Design of ceramic pastes for the co-extrusion of solid oxide fuel cells
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Transcript of Design of ceramic pastes for the co-extrusion of solid oxide fuel cells
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Rheological design of
ceramic pastes for the co-
extrusion of solid oxide
fuel cells
Jonathan Powell1 and Stuart Blackburn2 1. Faculty of Engineering, Chulalongkorn University, Thailand
2. Department of Chemical Engineering, The University of Birmingham, UK
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Project summary
Binder rheological design
Paste rheological design
Co-extruder design
Pressure modelling
Co-extrusion
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Motivation
Sustainable energy production.
Wide range of fuels
Rapid start up
Thermally and mechanically stable
High power densities
Opportunity to reduce production
costs
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Objectives and scope Micro tubular
solid oxide fuel cell
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Co-extrusion
Liang & Blackburn, J. Mat. Sci., 37, 2002
Stage 1 Stage 2
Stage 3 Stage 4
Building of
repeat units Multi-billet extrusion
Building of
laminated tube
Liang & Blackburn, J. Mat. Sci., 37, 2002
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Phase migration
Preferential flow of liquid – Unstable extrudate composition
– Initially low extrusion pressures,
followed by very high pressures
(due to depletion of liquid from
barrel)
l
PRum
2
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Paste rheology
Yield stress and shear thinning behaviour – Retain shape after extrusion
– Low extrusion pressures required
Main controlling factors – Liquid volume fraction
– Rheology of liquid phase
– Particle properties and behaviour
Shape and size
Particle wetting
Particle dispersion and stability
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Paste rheology unification
The pastes must flow in a uniform manner
The pastes must therefore have unified rheological properties
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Binder properties
High apparent viscosity – Reduce tendency for phase migration
Shear thinning – Lower apparent viscosity at high shear rates where less tendency
for phase migration
– Increased apparent yield stress
Very high polymer content stabilises powder
dispersion
Low volatility liquid carrier – Prevent localised loss of liquid
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Binder rheology
Controlled stress rotational cone and plate
rheometer
Time sweep, change in viscosity with time
Flow curve
Dynamic flow curve
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Time sweep
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Steady shear and complex viscosity
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Paste rheological characterisation
nm VD
L
D
DVPPP
0
0021 4ln)(2
σo Bulk yield stress
α Velocity factor convergent flow
n Velocity exponent convergent
flow
τo Die wall shear stress
Die wall velocity factor
m Die wall velocity exponent
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Binder volume fraction – twin roll
mill mixed
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Binder volume fraction – twin roll
mill mixed
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Binder volume fractions – z-blade
mixed
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Binder volume fractions – z-blade
mixed
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Bulk shear and plug flow
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Acknowledgements
Thanks goes to;
EPSRC for the funding of this research
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S Blackburn 2004
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0 m 0 nPaste
Benbow Bridgwater parameters
1 0.20 19.08 0.37 0.04 12.85 0.45
2 0.75 53.69 0.50 0.02 9.55 0.41
3 0.71 40.68 0.48 0.00 6.27 0.35
4 0.74 61.15 0.55 0.08 11.05 0.44
5 0.58 34.92 0.48 0.14 15.25 0.54
42
3
1
3
41
8 w
i
w
im
l
PRu