Presentation on Flash Sintering submitted for the evaluation of Course "Seminar and Technical Writing CR798"

1. 1
Department of Ceramic Engineering
National Institute of Technology
Rourkela, Odhisa
Field Assisted Sintering Technology
Presentation on
Flash Sintering
Seminar and Technical Writing (CR798)
Autumn-2021
Presented by
Kumar Sanket (519cr1011)
Course Instructor- Prof. Debasish Sarkar

2. Seminar and Technical Writing
Department of Ceramic Engineering
Content Table
2
Contents:-
 Sintering Technology
 Mechanism of Sintering
 Types of Sintering
 Conventional Sintering Process
 Advance Sintering Process
 Flash Sintering
 First Publication on Flash Sintering
 Specimen Geometries and Experimental setup
 Flash Sintering setup
 Flash Sintering Mechanism
 Operating Condition for Flash Sintering
 Stages of flash Sintering
 Flash Sintered materials
 Microstructure comparison: Flash Vs. Conventional
 Advantages and Disadvantages of Flash Sintering
 Global Research data on flash sintering
 Application of flash Sintering

3. Seminar and Technical Writing
Department of Ceramic Engineering
Sintering Technology
What Does Sintering Mean?
Sintering is basically a process of heat treatment in which a huge
quantity of loose material’s particles are subjected to a sufficiently
high temperature and pressure to bring the loose materials into a
solid form. The amount of heat and pressure given during the
sintering process must be slightly less than the material's and it
melting point.
The aim of sintering process is to increase the mechanical
strength of the material and to prevent deformation and
cracking of samples.
Figure 1. Conventional Sintering setups
Credit-Mater. Res. Express 3 (2016) 102001 C E J Dancer
3

4. Seminar and Technical Writing
Department of Ceramic Engineering
Mechanism of Sintering
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Figure 2a . Stages of densification in ceramic materials
(I) Initial stage—particles bond together, organic additive burn out surface become smooth
(II) intermediate stage—particles form a continuous network,densification and pore shrinkage begins,
(III) final stage—pores become isolated , densification rate slows down significant shrinkage achieved
Figure 2b . Transportation of matter mechanism.
Refrence- Ceramic Processing and Sintering ,M.N Rahman
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5. Seminar and Technical Writing
Department of Ceramic Engineering
Types of sintering
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a) Solid state sintering: Atomic diffusion in solid material is the main driving force for the solid state sintering.
b) Liquid phase sintering: In this process the densification is enhanced by using a small quantity of liquid (upto
10% volume) for the materials which are difficult to sinter because of high temperature requirement.
c) Activated sintering : An alloying element termed ‘dopant’ is added in a small amount to the material to be
sintered which further increases the densification by as much as 100 times upper than the undoped to be sintered
samples.
d) Reaction sintering:Reaction sintering takes place when two or more constituents of the sample undergoes a
chemical reaction and generates a higher temperature to process the sintering and create a final densed product.
Types of Sintering
Solid State
Sintering
Liquid State
Sintering Activated Sintering Reaction Sintering

6. Seminar and Technical Writing
Department of Ceramic Engineering
Types of Sintering Process
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Conventional Sintering
Dense ceramic with Nano structural composition is achieved by conventional
types of sintering by pressing together of the nano powders constituents just
simply by the application of pressure assisted methods like hot isotactic
pressing,uniaxial pressure and hot press.
Types of Sintering Process
Conventional Sintering Advanced Sintering:Field
assisted Sintering

7. Seminar and Technical Writing
Department of Ceramic Engineering
Advanced Sintering Techniques: Field Assisted Sintering Technology
Figure 3 Time Vs. temperature plot obtained for sintering YSZ by
altered Technique
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Flash
Sintering
Laser
Microwave
Adavantages
 Enhances the kinetics
 Reduces the temperature
 Reduces the Sintering Time
Spark plasma Sintering

8. Seminar and Technical Writing
Department of Ceramic Engineering
Non-conventional Ceramic Sintering Techniques
Field Assisted Sintering Technology
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 Microwave sintering
 Electromagnetic radiation (300 MHz−300 GHz)
 Temperature below conventional temperature
 Within few minutes
 Spark Plasma Sintering
 Graphite mould, pressed with graphite plungers
 DC current is passed through the sample
 The die as a heating source, heat the sample to high temperatures
 Within couple of minutes
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Figure 4
Figure 5

9. Seminar and Technical Writing
Department of Ceramic Engineering
Non-conventional Ceramic Sintering Techniques
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 Flash Sintering
 Higher electric fields
 Faster increase in the sintering rate, accompanied by a power surge
 Much lower temperature than conventional sintering
 Couple of seconds
Energy efficient & Cost effective method
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 Laser Sintering
 laser as the power source to sinter powdered material
 Sample built layer by layer,3D Structure can be formed
 No mould is required
 Within couple of minutes to hours
Refrence- https://doi.org/10.1016/j.mex.2015.10.004
Figure 7
Figure 6

10. Seminar and Technical Writing
Department of Ceramic Engineering
Flash Sintering
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Flash Sintering (FS) is the type of advanced
sintering process in which sintering takes place
by the application of a direct electric field via
customized electrodes to a material to be
sintered.
It is a cost and energy efficient sintering
technique which involves electrical Joule
heating, and rapid densification of the material
can be achieved in less than a minute(<60s)
Sample temperature given as a function of time (a) 30secs, (b) 32.5 secs , (c) 80 secs and (d) after the
power turned off.
Figure 8:
Credit- Journal of the European Ceramic Society 40(15):5829-5836

11. Seminar and Technical Writing
Department of Ceramic Engineering
First Publication on Flash Sintering
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1) Yttrium-stabilized zirconia(YSZ) was sintered in a few seconds to full density just by providing
the temperature of 850°C, starting green density of the material was 0.5, by the application
of a dc electrical field of 100V/Cm…
2) In normal sintering conditions, the same material will take upto several hours at 1450°C are
needed to complete the complete sintering Process…
3) Author explained the finding by the local Joule heating at the grain boundaries sites, which
on the one side initiates the grain- boundary diffusion (a kinetic effect), while at the same
time restricts grain growth (a thermodynamic effect).

12. Seminar and Technical Writing
Department of Ceramic Engineering
Specimen Geometries and Experimental setup for Flash
Sintering
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Electrical contact-
Electrodes Materials Pt (ink, paste, wires, and plates) Mo, Cu
 alumina dog bone sample
Pt
C onset flash sintering temperature decreases by 250ºC
Ag
Three fundamental components for flash
sintering setup:
i) Furnace: For heating the sample
ii) Power supply: For AC/DC Current Source
iii) Electrodes:Estabilishing connection
between sample and power source
Figure 9-Specimen geometry for a typical Flash Sintering Experiment

13. Seminar and Technical Writing
Department of Ceramic Engineering
Flash Sintering Set-up
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(a) Vertical tube
furnace/ Box furnace
(b) Adapted dilatometer/
Mechanical loading frame
(c) Hot pressing apparatus/SPS
Sample Dog-bone Pellet Pellet
Shrinkage Camera Displacement sensor/LVDT Power surge/displacement of
die
Applied load
No standard flash sintering configuration of apparatus exists
Saunders, T. et al. Ultrafast-Contactless Flash
Sintering using Plasma Electrodes. Sci. Rep. 6,
27222; doi: 10.1038/srep27222 (2016).
Figure 10 FS setup outlines.
Figure 11
Credit-CEJ Dancer

14. Seminar and Technical Writing
Department of Ceramic Engineering
Flash Sintering Mechanism
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Differential heat generation & dissipation rates vs temperature of the specimen
[14] Credit- Zhang Y, Jung J-I, Luo J. Thermal runaway, flash sintering and
asymmetrical microstructural development of ZnO and ZnO‐ Bi2O3 under direct
currents. Acta Mater. 2015;94:87–100 Diagram showing when joule is sufficient(Red color) ,when joule heating is not self-sufficient(Blue Color)
Credit- Raj R. Analysis of the power density at the onset of flash sintering. J Am Ceram Soc. 2016;99:3226–
32.
Figure 12
Figure 12
Refrence- J Am Ceram Soc. 2019;102:5–31. DOI: 10.1111/jace.16061

15. Seminar and Technical Writing
Department of Ceramic Engineering
Operating conditions for flash sintering
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Figure 13: Process parameters that influence the flash sintering behavior.
Refrence- M. Biesuz, V.M Sglavo,:Journal of the European
Ceramic Society 39 (2019) 115–143116

16. Seminar and Technical Writing
Department of Ceramic Engineering
Stages of Flash Sintering
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Stage 1 : Here the Power supply is kept under the control of voltage and heating of the sample is due to Joule
heating, while keeping the sample at the stable furnace temperature, increase in current is dependent on the
nature of the increase in temperature.
Stage 2: The flash process tend to start by this stage. The power source is changed from voltage control to
current control and the sintering starts within 1–5 s.
Stage 3: At the last stage the Power source is still kept under current control, and flash state is maintained.
Sample is almost sintered by this stage completely, grain growth take place very promptly, The furnace may be
switched off by now and the sample cooling starts.
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Stage I - Incubation stage
Stage II-Transient stage/Flash stage
Stage III-Steady state stage
Jha et al. summarise the findings of earlier isothermal experiments with flash sintering of 3Y-
TZP, describing three distinct stages of the process, specifically:
The length of each stage depends on the material and the process conditions(electric field and furnace temperature). A
complete theory of flash sintering needs to explain the mechanisms for the behaviour during each stage
Mater. Res. Express 3 (2016) 102001 : C E J Dancer

17. Seminar and Technical Writing
Department of Ceramic Engineering
Flash Sintered Materials
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Materials Sintering
(Conventional)
°C
Flash
Sintering
Temp (°C)
Pressure
(Mpa)
Electric
field
(V/cm)
Current
(A)
Current
Density
(Amm−2)
Grain size
(mm)
Density
(%)
3%YSZ 1400°C/ hours 850 120 0.3 0.06 1-5 >90
BaTiO3 1300°C/ 5h 1020 100
SiC >2000 1029 300 10 1-2 99.2
B4C 2250-2350 1931 15.3 - 2000 3.5
ZrB2 2198 25 11 95
Y2O3 985
1133
- 1000
500
0.06
0.06
97.9
99.6
Al2O3 1600 1260 1000 0.06
TiO2 1000/20h 1150
600
250
1000
0.06 12 1.5
SnO2 900 80 5 91.8
ZnO 625
675
160
80
0.151 94.5
Co2MnO4 325 12.5
SrTiO3 1400/1h 1200 150 0.5 1 >95

18. Seminar and Technical Writing
Department of Ceramic Engineering
Microstructure Comparison :Flash Sintering Vs. Conventional Sintering
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Figure 14:. Comparison of grain size determined from polished surfaces (top row) and fracture surfaces (bottom
row) of 3Y-TZP samples prepared by conventional and flash sintering.
Source- C E J Dancer 2016 Mater. Res. Express 3 102001

19. Seminar and Technical Writing
Department of Ceramic Engineering
Field Assisted Sintering Technology
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Credit: Marco
Cologna & Rishi
Raj, Univ. of
Colorado
Sintering strain as a function of the furnace temperature for specimens
subjected to different electric fields for flash sintering vs Conventional
sintering.
M. Biesuz, V.M Sglavo,:Journal of the European Ceramic Society 39 (2019)
115–143116
Figure 15
Figure 16:
Credit: Marco Cologna & Rishi Raj, Univ. of Colorado.
Source-

20. Seminar and Technical Writing
Department of Ceramic Engineering
Advantages of Flash Sintering
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i) The most obvious one is clearly related
to the huge reduction of time and
temperature thus this process is energy
efficient thus become economical and
serves environmental benefits.
iii) Absence of con-strained sintering:
Shear stresses which are responsible for
constrained sintering are quickly released
in the flash state.
ii), Flash Sintering requires much simple and
less expensive experimental setup
iv) It becomes possible to sinter metastable
materials or to avoid undesired phase
transitions as it is out of equilibrium process.

21. Seminar and Technical Writing
Department of Ceramic Engineering
Thermal Gradient upon Flash Sintering:A Major Concern
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Thermal management can be
achieved by:
•Altering the method for applying
electrodes
•Improving thermal homogeneity
through insulation
•Tailoring the frequency of the AC
current
•Developing contactless methods for
applying the electric current, which
are currently limited to consolidation
of thermal barrier coatings.
i) Sometimes Low quality ceramics
product due to weaknesses caused by
inhomogeneities in the microstructure.
The origins of these inhomogeneities can
be given by the rise of thermal
gradients in the material
during flash sintering.
Disadvantages of flash Sintering
ii) The main limitation of the flash process
resides in the fact that it is “autocatalytic”
and hot spots i.e. electric current
concentration along preferential paths, can
be formed in components larger than few
millimetres.
iii) Conductive pastes used for
conductivity may causes a local
contamination of the component
Figure 17
Credit- Jones, G.M., Biesuz, M., Ji, W. et al. Promoting microstructural homogeneity during flash
sintering of ceramics through thermal management. MRS Bulletin 46, 59–66 (2021).
https://doi.org/10.1557/s43577-020-00010-2

22. Seminar and Technical Writing
Department of Ceramic Engineering
Global Research data on flash Sintering
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Figure 18. (a) Research papers published on flash sintering during
the period of July 2010 to May 2016. (b) Pie chart showing the
country of first author’s affiliated institute.
Figure 19. Pie chart showing the number of papers
published on Flash material categorised by the different
materials group.
Refrence- Min Yu, Salvatore Grasso, Ruth Mckinnon, Theo Saunders & Michael J. Reece (2017)
Review of flash sintering: materials, mechanisms and modelling, Advances in Applied Ceramics,
116:1, 24-60, DOI: 10.1080/17436753.2016.1251051
It can be concluded from the two figures that near about 50%(42/88) of the
published articles belongs to the research group from USA.Professor Rishi Raj’s
(Colorado University) and his group has made a significant contribution in the
field of flash sintering and had published nearly 20 publications and he is one of
the author first published articles on flash sintering. Whereas the research group
from UK,Italy and Brazil have also successfully published some good articles and
emarked their presence in research field of flash Sintering. Out of seven patents
have been registered on flash sintering out of which four belongs to USA[16].
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23. Seminar and Technical Writing
Department of Ceramic Engineering
Application of Flash Sintering
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Healthcare
Advanced Materials Traditional Ceramics
Application Orthopaedic Implants Optical devices, electroceramics Tiles, tableware, sanitaryware
Challenge
(all three relevant to all sectors)
To improve materials properties
Reduce processing costs/time whilst
maintaining material properties
To reduce high production costs and
CO2 emissions
Image Credit: Aumm graphixphoto/Shutterstock.com
Image
Credit: https://www.lucideon.com/materials-
technologies/flash-sintering
Source: https://www.lucideon.com/materials-technologies/flash-sintering
Figure-20- First floor tile produced by flash sintering method at lucideon
Figure-21-Flash Sintered products
First industry to adapt flash sintering

24. Seminar and Technical Writing
Department of Ceramic Engineering
Significant articles on Flash Sintering
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25. Seminar and Technical Writing
Department of Ceramic Engineering
Thank You for Your Valuable time and Attention