I have prepared cobalt ferrite through co-precipitation technique using different alkali as precipitating agent and calcined at 600 °C. But incase of NH4OH , some peaks in XRD for hematite are observed. I could not understand the reason behind this impurity phase. With the same condition (Stoichiometric ratio, pH=13, calcination temperature), using strong alkali like NaOH, no impurity phase (hematite) is observed.
Dear Lutfor Rahman
May be it's because of an error in Fe/Co stoichiometric ratio. Excess of Fe in ratio lead to appearance of hematite in XRD
During the synthesis of this type of compound, it is possible that impurities appear, such as hematite that did not crystallize with the cobalt. I do not know the synthesis conditions of your experiment, but if you look at the phase diagram in the image it can be concluded that depending on the pH and temperature it is possible that certain types of impurities appear. Remember that it is impossible to obtain 100% yield, unreacted reactive remains or other unexpected phases appear or something precipitate before calcination. Therefore, the conditions must be controlled and evaluated by different parameters to obtain the highest performance. I attached the reference of the image.
Han, Haisheng & Sun, Wenjuan & Sun, Wei & Hu, Yuehua. (2020). Magnetic Separation of Impurities from Hydrometallurgy Solutions and Waste Water Using Magnetic Iron Ore Seeding. 10.5772/intechopen.93728.
Excess amount of Fe in the stoichiometric ratio must be the reason for the appearance of Hematite
Lutfor Rahman
I agree that the appearance may be from excess iron hydroxide. Consultants must use precise terms. Hydroxide and iron are not the same thing. When you count the stoichiometry, then count the ratio of oxides, not the elements of iron and cobalt. Overheating during ignition is possible. For comparison, an article on cobalt ferrite will be useful to you
Article The structure and magnetic properties of cobalt ferrite nano...
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