FERROFLUID- You may know, but not that clearly

[bennyquach]

HOW TO MAKE LIQUID MAGNETS

Introduction

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 sticking together. Ferrofluids can be suspended in water or in an organic fluid. A typical ferrofluid is about 5% magnetic solids, 10% surfactant, and 85% carrier, by volume. One type of 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.

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 ferrofluid.

Materials and safety
Safety Considerations


This procedure uses flammable substances and generates heat and toxic fumes. Please wear safety glasses and skin protection, work in a well-ventilated area, and be familiar with the safety data for your chemicals. Ferrofluid can stain skin and clothing. Keep it out of reach of children and pets. Contact your local poison control center if you suspect ingestion (risk of iron poisoning; carrier is kerosene).

Materials

• household ammonia
• oleic acid (may be found in some pharmacies, craft, and health food stores)
• PCB etchant (ferric chloride solution) - from an electronics store or you can make your ferric chloride or ferrous chloride solution or you can use magnetite or magnetic hematite powder if you have either of those minerals handy (magnetic hematite is an inexpensive mineral used in jewelry)
• steel wool
• distilled water
• a magnet
• kerosene
• heat source
• 2 beakers or measuring cups
• a plastic syringe or medicine cup (something to measure 10 ml)
• filter papers or coffee filters

Procedure for Synthesizing Magnetite

The magnetic particles in this ferrofluid consist of magnetite. If you aren't starting with magnetite, then the first step is to prepare it. This is done by reducing the ferric chloride (FeCl3) in PCB etchant to ferrous chloride (FeCl2). Ferric chloride is then reacted to produce 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. Pour 10 ml of PCB etchant and 10 ml of distilled water in a glass cup.
2. Add a piece of steel wool to the solution. Mix the liquid until you get a color change. The solution should become bright green (green is the FeCl2).
3. Filter the liquid through filter paper or a coffee filter. Keep the liquid; discard the filter.
4. Precipitate the magnetite out of the solution. Add 20 ml of PCB etchant (FeCl3) to the green solution (FeCl2). If you are using stock solutions of ferric and ferrous chloride, keep in mind FeCl3 and FeCl2 react in a 2:1 ratio.
5. Stir in 150 ml of ammonia. The magnetite, Fe3O4, will fall out of solution. This is the product you want to collect.
The next step is to take the magnetite and suspend it in the carrier solution.

Procedure for Suspending Magnetite in a Carrier

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 like a liquid. Since you are going to be working with ammonia and kerosense, prepare the carrier in a well-ventilated area, outdoors or under a fume hood.
1. Heat the magnetite solution to just below boiling.
2. Stir in 5 ml oleic acid. Maintain the heat until the ammonia evaporates (approximately an hour).
3. 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 (which is why you need ventilation). When the oleate ion binds to a magnetite particle it is reconverted to oleic acid.
4. Add 100 ml kerosene to the coated magnetite suspension. 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. If you make a substitution for the kerosene, you want a solvent with the same property: the ability to dissolve the oleic acid but not uncoated magnetite.
5. Decant and save the kerosene layer. Discard the water. The magnetite plus oleic acid plus kerosene is the ferrofluid.

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 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. Have fun!

Some interesting videos:

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