For synthesizing magnetic composite materials sometimes both Ferrous and Ferric chloride is used in some particular proportion. What is the necessity of using both?
And is there any significance of the particular proportion?
Link - http://www.sciencedirect.com/science/article/pii/S030488531632515X
This is a stoichiometric ratio of 2:1 Fe3+ / Fe2+ involved in the co-precipitation of Fe3O4.
Fe2+ + 2Fe3+ +8OH- ---> Fe3O4 + 4H2O.
Fe3O4 is not very stable and further oxidized into Fe2O3 the gamma structure of Fe2O3 aka maghemite should be the most stable.
the initial ratio between ferrous and ferric ions substantially determines the crystalline structure and the size of the precipitating particles and so their magnetic properties especially if you're looking for superparamagnetism.
For example it is known that the mean size and the preparation yield of magnetic particles increases as Fe3+/Fe2+ ratio lowers.
Conversely, higher ratioes lead to different crystals like ferric oxide-hydroxides which may not have paramagnetism properties at all.
I agree with the previous reply. You can get also more information on the Pourbaix diagram of iron and oxygen. Pourbaix diagrams are available on internet.
In older text book it is written as ferrosoferric oxide meaning a double oxide of FeO and Fe2O3 if one add these two then you get Fe3O4. Here the ratio is Fe(II) is one and Fe(III) is two. So the matter is simple. One takes one part Fe(II)Cl2 and two parts Fe(III)Cl3 after mixing just raise the pH and the mixed hydroxide will appear and on standing the thermodynamics will drive to its self aggregation and stability and you need not do anything. Later you can play with this by heating , cooking and following any exotic lab procedure.
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