300
CYO
bi-layer electrolyte (no.GSN76)
Figure 6.14).
same
the
CYO
occurred at
(see
of the
Under the
layer rapidly
higher
current
mA/cm2 respectively. Suspected
aging of the electrolyte bi-layer and the deactivation of
grain growth.
Also the
durability of anodes
at
high
current densities
mA/cm2) was found to be insufficient [26]. In
generated
spite of the decreasing performance a
reasonable power
density after
at
over
136
high
current
loads, the cell (no.GSN76) still
450 hours of operation at 720°C
(see Figure
SOLID OXIDE FUEL CELLS WITH ELECTROLYTES PREPARED VIA SPRAY PYROLYSIS
6.15).
A
relatively high
power output of 200
mW/cm2
was
obtained
even at
lower
operating
temperatures (620°C).
400
r^—-^
_
600
300
mA/cm2
-
E
360
o
mA/cm2
.
£
200
"240 mA/cm2
CD o
Q.
100
-
720°C 0 100
0
i
i
200
300
Time
Figure
6.14 Effect of current
400
500
[h]
density on the aging behaviour at 720°C (no.GSN76).
500
Cell Current
Figure
6.15 Power output of a
of operation
single
fuel cell with
(no.GSN76).
137
[mA/cm ] a
bi-layer electrolyte
after
over
450 hours
SOLID OXIDE FUEL CELLS WITH ELECTROLYTES PREPARED VIA SPRAY PYROLYSIS
6.3.3 Cells with composite electrolyte films
Although ceria based
[27].
YSZ is the favoured
electrolytes
On the other
are
hand, it is well known that in
[28].
is shown in
the
single layer
buffer
serves as a
the
through
ceria
The CYO/YSZ/CYO CYO
substrate, then the sample that temperature in order
protective layer
and cathode
The cell
electrolyte layer was
to
heated at
crystallize
deposited
was
multi-layer
serves as
the
expected
compared to ceria,
to
be lower
the
compared
to
a
was
rate
the film was
on
the
anode
was
sprayed by
deposited
use
of
an
air blast anode
of 2 K/min to 700°C and held for 2 hours at as
well
as
to
complete
subsequently deposited was
carried out
the LSCF cathode
770°C. As shown in the cross-sectional
the
onto a porous NiO-YSZ
previously deposited
then heated up to the
(Ni-YSZ cermet), multi¬
(LSCF).
multi-layer electrolyte
treating the protective CYO film, electrolyte.
is also
consisting of
The heat treatment at 700°C was
between the NiO-YSZ
a
CYO component between the YSZ and LSCF also
the Ce and Y compounds. A thin YSZ film
electrolyte.
solid oxide fuel cell with
of
option
The purpose of a YSZ film is to block electronic
solid oxide fuel cell
a
layer electrolyte (CYO/YSZ/CYO)
CYO
there is the
problem,
solid state reactions at the cathode side.
against
First, the
reducing atmosphere, ceria develops this
layer
multi-layer electrolyte
electrolyte. The
Figure 6.16 Sketch of
atomizer.
layer.
a
high specific conductivity
transference number of YSZ is much smaller
current. As the electronic
electronic current
active
a
overcome
6.16. The CYO
Figure
electrolyte and the catalytically
To
The sketch of
employing multilayer electrolytes. electrolyte
much attention due to the
attracting
electronic conduction
significant
electrolyte material for intermediate temperature SOFC,
the on
decomposition top of the
sprayed
again. Finally, another
YSZ film. Without
was screen
printed
working temperatures
onto
the
of
CYO
thermally multilayer
in the range of 700°C to
image (Figure 6.17), the multilayer electrolyte 138
SOLID OXIDE FUEL CELLS WITH ELECTROLYTES PREPARED VIA SPRAY PYROLYSIS
(no.SR3) grain
had many closed pores and
size of the
electrolyte
was
This either indicates that the cross-over
block
through the
CYO's
electronic
film
Figure
nm.
or
The
highest was
OCV value
not
nm.
0.85 V at 700°C.
was
sufficiently
dense to
multilayer
completely. The thickness
to 1200
nm
connected to the film surface. The
were
the YSZ component in the
conduction
electrolyte film varied from 400 needs to be
50 to 80
of them
multi-layer electrolyte
of gases
the
some
It is clear that the
prohibit the
structure did not
multi-layer
of the
quality
of the
multilayer
improved.
6.17 Cross-sectional
image
of
a
solid oxide fuel cell. From the top to the bottom:
screen-printed LSCF cathode, sprayed electrolyte multi-layer (CYO/YSZ/CYO) (no.SR3)
and
tape-casted anode substrate (Ni-YSZ cermet).
Although relatively generated
at 700°C.
Figure
low OCV values
6.18 shows I-V and I-P
multilayer electrolytes (no.SR2 were
0.5
g/h of hydrogen
similar power
and 32
performance
of the
curves
g/h
of air. At 700°C the
and
at
950
of two cells with CYO/YSZ/CYO
The gas flow rates
no.SR3).
mA/cm2
makes it
current
possible
multilayer electrolyte 139
during
the measurements
multilayer cell (no.SR3) generated
no.GSN71) operated
multilayer electrolyte, therefore,
70°C. The
measured, high power density could be
and
density of 540 mW/cm2
single layer electrolyte (no.P228 of the
were
load,
at 770°C
to
reduce
fuel cells
was
as
the cells with
(see Figure 6.7).
a
sprayed The
use
operation temperature by limited
by
the low OCV.
SOLID OXIDE FUEL CELLS WITH ELECTROLYTES PREPARED VIA SPRAY PYROLYSIS
Further
in power
improvements
by assuring
a
gas-tight
density
CYO/YSZ/CYO
and reductions in
operating temperature
electrolyte with
thickness of 1 to 5
a
can
be made
um.
600
900
800 700 E
600
g>
500
-I—'
>
400
Ü
300 200 100
0
Cell Current
Figure
6.18 Effect of spray parameters
layer electrolyte (o«) (no.SR3)
The
electrolyte
cells
stability
term
The CYO
using Ce(N03)3-6H20 (am) (no.SR2)
of the cell
or
layers
in multi¬
(NH4)2Ce(N03)ô
performance
also needs to be enhanced.
(no.SR2 and no.SR3) showed significant degradation. The major
damaged in hot spot
of -0.38 %/h at
a
current
similar conditions, the cell with at
performance.
appears to be the existence of many defects in the
were
degradation
either
fuel cell
salt solution.
long
degradation materials
sprayed
were
on
[mA/cm ]
a
areas
cause
electrolyte film.
of cell
The cell
leakage through these defects.
due to gas
load of 240
Multilayer
mA/cm2
was
bi-layer electrolyte (no.GSN76)
A
observed at 700°C. Under did not exhibit
degradation
all. Film
Previously, tightness
quality we
of
solution also
can
be
improved by optimizing
showed that the
sprayed plays
an
YSZ
electrolytes (see Figure 6.8).
Figure
ammonium nitrate solutions solutions
deposition temperature
important role in the
salt used is demonstrated in
the
has
a
The
pyrolysis
6.18. Much denser CYO
(no.SR3),
(no.SR2). Obviously,
spray
electrolyte deposition parameters. strong influence
composition
the gas-
of the precursor
process. The effect of the type of
layers
were
sprayed using
in contrast to the films obtained
using
cerium ammonium nitrate increases the
140
on
cerium
cerium nitrate
spreading
rate of
SOLID OXIDE FUEL CELLS WITH ELECTROLYTES PREPARED VIA SPRAY PYROLYSIS
droplets
on a
heated substrate, and
substrate. However, the
optimisation In
operating
improvement
of spray parameters is
spite of the low OCV,
CYO/YSZ/CYO a
consequently
multilayer
is
was
enhances the closure of pores in the anode
insufficient to close all pores. Therefore, further
required to deposit gas-tight CYO layers.
a
promising
an
attractive
cell
performance
was
obtained at 700°C. The
electrolyte which offers
fuel cell at temperatures from 500°C to 700°C.
141
the
possibility
of
SOLID OXIDE FUEL CELLS WITH ELECTROLYTES PREPARED VIA SPRAY PYROLYSIS
6.4
Conclusions
In the present paper,
with
approximately
and crack-free demonstrated
cells with
1
urn
we
thin
presented
electrolytes
electrolyte films
by
voltage
a
single
YSZ
atomizer. This indicates that
supported
anode
pyrolysis
SOFCs
process. Dense
NiO-YSZ anode substrates. This
on
was
was
close to the theoretical value for
electrolyte layer to
the
a
prepared using
an
air blast atomizer.
electrolytes deposited using
density
power
were
are
obtained
of 550
using
mW/cm2
an
was
an
reduced
was
by
the
deposition
bi-layer electrolyte achieved
a
high
of
a
CYO
power
layer
density
on
in
electrostatic
air blast atomizer. At
attained but
occurred due to the reaction between the LSCF cathode and the YSZ
degradation
with the
the spray
by
achieved that
higher quality films
OCV of 0.97 V and
degradation The
on
bi-layer electrolytes (see Table 6.4).
They exhibited higher OCV, compared
an
fabricated
prepared
were
the open circuit
Cells with
770°C
and discussed results
significant
electrolyte.
top of the YSZ. The cell
excess
of 750 mW/cm
at
770°C.
By depositing reduce the
a
CYO/YSZ/CYO
improvement outputs
are
The influence
of the SOFC. Good cell
operating temperature
700°C, however the degradation of the
rate was too
multi-layer electrolyte
promising
and the
high.
film is
for intermediate and low
deposition temperature
on
multi-layer electrolyte
pyrolysis
further attempt
performance
was
was
made to
demonstrated
at
Low OCV values indicated that further
required.
In
spite of that the high
power
temperature SOFC.
composition
of the precursor solution has
a
strong
the OCV of the cells.
We have shown that pores with sizes of up to 3
electrolyte
a
film
can
be
using the
spray
pyrolysis technique.
successfully applied in
SOFC
um can
by
a
500
nm
thin
We have demonstrated that spray
technology
142
be coated
as a
thin film
deposition technique.
Max. power
density [mW/cm2] 320
450
540
760
460
540
290
310
380
840
740 1010
970
880
810
OCV[mV] 400
700 700 770
770
770
770
Operation temperature [°C]
360
LSCF
LSCF
LSCF
LSCF
LSCF
LSCF
Cathode
320
NiO-YSZ NiO-YSZ
NiO-YSZ
NiO-YSZ
NiO-YSZ
NiO-YSZ
Anode
[mW/cm2]
0.4-1.2
0.3-1.5
0.4-0.8
0.3-0.5
0.7-1.4
0.5-1.2
Electrolyte thickness [jum]
mA/cm2
CYO/YSZ/CYO
CYO/YSZ/CYO
YSZ/CYO
YSZ
YSZ
YSZ
Electrolyte
Power at 550
SR3
SR2
GSN76
GSN71
P229
Summary ofthejuel cell performances
P228
Table 6.4
SOLID OXIDE FUEL CELLS WITH ELECTROLYTES PREPARED VIA SPRAY PYROLYSIS
6.5
[I] [2]
Singhal, "Advances
S.C.
4),
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E.
Wiessen,
U.
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Commercial Solid Oxide Fuel Cells", in Fith ed.
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Huijsmans,
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Voisard,
C.
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Badwal, R. Délier, K. Foger, Y. Ramprakash and J.P. Zhang, "Interaction
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between chromia
[4]
Ishihara, H. Matsuda and Y. Takita, "Doped LaGa03 Perovskite Type Oxide as a New Oxide Ionic Conductor", Journal of the American Chemical Society, 116(9), p. 3801-3803, 1994.
[5]
M. Gödickemeier and L.J.
T.
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[6]
S.W. Tao, F.W. Poulsen, G.Y. Meng and O.T. Sorensen, "High-temperature stability study of the oxygen-ion conductor Lao.9Sr0.iGao.8Mgo.203.x", Journal of Materials
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[9]
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Design Based
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Electrolytes",
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Will, A. Mitterdorfer, C. Kleinlogel,
B.C.H.
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414(6861), [10]
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S.A. Barnett, "A New Solid Oxide Fuel Cell
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p.
D. Perednis and L. J.
"Materials
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fuel-cell
technologies", Nature,
Ban, "Properties of sprayed YSZ buffer layers on alumina substrates for YBCO thick films", Journal ofAlloys and Compounds, 268(1-2), p. 226-
Y. Matsuoka and E.
232, 1998. Beltran, C. Balocchi, X. Errazu, R.E. Avila and G. Piderit, "Rapid Thermal Annealing of Zirconia Films Deposited by Spray Pyrolysis", Journal of Electronic Materials, 27(2), p. L9-L11,1998.
[II]
N.H.
[12]
T.
Setoguchi,
K.
Eguchi
and H.
Solid Oxide Fuel Cells",
Arai, "Thin film fabrication of stabilized zirconia for
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Applications, ed. S.X. Zhou and Y.L. Society for Optical Engineering, p. 74-79. [13]
CH.
Chen, E.M. Kelder, P.J.J.M.
van
[14]
I.
Taniguchi,
Film
R.C.
Cathodes
van
for
"Morphology control spray deposition (ESD)
der Put and J. Schoonman, the electrostatic
films fabricated
using technique", Journal ofMaterials Chemistry, 6(5),
of thin LiCo02
p.
765-771, 1996.
Landschoot, H. Huang and J. Schoonman, "Preparation of Thin
Intermediate-Temperature 144
Solid
Oxide
Fuel
Cells
Using
SOLID OXIDE FUEL CELLS WITH ELECTROLYTES PREPARED VIA SPRAY PYROLYSIS
Spray Deposition", in Fifth European Solid Oxide Fuel Cell Forum, ed. J. Huijsmans, vol. 1, (2002), European Fuel Cell Forum Oberrohrdorf Switzerland, p.
Electrostatic 297-304.
[15]
[16]
Choy, W. Bai, S. Clarojrochkul and B.C.H. Steele, "The development of intermediate-temperature solid oxide fuel cells for the next millennium", Journal of Power Sources, 71(1-2), p. 361-369, 1998. K.
T.
Setoguchi,
Eguchi and H. Arai, "Application of the Stabilized Prepared by Spray Pyrolysis Method to SOFC", Solid State Ionics,
M. Sawano, K.
Zirconia Thin Film
40-41, p. 502-505,1990.
[17]
Charpentier, P. Fragnaud, D.M. Schleich and E. Gehain, "Preparation of thin film SOFCs working at reduced temperature", Solid State Ionics, 135(1-4), p. 373-380,
P.
2000.
Michaels, "Growth Rates and Mechanism of Electrochemical Vapor Deposited Yttria-Stabilized Zirconia Films", Solid State Ionics, 37(2-3), p. 189195, 1990.
[18]
M.F. Carolan and J.N.
[19]
Honegger, E. Batawi, C. Sprecher and R. Diethelm, "Thin Film Solid Oxide Fuel Cell (SOFC) for Intermediate Temperature Operation (700°C)", in the Fifth International Symposium on Solid Oxide Fuel Cells (SOFC-V), ed. U. Summing, S.C. Singhal, H. Tagawa and W. Lehnert, vol. 97-18, (1997), The Electrochemical Society, Inc., Pennington, NJ, USA, p. 321-329.
[20]
M.
[21]
N.Q. Minh and K. Montgomery, "Performance of Reduced-Temperature SOFC Stacks", in the Fifth International Symposium on Solid Oxide Fuel Cells (SOFC-V), ed. U. Stimming, S.C. Singhal, H. Tagawa and W. Lehnert, vol. 97-18, (1997), The Electrochemical Society, Inc., Pennington, NJ, USA, p. 153-159.
[22]
Herle, R. Ihringer, R.V. Cavieres, L. Constantin and O. Bucheli, "Anode supported solid oxide fuel cells with screen-printed cathodes", Journal of the European Ceramic Society, 21(10-11), p. 1855-1859, 2001.
[23]
K.
Schaper and G. Schiller, "Development and Characterization of Vacuum Plasma Sprayed Thin Film Solid Oxide Fuel Cells", Journal of Thermal Spray Technology, 10(4), p. 618-625, 2001. Lang,
R. Henne, S.
J. Van
C.C.
Chen, M.M. Nasrallah and H.U. Anderson, "Cathode/Electrolyte Interactions and
Performance", in the Third International Symposium S.C. Singhal and H. Iwahara, vol. 93-4, (1993), on Solid Oxide Fuel Cells, ed. Electrochemical Society, Pennington, NJ, USA, p. 598-612.
their
[24]
Expected Impact
Chen, M.M. Nasrallah and H.U. Anderson, "Synthesis and Characterization of (Ce02)(o.8)(SmOi.5)(o,2) Thin Films from Polymeric Precursors", Journal of the T.
Society, 140(12),
p.
3555-3560, 1993.
Barnett, "Increased solid-oxide fuel cell power density using layers", Solid State Ionics, 98(3-4), p. 191-196, 1997.
Tsai and S.A.
interfacial ceria
[26]
SOFC
C.C.
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on
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Mogensen, "Improving durability of SOFC stacks (IDUSOFC)", (2000),
European Solid Oxide Fuel Cell Forum, ed. A. J. McEvoy, vol. 1, Fuel Cell Forum, Oberrohrdorf, Switzerland, p. 141-150. European in Fourth
[27]
B.C.H.
Steele, "Appraisal
of
Cei.yGdy02-y/2 electrolytes
500°C", Solid State Ionics, 129(1-4),
p.
95-110,
145
2000.
for IT-SOFC
operation
at
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[28]
Nowick, "Doped Ceria as a Solid Oxide Electrolyte", Journal of the Electrochemical Society, 122(2), p. 255-259,1975. H.L. Tuller and A.S.
146
/
General conclusions
Electrostatic
have been studied and
applied
to
thin
deposit
PSD
technique is more robust and offers an
ESD
technique.
high
decompose
to
high
At too
decomposition
and the
morphology
a
YSZ and CYO films. The
conducting
ion
deposit dense
pyrolysis set-ups.
a
as
soon
the solvent with the
containing
the zirconium
by spraying
lower temperatures than is the
higher boiling point.
acetylacetonate
The measurements of the
leads to film
can
droplet
Films of the best
be
the
the
film
sufficiently
cracking.
the solvent in
as
evaporate completely during the droplet transport. Crack-free films at
was
strongly affects the
It
deposition temperature
temperature powder will be produced
boiling points
compared to
of the precursor. The temperature has to be
precursor salts. Too low
solvents with low
films
films, the substrate surface temperature
for both spray
important parameter
O2"
easier way to
In order to obtain smooth and dense most
Spray Deposition (PSD) set-ups
and Pressurized
Spray Deposition (ESD)
droplets
deposited using of
case
quality
a
were
solution
deposited
precursor solution.
sizes indicated that for the PSD set-up and the ESD
multi-jet spraying mode the droplet number distribution is dominated by droplets smaller than 10
On the other
urn.
than 10 case
ujn.
Notable
of the PSD and
attributed to the
hand, the droplet volume distributions
evaporation of droplets a
distance of 10
mm
starts at
dominated
distance of 5
mm
by droplets larger
from substrate in the can
be
PSD set-up and/or reflection of the air flow
on
important
for
in the
larger temperature gradient in
a
were
case
of the ESD
multi-jet
mode. This
the substrate. Due to the
film
growth
higher
than the small
precursor, evaporate
spread as
on
these
during
mass
of the
the
often
10
urn)
these
are more
carry most of the
droplets. The large droplets
mass
of the
slowly during transportation and consequently contain enough solvent
the substrate. The smaller
are
larger droplets (>
deposited
decomposition
on
as
droplets
are
responsible
powder particles.
the substrate
for most of the surface
roughness
acetylacetonate
that melts
The zirconium
improves
the
to
spreading behaviour
of the
droplet
and facilitates the formation of a smooth, dense film. XRD
analysis revealed that the as-deposited films
crystallization begins
upon
annealing
are
amorphous
at about 450°C. Grains of 10
147
nm
in size
and
significant
were
observed
GENERAL CONCLUSIONS
after
grain growth at
at 700°C. The
annealing
annealing
Dense and crack-free
Surprisingly,
electrolyte
film
using
voltage (OCV) close prepared via the
using
electrolyte
the spray
to the theoretical value
LSCF cathode and the YSZ of
a
CYO buffer
layer electrolyte attained The
application
a
was
superior electrolyte
performance
electrolyte. layer
on
The
a
a
by
500
a
mode
operation
nm
an
ultra-thin
open circuit
electrolyte layer,
electrolytes deposited
to the
films
power
be
can
deposited using
of 550
density
mW/cm2
was
considerably
reduced after the
CYO/YSZ/CYO
in
excess
of 750
mW/cm2
at
multi-layer electrolyte is
770°C.
very
generated high
promising
power
the
processing
and when
low costs. It
technology
can
as a
pyrolysis
controlled it
is
a
coating technique equipment
yields nano-structured
be concluded that spray
thin film
at
were
multi-layer electrolyte.
of ceramic films. The process
properly
for
density
700°C, but also showed considerable degradation. The degradation and low OCV values
In summary, spray
was
top of the YSZ electrolyte film. This cell with the bi-
intermediate and low temperature SOFC. One of these cells
attributed to defects in the
the
occurred due to the reaction between the
degradation
high power density
of
annealing
would sustain the
achieved. Cells with YSZ
OCV of 970 mV and
but continuous decrease in
deposition
on
porous NiO-YSZ anode
coated
um were
In SOFC
on
higher OCV, compared
PSD set-up exhibited
an
pyrolysis
spray
prepared
were
pyrolysis technique.
the ESD set-up. This indicates that
generated
films
pores with sizes of up to 3
PSD set-up. At 770°C
significant influence
observed after thermal
were
electrolyte deposited by
no
of at least 800°C.
operation temperature
substrates.
has
hours)
to 6
(1
cracks in the thin YSZ film
at 700°C. No
800°C. It follows that the thin
SOFC
time
pyrolysis
deposition technique
is rather
a
has been
lot of
simple, the
oxide films of
for ultrathin
148
that offers
advantages for
method is robust
high quality
successfully applied
electrolytes.
at
rather
in SOFC
O Outlook
General
This thesis
applied
to an
process
was
was
focused
on
studied for dense films in
advantages offered by this
technique thin film
important drawback. Therefore,
detail, it needs
be
pyrolysis
the spray
investigation
can
in order to
improve
the other thin film processes. Besides the many
over
deposition method, the low deposition
further work is
required
in the
following
rate
remains
an
areas.
deposition Electrostatic and the air blast atomizers
turned out that films of
using
further
that
pyrolysis technique
(SOFCs). Although
for solid oxide fuel cells
electrolyte
the competitiveness of this
Film
of a spray
development
the
slightly
the air blast atomizer.
better
quality
the substrate in the
electrostatic atomizer is coated
area can
our
and
pyrolysis set-up.
spray
larger
areas were
It
coated
However, the deposition efficiency of the air blast atomizer is
the substrate, the rest is blown away on
deposited
were
much lower than that of the electrostatic atomizer.
deposited
installed in
were
more
by air flow. case
In contrast, around 90% of spray solution is
of the electrostatic atomizer. It follows that the
promising
be increased either
Only 5-10% of sprayed solution reaches
for efficient film
by employing
an
deposition
array of nozzles
at a
or
high
rates. The
by moving
a
single
nozzle.
Properties of depositedfilms
It is
suggested
the electrical
possible
to
that
conductivity
identify
of the thin YSZ films.
over a
for
Impedance spectroscopy
the contributions of bulk and
conductivity of the nanocrystalline YSZ important
measurements should be made to
impedance spectroscopic
application
long time period
as
electrolyte
due to
film.
Long
in SOFC. It is
grain growth. 149
grain boundaries term
conductivity
possible
that the
to
study
could make it the total ionic
measurements
conductivity
are
decreases
OUTLOOK
In this
it
study
that the influence of should be
was
as-deposited
shown that the
deposition temperature It is
investigated.
crystalline. Furthermore,
it would be
interesting to investigate
might
substrates. Some substrates
polycrystalline
We also suggest
amorphous.
and grain size of
YSZ film
an
already be
above 450°C will
deposited
film microstructure, because different film microstructures and
are
crystallinity
on
that the film
expected
films
the influence of a substrate
can
be obtained
be used
single crystal
on
preferred
for
templates
as
on
film.
texturing of the oxide
Application ofspray pyrolysis in SOFC
In the present work
deposited by deposited.
It
We suppose that porous anode and cathode films
pyrolysis.
spray
follows, that
spray
pyrolysis
has
potential
a
Further work has to be invested here
in
deposit
to
of porous electrodes and dense
complete multilayer fuel cell proof is still missing.
electrolyte films
have demonstrated that dense
we
on
the
can
be
also be
production step
one
but
electrolyte,
mainly
can
a
experimental
deposition of porous
films.
Spray pyrolysis
can
zirconia, doped lanthanum gallate,
promising candidates that has
a
higher
ionic
ceria
conductivity of
to
replace
YSZ
conductivity
electrolyte
can
electrolyte that
already proposed
further
investigation.
electrolyte quality in
Miscellaneous
The spray such
as
strength
the
as
scandia-doped
significantly
short circuit due to the electronic
reduce the
by the
use
and tested in the
efficiency and performance
of the CYO/YSZ/CYO
Chapter
primary importance is
the most
mixed ionic-electronic conductor
a
a
are
the
6. This
of
multilayer
multilayer electrolyte
improvement
of the
multilayer
tightness.
applications
pyrolysis technique of
toughness.
plates sandwiched
For
example,
or
be
applied
the abalone
in hard
stop crack
also in other non-SOFC technical
A number of natural materials
protein interlayers,
Toughness
that deflect
can
tough coatings.
between
of the pure mineral. structures
terms of gas
deposition
and
Of
electrolytes such
ceria. Ceria-based solid solutions
electrolyte. Ceria is
be solved
can
alternative
than YSZ. However,
problem
requires
doped
or
the fuel cell. This was
produce
be used to
is
shell,
more
a
composite
famous for their
of calcium carbonate
fracture resistant than
biological materials is related
propagation. Spray pyrolysis 150
are
fields,
a
single crystal
to fibrous or
offers
a
lamellar
way to fabricate
OUTLOOK
such
layered structures with the aim of introducing toughness
and YSZ
multilayer should have higher toughness
151
than
a
YSZ
into brittle materials. A
single crystal.
polymer
Seite Leer / Blank leaf
152
Appendix
js
9.1
Measurement of droplet size distribution
PDA systems
and therefore
interferometry
phase Doppler anemometry is based
of
requires
no
calibration. The measurement
intersection of laser beams and the measurements move
the sample volume. Particles
through
generating projects
a
portion of the into
optical signal
velocity. measure
interference
optical
an
scattered
Doppler
a
particle
that is scattered
be 1
or
2
light
urn on
In this
by
a
scatter
light
a
multiple
light-scattering
on
point is defined by the
single particles
from both laser at an
as
they
beams,
off-axis location
detectors. Each detector converts the
frequency linearly proportional
to
the
from different detectors is
Doppler signals
particle a
direct
diameter. can
very small
be measured is limited at the lower end
particles. Typical limits
the lower end and 500
study
onto
burst with
The size of particles that
light
thereby
on
pattern. Receiving optics placed
The phase shift between the of the
performed
are
PDA
velocity of droplets.
measurements of the size and
perform non-intrusive
underlying principle
The
using
mm
to 1 mm at
for
common
by
configurations might
the upper end.
system of TSI GmbH company (Aachen, Germany)
used. The main
was
components of the PDA system are listed in the Table 9.1
Table 9.1 Components ofPDA system
Component
Model No.
Laser
L70-5E
Fiber optic receiver
RV2070-X-15M
Fiber
light multi-colour
beam
FBL-2
separator PDM1000-2P
Photodetector module Multibit
digital processor
FSA4000-P
Multihit
digital processor
FSA4010 9450-XYZ500
Traversing system 153
the amount of
1
APPENDIX
9.2 Forces acting
on
droplet
F
Themophoretic force
=
3x-T]a2r
2«-„
Pa where tc, and Kd
(about
2),
r
0.19
are
Wm"1K"1
thermal conductivities of the air for
is the radius of the
of air
(250°C),
(about
0.025 Wm" K"
ethanol) respectively, 7}a is the viscosity
droplet, pa
of air
density of the air (1.29 kg
is the
and grad(Ta) is the thermal
+ K,,
)
m"3),
/is
s
m"
gradient of air (105 K/m).
Fg
=
—
.Pdr g
density of the droplet (780 kg m" ) and g is the acceleration of gravity
Fs
velocity
of the
the
FE=qE, liquid-gas
surface tension
vacuum, E is the electric field
=
67rrjavdr
droplet (1 m/s).
Electrical force where
N
Ta is the temperature
Stokes force where Vd is the
droplet
and the
(about 2.2-10"5
Gravitational force
where pd is the
grad(Ta)
3Ka
(0.02 N/m),
q^^Tt^p
So is the electrical
permittivity
strength (105 V/m).
Table 9.2
Magnitudes offorces
Radius, pm
Thermophoretic, N
Gravitational, N
Stokes, N
Electrical, N
1
2.1-10'13
3.2-10-14
4.1-10"10
1.1-10"9
10
2.1-10-12
3.2-10"11
4.110"9
3.3-10"8
100
2.1-10"11
3.2-10-8
4.1-10s
1.1-10"*
154
of
10
Abbreviations
AFM
Atomic Force
Microscopy
ALE
Atomic Layer
Epitaxy
ASR
Area
Bi-2212
Bi2Sr2CaCu2Ox
CGO
Ceo.8Gdo.202-x
CSZ
15 at% Calcium-Stabilized Zirconia
CVD
Chemical Vapour
CYO
Ceo.8Yo.2O2-*
DTA
Differential Thermal
EDS
Energy Dispersive X-Ray Spectroscopy
ESD
Electrostatic Spray
IR
Infrared
LSCF
Lao.6Sro.4Coo.2Feo.sO3
MOCVD
Metal-Organic Chemical Vapour Deposition
Ni-YSZ
Mixture of Nickel and YSZ
OCV
Open Circuit Voltage
PDA
Phase
PSD
Pressurized
PVD
Physical Vapour Deposition
SEM
Scanning
SOFC
Solid Oxide Fuel Cell
TEM
Transmission Electron
TG
Thermogravimetry
THF
Tetrahydrofuran
XRD
X-Ray
YBCO
YBa2Cu309-x
YSZ
8 mol% Yttria-Stabilized Zirconia
Specific Resistivity
Deposition
Analysis
Deposition
Doppler Anemometry Spray Deposition
Electron
Microscopy
Microscopy
Diffraction
155
Spïtp JvJÏ
156
11
Curriculum vitae
PERSONAL
Full Name:
Dainius Perednis
Date and Place of Birth:
August 9,1973, Kaisiadorys, Lithuania
Nationality:
Lithuanian
EDUCATION
1998-present
Research associate and Ph.D. Student, Chair of Nonmetallic
Inorganic Materials, Department of Materials,
ETH
Zurich,
Switzerland 1995-1998
Swiss Federal Institute of
Physics studies,
Technology, ETH,
Zurich, Switzerland thesis
Diploma
of
"Imaging
Distribution
Current
in
Bi2Sr2CaCu20x Superconducting Films Using Magnetic Force
Microscopy" 1995
Bachelor in
Grading
Physics,
work
Vilnius
University,
"Preparation
Lithuania
Properties
and
of
MgO-CuO
Ceramics" 1994-1995
Exchange student at the
ETH
Zurich, Switzerland
(The EPS/SOROS mobility grant
of the
European Physical
Society) 1991-1995
Physics studies, Vilnius University, Lithuania
1991
Matriculation at the
157
secondary school
in
Kaisiadorys,
Lithuania
CURRICULUM VITAE
LIST OF PUBLICATIONS
Papers:
(1)
Will, A. Mitterdorfer, C. Kleinlogel, D. Perednis and L.J. Gauckler
J.
Fabrication
of thin electrolytes for second-generation solid oxide fuel cells
Solid State Ionics,
(2)
D.
131(1-2),
p.
79,2000
Perednis, L.J. Gauckler
Solid oxide fuel cells with
electrolytes prepared via spray pyrolysis
submitted to Solid State Ionics
(3)
D.
Perednis, L.J. Gauckler
Thermal treatment In
(4)
D.
preparation
Perednis,
State
(5)
of metal oxide spray pyrolysis layer
L.J. Gauckler
of the art:
spray pyrolysis
In
preparation
O.
Wilhelm, D. Perednis, L.J. Gauckler, S.E. Pratsinis
Spray pyrolysis deposition of YSZfilms by different spraying techniques In
(6)
D.
preparation
Perednis, O. Wilhelm, S.E. Pratsinis, L.J. Gauckler
Deposition of thin metal oxide films using spray pyrolysis In
preparation
158
CURRICULUM VITAE
Proceedings:
(1)
D.
Perednis, L.J. Gauckler
Solid oxide fuel cells with YSZfilms prepared using spray pyrolysis
Proceedings
of the 8th International
Symposium
on
SOFCs
(2003, Paris, France),
vol.
2003-07, p. 970
(2)
D.
Perednis, L.J. Gauckler
Solid oxide fuel cells with thin
Proceedings
of the 5th
Switzerland), vol. 1,
(3)
D.
electrolytefilms deposited by spray pyrolysis
European
Solid Oxide Fuel Cell Forum
p. 72
Perednis, M.B. Joerger, K. Honegger, L.J. Gauckler
Fabrication
of thin YSZ electrolyte films using spray pyrolysis technique
Proceedings of the 7th International Symposium vol.
(4)
D.
electrolytes by
(2001,
Les
Workshop, IEA Program
Diablerets, Switzerland),
of R&D
on
Advanced Fuel Cells,
p. 110
Perednis, K. Honegger, L.J. Gauckler YSZfilms
Proceedings of the Switzerland), vol. 2,
O.
(2001, Tsukuba, Japan),
spray pyrolysis
of the SOFC
Deposition of thin
(6)
SOFCs
Perednis, L.J. Gauckler
Proceedings
D.
on
2001-16, p. 989
7%/«
(5)
(2002, Lucerne,
4th
by spray pyrolysis
European Solid Oxide Fuel Cell Forum (2000, Lucerne,
p. 819
Wilhelm, L.J. Gauckler, L. Mädler,
D.
Perednis, S.E. Pratsinis
Spray processing in nanoparticle technology Proceedings
of the
16th European
Conference
Systems (2000, Darmstadt, Germany),
p. VIII.7.1
159
on
Liquid
Atomization and
Spray
CURRICULUM VITAE
Presentations:
(1)
D.
Perednis, and L.J. Gauckler
Solid oxide fuel cells with YSZfilms prepared
8th International Symposium
using spray pyrolysis
Solid Oxide Fuel Cells, Paris, France,
on
April
27
-
May
2, 2003 (talk)
(2)
D.
Perednis, and
L.J. Gauckler
Thin metal oxide films for solid oxide fuel cells
Colloquium 2003
(3)
D.
of the
Department
of
Materials, ETH Zurich, Switzerland, January 29,
(talk)
Perednis, and L.J. Gauckler
Solid oxide fuel cells with thin
5th European
electrolytefilms deposited by spray pyrolysis
Solid Oxide Fuel Cell Forum, Lucerne, Switzerland,
July 1-5,
2002
(poster)
(4)
D.
Perednis, C. Vanoni, M.B. Joerger, and L.J. Gauckler
Effect of additives 13th
in
deposition of thin YSZfilms using spray pyrolysis technique
International Conference
on
Solid State Ionics, Caims, Australia,
July 8-13,
2001
(talk)
(5)
D.
Perednis, M.B. Joerger, K. Honegger, and
Fabrication
7th
International
2001
(6)
D.
of thin
YSZ electrolyte films
Symposium
on
L.J. Gauckler
using spray pyrolysis technique
Solid Oxide Fuel Cells, Tsukuba, Japan, June 3-8,
(talk)
Perednis, M.B. Joerger, K. Honegger, and L.J. Gauckler
Fabrication
of thin
YSZ electrolyte films
using spray pyrolysis technique
Laboratory of Electrochemical Energy Conversion, Yamanashi University, Kofu,
Japan,
June
1,2001 (talk)
160
CURRICULUM VITAE
(7)
D.
Perednis,
Fabrication
M.B.
Joerger, K. Honegger, and L.J. Gauckler
of thin
YSZ electrolyte films
using spray pyrolysis technique Institute of
Laboratory, Tokyo
Materials and Structures
Technology, Yokohama,
Japan, May 31, 2001 (talk)
(8)
D.
Perednis, and L.J. Gauckler
Thin
electrolytes by
SOFC
Workshop,
spray pyrolysis
IEA
Program of R&D
on
Advanced Fuel Cells, Les Diablerets,
Switzerland, January 16-19,2001 (talk)
(9)
D.
Perednis, K. Honegger, and L.J. Gauckler
Deposition of thin 4th European
YSZfilms
by spray pyrolysis
Solid Oxide Fuel Cell Forum, Lucerne,
Switzerland, July 10-14, 2000
(poster)
(10)
D.
Perednis, and L.J. Gauckler
Deposition of thin Colloquium
of the
YSZfilms
by spray pyrolysis
Department of Materials, ETH Zurich, Switzerland, April 12,
2000
(talk)
(11)
D.
Perednis, and L.J. Gauckler
Imaging
current
flow
in
complex superconducting
microstructures
by magnetic
force microscopy
8th European Spain,
(12)
D.
Conference
October 4-8, 1999
on
Applications
of Surface and Interface
Analysis, Sevilla,
(talk)
Perednis, M.K.M. Hruschka, K. Honegger, and L.J. Gauckler
Preparation of YSZ thin films by spray pyrolysis 8th European Conference
Spain,
October 4-8,1999
on
Applications
(poster)
161
of Surface and Interface
Analysis, Sevilla,
