I have prepared magnetic nano-particles (as supposed to be) by mixing of Fe2+ and Fe3+ chlorides taking into account the stoichiometry required. I have dripped the Fe solution into 0.6M NaOH solution at room T, I then heated the solution to 60 C for about 1hr. I then washed my particles with water/ethanol mixture several times.
I then vacuum dried the particles in a vacuum oven for 24hrs at 60C.
when I removed the particles from the oven they were clustered and very black. After cooling in a desiccator, I ground them using pestle and mortar, once started grinding the ground material became brown in color. So I am not sure if magnetite have turned into maghemite.
As you know by XRD it is difficult to distinguish between them.
Did I do something wrong that I obtained maghemite instead of magnetite?
After grinding my particles are still attracted by magnet strongly.
Mohammad Al-Harahsheh,
Usually an aqueous solution of ammonia is added to the solution of the mixture of iron salts to obtain hydroxides. Then they decay to form the crystalline structure of magnetite nanoparticles. See for example
T.Fried, G.Shemer, G.Markovich. Adv. Mater., 13, 1158 (2001)
You could try and measure their Curie temperature. Maghemite usually transforms into hematite around 400-500˚C but does not show a sharp transition. Magnetite on the other hand should show a sharp curie point at 580˚C. This way you would know that there is some maghemite. The brown color could also indicate Goethite (FeOOH), but Goethite is only weakly magnetic and may not show up. Finally, you could try and reduce the particles in H2 or a CO/CO2 mixture.
Hope this helps.
Mike
Hello Dr Mohammad Al-Harahsheh
In these recently published two articles, the magnetic nanoparticles (Fe3O4) that you mentioned have been prepared nicely by a one-pot chemical coprecipitation method. The method is a little bit different from yours and many characterization techniques are included e.g. FTIR, XRD, zeta potential, etc. So, I suggest you follow this method after carefully read. Best Wishes
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