8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

1/25

Microwave Hydrothermal

synthesis of Nano materials

by

Dr. k.Venkateswara Rao

HOD of CNST,JNTU-H

Hyderabad.

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

2/25

Micro waves are electromagnetic radiations in the

frequency range of 300MHz to 300 GHz .

Their wavelengths are with in few mm to 30 cm.

800-900 MHz

50-600MHz

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

3/25

Invented accidentally by Dr. Percy Le Baron Spencer

While testing a magnetron during work, he discovered

the candy bar in his pocket melted

Experimented with other food products (popcorn and

eggs), and realized microwaves can cook foods quickly

At 1947, 1st commercial microwave oven produced

(called Radio range).

Improvement and refinements made ~by 1967, 1st domestic microwave oven

produced

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

4/25

Microwave ovens use a frequency of2.45 GHz 12 cm wavelength

This is ideally suited for the time it takes to flip a

water molecule around half-cycle is 200 picoseconds

Imagine microwaving steam molecules are far apart

they flip back and forth. Now crowd molecules into liquid water no elbow room to do their exercise

bump into each other and get mad (heat up)

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

5/25

Micro wave-associated hydrothermal method is novelsynthesis ofNano materials is rapidly developing area in

research. Useful frequency is 2.45 GHz in laboratories . At 2.45 GHz, microwaves penetrate into materials (looks

partially transparent) and excite water moleculesinternally.

2.45 GHz is a good compromise: lower frequency wouldnot be readily absorbed ,higher frequency would notpenetrate well.

During microwaves irradiating , the material dielectric

loss which function of frequency of micro waves .

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

6/25

0

0.05

0.1

0.15

0.20.25

0.3

0.350.4

0.01 0.1 1 10 100

Absorbti

o

n

Frequency

Well below the naturalfrequency

Not much absorption

Well above thenatural frequency

Not muchabsorption

Near the naturalfrequency

Absorption

2.4 GHz

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

7/25

1.Microwave heating of the aqueous liquid precursorstransfer of energy to solution through ions present in in

solution from the microwave due to conductive current .

2. the realignment of dipole or ion field in the alternatingelectric field and as a result the solution is heated .

because of this doubly internally heating method , thematerials coupled to microwave field will be heated rapidly .

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

8/25

Power

watts

Intensity watts per square metre

Specific energy Absorption Rate (SAR)

watts per kilogram

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

9/25

700 watts

Around 140 000 volts per metre

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

10/25

Power

This is a 700 watt oven

Think of 7 x 100 watt light bulbs

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

11/25

Electricity from the wall outlet travels through the power cord

and enters the microwave oven through a series of fuse and

safety protection circuits These circuits include various fuses and thermal protectors that

are designed to deactivate the oven in the event of an electricalshort or if an overheating condition occurs

When the oven door is closed, an electrical path is also

established through a series of safety interlock switches

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

12/25

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

13/25

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

14/25

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

15/25

The magnetron tube transforms thehighvoltageinto electromagneticenergy.

A stirring blade spreads the microwaves

evenly

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

16/25

The microwaves that penetrate in to materials have anelectric field that oscillates 2.45 billion times a second, afrequency that is well absorbed by polar liquid moleculessuch as water, sugars, fats and other material molecules.

Water interacts with the microwave: flipping its orientation back and forth very rapidly bumping into one another and producing heat.

Glass, paper, ceramic, or plastic containers are used inmicrowave cooking because the microwaves pass throughthem

Metal reflects microwaves Unsafe to have metal pans/aluminum foil in oven, may

damage oven

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

17/25

Stirring the solution of distal water and required precursors with

required concentration and add required PH agent .

Placed the solution in micro oven. Select required temperature level and voltage level. After prescribed time , precipitate is formed ,switch off power

supply. P

recipitate washed by deionized water several times and filterthe precipitate with filter paper several times. The filtered precipitate was aged over night at bellow 80 degree

Celsius.

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

18/25

Lower processing timings.

uniform densification.

Selective heating .Reduction in vaporization of volatile species.

Minimum grain growth and bettermechanical properties.

High homogeneity .

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

19/25

Continuity variable micro wave output power

from 1kw to 6kw.

Gas passing facility .Vacuum control up to 10 torr.

Selective heating.Controlled reactions possible.

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

20/25

the ability of materials to absorb microwaves.

MaterialDielectric loss property . PH agent . Medium . Concentration of solution. Temperature . Vacuum surrounded by solution. Different gas atmosphere .

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

21/25

PH agents like KOH,NaOH, ammonia neutralize

acidic nature the solution .

PH agent prevent fire in micro oven.PH agent control crystalline growth, suitable to

formNano particles.PH agent control excess oxidation.

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

22/25

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

23/25

Solution combustion Microwavehydrothermal

method

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

24/25

1. It is known that microwave radiation can heat body tissue the same

way it heats food.

2. Exposure to high levels of microwaves can cause a painful burn

Ex. the lens of the eye ~ exposure to high levels of microwaves cancause cataracts.

3.Microwave oven used low level of microwaves, within the region of

non-ionizing radiation

4.Still uncertain in the effects of humans from long term exposure to low

level of microwaves

Still experimenting

5. Best to stay a way (an arms length) in reducing exposure to

microwaves

HealthHazards and Percussions

8/8/2019 DR KVR Mirco Wave Hydrothemal Synthesis of Nano Materials

25/25