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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
Project summary
Binder rheological design
Paste rheological design
Co-extruder design
Pressure modelling
Co-extrusion
Motivation
Sustainable energy production.
Wide range of fuels
Rapid start up
Thermally and mechanically stable
High power densities
Opportunity to reduce production
costs
Objectives and scope Micro tubular
solid oxide fuel cell
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
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
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
Paste rheology unification
The pastes must flow in a uniform manner
The pastes must therefore have unified rheological properties
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
Binder rheology
Controlled stress rotational cone and plate
rheometer
Time sweep, change in viscosity with time
Flow curve
Dynamic flow curve
Time sweep
Steady shear and complex viscosity
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
Binder volume fraction – twin roll
mill mixed
Binder volume fraction – twin roll
mill mixed
Binder volume fractions – z-blade
mixed
Binder volume fractions – z-blade
mixed
Bulk shear and plug flow
Acknowledgements
Thanks goes to;
EPSRC for the funding of this research
S Blackburn 2004
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
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