How can I produce Red Iron oxide with electrolysis

Question

I am producing Iron Oxide with the intention of using it for pigmentation. My attempts so far have been to use electrolysis. My first attempt I used Borax as an electrolyte and a 12 volt adapter with 3-4ish amps. The result was a typical light orange rust color, however the process was rather slow, 24 hours resulted in about a tablespoon of rust. My next attempt I used table salt instead. This was far faster, it produced nearly a cup of black sludge in 10 hours. As per the tutorials I watched on youtube, I then filtered the matter through a coffee filter and a funnel, then heated the result in a pan. The result however was a rust color covered in a layer of black crust, as if I had burnt a sheet of cookies. Powdering the result gave me a powder of very dark brown color.The Residue left over on the coffee filter and in the container I used for electrolysis are the typical rust orange color I would expect. It is my understanding that heating the black matter that results from the electrolisis usually produces a more red color. So my question(s) are:

• how I can change my approach to produce red pigmentation using this process, and why may I have ended up with black residue instead of orange or red?
• What are the variables that change the pigmentation of rust?
  • Is it the speed at which it drys? the temperature in which it is heated? the electrolyte used in the process of electrolysis?

Answer 1

Red iron oxide is Fe2 O3 , it forms in air at roughly 700F. In a water solution you will make "rust", brown/red. Rust is a complex mixture of hydroxides and hydrated oxides such as Fe3 O4 -H2O. At temperatures higher than 700 F you start getting black Fe3 O4 ( aka mill scale). At very high temperature you get black Fe O. Fretting corrosion will produce Fe2 O3 at room temperature but is not a practical source.