I have a friend trying to make ferrofluid. He is following these steps, but when he adds the ammonia in step 5, he gets rust. What is wrong? The only way I know that he deviated from most instructions is that he used a plastic stirrer.
Contaminants can play hell with redox reactions. I don’t have access to the exact chemical reactions the process is undergoing, but if he’s really getting solid rust then he’s over-oxidizing the iron somehow. Some things which might play a part in that:
Unclean glassware. This includes residue of soaps as a potential contaminant. To combat this wash the glassware with soap and water, rinse liberally with distilled water, and then dry in an oven.
Contaminants in the stirrer: Commercial grade plastics could have all sorts of stuff that would be bad in a redox reaction. Get a glass swizzle stickto stir with, clean it in the same manner as the glassware.
Proper measurement: The measurements given are designed to accurately maintain the proper chemical ratios to react the way you want. Magnetite is FeO.Fe2O3. Rust is pure Fe2O3. FeO is less oxidized than Fe2O3 (Iron(II) +2 instead of Iron(III) +3) so if you just slightly mess up your balance you shift toward mainly rust. If he’s getting the FeCl2 solution properly done, all the iron in that part should be at an oxidation state of +2. So somewhere else to check is that his solution really is the bright green it’s supposed to be. Check the color here for comparison. If this color is good, make sure you’re not adding too much ammonia. Also make sure the ammonia is pure, ratherthan a mixture with excess chemicals in it (as is the case with a lot of cleaning solutions).
Thanks. I got a text message from him saying that he “made it work”, whatever that means. I suspect that he ditched the plastic.
Apparently what he did was to change step 5 to adding the solution to the ammonia, instead of vice versa.