How can I avoid the ppt from turning brown-green from black? When I apply the ppt on a piece of paper to check the shade of the ppt, they start turning into Maghemite. I am concerned about the color of the ppt since I will be using these as pigment in my later study.
I am preparing Magnemite from FeSO4 + 2NH4OH -> Fe(OH)2 + (NH4)2SO4
Later I am filtering Fe(OH)2 ppt and heating them in the presence of water at 90C. This process is commonly known as Schikorr reaction.
I took some of the black ppt into another container and added water to it. Later I placed the beaker on a hot plate and heated the solution to 90C.
After this, these black ppt remained unchanged in air even after 24 hours. Is this the result of nucleation? Or adding water to the solution had any other effect?
Immad Amir
This question has been discussed frequently.
https://www.researchgate.net/post/During_the_synthesis_of_iron_oxide_nanoparticle_I_want_magnetite_by_co_precipitation_method_using_NH4OH_but_sometimes_i_get_maghemite_why
You wrote in the reaction the preparation of ferrous hydroxide. Maghemite ferrous oxide. Nitrogen is used to prevent oxidation. For magnetite, the ratio of precursors matters.
Yuri Mirgorod
How do I achieve this at an industrial scale if the cost of N2 is not feasible? Are the black ppt that turn to brown upon air contact "Maghemite ferrous oxide"?
In the thread you shared, it says that if I increase the % of ammonia in the solution, the reaction might favor magnetite. Is this possible? Or should I change something else?
Immad Amir
These articles have answers to all your questions.
https://www.sciencedirect.com/science/article/abs/pii/S0921510712000499
https://www.sciencedirect.com/science/article/abs/pii/S0254058416307210
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