A while back, I decided that I wanted to make all the amazing things in chemistry I never got to learn in school. First on this list is making a ferrofluid.
A ferrofluid is a liquid with the mesmerizing ability to respond to magnetic fields. Descriptions do no justice – videos and images are the best explanation:
A classic ferrofluid is made of magnetite nanoparticles in a colloidal suspension. Let’s look at this piece by piece.
Magnetite is an iron oxide – it’s “black rust” Fe3O4 (by comparison, “red rust” is Fe2O3), it is ferromagnetic – that is, it’s attracted by magnets (red rust is not ferromagnetic)
Nanoparticles are solid particles less than 100 nanometers in diameter. This is extremely small – by comparison, the wavelength of visible light is about 6 times larger (~650 nm). Human hair is about 1,000 times larger (100 micrometers). In other words, if you can see the particles, you don’t have nanoparticles.
If you look around on the internet, you’ll find a lot of recipies for ferrofluids that involve burning, dissolving, or crushing to make magnetite particles suspended in a colloid. These methods all have a central cognitive failure: the idea that one can somehow make nanoparticles by grinding something large into something smaller. This can never happen.
The reason this can’t happen is because nanoparticles are so small that if they ever physically touch, the surface interactions are so strong that they will never separate. What this means is that you have to build nanoparticles from individual molecules up, not by grinding material down.
In other words, when I say nanoparticle, you think chemistry.
A colloidal suspension is a mixture of one material evenly distributed (but not dissolved) in another. Good examples are milk (milkfat in water), mist (water in air), and smoke (solids in air). Ferrofluid is a solid suspended in a liquid.
We’ll discuss colloids more when the time comes.
Notice that a classic ferrofluid is significantly different from getting iron filings wet with oil. The iron filings will eventually fall to the bottom – nanoparticles in a true ferrofluid will never fall to the bottom of the jar. If you look at the ferrofluid in the above images, you’ll notice that the liquid appears smooth and fluid and maintains the same color density throughout. This is not the case with the fake ferrofluid recipes you’ll find online.
The one good homebrew recipe I found online was from SciSpot (and copied without attribution many times around the internet). It’s well-written and well-regarded in the homebrew chemistry world. I tried out the recipe, and it works.
I have a few issues with the recipe:
- It uses RadioShack’s PCB etchant (a chemical useful for etching copper plates to make circuit boards). PCB etchant is a proprietary mixture of ferrous chloride, ferric chloride, hydrochloric acid, and other unknown stuff in unknown quantities. I’m unhappy basing a chemical reaction on a proprietary mixture.
- You know how you’re not ever supposed to combine chlorine bleach and ammonia? Yeah, this recipe involves creating a little of the same poisonous gas that results from combining bleach and ammonia.
- The final step of the recipe involves boiling ammonia in my house and I don’t own a fume hood. This step has to go away.
I have other minor problems too, but those are mostly nit-picky things – I don’t like some separation steps at the end, there are a few vague areas where a beginner could get lost, and the author is flat-out wrong in some of the scientific explanation of what’s going on in some steps.
In the next post, I’ll discuss my first step in making ferrofluid and discuss my research notes.