Ceramics UK 2019 presentation

1. ADDITIVE MANUFACTURING OF
ADVANCED CERAMICS FOR
DEMANDING APPLICATIONS
William Rowlands
Research Engineer in Additive Manufacturing
CDT alumni from Loughborough University

2. Project Overview
• PhD project aim:
• To investigate the feasibility of fabricating a functional barium
titanate based PTC (Positive Temperature Coefficient) heating
element via additive manufacturing
• Introduction to PTC
• Robocasting
• Analysis
• Conclusions and future work
• Introduction to the Manufacturing Technology Centre
Contents

3. Introduction to PTC Heaters
• Used in hairdryers, space heaters, automotive
and aerospace applications
• Self regulating:
• Constant output over varied input
• Pre-determined temperature:
• TC is the Curie temperature
determines the temperature during
use and can be modified by dopants
during manufacture
• Positive Temperature Coefficient (of
Resistivity) – the increase in
resistivity leads to rapid temperature
increase
PTC vs conventional
heater, temperature /
power over time

4. PTC Effect in Barium Titanate
• At TC the resistance increases by orders of magnitude - PTC effect
caused by donor dopants (La) substituted in the bulk BT providing
electrons that are trapped at the grain boundaries by acceptors
(oxygen vacancies) after overcoming the ‘Schottky barrier’
* D. Fu and M. Itoh, ‘Role of Ca off-Centering in Tuning Ferroelectric Phase Transitions in Ba(Zr,Ti)O3System’, in Ferroelectric Materials - Synthesis and
Characterization, Intech, 2015.
Ti displacement in the oxygen octahedron of the
perovskite structure in BT single crystal*
DielectricPermittivity
Schematic of a Schottky barrier

5. Formulations – Co-precipitation
1 2
3
Raw powder and salts
BaTiO2, Mn(NO3)2, La(NO3)3
Mixing
Mixed 1hr in water, dried, ground and sieved
Paste preparation
Water, viscofier/binder,
dispersant
Printable pastePaste printing
Print parameters, drying
Firing
Binder removal, calcination, sintering
45

6. Extrudable Paste Rheology
• Flow initiates at the
yield stress
• Paste must remain
where it is
deposited after
extrusion
• Extrude must retain
its shape during
drying without
cracking or warping
10
100
1000
0 1 2
LogYieldStress(Pa)
HPMC wt%
Chamber
Material
feed
Motor
Feed
screw
Auger Valve extrusion
Binder content vs yield stress
• Different paste extrusion mechanisms – air
pressure through syringe and auger valve

7. Honeycomb – Ceramic Prints
5mm
1st layer Final layer
Honeycomb print
Commercial PTC honeycomb*
25mm
5mm
*https://honeycombptc.en.ecplaza.net/products/honeycomb-shape-ptc-stone_556623
25mm
40mm
Dried green sample Same sample sintered

8. SEM Microstructure of Extrusions
• Extruded filaments can form bridge structures
Control on distance and filament adhesion
• Printing speed can be used to alter paste elasticity
and to modify the filaments diameter in-situ

9. Electrical Measurements
C.-J. Ting, C.-J. Peng, H.-Y. Lu, and S.-T. Wu, “Lanthanum-Magnesium and Lanthanum-Manganese Donor-Acceptor-
Codoped Semiconducting Barium Titanate,” Journal of the American Ceramic Society, vol. 73, no. 2, pp. 329–334, Feb. 1990.
PTCR in literature
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
60 80 100 120 140 160 180 200
Resistivity,ρ(Ω·cm)
Temperature, T (°C)
PTCR of my 3D printed heaters
0.3La0.08Mn pressed sample
0.3La0.08Mn Solid print
0.135La pressed sample
0.135La solid print
109
108
107
106
105
104
103
102
101

10. 3D Printed Heating by applied power
7.5W
5W
3W
1.25W
7W
4.75W
2.5W
1W
6.5W
4.5W
2.25W
0.875W
6W
4.25W
2W
0.75W
5.5V
4W
1.75W
5.25W
3.75W
1.5W

11. PTC IR heater measurements
Heating behaviour of 3D printed
PTC samples at varied power levels;
0.3La0.08Mn solid printed sample
(notation – SP), 0.3La0.08Mn
porous printed
Stability across the 0.3La 0.08Mn PTC heater
as a function of time drawn for solid and
porous 3D printed samples compared with
industrial benchmark
25
50
75
100
125
150
175
1 10 100
Temperature(°C)
Time (s)
SP 3W SP 2W
SP 1W PP 1W
PP 2W PP 3W
IB 1W IB 2W
IB3W
SP3W
IB2W
PP3W
PP2W
SP2W
IB1W
PP1W
SP1W
-4
-3
-2
-1
0
1
2
3
0 500 1000 1500 2000
Temperaturedeviationfrommean(°C)
Time (s)
0.68
0.98
1.03
Standard
Deviation
-4
-2
0
2
4 0.3La0.08Mn porous printed…
-4
-2
0
2
4 0.3La0.08Mn solid printed…
-4
-2
0
2
4 Industry Benchmark…

12. Geometrical Freedom
Heating of alternative 3D printed geometries – (electrode
placement can alter heating characteristics)

13. Conclusions
• Honeycomb printing of PTC
material – demonstrated
feasibility and repeatability
• Variations of dopant
concentration affects the
material properties, but is not
affected by the extrusion
process
• Paste rheological properties and
print variables vital for control;
allows manufacturing of
accurate, high quality parts with
designed porosity – hence
tailored performance
A holistic
approach: powder
to product
manufacturing of
PTCR ceramic
heaters

14. Future Work
• Thorough characterisation of 3D printed parts at
BorgWarner – cycle fatigue, reliability tests
• Use of field assisted sintering techniques in
combination with 3D printing
• Functionally Graded Materials (FGM) – the
potential to use in fuel filters, complex shaped
zonal heating components and use of multi-
material extrusion
• Increased efficiency from design freedom provided
by AM can allow for manufacture of
unconventional geometries – suitable for other
demanding applications by further design
optimisation FGM heaters

15. 15
▪ Deliver a series of ESA AM projects through a
frame contract allowing access to state-of-the-art
AM capabilities
▪ Be a centre for space sector companies to
approach to mature their AM products and
process understanding
▪ Consolidate European leadership on AM for space
ADDITIVE MANUFACTURING AT THE MTC
▪ Accelerate standardisation and close standards
gaps in AM
▪ Create strong global partnerships among AM
developers, users and stakeholders
▪ Support education, training, proficiency testing,
and certification programs
▪ >100 (out of 800) staff working on AM projects
▪ Accelerate the uptake of AM by developing the
technology and systems required to address the
key challenges within the AM value chain by:
▪ Developing a robust AM supply chain
▪ Developing AM process chain technology
▪ Building confidence in AM and improve uptake by UK
UK National Centre for AM
since 2014
ASTM Centre of
Excellence for AM
since April 2018
European Space Agency (ESA)
AM Benchmarking Centre
since May 2017

16. 16
MANUFACTURING INNOVATION

17. Inspiring Winners Since 1909
Thank you for listening
William Rowlands
w.rowlands@lboro.ac.uk
W. Rowlands, B. Vaidhyanathan, Additive manufacturing of barium titanate based
ceramic heaters with positive temperature coefficient of resistance (PTCR), Journal of
the European Ceramic Society. (2019). doi:10.1016/j.jeurceramsoc.2019.03.024.