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How to make Liquid Magnets - Ferrofluid
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So far I have only found one valid recipe for ferrofluid. It works pretty well and the chemicals are easy to obtain. The cost of the project depends on the source of your chemicals and the quality of equipment you wish to invest in. I prefer Pyrex glass goods for working with any chemical reaction because I know they make good quality heavy-weight products which will hold up against fast changes between temperature extremes. They also respond well to the regular wear-and-tear abuse. However, if budget is of concern, you can find cheaper glassware from a surplus store. When I work with chemicals I use a fume hood. It's good practice to use a fume hood in this case since some of the components are flammable and the gas created from some of the reactions will be toxic. Another great thing about fume hoods is that they can snuff out a fire quickly by removing all the air from the fume hood cavity. | |||||||||||
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Make the magnetite: The magnetite is the nano-scale metal particles which will react to the magnetic fields in its vicinity. The first step in manufacturing ferrofluid is to create a sufficient amount of these particles. Some mistakenly think they can just use metal shavings as the magnetite, but this is not true. Although the metal shavings will react to magnetic fields, they will be too large to be suspended in a ferrofluid solution. The best way to get the magnetite is to create individual iron molecules using Ferric Chloride. PCB Etchant is the most common source of Ferric Chloride for home use. It is typically a 1.5M solution and that is what this recipe is based on. So if you have some alternative source of Ferric Chloride make sure your solution is at the same molar strength as I have specified, or you will have to adjust the amount of chemicals to your own applications. Dilute FeCl3: Measure 25ml of Ferric Chloride in a small beaker. Dilute this by adding 25ml of distilled water. That will help the reaction process. In the end we only need 40ml of the reacted solution, but giving us an extra 10ml to work with will be useful because you will likely have some get stuck to the sides of the dish or inside the steel wool remnants. React with Steel Wool: Put a very small piece of steel wool into the solution. If you put too much steel wool it will just act like a sponge and soak up all the liquid with insufficient reaction. If this happens you'll have to start over. After adding the steel wool, stir the solution with a glass stirring rod. As you can see in the picture below, it will start to look like something you pulled out of the shower drain. Mash the steel wool a bit with the rod to speed up the reaction. As the reaction starts getting going you'll notice that the beaker becomes warm to the touch. Keep adding small tufts of steel wool to the solution until the liquid becomes a transparent neon-green color. At this point you have saturated the solution with iron to create FeCL2. Some of the steel wool won't dissolve, but that's ok since you will filter all of that out.
Filter: Position a filter over a clean beaker. You can put the filter in a funnel if you want more stability. Filter the FeCL2 solution into the beaker. This gets rid of any steel wool pieces leftover or particles of dirt and dust which might have been stuck onto the steel wool.
Precipitate: Now we need to get the magnetite particles to fall out of solution. Measure out 40ml of the resulting solution that you just filtered. To this solution add 40ml of Ferric Chloride (PCB etchant). If you don't have 40ml of the filtered solution it's not important - just make sure to adjust the amount of Ferric Chloride that you're adding to it. It's a 1:1 mixture, so if you have 35ml resulting from filtering then add 35ml of Ferric Chloride. The Ferric Chloride, FeCl3, and neon-green solution, FeCl2, react in a 2:1 ratio. But since the filtered solution is half distilled water it means we are mixing them in a 1:1 ratio. Now we start adding ammonia. As you can see in the image below, mixing Ammonia with any chlorinated chemical will create poisonous fumes. That means you will need a fume hood or another form of reliable ventilation if you want to perform this experiment safely. At this point it is easiest if you have a magnetic stirring rod with a stirring plate to leave your hands free. Ideally, you would also set up a 100ml Burrette on a clamp stand to dispense the liquid slowly. Add the ammonia to the burrette and set it up above the solution in your beaker. Let the ammonia slowly drain into your solution. If you don't do this slowly then it will end up clumping together. You will need to refill the burrette a couple times because you'll need a total of about 400ml of ammonia added. We just want to keep adding ammonia until it gets fully saturated. If the beaker starts getting close to filling up you will need to transfer the solution to a larger beaker. Use a 1000ml or larger beaker to make sure you have adequate space for the solution.
Initially it will turn light brown. As it gets close to getting saturated with ammonia you'll notice that where the ammonia is dropping in, the solution will turn black. The black trail will fade away as it is stirred. When the reaction is complete the whole solution will be a dark black color and you won't be able to see a color difference where the ammonia is being added. It's OK to keep adding a bit more after this point to make sure it's saturated fully. The black result is the precipitate that we desire, magnetite. This is Fe3O4. If you stopped stirring at this point and let it sit over night you would notice the magnetite precipitate fall out of solution into the bottom of the beaker. To make it useful, though, we need to add a coating and suspend it in a proper carrier.
Coating and Suspending: For this step you will want to move to a hot plate which does not have the magnetic stirring rod feature. The coated magnetite will get pulled onto the magnet surface and create a real mess when you try to take the magnet out. Also, the magnets in the hot plate will attract all the magnetite to the bottom of the beaker. It would probably be better if they are free to roam around in solution so they have the opportunity to properly react with all the chemicals swirling around. Alternatively, you could use a bunson burner or even a small camp stove. Start heating: Start heating up the solution. Use a thermometer to monitor the temp. I used a candy thermometer because the temperature range was adequate and it even came with a metal clip which worked perfectly to attach to the side of the beaker. The clip also suspends it in the solution keeping it from touching the bottom of the beaker which would give you false temp readings.
Add Oleic acid: Once it gets to about 120 degrees F it will start to steam. This is a good point to add the oleic acid to solution. The oleic acid will provide the coating for our magnetite particles so they don't get all clumped together in the final product. Using a pipette with a bulb at the end (don't suck on the end) siphon out 10ml of oleic acid. While stirring, slowly add this a few drops at a time into the solution. Adding it too quickly will cause it to clump together which will ruin the final product. Adding it slowly allows the appropriate reactions to take place.
Keep heating: Continue to heat the solution until the boiling point. You will notice it start bubbling once it gets to about 200 degrees F. Keep a close eye on the solution at this point. If it boils too rapidly it will froth up and overflow out of the beaker, spilling out and covering everything below it with a black stain and ruining your camp stove...yep that happened to me. Just don't get it above 200F and you should be fine. Allow the solution to stay at this temperature until it reduces down to about 400ml. This will take about an hour Add Kerosene: When you are finished heating, take the beaker off the burner and let it cool completely. When it is no longer hot to the touch, add 200 mL of kerosene to the solution. Stir it around until it is well mixed. When it settles you will see two distinct layers. The black layer is the coated magnetite particles which are soluable in the kerosene. The other layer is the remaining kerosene and some leftover water. You can pour off the ferrofluid layer since that's the one on top. You'll have to get rid of the kerosene layer by looking up your local hazardous waste drop-off zones. Alternatively, you can burn kerosene, but since it is slightly contaminated it probably isn't a good idea in this case. What you are left with is the finished product, Ferrofluid!
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The three images below show you my ferrofluid results. I took these pictures with macro in order to get some really crisp close-ups. In order for you to judge the size a little better I placed a dime in the background in two of the pictures.
Getting what you want out of the final output solution can be a bit of a trick. At first I thought I had failed miserably because it wasn't working as I expected it to. The result was definitely responsive to magnetic fields, but it only created a tight lump instead of the spike protrusions that we want. I think the reason for this was that there was too much kerosene in the solution at the end. I guess if I tried it again I would try adding a little bit at a time and see if that worked better. The way I remedied the problem was as follows:
The problem I think most people face when playing with the resulting ferrofluid is that they position the magnet too close. If you leave the magnet about a half-inch away from the base of the ferrofluid and wiggle it back and forth you'll see much better spikes form. I think I'll have to buy some commercial-grade ferrofluid just to compare the results. I have also heard that it's pretty fun to stick your hand in a ziplock bag along with a magnet then play around with the ferrofluid that sticks to it. This technique is also great for cleaning up spills. All in all, this is a fairly good method for synthesizing home-brew ferrofluid if you know the pitfalls to steer around.
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