Liquid-Feed Flame Spray Pyrolysis.
Conquering the Tyranny of Thermodynamics
Synthesis of Mixed-Metal Oxide Nanoparticles
R.M. Laine, J. Marchal, J. Azurdia, S. Kim, M. Kim
Dept. of Materials Science and Engineering
University of Michigan
talsdad@umich.edu
Funding:
AFOSR Contract No. F49620-03-1-0389, NSF (IGERT),
Maxit Group, Defense Sciences National Labs, Singapore
June, 2004
1
Outline
• What do nanopowders offer?
• A brief history of FSP
• Key problems in nanopowder synthesis
• Liquid-feed FSP (LF-FSP)
Combustion of low-cost, alcohol soluble precursors
Nanopowder formation mechanism(s)
• Mixed-metal oxide nanopowders for
Catalysts
Photonics
• Conclusions
2
June, 2004
1. What do nanopowders offer?
What are nanopowders?
< 100 nm
Surface Area / Volume
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
50
100
150
200
250
300
Particle Diameter
3
June, 2004
2. What do nanopowders offer?
Passive Physical Size Applications
• Finer powder sizes
Inkjet Printed
Little or no grinding
Nanophosphors
• Avoids impurities and costs
• Transparency for films and coatings
Abrasion resistant floor coatings
• Nanophase
Higher gloss inks
Finer grain size in sintered ceramics
• Better mechanical properties
Smaller flaw sizes, therefore more robust
G. Jabbour U. Arizona
4
June, 2004
3. What do nanopowders offer?
New Science Through New Materials
Novel phases with unexpected:
• Conductivity
Thermal, electrical
• Catalytic properties
Unusual combinations of phases
• Photonic properties
5
June, 2004
Brief History of FSP
• One of oldest materials processing methods
• Used to make lamp black, carbon soot
reductive flames
• Gaseous feed FSP
•
SiCl4 + H2 + O2 ---> SiO2 + 4HCl + H2O
• Currently used to make kilotons of nano TiO2 &
SiO2, some Al2O3
6
June, 2004
Brief History of FSP
Some interesting quotes:
• “As a general rule, flame-generated particulate materials
require expensive raw materials”
• “Mixed-oxides comprise a relatively undeveloped avenue
of flame technology”
G. Ulrich, C&EN News, April, 1984, pp. 25-
• Disadvantages include difficulties in producing multicomponent materials, low production rates …and
hazardous gaseous reactants and by products,”
• Another major disadvantage is formation of hard
agglomerates in the gas phase leads to difficulties in
producing high-quality bulk materials,”
T. Kodas , “Aerosol Processing of Materials,” Aerosol. Sci. and Tech.
7
19, 411-52 (1993)
June, 2004
Key problems in nanopowder synthesis
• No very general ways of making large quantities of
mixed-metal oxides
• Difficult to control particle sizes and distributions
• Difficult to tailor compositions and surface
chemistries
• Can be hard to control degree of agglomeration
And therefore processability of as-produced powders
• Liquid-feed flame spray pyrolysis (LF-FSP)
offers a solution to many of these problems
8
June, 2004
What is LF-flame spray pyrolysis?
Fafnir
• Low cost precursors
• Dissolved in alcohol
• Aerosolized with O2
• Combusted ≤1500°C
• Quenched rapidly
• Limited
agglomeration
• What you shoot
is what you get!
9
June, 2004
Commercial Scale Production
•
•
•
•
Tal
June, 2004
1- 3 kg/h
Continuous operation
Same quality
Or better
10
Low cost metalloorganic precursors
• SiO2 (TiO2) + N(CH2CH2OH)3 200°C/-H2O>
O
O
Silatrane (titanatrane) glycol
• Water soluble and stable
N
Si
O
O H
O
• Al(OH)3 + N(CH2CH2OH)3 200°C/-H2O>
O
O
Alumatrane
• Air and moisture stable
N
Al
O
4
11
June, 2004
Low cost, mixed-metal precursors
• Spinel-MgO.Al2O3
MgO + 2Al(OH)3 + 3TEA 200°C/-H2O>
O
N
O
N
Al
O
O
2+
O
Al
N
Mg
O
O
• BAS (SAS)
O
O
BaO(SrO).2SiO2.Al2O3
H
H
O
N
O
N
Al
O
• The art is in the chemistry
O
O
O
O
O
Si
H
H Ba2+
O
O
O
O
N
Si O
O
N
O
O
N
Al
N
O
O
12
June, 2004
Powder Formation Process
Stage 1
Metal
Alkoxide
Vapor
Metal
Oxide
Vapor
Combustion
(Al(Al-O)x Clusters
Coalescence/
Collisions
Stage 2
Al2O3
Particle
Formation
Condensation
Stage
3 Stage 4
Al O
2 3
Particle
Growth
Al2O3
Particle Growth
Al2O3
Al2O3/SiO2
Particle Formation Al2O3/SiO2
(SiO2 or SiO2Particle
(Al(Al-O)x/(Si(Si-O)x
coated Al2O3
Growth
Clusters
particles)
Mullite
Coalescence/
Collisions
Condensation
Possible scenarios for mullite particle formation
(Si(Si-O)x
Clusters
SiO2
Particle
Formation
SiO2
Particle
Growth
Coalescence/
Collisions
Condensation
What you shoot is what you get
June, 2004
SiO2
13
Baranwal
Single-Metal Oxide Nanopowders
δ−Al2O3
LF-FSP of AlCl3
LF-FSP of Al(OCH2CH2)3N
June, 2004
LF-FSP of Al(NO3)3
LF-FSP of Al(OCH2CH2)3N 14
Single-Metal Oxide Nanopowders
Al2O3
• δ-alumina
Novel phase
3.5 g/cc
• Log normal size distribution
φ ≈ 30 nm
• Unaggregated,
self-disperse in water,
polar polymers
• Can dope to 10 ppth
with rare earth ions
15
June, 2004
Marchal
2. Thermal Behavior of Ce3+ Doping
• δ- to α transformation
1360
0.015
Inhibited by increases in
[RE]
Can inhibit to ≈ 1400 °C
p
T (° C )
1320
0.010
1300
0.005
1280
1260
Exo Up
1200
1240
0.01
0.1
•
Sintering behavior?
•
Catalyst support?
Ce:Al2 O3 10 wt%
Ce:Al2 O3 1 wt%
Ce:Al2 O3 0.1 wt%
Ce:Al2 O3 0.01 wt%
1250
1300
Temperature (°C)
1
CeO wt%
Temperature Difference (°C/mg)
1340
1350
10
0.000
1400
100
2
16
June, 2004
Hinklin
Ceria doped δ-alumina
• Above 1 wt. %
15 wt%
CeO2 phase
segregates
10 wt%
•
Relative Intensity
5 wt%
1 wt%
Sintering and phase
transformation
inhibition still
observed
0.1 wt%
150 ppm
50 ppm
25
30
35
2θ
40
45
50
17
June, 2004
Hinklin
Stability of Ce:δ-Al2O3
70
Implications for catalyst support
materials
60
2
Surface Area (m /g)
50
40
0.9
30
0.85
Ce 1000
Ce 10000
Un-doped
0.8
20
Relative Density
Ce 0.1 wt%
Ce 1.0 wt%
10
0
400
600
800
1000
1200
Temperature ( C)
10°C/min 2 h hold
Ce3+ addition significantly inhibits
surface diffusion and ∴sintering
0.75
0.7
0.65
1400
0.6
0.55
0.5
1200
1250
1300
1350
1400
1450
1500
1550
1600
Temperature ( C)
18
June, 2004
Hinklin
Ceria/Zirconia Solid Solutions
Selected XRDs
*
x=1.0
•
*100% (111) line for cubic
phase
•
Note shift as smaller Zr
substituted for Ce
Proof of solid solution
•
At x = 0.7, tetragonal
•
•
•
Φ ≈ 40 nm
Surface area ≈ 30 m2/g
Powders dispersible
*
x=0.9
*
x=0.7
*
x=0.5
*
x=0.3
*
x=0.1
20
June, 2004
30
Relative Intensity
*
x=0.0
40
2θ
50
60
19
Kim/Sutorik
Nanostructured Cerium Oxide "Ecocatalysts,”
Easily prepared
•
5 steps shown plus
• Product is 150 m2/g
solid solution
(1)
•
•
•
(2 & 3)
(4 & 5)
•
•
Annealed at > 500°C to
remove micropores gives
final SSA of 50 m2/g
Product is then ground
Mixed with sol-gel
alumina precursor and
coated on TWC monolith
Then Pd is added
Total of about 10 steps
M. Flytzani-Stephanopoulos, Mater. Res. Soc. Bulletin, Nov. 2001, pp. 885-9
20
June, 2004
Ce0.7Zr0.3O2 on Al2O3
δ-Al2O3
• δ-Al2O3 = 60 m2/g
• Ce0.7Zr0.3O2 = 16 m2/g
Now at 30 m2/g
Ce0.7Zr0.3O2
20 wt% 0.7
Ce
Zr0.3O2/ 80 wt%
δ-Al2O3
20
25
30
35
40
45
degrees two thet
50
55
• 20 wt. %Ce0.7Zr0.3O2:
80 wt. % δ-Al2O3
30 m2/g
• IDENTICAL ACTIVITY
60
TO COMMERCIAL TWC
WASHCOAT MADE IN
> 8 PROCESS STEPS
• Green process
21
June, 2004
Kim/Sutorik
(Y0.999-x-yYbxREy)2O3 Solid Solutions
Selected XRDs
• Cubic + some monoclinic
Proof of solid solution
• Upconvert 980 nm IR
light to red, green, blue
(Y0.949Yb0.05Pr0.001)2O3
•
Orasure.com
drug bioassays/picogram/g
quantities
(Y0.919Yb0.08Tm0.001)2O3
No biologicals upconvert
(Y0.86Yb0.08Er0.06)2O3
Y2O3
10
20
June, 2004
30
2θ
40
50
60
•
Taggants for counterfeit
deterrence
•
Nanomark has embedded
them in molten Al
22
Sutorik
Conquering the Tyranny of
Thermodynamics with LF-FSP
23
June, 2004
Ti:Al Oxide Nanopowders
δ-Al2O3:TiO2 87:13
b
a
a
FSP Particles:
• Φ = 90, 50, 15 nm
• δ-alumina XRD
b
• Disperses like δ-Al2O3
• Photoactive catalyst
Self-disinfecting Selfcleaning surfaces
Visible light??
TEM by H. Sun,
Prof. X. Pan UM, 01
• Epoxidation catalysts
24
June, 2004
S. Kim
Ti:Al Oxide Nanopowders
FSP Particles:
Pure δ-Alumina
0.16 Ti/Al
0.50 Ti/Al
0.65 Ti/Al
0.85 Ti/Al
• Φ = 30 nm
• All disperse easily
• Pure TiO2 90 mol %
anatase
• Add 15 wt % Al2O3,
See only rutile
Pure Titania
[21-1276]Rutile
[21-1272]Anatase
20
30
40
50
60
70
80
2θ
25
June, 2004
S. Kim
NiO.Al2O3 compositions
77.2
80
69.0
70
60.3
60.1
58.1
56.8
60
45.0
50
40
30
20
6.7
10
0
Al2O3
3 mol %
NiO
5 mol % 21 mol % 43 mol % 63 mol % 78 mol %
NiO
NiO
NiO
NiO
NiO
NiO
Sample
26
June, 2004
Azurdia
NiO.Al2O3 compositions
Al2O 3
Relative Intensity
3 mol % NiO:Al2O 3
22 mol % NiO:Al2O 3
45 mol % NiO:Al2O 3
64 mol % NiO:Al2O 3
NiO
15
25
35
45
55
65
75
2θ °
(Ni2+)1-x(Ni3+)xO1-x[]xAl2O3?
June, 2004
27
NiO.Al2O3 Thermodynamic
Phase Diagram
28
June, 2004
NiO.Al2O3 Kinetic Phase Diagram
TGA shows phase stable to 1500 °C
29
June, 2004
Transparent YAG?
K-I. Ueda, “High Power Laser Materials based on Ceramic Materials,” CLEO 2002, Long Beach, CA May 20, 2002
30
June, 2004
Transparent YAG?
Ueda needs 5 steps to get to 100 nm, 7 steps to compacts!
31
June, 2004
YAG Composition Nanopowders
Wrong
Y3/Al5 Nitrates
Right
Y3/Al5 carboxylates
The Art is in the Chemistry
June, 2004
32
Marchal
YAG Composition Nanopowders
SEM
• φ < 20 BET, SSA ≈ 90
m2/g
• φ = 16 by XRD
• φ ≈ 18 lineal analysis
• New Phase?
• Still dispersible
TEM by H. Sun, Prof. X. Pan UM, 02
33
June, 2004
Marchal
TEM
• Unusual phase formed
10 nm
• XRD Shows new peak at 8.4 °2Θ
•Transforms to YAG phase with
• Ea = 100 Kj/mol
•Transparent polycrystalline lasers
with Nd3+?
34
June, 2004
Marchal
Y3Al5O12 But Not YAG
Salient Features
• Same structure as hexagonal
YAlO4
• Double cell length
• Red: O2• Blue: Al3+
• Grey: Y3+
• Denser than YAG!
• New Phase?
35
June, 2004
Marchal
Sintering YAG Nanopowders to Full Density
a. 10°C/min 800°C/O2, 10°C/min 1400°C for 6h,
b. 10°C/min 800°C/O2, 10°C/min vacuum 1000°C/2h,
10°C/min 1400 for 2 h
a. Cut, polished surface
June, 2004
b. Cut, polished surface
36
Marchal
Novel Nano Processing
•
•
•
LF-FSP with nanoparticle feeds
Combinations of nanoparticles
LF-FSP with nanoparticle and precursor
feeds
• Why?
Coatings
Mixed phases
Particle nucleated growth
37
June, 2004
Novel Nano Processing
• LF-FSP with nanoparticle feeds
• Chromia coated alumina
• Cr(O2CEt)3
• ICDD 38-1479,
α-phase Green
• Cr2O3
38-1479
10
20
30
40
50
60
70
80
2θ
38
June, 2004
Novel Nano Processing
•
•
•
LF-FSP with nanoparticle feeds
8 Cr(O2CEt)3: 92 δ-Al2O3
φ ≈ 60 nm
39
June, 2004
Novel Nano Processing
• 8:92 feed
• No chromia in XRD
• Off-white powders
• α-Al2O3
• After sonication
• Color red/green
Cr3+/Cr2+
α
α
• It’s RUBY
α
α
10
20
α
30
α
40
50
60
2θ
40
June, 2004
Novel Nano Processing
• α-Al2O3 product
• 40-60 nm
4
3.5
Reshot: Small particles
3
2.5
Reshot: large particles
2
1.5
Degussa
1
0.5
PDF 73-1512
0
10
20
30
40
2 theta
June, 2004
50
60
41
Novel Nano Processing
• Pure α-Al2O3
• Less water by
FTIR
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
42
June, 2004
Novel Nano Processing
•
LF-FSP with Nano
δ-Al2O3 or α-Al2O3
• 20 titanatrane:
80 δ-Al2O3
• Product depends
on substrate
20
30
40
50
60
70
80
0.20TiO2 0.80Al2O3(Alpha)
0.20TiO2 0.80Al2O3(Delta)
0.85TiO2 0.15Al 2O3
Materials with
different band gaps
Photocatalysts
Pure TiO2
Rutile [21-1276]
Anatase [21-1272]
20
30
40
50
60
70
80
43
June, 2004
Novel Nano Processing
• LF-FSP with Nano
δ-Al2O3 or α-Al2O3
• 85 titanatrane to
15 δ-Al2O3
• Get chemically
graded coatings
0.85TiO2 0.15Al2O3(Delta)
0.85TiO2 0.15Al 2O3
0.95TiO2 0.05Al 2O3
• Novel band gap
• Photocatalysts
Pure TiO2
Rutile [21-1276]
Anatase [21-1272]
20
30
40
50
60
70
80
44
June, 2004
Novel Nano Processing
•
•
•
LF-FSP with Nano δ-Al2O3
Coatings?
Stainless steel in particle flame
• Iridescent adherent 1-2 µm α-Al2O3 coatings
June, 2004
45
Novel Nano Processing
• Pure nano α-Al2O3
• Abrasives
Chemical mechanical polishing
• Transparent ceramics
Sodium vapor lamps
Ti:Sapphire lasers among other things.
• Coatings
• High strength monoliths
Ceramic prosthetics for example
• Catalyst supports that do not sinter
• Catalysts
June, 2004
46