basic science and technology of magnetic nano fluids

8/8/2019 Basic Science and Technology of Magnetic Nano Fluids

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Basic science and technology of

Magnetic Nanofluids


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Magnetic nanofluids

Also know as Ferrofluids

Stable colloidal suspensions of magnetic nanoparticles in polar and

non-polar carrier liquids.

First developed and classified in 1960 by Stephen Pappell at

NASA for controlling fluids in space.

Initially used as rotating shaft seals in satellites and for cooling

materials used in Space Research


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Nanotechnology

Deals with the study and applications of mattermanipulated on the nanoscale i.e. between 1-100 nm.

What happens at nanoscale ??-ratio of surface area to volume increases.

-quantum effects predominate.

- Structural changes e.g. opaque substances becometransparent (copper).

- A material such as gold, which is chemically inert atnormal scales, can serve as a potent chemical catalystat nanoscales.


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Nanoparticles

1st used in glazes for Chinese porcelain.

Carbon based nanomaterials, Nanocomposites,

Metals & alloys, Biological nanomaterials,Nanopolymers, Nano-glasses, Nano-ceramics.

Applications

Energy storage-batteries and capacitors,Bio-sensors, Catalysts, electronic devices

Fig: Carbon Nanotubes


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Magnetic properties

Derived from the crystal structure.

Magnetite crystallizes in a cubic close packed structure.

Fe2+ ions and Fe3+ ions have anti-parallel spins which lead to a net

magnetization effect.

This is known as Ferrimagnetism but Ferrofluids are

Superparamagnetic.

Fig1: Structure of magnetite nanoparticles


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FLOW PROPERTIES

The location of a ferrofluid can be precisely controlled

through the application of a magnetic field, and, by

varying the strength of the field, the fluids can be forced to

flow.

Fig2: Flow properties of a nanofluid


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thermal properties

Nanofluids show a large enhancement in thermal conductivity(k)

when they form aggregates.

Large enhancement in k is due to the efficient transport of heat

through the percolating nanoparticle paths.

Hence can be used as smart cooling devices.

Fig3: Percentage

enhancement andmechanism of heat

transport from a

cylindrical device

immersed in NF

without and with

magnetic field


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Preparation of magnetic nanofluids

. Synthesis of magnetic nanoparticles by chemical condensation

Usually magnetite Fe3O4 is used.

. Stabilization/dispersion of magnetic nanoparticles in various carrier

liquids.

Fig : preparation of ferrofluids


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For the particles to remain in suspension, its particle diameters needto be on the order of 10 nm.

At room temperature, the thermal energy of the particles is of thesame order of magnitude as the gravitational and magneticattraction.

This is sufficient to prevent agglomeration due to magneticinteractions.

A surfactant is added to generate electrostatic repulsions between

the magnetic particles.

E.g. cis- oleic acid, tetramethylammonium hydroxide

The stoichiometric ratio that results in the best ferrofluid is the one

that responds most dramatically to a magnet.


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leakage-free rotating seals

- Traditional rotary seals

-constant maintenance

-subject to wear-accumulation of particulate matter

Hence performance is compromised.

Ferrofluid is used in conjunction with rotary seal.

-Ferrofluid acts like a magnetic liquid O-ring


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Wear is minimal as the fluid consists of high quality lubricating oil.

Leak free Operation

High Vacuum Operation - advanced magnetic fluid formulations mean thatvacuums up to 10-9 mbar or better can be achieved.

Positive Pressure capability - feedthroughs also have a minimum positivepressure capability of 2 atmospheres, with higher pressures possible withminor design changes.

Optimum Torque Transmission - the use of liquid o-ring seals give lowfriction, slip-stick free rotation, high torque transmission and a large speedrange from indexing to many thousands of rev/min.

Non Contaminating - the sealing element is non-rubbing and so no particlesare generated and the seals are ideal for ultra clean environments.

Long Life and High Reliability - the sealing medium is a low vapor pressurefluid, friction is very low and wear insubstantial. Seals can therefore have

exceptionally long lives, with maintenance free lives of over a decade beingrecorded.


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Biomedical

-Here magnetic nanoparticles are coated with a biological

molecule.

-These particles can then be manipulated by an external

magnetic field.o DrugDelivery

o Plant genetics e.g. Biostimulators

Fig: Ferrofluids used in cancer therapy


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NDT Sensors

- Based on the magnetic flux leakage technique(MFL).

- Used to detect defects in ferromagnetic materials.

- Upon application of a magnetic field, the fluid shows different

colours due to Bragg phenomenon.

Fig. : Colour pattern

observed in the

ferrofluid cell due tonormal component of

leakage magnetic field

in absence (left) and

presence of a

rectangular slot (right).


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Nanofluid based optical filters

In spectroscopy and interferometry, filters are used to

eliminate stray light from entering the detector head.

The filter consists of a nanofluid based emulsion, a

miniature solenoid and a variable Direct Currentsource for changing the magnetic field.


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Advantages

1. Simple to operate and less expensive as compared to other

filters.

2. a single filter can be used for a range of central wavelengths.

3. It is suitable for selecting wavelengths in the ultraviolet,visible and infrared regions

4. There is no need to change the optical element for different

wavelength regions.

5. Tuning can be easily achieved by changing the field strength.6. Intensity of transmitted light can be controlled by adjusted by

changing the emulsion concentration.


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Magnetorheological suspensions

damping mechanisms

-An MR fluid usually consists of 20-40 percent iron particles,

suspended in mineral oil, water.

-When the MR fluid is not magnetized, the particles inside distributed

randomly, allow the fluid to move freely, acting like a regular

damper fluid.

-When a magnetic field is applied, the particles become energized

and align into fibrous structures, perpendicular on the direction of

the magnetic flux. This restricts the movement of the fluid,

proportional to the power and intensity of the magnetic field.- Used in automobile damping systems.

Fig: Magnetic fluid as a Magnetorheological fluid in damping


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Overwhelming Benefits

1. Lesser number of moving parts.

2. Enhanced stability even on gravel, slippery road surfaces.

3. Since magnetic polarization is not affected by temperature,

the performance is relatively insensitive to temperature over a

broad temperature range (-40 degrees Celsius 105

degrees Celsius).

DRAWBACK

High Cost.


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Conclusions

Magnetic nanofluids are fluids with magnetically

controllable fluid properties and have a widerange of technological applications in today's

world.


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THANK YOU

basic science and technology of magnetic nano fluids

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