Dr S A Acharya

Combustion and Micr owave Routes for Synthesis of Nanomaterials: A case study

Smita Acharya 12/03/09

Asst Professor, Deptt of Physics St Vincent Pallotti College of Engg. & Tech., Nagpur

Outline  Combustion Synthesis of rear earthdoped CeO2

 Microwave Synthesis of Metal sulfide & Metal oxide semiconductor.

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Nanomaterials Preparation by Combustion Technique

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Calculation of oxidizing and reducing valences for combustion ---• Concept of propellant chemistry is used for valence calculation. • The valence of N = 0, O = -2, C = +4, H = +1, divalent metal ions = +2, Trivalent metal ions = +3 and trivalent metal ions = +4.

• Based on this consideration, divalent metal nitrate Ca4(NO3)3 have oxidizing

valency is ?, trivalent metal nitrate Gd2(NO3)3 ? and tetravalent metal nitrate Ce(NO3)3?

• Glycine (C2NH5O2) has reducing valency ?

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Precursor calculation for 5 gm sample

Sample

Sample

Weight (gm)

CeO2

5.00

?

Gd2O3

5.00

?

Ca4O3

5.00

?

Ce(NO3)3

Ce0.95 Gd0.05 O2- δ 4.7406

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C2NH5O2

Gd2(NO3)3

C2NH5O2

0.2593

?

combustion synthesis Ce (NO3)3

Dissolved in distilled water at 80°C

Introduce into furnace at 550°C 5 min. Foam of CeO2 Product

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Glycine

X-RD

By Scherrer Equation: 6000C

28.9 nm 5000C

20.6 nm

As prepared powder [loosely agglomerated to form porous network]

4000C 4000C

17.2 nm

X-RD of pure ceria

X-RD of Sm-doped-Ceria 12/03/09

Calcined powder at 5000C for 2 h. [particles are roughly in spherical morphology with particles size 1217 nm]

X-RD continue  XRD of powders calcined at 500oC show that samarium form solid solution with fluorite structure in ceria

Ce(1-x) SmxO2- δ (SDC) for x = 0.05 to 0.30 mol %

Unit cell parameter increases with increasing Sm content in good agreement with effective ionic radii considerations rCe 4+ = 0.96 nm, rSm 3+ = 0.121 nm.  Solubility limit of samarium in ceria is around 20 mol %

Dopant content vrs lattice parameter

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Impedance spectroscopy and conductivity of Sm-doped-Ceria calcined at different temperature

-10

0

SDC2080 (380 C) o 0C 1- Sintered 1300 1 - calcined at at600 C 0 2Sintered at 1100 C 2 – calcined at o 500 C

Z"(K.ohm)

-8 -6 -4 -2 0

1

2

0

2

4

6

8

10

Comparison of Impedance plot of SDC2080 pellets calcined at (1) 600oC and (2) 500oC for 2 h.

Z'(K.ohm)

Log(σ T) (S/cm)K

1.5 0 -1.5 -3 -4.5 1

1.2

1.4

1000/T (K ) -1

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1.6

Arrhenius plot of SDC2080 calcined at (° ) 500oC and (♦ ) 600oC for 2 h.

Microstructure of pellets sintered at different temperature

SEM of SDC15 pellets sintered at © 900oC (d) 1000oC (e) 1100oC and (f) 1200oC for 3 h . [Isothermal sintering give rise different grain sizes with varying sintering temperature.]

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Impedance spectroscopy and conductivity of Sm-doped-Ceria Sintered at different temperature Sintering temperature a- 1100C b- 1200C c- 1300C d- 1400C

Impedance diagram of pellets sintered at different temperature for 3 h. measuring temperature 350oC

1100 1200 1300 1400 1500

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Arrhenius plots of conductivity

Microwave Synthesis • Microwave is electromagnetic waves with frequencies between 300 MHz to 300 GHz. • The electric field applies a force on charge particles start to migrate or rotate. Due to the movement of charged particles, further polarization of polar particles takes place.

• The concerted forces applied by the electric and magnetic components of microwave are rapidly changing in direction, which creates friction and collisions of the molecules.

• As microwave can penetrate materials and deposit energy, heat can be generated throughout the volume of the materials.

• Thus, microwave energy is delivered directly to materials through molecular interaction, which enable to achieve rapid and uniform heating of thick materials.

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Magnetic Materials •

•

Hard disk drive (HDD) technology has achieved recording density over 100 Gbit/(inch)2.

Forfurtherincreaseofthedensitytowardsterrabitrecording, nanosizedmagneticcrystallitesarerequiredinrecordingmedia.

An array of Fe-Pt nanoparticles is one of the candidates to satisfy the requirement of the terabit recording. •

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Fe-Pt Materials Ferrious acetylacetone + Platinum diacetylacetonate

Mixed in inert atm. with Tetraethylen e glycol

280 W for 30 min

Precipitate washed / centrifugation with argon for 4 times at 7000 rpm Washed with deionized water

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Dried in vacuum

10 nm

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Zinc Sulfide

• Zinc sulfide is wide band gap semiconductor material. • An efficient phosphor in flat panel displays, cathode ray tubes, in thin film electroluminescent devices and infrared window. • Zinc doped with metal cations are reported to emit intense light upon application of stress. • This makes materials promising candidates in newly emerging mechanooptical devices.

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Experimental Details ZnCl2.6H2O + thiourea

0.05 M solution in double distilled water

140 W & 30 min

Precipitate washed / centrifugation with argon for 4 times at 7000 rpm

Dry a room temperature

Washed with deionized water

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3.5

10m 15m 20m 25m 30m 40m

Intensity

3.0 2.5 2.0

309nm

1.5

1.0 0.5

0.0

300

400

500

600

W avelength(nm )

3.5

Intensity

3.0

20% 30% 35% 40% 50%

2.5 2.0 1.5 1.0 0.5 0.0

300

400

W avelength(nm )

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500

600

200 nm

100 nm

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500

Experimental Details TbCl2.6H2O + MnCl2.4H2O 1:1 0.05 M solution in double distilled water

•0.05 M solution of KOH

140 W & 30 min Vacuum Evaporation

Calcined at 8000C for 90 min

Dry at room temperature Precipitation separated by acetone

TbMnO3 by microwave and conventional methods

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Thank you 12/03/09