Warning: The electrolysis method in this video produces hydrogen gas,
perform either outside, in well-ventilated area, or in an electrolysis box.
Ferric chloride is corrosive, wear gloves when handling it.
Greetings fellow nerds.
I’ve gotten a lot of requests for this so in this video we’re going to make iron oxide for use in the famous thermite reaction.
And we’re going to show three ways of doing it.
However first I need to crush your expectations:
Iron oxide is generally cheaper to buy than it is to make.
It’s only cheaper to make if you have free scrap iron.
As usual our objective here is to explore the science.
Now our first, and worst, approach is straightforward rusting.
Iron when exposed to water and air, will spontaneously rust.
Here I’m using a pad of steel wool that i’ve soaked in salt water.
The water helps to accelerate the reaction with air.
As I leave it out you can see it rust over the course of a few hours.
While this method does work the rust layer is rather thin and you need to keep it wet to keep the rusting going.
After a few days the steel wool pad will crumble into a powder of iron oxide rust.
Any unreacted wool will need to be soaked again and allowed to continue rusting.
The resulting powdered rust is actually a mixture of iron oxides, iron hydroxides, and unreacted iron.
You can convert the iron hydroxides to iron oxides by heating the powder to drive off the water.
This iron oxide is somewhat low quality due to the presence of unreacted iron.
You can improve the quality by separating out the unreacted iron with a magnet and re-soaking it.
You can also burn the steel wool before you start.
Now making iron oxide by rusting is just barely viable for extremely fine iron like steel wool.
But for bulk iron, like nails, this is just far too slow and labor intensive.
For this you’ll need to use either the wet chemical process or the electrolytic process.
In the wet chemical process we first convert our iron metal into iron chlorides by dissolving them in hydrochloric acid.
I already have a video on this process which i’ll link the in video description so i won’t waste your time here.
You can also skip the oxidation parts of that video using hydrogen peroxide or air as the thermite will still work.
Anyway, get your solution of iron chlorides and start adding sodium bicarbonate, also known as baking soda.
I’m using an iron chloride solution that’s actually a waste product contaminated with other metals from one of my other experiments.
So if yours is a different color don’t worry about it.
Anyway what we’re doing here is converting the iron chlorides into a mixture of iron hydroxides and iron carbonates which will precipitate out.
Keep adding the sodium bicarbonate until the solution stops bubbling.
Now you might run into the situation where the precipitate becomes so dense that it turns the mixture into a thick paste.
If this happens, you’ll need to transfer it to a larger container and add enough water to make it fluid again.
Now before anyone makes that joke in the comments, yes i am aware this looks like i’m stirring around a piece of turd.
Anyway, continue adding the sodium bicarbonate.
Looking back i probably should have started with the bigger container but oh well.
Once again keep adding sodium bicarbonate until it stops bubbling.
When that point is reached we have a mixture of iron hydroxides, carbonates and salt.
Now we need to separate the two but we can’t use filtration because the particles are so fine that they’ll clog up the filter paper and stop the filtration.
So instead we’re going to use dilution and decantation.
To do this, add water and massively dilute the mixture.
Fill up your container almost to the top.
It’s important to use a lot of water.
You’ll need at least ten times the volume of the precipitate for this to be effective.
Stir everything and then let it settle for half an hour.
The insoluble iron hydroxides and carbonates will quickly settle to the bottom,
leaving behind the solution of salt and a very small amount of suspended iron.
This ability of iron to bind together suspended particles is also used in some types of water treatment systems
to remove things like dirt, wastes, or even harmful pathogens.
Moving on, once the mixture is sufficiently settled.
Decant the supernatant by siphoning it off with a tube.
I don’t recommend tipping the container and pouring it as you might kick up the mixture and lose some of your product.
Once you have most of the supernatant out you can stop here
but i’m going to wash out more of the salt by adding fresh water back in, stirring, and repeating the process.
This is to ensure i remove as much of the salt and unreacted sodium bicarbonate as possible.
I did this two more times for a total of three.
It was very hard to remove the last bit of supernatant without also siphoning out the precipitate so i didn’t bother.
Now the remaining precipitate is allowed to dry.
As it dries it will actually break up as it loses water and contracts.
Heat the resulting pieces to drive off the remaining water as well as convert the iron hydroxides and carbonates into iron oxides.
This method is fairly robust for moderate amounts of iron oxide and is easily scaled up.
But if you don’t like spending money on hydrochloric acid and sodium bicarbonate then you can try making iron oxide by electrolysis.
The best way i found was to start with a nearly saturated salt solution.
I’m using 400 mL of water and 120 grams of table salt.
The higher the salt concentration the more conductive the solution is and allows you to use more current,
making the electrolysis proceed faster.
My solution is a bit dirty from using a dirty stir bar, but it will still work.
Anyway, stop stirring.
And for our anode stick in an iron object like a nail attached to the positive side of a power supply.
This will be the source of iron for the iron oxide produced.
Now for our cathode, we get a wire attached to the negative terminal of our power supply.
I’m using iron wire but you can also use copper.
Now turn on the power.
Adjust the current so that just the cathode bubbles.
You want the iron anode to dissolve but not to bubble.
If you don’t have a variable power supply like i do,
you can also raise the wire so less of it is in solution and reduce the current that way.
What’s happening is that at the cathode, or negative terminal,
we’re reducing water with electricity to form hydrogen gas and hydroxide ions.
Now hydrogen gas is flammable so you should do this either in a fume hood, outside,
in a well ventilated area or in the handy electrolysis box i showed in an earlier video.
Anyway, at the anode, or positive terminal,
we’re oxidizing iron to form iron ions that react with the hydroxide ions to form iron hydroxides.
The reaction is actually a lot more complex than this with numerous side reactions like the formation of iron chlorides,
sodium hypochlorite bleach, iron oxychlorides, oxyhydroxides and other chemicals.
But overall this is what’s happening.
I said before that you didn’t want too much current to produce bubbles at the anode
because when you overvoltage the system the anode will start oxidizing water to produce oxygen gas and some chlorine gas.
Both of these waste power and don’t contribute to the formation of iron hydroxides.
Now you might be wondering if there is any special reason why i used table salt as the electrolyte.
Actually there is.
I first tried sodium bicarbonate baking soda and while it did work at first the iron quickly passivated and stopped further current flow.
The electrolysis stopped despite there still being plenty of electrolyte and electrodes available.
I then tried sodium bisulfate which is an acid available as a pool chemical.
This worked but the instead of precipitating out, the iron in solution just migrated over to the cathode and started plating out.
It’s a fun way to make iron filings but a useless way to make iron oxide.
Only salt worked effectively and was commonly available enough for everyone to try.
Anyway, let this run and after a few hours you’ll notice the iron anode dissolving or developing a crust as seen here.
Don’t worry the crust is just some adherent iron hydroxide and easily comes off.
As you can see, the actual iron nail has been greatly corroded.
We’ll put this back in for further electrolysis.
If it corrodes away completely then you can switch it out with another source of iron,
Now I recommend rotating your electrodes to get maximum use out of them.
As the iron hydroxide forms it will fall to bottom of the cell so it’s important you have a container big enough to contain it.
You don’t want the electrodes getting covered in the rising level of iron hydroxides as that will insulate the anode from the reaction.
And if it gets on the cathode it will start plating out of solution as iron metal which you don’t want.
Oh yeah, one more thing, remember to top off the cell with water as it evaporates.
Anyway, after a few hours or days, when you’ve either run out of iron to convert,
or have filled up the cell with too much iron hydroxides,
remove the electrodes and filter the solution.
Be sure to wash the residue with water to remove any salt.
Alternatively instead of filtering you can also use the same dilution and decantation method i showed for wet chemical iron oxide.
Now let it dry.
Break up the chunks and dry it to remove any remaining water as well as convert the iron hydroxides to iron oxides.
An interesting thing i noticed as i was heating this is that it slowly went from black to red with repeated heating and cooling cycles.
Red is the common color of high quality of iron (III) oxide.
It was quite amazing to me see black crud become red crud.
Yes i am still easily impressed despite having a Ph.D.
Anyway, that is how you produce iron oxides.
Personally i think the electrolytic method is best as it strikes a good balance between speed, cost and quality.
Now to use them in thermite just mix the iron oxide with one third its mass of aluminum metal, and ignite it with a sparkler or magnesium ribbon.
I’ll be exploring thermite in a later video.
Thanks for watching.