1 LTP ÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE Powder Technology From Landslides and Avalanches to Concrete and Chocolate Prof. P. Bowen (EPFL), Dr. P. Derlet (PSI) WEEK 14 – file no. 12 Sintering Mechanisms & New Technologies- (4) New Technologies – Sintering Methods
88
Embed
Powder Technology From Landslides and Avalanches to ... · – Isothermal, controlled rate, two-step, hot press, hot isostatic pressing – Solid state, liquid phase, reactive sintering
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
- x component of the shrinkage rate contributed by power-law creep
- mesoscopic strain rate corresponding to the temperature gradient driven
grain boundary (thermal) diffusion
28
Eugene A. Olevsky, Ludo Froyen, J. Am. Ceram. Soc., 92 [S1] S122–S132 (2009)
Grain-boundary diffusion contribution – from surface
tension and external load
29
shrinkage rate - power-law creep mechanism
30
Eugene A. Olevsky, Ludo Froyen,
J. Am. Ceram. Soc., 92 [S1]
S122–S132 (2009)
Temperature evolution and the local temperature gradient of
an alumina powder specimen subjected to SPS.
Contribution to shrinkage rate from different mechanisms of mass transport
for an alumina powder; G= 0.5 mm;
• Results indicate that the effect of thermal diffusion can be significant, especially for small particle sizes.
• Its contribution is considerable not only in the case of free sintering and low pressure-assisted sintering,
but it competes with the contribution of external pressure-driven power-law creep within certain
temperature ranges.
Porosity kinetics during SPS of alumina powder.
34
• The thermal diffusion-including model predictions for the shrinkage kinetics are compared with the
experiments on SPS of a pure alumina powder and exhibit good qualitative agreement.
• however, the model emphasizes only one factor of a thermal nature—thermal diffusion
• The model developed, thus, should be considered a part of the larger-scale efforts in including various
phenomena, listed in this paper….
Transparent Ceramics by SPS8YSZ PLZSTAl2O3
35
Ferroelectrics_BaTiO3
100nm
50nm
30nm
SEM microstructure of samples with grain size of 100nm, 50nm and 30nm. The final microstructure depends on the starting powder.
“Spark plasma sintering of nano-crystalline ceramics”, Zhao, Z ; Buscaglia, V ; Bowen, P and Nygren, M , KEY ENGINEERING MATERIALS, Volume: 264-268 Pages: 2297-2300 , 200436
SPS to make complicated shapes
Silicon-Nitride and Al2O3/SiCw
55mm hip joint bowl for medical application
Zhe Zhao, Nanoker report, 2007
37
Flash Sintering – Direct applied voltage
CE J Dancer - Mater. Res. Express 3 (2016) 102001
• In its most basic form, a flash sintering apparatus consists of a high-temperature furnace and a power supplyattached in some way to a ceramic sample.
• Additional monitoring equipment is required to determine the voltage, current, and sample displacement/shrinkage during the heat-treatment.
• From the literature to date,three main types of flash sintering apparatus have been identified.
• Representative schematic diagrams based on typical designs are shown in figure 3. and specimen geometry in Fig 4
Flash Sintering of TZP
M. Cologna, B. Rashkova, and R. Raj, “Flash Sintering of Nanograin Zirconia in <5 s at 850°C,” J. Am. Ceram. Soc., vol. 93, no. 11, pp. 3556–3559, Nov. 2010.
➢ A threshold electric field intensity is needed for the start of flash sintering
➢ It’s the high local grain boundary temperature leads to flash sintering, which is very different from the conventional Joule heating.
➢ The local GB temperature is dependent on the relative density.
Flash Sintering of TZP
M. Cologna, B. Rashkova, and R. Raj, “Flash Sintering of Nanograin Zirconia in <5 s at 850°C,” J. Am. Ceram. Soc., vol. 93, no. 11, pp. 3556–3559, Nov. 2010.
➢ Power instability is consistent with the onset of flash sintering.➢ Instability resulted from the poor neck growth can be of importance➢ The “run away” effect mostly contribute the high GB temperature gradient
Flashing Sintering Super-Fast processing at relatively lower temperature
For high resistance material, it will not work that efficiently! For example, high purity alumina.
The set-up is simply based on conventional sintering furnaces. This is one advantage for industrial interest.
Not very consistent about the sintering mechanisms.
Need more development for the future applications.
Cold Sintering Process (CSP)Cold Sintering: Progress, Challenges, and Future Opportunities*
Abstract:
Cold sintering is an unusually low-temperature process that uses a transient transport phase,
which is most often liquid, and an applied uniaxial force to assist in densification of a powder
compact. By using this approach, many ceramic powders can be transformed to high-density
monoliths at temperatures far below the melting point. In this article, we present a summary
of cold sintering accomplishments and the current working models that describe the operative
mechanisms in the context of other strategies for low-temperature ceramic densification.
Current observations in several systems suggest a multiple-stage densification process that
bears similarity to models that describe liquid phase sintering. We find that grain growth
trends are consistent with classical behavior, but with activation energy values that are lower
than observed for thermally driven processes. Densification behavior in these low-
temperature systems is rich, and there is much to be investigated regarding mass transport
within and across the liquid-solid interfaces that populate these ceramics during densification.
Irrespective of mechanisms, these low temperatures create a new opportunity spectrum to
design grain boundaries and create new types of nanocomposites among material
combinations that previously had incompatible processing windows. Future directions are
discussed in terms of both the fundamental science and engineering of cold sintering.*Jing Guo, Richard Floyd, Sarah Lowum, Jon-Paul Maria, Thomas Herisson de Beauvoir, Joo-Hwan Seo, and Clive A. Randall, Annual Review of Materials Research , Vol. 49:275-295 (2019)https://doi.org/10.1146/annurev-matsci-070218-010041
Clive Randall – video - https://www.youtube.com/watch?v=dVTWq8s7y4E
*Jing Guo, Richard Floyd, Sarah Lowum, Jon-Paul Maria, Thomas Herisson de Beauvoir, Joo-Hwan Seo, and Clive A. Randall, Annual Review of Materials Research , Vol. 49:275-295 (2019), https://doi.org/10.1146/annurev-matsci-070218-010041
(a) Summary of relative density-sintering temperature plot for BaTiO3 ceramics in regard to various sintering techniques. CS = conventional sintering; TSS = two-step sintering; RCS = rate-controlled sintering; SPS = spark plasma sintering; MVS = microwave sintering; HPS = high-pressure sintering; FS = flash sintering; CSP = cold sintering process. A theoretical density of 6.02 g cm3 is adopted for BaTiO3 .
(b) Density evolution of cold-sintered and subsequently annealed BaTiO3 ceramics as a function of cold
sintering time.
Method : Mixture of submicron and nanoparticles in water – heat - get dissolution of nano-precipitation onto larger particles – Ostwald ripening – same phase….cement precipitates new phase
H. Guo, et al, ACS Nano, vol. 10, no. 11, pp. 10606–10614, Nov. 2016.
• Microstructure very inhomogeneous …not a good ceramic…
• even if 98% dense after annealing at 900°C –
• even if dielectric properties are starting to be interesting
• mechanical properties and lifetimes probably very low..
H. Guo, A. Baker, J. Guo, and C. A. Randall, “Protocol for Ultralow-Temperature Ceramic Sintering: An Integration of
Nanotechnology and the Cold Sintering Process,” ACS Nano, vol. 10, no. 11, pp. 10606–10614, Nov. 2016.
Potentials and further needs of CSP Mainly a dissolution-precipitation route cf liquid phase sintering Have not yet obtained close to 100% dense bodies may be an issue of using the
right powder and solvent (P&T), but maybe the method itself cant has limitations. CSP can be good for biomimetic application e.g. polymer ceramics composites–
low temp – low energy CSP is it a true sintering. If yes cement & concrete and ultra-high pressure compaction of metal are also
cold-sintering… future needs (Guo et al Annual Review of Materials Research , Vol. 49:275-295 (2019), )
Paul Bowen, Michael Stuer
Laboratoire de Technologie des Poudres, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
Fundamental Issues in the Processing of
Transparent Aluminas : From Interparticle Forces to
Interparticle Forces - simple to use freeware – Hamaker*
⚫ Repulsive
Electrostatic, ion adsorption, dissociation, polyelectrolyte
h
(a)
(b)
++
+
+
++
+
+
+
++
++
+
+
++
+
+
+
++
(distance h between particles)
hak
al
r = ( h + 2a )
*U. Aschauer, et al J. Dispersion Science Technology, 32(4), 470 – 479 (2011).
( ) ( ), , 212k lha a h
aF A
h= − 2 k l
k l
a aa
a a=
+
Harmonic average radius
( )
( )( )
2
2
0 22
1
h L
ES h L
eF a
e
− −
− −= −
+
Electrostatic potential
From zeta potential)
1/− Electrical double
layer thickness
( )5
3
2
3 2, 2 1
5
Bster k l
k T LF a a a
s h
= −
L - Adsorbed layer thickness, s - Spacing of adsorbed moleculesIn mushroom configuration – geometry important
⚫ Attractive - dispersion or Van der Waals forces – A(h) – Hamaker constant
53
Overall Interaction Energy – DLVO*
♦ Net force is algebraic sum of
repulsive and attractive forces
0
Inte
rac
tio
n E
nerg
y
charge
polymer
Attraction - VdW
h
(-)
(+)
1-4 nm
Repulsion total
♦ Bergström$- good qualitative
results with alumina & fatty acids
♦ Not quantitative - used identical
spheres - need to use PSD
♦ Yield stress mODEL (YODEL)#
Uses PSD
♦ Predicts yield point
♦ Used for cement £ – complex
mixture of 4 or more minerals –
certain degree of success ( ),h Disp ES Steha rG F F F= + +
$Bergström, et al J.Am.Ceram.Soc., 75(12) 3305-14 (1992). *Derjaguin & Landau - Vervey & Overbeck #Flatt&Bowen, J. Am. Ceram. Soc., 89 [4] 1244–1256 (2006), £Houst et al 38 1197–1209 (2008), Perrot et al
Cem.&Conc.Res. 42 (2012) 937–944, Palacios et al Mater. de Construcción, 489-513, 62(308), 2012
Total Interaction
VT = VA + VR
Maximum Energy Barrier,
54
Taking into account Particle Size Distributions (PSD)
• Suspension may form an attractive
network - yield stress
• To flow have to break ”pairs”
• Reduces the effective volume
fraction
• To predict - need all the possible
pair interactions as a function of
zeta potential, adsorbed layer
thickness, PSD etc....
• Suzuki & Oshima* statistical model
( ),h Disp ES Steha rG F F F= + +
Total Interaction Force
1 2
1 2
2
a a
a aa =
+
All forces – function of harmonic radius
(*M. Suzuki, T. Oshima, Estimation of the coordination number in a multicomponent mixture of
spheres, Powder technology, 1983, 35, pp. 159-166) 55
YODEL - Effective volume - aggregates
No. of “bonds” – coordination number from packing models
Strength of bond from interparticle force calculations
Certain no. of “bonds” break under a certain shear
How does effective volume of solids change?
Robert J. Flatt, Paul Bowen, J. Am. Ceram. Soc., 89 [4] 1244–1256 (2006)
Yodel: A Yield Stress Model for Suspensions
56
YODEL - Effective volume - aggregates
No. of “bonds” – coordination number from packing models
Strength of bond from interparticle force calculations
Certain no. of “bonds” break under a certain shear
How does effective volume of solids change?
Robert J. Flatt, Paul Bowen, J. Am. Ceram. Soc., 89 [4] 1244–1256 (2006)
Yodel: A Yield Stress Model for Suspensions
57
YODEL - Increased effective volume - aggregates
Truncated coneEnclosing sphere
Several geometries looked at – some minor differences but all
give same general trends
Best fit to alumina slurries – Enclosing sphere model
Robert J. Flatt, Paul Bowen, J. Am. Ceram. Soc., 89 [4] 1244–1256 (2006)
Yodel: A Yield Stress Model for Suspensions
58
YODEL - Volume fraction functionality
( )
( )
−
−=
**
01m
Factor, m1 includes:
- particle size (a)
- particle size distribution
- interparticle force, G (a,h)
- distance of closest approach, H
- radius of curvature of contact, a*
0
1000
2000
3000
4000
5000
6000
7000
0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55
AKP-50AKP-30AKP-20AKP-10
Yie
ld s
tress
[Pa]
Volume fraction [-]
Model validated with data from attractive network - careful study on alumina
slurries near the isoelectric point$
Yield stress, , as a function of volume fraction () and maximum packing
fraction () , percolation threshold 0
$Zhou, Z., Solomon, M. J., Scales, P., Boger,
D. V. - J. Rheol. 43(3) 651-671(1999)
➢ Pores / precipitates
➢ Grains themselves
Transparent Polycrystalline Alumina - General Context