Magnet

article ini diambil dari chemistry.com 

How to Make Liquid Magnets  Imtroduction 

1. A liquid magnet or ferrofluid is a colloidal mixture of magnetic particles (~10 nm in diameter) in a liquid carrier. The carrier contains a surfactant to prevent the particles from clumping together. Ferrofluids can be either water-based (the usual form for chemistry demonstrations) or organic-based (as in oils or fluorocarbons used for industrial applications). A typical ferrofluid is about 5% magnetic solids, 10% surfactant, and 85% carrier, by volume. The ferrofluid you can make uses magnetite for the magnetic particles, oleic acid as the surfactant, and kerosene as the carrier fluid to suspend the particles. Stir the suspension until most of the black color has been transferred into the kerosene. Magnetite and oleic acid are insoluble in water, while oleic acid is soluble in kerosene. The coated particles will leave the aqueous solution in favor of the kerosene.
4. Decant and save the kerosene layer. Discard the water. The magnetite plus oleic acid plus kerosene is the ferrofluid.

How to Make Liquid Magnets – Procedure for Synthesizing Magnetite

The first step is to prepare the magnetite, which will be the source of the magnetic particles in the ferrofluid. This is done by reducing the ferric chloride (FeCl₃) in PCB etchant to ferrous chloride (FeCl₂), which will be used to make magnetite. Commercial PCB etchant is usually 1.5M ferric chloride, to yield 5 grams of magnetite. If you are using a stock solution of ferric chloride, follow the procedure using a 1.5M solution.

1. Use the syringe or medicine cup to measure and dispense 10 ml of PCB etchant into a glass measuring cup. Add 10 ml of distilled water.
2. Drop a piece of steel wool into the diluted etchant solution. Agitate the liquid until it turns bright green (green is the FeCl₂).
3. Filter the liquid through a coffee filter.

Several people have asked me if they can make substitutions for the oleic acid and the kerosene. The answer is yes, though changing the chemicals will change the characteristics of the ferrofluid somewhat. You can try other surfactants and other organic solvents. The surfactant must be soluble in the solvent.

When no external magnetic field is present the fluid is not magnetic and the orientation of the magnetite particles is random. However, when an external magnetic field is applied, the magnetic moments of the particles align with the magnetic field lines. When the magnetic field is removed, the particles return to random alignment. These properties can be used to make a liquid that changes its density depending on the strength of the magnetic field and that can form fantastic shapes.

You can find ferrofluids in high-end speakers and in the laser heads of some CD and DVD players. They are used in low friction seals for rotating shaft motors and computer disk drive seals. You could open a computer disk drive or a speaker to get to the liquid magnet, but it’s pretty easy (and fun) to make your own.

How to Make Liquid Magnets – Materials and Safety

Safety Considerations
This procedure uses flammable substances and generates heat and toxic fumes. Please wear safety glasses, work in a well-ventilated area, and be familiar with the safety data marked on the chemical containers (MSDSs). Be advised that ammonia fumes are toxic. The resulting fluid is very strongly attracted to magnets and can splash, staining skin and clothing. Wear eye and skin protection when working with the ferrofluid. Don’t drink the fluid. Keep it out of reach of children and pets.

Materials

• oleic acid (may be found in some pharmacies, craft, and health food stores)
• household ammonia
• PCB etchant (ferric chloride solution) – from an electronics store or you can make your own solution
• distilled water
• steel wool
• a magnet
• kerosene
• heat source
• 2 beakers or measuring cups
• a plastic syringe or medicine cup (something to measure 10 ml)
• coffee filters

How to Make Liquid Magnets – Procedure for Suspending Magnetite in a Carrier

Next, the magnetic particles need to be coated with a surfactant, so that they won’t stick together when magnetized. Finally, the coated particles will be suspended in a carrier, so the magnetic solution will flow. Prepare the carrier in a well-ventilated area, preferably under a fume hood.

1. Heat the magnetite solution to just below boiling. Stir in 5 ml of oleic acid. Hold the temperature near boiling until the ammonia evaporates (approximately an hour). Remove the mixture from heat and allow it to cool. The oleic acid reacts with ammonia to form ammonium oleate. Heat allows the oleate ion to enter solution, while the ammonia escapes as a gas. When the oleate ion binds to a magnetite particle it is reconverted to oleic acid.
2. Add 100 ml of kerosene to the coated magnetite suspension.

How to Make Liquid Magnets – Things to Do with Ferrofluid

Ferrofluid is very strongly attracted to magnets, so maintain a barrier between the liquid and the magnet (e.g., sheet of glass). Avoid splashing of the liquid. Both kerosene and iron are toxic, so do not ingest the ferrofluid or allow skin contact (don’t stir it with a finger or play with it).Here are some ideas for activities involving your liquid magnet ferrofluid. You can:

• Use a strong magnet to float a penny on top of the ferrofluid.
• Use magnets to drag the ferrofluid up the sides of a container.
• Bring a magnet close to the ferrofluid to see spikes form, following the lines of the magnetic field.

Explore the shapes you can form using a magnet and the ferrofluid. Store your liquid magnet away from heat and flame. If you need to dispose of your ferrofluid at some point, dispose of it the way you would dispose of kerosene.

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