اPlease, How can I differentiate between the different amorphous phases of the iron (III) oxides? what is the simplest and suitable way that can differentiate between: Alpha-Fe2O3 , Beta-Fe2O3 and Gamma-Fe2O3.
Dear Ahmad,
The following text describes the differences between iron (III) oxide phases:
Alpha phase
α-Fe2O3 has the rhombohedral, corundum (α-Al2O3) structure and is the most common form. It occurs naturally as the mineralhematite which is mined as the main ore of iron. It is antiferromagnetic below ~260 K (Morin transition temperature), and exhibits weak ferromagnetism between 260 K and the Néel temperature, 950 K. It is easy to prepare using both thermal decomposition and precipitation in the liquid phase.
Beta phase
The β-phase is cubic body centered (space group Ia3), metastable, and at temperatures above 500 °C (930 °F) converts to alpha phase. It can be prepared by reduction of hematite by carbon, pyrolysis ofiron(III) chloride solution, or thermal decomposition of iron(III) sulfate.
Gamma phase
γ-Fe2O3 has a cubic structure. It is metastable and converted from the alpha phase at high temperatures. It occurs naturally as the mineral maghemite. It is ferromagnetic and finds application in recording tapes, although ultrafine particles smaller than 10 nanometers are superparamagnetic. It can be prepared by thermal dehydratation of gamma iron(III) oxide-hydroxide, careful oxidation of iron(II,III) oxide.
Therefore, the differences are in (1) stability (2) Ferromagneticity & (3) Structure shape.
Greedon, J. E. (1994). "Magnetic oxides". In King, R. Bruce. Encyclopedia of Inorganic chemistry. New York: John Wiley & Sons. ISBN 0-471-93620-0.
Housecroft, Catherine E.; Sharpe, Alan G. (2008). "Chapter 22: d-block metal chemistry: the first row elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 716. ISBN 978-0-13-175553-6.
Hoping this will be helpful,
Rafik
Dear Kenneth,
You are absolutely right. he has to have crystalline forms.
Rafik
@Rafik Karaman
@Kenneth M Towe
My thanks for Prof. Rafik Karaman and Prof. Kenneth M Towe for their contributions.
My Dear Colleagues
How can I differentiate between the different phases of Non-Crystalline of the iron (III) oxides?
what is the simplest and suitable way that can differentiate between: amorphous Alpha-Fe2O3, amorphous Beta-Fe2O3 and amorphous Gamma-Fe2O3.
I already got amorphous iron oxides from the thermal decomposition of Iron (III) nitrate and I want to know what are these oxides and what do they belong to any oxide ?
Hi Ahmed, you could try to measure the oxides using Raman Spectroscopy. Oxides can be quickly identified using this technique, but you have to be careful not to use too much laser power or you can burn and change the oxide structures. To avoid this, you need to use low power and long integration times.
There are a lot of papers regarding the identification of iron oxides (mainly in archeological journals), so you will be able to find the typical spectra of your oxides to compare.
Regards!
Mossbauer spectroscopy should allow you to differentiate between the different phases of Fe2O3.
According to Schwertmann in his book of iron oxides, synthesis of iron (III) oxides using thermal degradation methods produces poorly crystalline forms of these compounds. So while not truly amorphous they aren't as crystalline as their naturally occuring counterparts. XRD isn't a good method as the alpha form (hematite) and the gamma form (maghemite) both have similar diffraction patterns, with many of the major peaks occuring at the same 2theta angles. The fact that the crystal structure isn't ideal just makes it that much more problematic.
Mossbauer spectroscopy, because of the nature of the technique, allows a researcher to look at tiny differences in the environment around the iron nuclei. I am running samples of a thermally degraded schwertmanite (ferric oxyhydroxide sulphate) and have encountered this problem. XRD made me think that the main degradation product was hematite but Mossbauer data contradicted that.
Kenneth, Schwertmann devotes an entire chapter to the properties and synthesis of the ferric oxide phases Ahmed is inquiring about. Once I get to work I'll cite the book and the relevant chapters.
Ok... at work now. The book is "Iron Oxides in the Laboratory: Preparation and characterization", Schwertmann, U and R.M Cornell; Wiley-VCH Weinheim, 1991. Chapter on Hematite p121-134, Maghemite p 141-142
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