Transcript
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Top-down techniques take a bulk material, machine it, modify it into the
desired shape and product- classic example is manufacturing of integrated circuitsusing a sequence of steps sush as crystal growth, lithography, deposition,
etching, CMP, ion implantation
(Fundamentals of Microfabrication: The Science of
Miniaturization, Marc J. Madou, CRC Press, 2002)
Bottom-up techniques build something from basic materials
- assembling from the atoms/molecules up
- not completely proven in manufacturing yet
Examples:
Self-assembly
Sol-gel technology
Deposition (old but is used to obtain nanotubes, nanowires, nanoscale films)
Manipulators (AFM, STM,.)
3-D printers (http://web.mit.edu/tdp/www)
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Production of NanomaterialsThere are five widely known methods to produce nanomaterials,and they are as follows: Sol-gel synthesis, Inert gas condensation, Mechanical alloying or high-energy ball milling,
Plasma synthesis, and Electrodeposition.
A sol is a dispersion of the solid particles (~ 0.1-1 mm) in a liquidwhere only the Brownian motions suspend the particles.
A gel is a state where both liquid and solid are dispersed in eachother, which presents a solid network containing liquid components
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Sol-Gel SynthesisAll the above processes synthesize nanomaterials to varyingdegrees of commercially-viable quantities.To date, of all the above process, only sol-gel synthesis can Produce materials (both metals and ceramics) at
low temperatures Large quantities (to be commercially viable) relatively
cheaply,
Synthesize almost any material,
Co-synthesize two or more materials simultaneously,
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Coat one or more materials onto other
materials (metal or ceramic particulates, and three-dimensional objects),
Produce extremely homogeneous alloys andcomposites,
Synthesize ultra-high purity (99.9999%)
materials, Tailor the composition very accurately even in
the early stages of the process, because thesynthesis is actually performed on an atomic level,
Precisely control the microstructure of thefinal products, and Precisely control the physical, mechanical, and
chemical properties of the final products.
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In general, the sol-gel process involves the transition of asolution system from
a liquid "sol" (mostly colloidal) into a solid "gel" phase.
Utilizing the sol-gel process, it is possible to fabricate advancedmaterials in a wide variety of forms:
ultrafine or spherical shaped powders,
thin film coatings, fibers, porous or dense materials, and
extremely porous aerogel materials.
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The starting materials used in the preparation of the "sol" areusually inorganic metal salts or metal organic compoundssuch as metal alkoxides.
In a typical sol-gel process, the precursor is subjected to a seriesof hydrolysis and polymerization reactions to form a colloidalsuspension, or a "sol".
Further processing of the "sol" makes it possible to makematerials in different forms.
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a flexible method for preparation of (nano)materials
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Orgin of Ferroelectricity
* The Existence of a Double-Well Potential.
* The Formation of Ferroelectric Domains.
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permittivity ordielectric constant of a material is
H2O is a polar liquid; ~ 80
Typical ionic solids; ~ 10
Air; ~ 1
BaTiO3 :-
vacC
C
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Below 120C, BaTiO3 is ferroelectric with aligned
dipoles.
Residual dipole disorder gives ~200-1000
At ~127C, tetragonal cubic phase transition.
Dipoles randomise and increases to ~5,000-10,000
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For capacitor applications,
need to increase capacitance [energy stored/mass orvolume] by increasing Q and thus increasing
How to do this?
BaTiO3 is very good at 120C
but want high at room temperature!
1) Partial substitution of Ba by a smaller M
2+
ion - Sr
2+
;unit cell volume decreases and the phase transition temperature
decreases
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Powder preparation
Shape forming
High temperature sintering
Finishing
Pressure-less hot press
hot isostatic press
mechanical
Laser, water jet
ultrasonic
Pressing, casting
plastic forming
colloidal processing
solid-state reaction
coprecipitation
sol-gel
spray pyrolysis
emulsion synthesishydrothermal synthesis
Four steps involved in typical powder processing for advanced
ceramics.
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Synthesis method Solid-state
Reaction
Coprecipita-
tion
Sol-gel Spray
/Freeze
Drying
Spray
Pyrolysis
Emulsion
Synthesis
Hydrother
mal
Synthesis
state ofdevelopment
commercial commercial R&D demonstration
R&D demonstration demonstration
compositional
control
poor good excellent excellent excellen
t
excellent excellent
morphology
control
poor moderate moderate moderate excellen
t
excellent good
powder reactivity poor good good good good good good
particle size (nm) >1000 >10 >10 >10 >10 >100 >100
purity (%) 99.5 >99.9 >99.9 >99.9 >99.9 >99.5
agglomeration moderate high moderate low low low low
calcination step yes yes yes yes no yes no
milling step yes yes yes yes no yes no
costs low-
moderate
moderate moderate-
high
moderate-
high
high moderate moderate
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Experimental procedurePb(NO3)2 + La(NO3)3.6H2O +Bi(NO3).5 H2O +ZrO(NO3)2.2H2O
distilled water
Stirring on magnetic stirrer for 2-3 hrs to get transparent solution
Drop wise addition of Titanium isopropoxide results in formation of Ti(OH)4
Few drops of nitric acid to dissolve Ti(OH)4& to get clear solution
white precipitate was obtained
Solution was vacuum filtered and washed several times with distilled water
Filtered cake powder was kept in oven for 24 hrs at 150C
Dropwise addition of NH3OH Soln
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DTG and TG curve of sample A
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DTG and TG curves of sample B
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XRD patterns of sample A at
various temperatures () TiO2, () Pb(NO3)2, () Bi2O3, () ZrO2.
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XRD patterns of sample B at different temperatures
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XRD pattern of sintered ceramics
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d values in (Sample A)
d values in (Sample B)
h k l
Observed Calculated Observed Calculated4.128 4.129 4.113 4.114 0 0 1
4.018 4.019 4.004 4.005 1 0 0
2.876 2.880 2.872 2.870 1 0 1
2.344 2.341 2.334 2.333 1 1 1
2.064 2.064 2.063 2.057 0 0 2
2.008 2.009 2.006 2.002 2 0 0
1.836 1.836 1.836 1.830 1 0 2
1.8080 1.807 1.801 1.800 2 0 1
1.6730 1.670 1.668 1.664 1 1 2
1.647 1.648 1.646 1.642 2 1 1
1.440 1.440 1.437 1.435 2 0 2
Comparison of observed and calculated d values
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Sample System tetragonal Unit cell
Volume(3)
a () c () a/c
A 4.0197 4.1298 1.0274 66.73
B 4.0057 4.1148 1.0272 66.02
Comparison of lattice parameters
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Sample r maxEDS methodPLZT (7/65/35)
PLZT (8/65/35)
PLZT (9/65/35)
PLZT (10/65/35)
1340
1610
1430
990
2815
3465
1690
1108
Co-precipitation
PLZT (7/65/35)
PLZT (8/65/35)
PLZT (9/65/35)
PLZT (10/65/35)
2245
3480
3055
2130
5905
6890
4020
3760
Comparison of Dielectric Constants of modified PZT Ceramics
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AVersatile process for making ceramic and glass materials(powders, coatings, fibers variety of forms).
Involves converting from a liquid solution to a solid gel
Start with inorganic metal salts or metal alkoxides (called
precursors); series of hydrolysis and polymerization
reactions to prepare a colloidal suspension (sol).
Next step involves an effort to get the desirable form- thin film by spin or dip coating
- casting into a mold
Further drying/heat treatment, wet gel is converted into
desirable final product
Conclusion
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Ceramic fibers can be drawn from the gel by adjusting theviscosity
Powders can be made by precipitation, or spray pyrolysis
Examples
- Piezoelectric materials such as lead-zircomium-titanate (PZT)
- Thick films consisting of nano TiO2 particles for solar cells
- Optical fibers
- Anti-reflection coatings (automotive)
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