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Topics - Debangshu Paul

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Please read the previous post : http://forum.daffodilvarsity.edu.bd/index.php?topic=21401.0 if u havent already.

Why does it do that?

Iron ore in oil reacts pretty much the way it reacts without the oil. Only one thing is really different. The oil allows the powder to slump more easily than it can when dry. This is because of its extra weight, its lubricating ability, its viscosity, and the fact that the ore is more buoyant in oil than in air.

Saying that it behaves like dry ore doesn't really answer the question unless we know why dry ore acts the way it does. If we look very closely at the ore with a magnifying glass or a microscope, we will notice that the pieces are a little longer than they are wide. They look like small footballs. Shapes like this do interesting things in a magnetic field.

Take a small iron nail in one hand, and a magnet in the other. Move the nail around the magnet, holding the nail loosely so it can move under the influence of the magnet. The nail will align itself with a bar magnet if you hold the two of them parallel to each other. As the nail moves toward one pole of the magnet, it will rotate so the point of the nail points toward the pole. Eventually, when the nail is above the pole, it will point straight at the pole.

There are two ways to think about what is happening. Pretend the attraction of the magnet is the attraction of the Earth, and the nail is a domino standing up on its end. A slight push makes the domino lie flat, and it takes a larger push to make it stand up straight again. We say that the domino has more potential energy when it is standing up than it has when it is lying down. There is a tendency for dominos to lose this energy by lying down. They have much less of a tendency to spontaneously gain energy and stand up by themselves. The nail tends to "fall down" so that it aligns with the magnetic lines of force that surround the magnet.

To illustrate the second way of thinking about the nail and the magnet we need a second nail. Hold the first nail parallel to the magnet, about half an inch to the right. Bring the second nail parallel to the first nail, a little to its right. We might expect the magnet to attract the second nail, just like the first nail. Instead we find that the two nails are repelling one another. If we lower the second nail so its top is near the bottom of the first nail, it now attracts the first nail.

The nails seem to have become magnets themselves while in the presence of the bar magnet. Their poles repel when they are parallel, and attract when they align vertically. If the bar magnet has its north pole facing away from you, the nails will have their south poles facing away from you. The nails attract the magnet because unlike poles attract each other. The nails repel each other because like poles repel each other. It is now easy to see why the nail follows the magnetic lines of force as it moves around the magnet. Its north pole points toward the magnet's south pole. Its south pole points to the magnet's north pole. When the nail is beside the magnet, it is parallel because the attractions are equal. When it is closer to the magnet's north pole, the nail's south pole attracts and the north pole repels, and it rotates.

Magnets repel one another when they are side by side. They attract one another when they are end to end. The natural state of a collection of magnets will thus be a string of them stuck end to end. If there are two strings next to each another, they will stagger so the poles of one string will be next to the centers of the other. Like poles are thus as far apart as possible. The strings will still repel from one another slightly. This is exactly the behavior of grains of iron ore sprinkled on paper above a magnet.

When a magnet is placed on the side of a jar of iron ore powder, the powder arranges itself into strings. Each grain of powder becomes a magnet and attracts the opposite pole if its neighbor. The strings thus formed repel each another, and the powder expands. If the powder has been mixed with oil, the oil wicks into the spaces created by the expansion, and sticks there by surface tension. The result is a dry appearing solid that does not leak oil.

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A magnetorheological fluid is a liquid that hardens near a magnet, and becomes liquid again when you remove the magnet. They are simple to make in your kitchen after a trip to a sandbox.

In the introduction to this section I described how to mine iron ore out of the sand from playgrounds or the beach. You may want to spend a while at the beach, because we will need a good handful of ore.

The ore that sticks to the magnets in the plastic bags has quite a bit of sand entrained in it. We can remove the sand by some additional refining. Make sure the ore is dry. Spread the ore out on a paper plate, and hold the bag with the magnet over the plate until a small amount of ore jumps up to the bag. Put this ore onto another plate, and continue until no more ore rises to the magnet in the bag. Don't get the bag too close to the plate, since there are many sand grains with ore stuck to them. We wish to keep only the ore that does not stick to grains of sand. The ore in the second plate should be visibly darker than what is left in the first plate. If you can see a lot of sand in the second plate, repeat the process, using a third plate.

Put the ore into a small cup. Soft plastic cups work nicely. The cup should be small enough that the ore fills it at least a third of the way up. Add some vegetable oil to the ore, and stir with a plastic spoon, or another nonferrous object, such as a popsickle stick. Keep adding oil until you get a thin black paste. Now gently place a strong magnet on the side of the cup. It should stick to the side as it attracts the ore. The ore should become quite stiff. Tip the cup over another cup to let excess oil and ore pour off. What remains in the first cup is our magnetorheological fluid.

We are now ready for the fun part. Hold the cup upright, and remove the magnet. Stir the liquid with the plastic spoon. It may be a little stiff at first, but will soon stir easily. Tip the cup a bit to the side, and bury the bowl of the spoon in the liquid. Now place the magnet on the side of the cup to stiffen the goop. The spoon will now stand upright when the cup is righted. The cup can even be inverted without losing any fluid, although a little oil may still drip out the first few times. Set the cup upright again, remove the magnet, and the solid mass slumps back into the cup, and the spoon falls over.

Put some fluid into a plastic bag, and let a magnet stick to the side of the bag. Now you can form the fluid into shapes by pressing the bag. The fluid will act like clay, and hold its shape. When you remove the magnet, the shapes slump into puddles.
Why does it do that??? Lets wait for the next part :)

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Textile Engineering / Nano-particles & their uses in textiles: Part 6
« on: July 14, 2014, 10:11:17 PM »
Polymer and polymer nano-composites

It has been established in recent years that polymer-based composites reinforced with a small percentage of strong fillers can significantly improve the mechanical, thermal and barrier properties of the pure polymer matrix. Moreover, these improvements are achieved through conventional processing techniques without any detrimental effects on processability, appearance, density and aging performance of the matrix. Now-a-day's hybrid polymers (such as Organoallcoxy silanes), which are the hybrid structure of inorganic-organic nano-composite materials are being used to impart the combination of scatch resistance with dirt-repellent effect, high transparency, special barrier properties or antimicrobial function to the material.

Clay nano-particles: Clay basically consists of hydrous aluminosilicate and is low in density. Nanosize clay particles or flaks can impart excellent flame retardant functionality to the textile due to the heat resistant behaviour of the nanoclay (14). UV blocking power and outstanding barrier functionality are due to the internees of nanoclay to corrosive chemicals and its neatly layers configuration inside fibre. In terms of mechanical attributes, nylon6 clay composite with a clay mask fraction of 5% shows 40% higher tensile strength, 68% greater tensile modulus, 60% higher flexural strength, and 126% greater flexural modulus.

Such a significant improvements in composite strength even leads to application of nano clay filler as a protective insert in infantry helmets. Nano clay fillers modified with quaternary ammonium salt have been introduced into polypropylene fibre, the resultant fibre can be coloured by acid and disperse dyes to 1-4% colour shades for incorporation of less than 5% nano-dry fillers. The modified nano clay introduces dye attaching sites to the polypropylene fibre generates void space inside the fibre to entrap dyes without degrading the beneficial properties of polypropylene.

Carbon nano particles: Carbon nano black particles are extremely effective reinforcing material for composite fibres . With their high aspect ratio, carbon black nano particles can improve abrasion resistance and hence increase the durability of composite fibres. Carbon black nano particles can also result in high chemical resistance and electric conductivity after they are mixed with fibre polymer matrix. Polyester, nylon and polypropylene have been used as polymer matrix with weight percentage of nano size filler range from 5% to 20%.

Dapeng Li and Gang Sun have reported that carbon black nano-particles can directly be used in traditional dyeing processes to dye polyester and acrylic fabrics. Polyester and acrylic fabric were dyed with nano carbon black particles using a dip-pad, dry and cure technique. Effective colouration of these fabrics has been reported with 8 nm particles, using cationic dispersing agent, at 1800C treatment temperature.

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Textile Engineering / Nano-particles & their uses in textiles: Part 5
« on: July 14, 2014, 10:09:54 PM »
Metals and metal oxides nano-particles

Nano-size particles of Pd/Pt, Ag and Fe can be applied on textiles to impart antibacterial, conductive magnetic properties and remote heating properties. Silver has been used for the treatment of medical ailments for over 100 years due to its natural anti-bacterial and anti-fungal properties. Nano-silver particles are widely applied in socks to prohibit the growth of bacterial. In addition, nano-silver can be applied to a range of other healthcare products such as dressings for burns, scald, and skin donor and recipient sites.

Nano-silver particles can be applied on textiles by padding method with good laundering durability. Hoon Joo Lee and Song Hoon Jeong  have reported that nano-sized silver colloids and nano-silver treated polyester nonwovens have good bacteriostasis. Water based and ethanol based nano-silver colloids with spherical nano-particals of diameter 2-5 nm can be applied to polyester nonwoven fabric. It has been reported that the growth of bacteria colonies is absolutely inhibited with only 10 ppm colloidal silver nano-particles.

Nano-size particles of TiO2, ZnO, Al2O3, and MgO are a group of metal oxide that possesses photo catalytic ability, electrical conductivity, UV absorption, and photo-oxidising capacity against chemical and biological species. Intensive research involving the nono-particles of metal oxides have been focusing on antimicrobial, self decontaminating, and UV blocking functions for both military protection gears and civilian health products. Nylon fibre filled with ZnO nano-particles can provide UV shielding function and reducing static electricity of nylon fibre. A composite fibre with nano-particles of TiO2/MgO can provide self-sterilising function.

TiO2 and MgO nano-particles can be entrapped into a textile fibres during the spinning process or incorporated into a textile material via normal textile finishing methods with a resultant material having chemical and biological protective performance.Cellulose fibre filled with nano-particles of metal oxides (such as TiO2) from in situ synthesis can be used as a catalyst in fuel cells .

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Textile Engineering / Nano-particles & their uses in textiles: Part 4
« on: July 14, 2014, 10:08:18 PM »
Some commercially available nano-particles

Nano-particles may consist of various elements and compounds. The size of the molecules is the sole criterion for inclusion in the category of nano-particles. Nano-particles have a length of 1 to 100 nm. Conventional materials have grain sizes ranging from microns to several millimeters and contain several billions atoms each, nanometre sized grains contain only about 900 atoms, exhibit new and improved properties compared to the corresponding bulk material (Table1). Some nano-particles currently available are as follows (5-7):

Metals: Pd/Pt, Ag, Fe, etc.

Compounds: - Organic: Vitamins, DNA, Hydroxylapatite, Colour pigments.
                    - Inorganic: TiO2, ZnO, Fe2O3, MgO, SiO2 etc.

Polymer: - cellulose nano-whiskers
              - carbon nano-whiskers.

Some Nano-Particles and their properties
1   Silver Nano-Particles:               Anti-bacterial finishing
2   Fe Nano-Particles:                   Conductive magnetic properties, remote heating.
3   ZnO and TiO2:                           UV protection, fiber protection, oxidative catalysis
4   TiO2 and MgO:                           Chemical and biological protective performance, provide self-sterilizing function.
5   SiO2  or Al2O3 Nano-particles with PP or PE coating:   Super water repellent finishing.
6   Indium-tin oxide Nano-Particles:   EM / IR protective clothing.
7   Ceramic Nano-Particles:           Increasing resistance to abrasion.
8   Carbon black Nano-Particles:   Increasing resistance to abrasion, chemical resistance and impart electrical conductivity, colouration of some textiles.
9   Clay nano-particles:                   High electrical, heat and chemical resistance.
10   Cellulose Nano-whiskers:     Wrinkle resistance, stain resistance, and water repellency.

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Textile Engineering / Nano-particles & their uses in textiles: Part 3
« on: July 14, 2014, 10:05:31 PM »
Some other type of clothing niche being explored on many fronts, with perhaps more staying power than scratch-and-sniff shirts, involves the nanoscale improvement of fabrics and fibres. Nanotechnology is adding its labels to popular clothing brands with various products: Resists Spills, Resists Static, Coolest Comfort, and Repels and Releases Stains. Researchers all around the world are looking at all sorts of metal additives and polymer additives, inorganic, organic materials to take them at nanoscale to impart lots of interesting properties to textiles.

Preparation of nano-sized materials

There are several physico-chemical methods for preparation of nano-sized material mentioned as below :

  • Vapour phase reaction.

    Chemical vapour deposition.

    Inert gas condensation.

    Laser ablation.

    Plasma spraying.

    Spray conversion.

    Sputtering.

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Textile Engineering / Nano-particles & their uses in textiles: Part 2
« on: July 14, 2014, 10:04:12 PM »
The technology, utilising materials a thousand times smaller than the width of a human hair, is showing up in everything from auto parts to sunscreens and clothing (1,2). However, nanotechnology has been used to improve products that most of us use everyday. These include laundry detergent, 6-pack rings, and surgical tools. One of the most widespread applications of nanotechnology is in clothing. Nanotechnology is also called a "bottom up" technology owing to using such small-scale building units, in contrast to bulky material engineering that is considered a "top down" approach (3). Many textile industries and research organisation has already developed fabrics with distinguishing properties. Scratch-and-sniff clothing is one example. Pleasantly scented, tiny polymer beads are added to clothing, such as within a strawberry applied on a shirt. Then there are menthol pajamas, scented to open the nasal passages of people suffering from colds, ensuring a good night's sleep.

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Textile Engineering / Nano-particles & their uses in textiles: Part 1
« on: July 14, 2014, 10:03:24 PM »
These days, the word "nano" seems to be popping up everywhere. Wall Street, Hollywood, and major universities around the globe have all endeavored to associate their diverse enterprises with this word. "Nano" is a metric unit that means one billionth of a unit; as of late, it has been used most frequently in reference to nanotechnology. The term "nanotechnology" has never been used so broadly.

K Eric Drexler coined it in his 1986 book, Engines of Creation to refer to his theories for molecular manufacturing, following up on visionary ideas presented 27 years earlier by famed physicist, Richard Feynman. As the possibilities of molecular nanotechnology grew and excitement built in the scientific community many researchers began using the term for their own endeavors at the nanoscale, unrelated to molecular manufacturing.

Nanotechnology seeks to provide and apply knowledge of the behaviour of objects in the nanometre (nm) size range to the assembly of complex structures for use in a variety of practical applications. The tiniest substances promise to transform industry and create a huge market. In chemicals, cosmetics, pharmaceuticals, technology and textiles, businesses are researching and manufacturing products based on nanotechnology, which uses bits of matter measured in billionths of a metre.

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In the past years priorities with regard to the manufacture of aerospace structures have changed significantly. Cost savings have become more and more important relative to weight reduction. Hence, state-of-the-art composite manufacturing processes are regarded as being no longer cost-efficient enough. Some reasons for the high costs of FRP aircraft components are expensive materials (prepregs) and slow and labour-intensive manufacturing processes. In addition, extensive quality assurance processes have to be performed.
An approach to partly overcome these disadvantages is the use of textile techniques allowing the processing of dry fibres to near-net-shape preforms additionally offering the possibility of a three dimensional fibre architecture. Essentially, automatic manufacturing processes derived from the garment industry are modified to allow the processing of high-performance fibres.

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