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TUTORIAL SUMMARY

This tutorial is designed with middle and high school teachers and students in mind. It is intended to demonstrate a simple synthesis procedure for obtaining water-based magnetic liquids. The resulting ferrofluid is comprised of magnetite (iron oxide) nanoparticles with an average diameter of about 10 nanometers.

Where possible, we have tried to list the sources and vendors for basic materials.

You may see pictures from a recent implementation of this tutorial here.

Before We Begin

The synthesis procedure outlined in this section can be performed by teams of 2-4 students. 

For all the ferrofluid preparation steps, please remember to wear a lab coat, latex or nitrile gloves, and protective eye wear or goggles.

Make sure to work in a ventilated area. The chemical reactions involving ammonia should be run inside a working fume hood or under an aspirator. You may want to test the effectiveness of the hood or aspirator via a simple perfume test -- it should not be possible to smell the sprayed perfume outside the air suction region!!

Let's Get Started

Here is a list of utensils and containers that you will need during the synthesis process for the water-based magnetic liquid:

  1. A strong permanent magnet
  2. A stirring rod (preferably glass or plastic
  3. Two glass flasks (125 ml and 50 ml). If not available, transparent plastic cups may do.
  4. Several plastic weighing boats. If not available, a clean sheet of paper may do.
  5. Simple pipettes
  6. A liquid waste container (could be a glass beaker or a large jar)
  7. A small spatula. If not available, a simple tea or dessert spoon may do.

Fig. 1. Containers and other materials that will be used during the synthesis of the magnetic liquid.

Below is a list of chemicals and materials that you will need:

  1. Iron(iii)chloride
  2. Iron(ii)chloride
  3. Ammonium hydroxide
  4. Tetramthyleammoniumhydroxide
  5. hydrochloride acid
  6. mineral oil
  7. distilled water

Fig. 2. Chemicals for ferrofluid synthesis.

Procedure Summary

The synthesis procedure outlined below is divided into eight steps. The first two steps are similar; they involve the preparation iron (II) and iron (III) salt solutions. In the third step, we will react these solutions (as shown in the chemical reaction below) to form and precipitate iron oxide (magnetite) as nanoparticles.

2 FeCl3 + FeCl2 + 8 NH3+ 4H2O → Fe3O4 + 8 NH4Cl

We will then eliminate excess chloride ions from the resulting solution, and change the pH to neutral.

The fifth step will modify the surface of the magnetite particles so that they are stabilized in water. In the sixth step, we will adjust the concentration of the ferrofluid so that it spikes with our magnet.

The final step is to prepare the sample for demonstration.

STEP 1: Preparation of the iron (III) solution

Summary: We will weigh the right amount of iron (III) chloride and dissolve the iron salt in hydrochloric acid. We need 10 ml of 1M solution of iron(III).

  1. Place the weighting boat on the balance
  2. Set the Tare to zero.
  3. Weigh 2.7 g of iron (III) salt into the weighting boat.
  4. Take a 125 ml Erlenmeyer flask or a beaker and place the iron salt in it.
  5. Measure 25 ml of distilled water and add to the iron salt in the flask.
  6. Measure 10 ml of 1M hydrochloric acid and add that to the iron solution.
  7. Shake the flask until the iron salt has been completely dissolved.

Note: You always can add and remove salts until you reach the right amount.

Question 1:

  1. Calculate how much iron (III) chloride we need to get a 1M, 10 ml solution of iron (III)?
  2. How many moles iron (II) is needed to get Fe3O4?

Molecular weight of iron(III)chloride hexahydrate is 270.3 g/mol

Answer: Click here to find the solution

STEP 2: Preparation of the iron (II) solution

Summary: We will weigh the right amount of iron (II) chloride and dissolve the iron salt in hydrochloric acid. We need 2.5 ml of 2M solution of iron (II).

  1. Place the weighting boat on the balance
  2. Set the Tare to zero.
  3. Weigh 1 g of iron (III) salt into the weighting boat.
  4. Take a small beaker or container place the iron salt in it.
  5. Measure 2.5 ml of 1M hydrochloric acid and add that to the iron salt.
  6. Shake until the iron salt has been completely dissolved.

Question 2:

  • Calculate how much iron (III) chloride we need to get 10 ml a 1 molaric solution of iron (III)

(Molecular weight of iron(II)chloride tatrahydrate is 198.1 g/mol).

Answer: Click here to find the solution

STEP 3: Precipitation

Summary: Now you are ready for reacting the iron salts in the presence of ammonium hydroxide, and precipitating the resulting iron oxide (about 10 nm in diameter).

  1. Combine the iron solutions by adding the iron (II) solution to the iron (III) solution.
  2. Mix it well by shaking.
  3. You can wash out the beaker with a small amount of distilled water and add this to the solution.
  4. Mix the solution again by shaking
  5. Add the ammonium hydroxide solution drop-wise to the iron solution.
  6. You should shake as much as possible.
  7. After adding all the ammonium hydroxide, shake for at least 3 minutes

Question 3:

  • Instead of using ammonium hydroxide you can also use sodium hydroxide (NaOH). What are the rection products then? Try to write down the formula for this reaction in the same way like for ammonium hydroxide.

Answer: Find here the answer.

STEP 4: Washing Step

Summary: In this step, you will separate the magnetic particles from the solution using a magnet. The particles will move towards the magnet and the rest of the solution will get clear. The particles may then be separated and washed with distilled water. You will then get rid of the excess ions and adjust the pH.

  1. Put the magnet under the beaker.
  2. Wait until the upper solution gets clear.
  3. Decant the above solution into a waste beaker. Don't forget to hold the magnet while decanting.
  4. Now take 50 ml distilled water and add it to the magnetic  particles.
  5. Mix the dispersion by shaking.
  6. Repeat this washing step at least two more times.

STEP 5: Surface Modification

Summary:In this step, you will modify the surface of the magnetic particles, so that they can be stabilized later in water.

  1. First transfer the solution step by step into a weighting boat.
  2. Use the magnet to settle down the magnetic particles.
  3. Decant the clear upper solution into the waste beaker.
  4. Always remember to hold the magnet when decanting the water.
  5. To get everything out of the Erlenmeyer flask, you may add some more distilled water.
  6. Once you have all the magnetic particles in the weighing boat, try to get rid of as much water as possible.
  7. Measure 5 ml of 25% surfactant (tetramethyl ammonium hydroxide) by using a pipette and add it to the magnetic particles. Mix the dispersion  with a glass rod. Wait for at least 3 minutes. Remove the black liquid on top.

STEP 6: Spikes

The remaining ferrofluid will spike under the magnetic field of a moderately strong permanent magnet. If it does not, the amount of liquid remaining is too much.

STEP 7: Demonstration Sample Preparation

Summary: This is the final preparation step; it involves creating a demonstration kit to show off your ferrofluid sample.

  1. Take a small container, such as a transparent plastic tube, and fill it up almost completely with mineral oil.
  2. Top the container with a small amount of ferrofluid (several drops may do).
  3. Carefully seal the container so that there are essentially no air bubbles left inside it.

STEP 8: Have Fun!

Your demonstration sample is now ready. Take a small, moderately strong permanent magnet and show off your work to your friends, teachers and parents.

If you shake the sample tube rigorously, the ferrofluid will break into many tiny droplets within the mineral oil. Watch how these droplets find each other and merge into a large ferrofluid drop again as you bring the magnet slowly towards the tube.

The spike pattern depends on the strength of your magnet and how far you hold it away from the plastic tube. Can you determine an optimum distance between the magnet and the tube that maximizes the height of the spikes?

If your magnet is strong enough, you should be able to hold the tube upside down with it. Use the magnet to let the ferrofluid sample defy gravity in creative ways!

 

This material is based upon work supported by the National Science Foundation under Grant No. EECS-0449264 and EECS-0529190. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and researchers, and do not necessarily reflect the views of the National Science Foundation.

  
Yale University, 2006