High temperature stability of maghemite (γ-Fe2O3)
Abstract
The temperature stability of acicular maghemite (γ-Fe2O3) was studied between 20°C and 600°C by x-ray diffraction and magnetic measurements. Synthetic monodomain maghemite was found to be stable with respect to hematite (α-Fe2O3) at temperatures as high as 500°C, inverting to α-Fe2O3 between 510-660°C. However, a complete inversion of the γ to α form for the sample was not achieved even at 660°C, the final product was a two-phase mixture, with 65% of the original γ-Fe2O3 unchanged. Two conclusions are made: (a) the absence of maghemite in a natural sample cannot be proven if heating has been restricted to moderate temperatures (300°-400°C) and (b) the true Curie point of pure maghemite is close to 645°C.
- Publication:
-
Geophysical Research Letters
- Pub Date:
- March 1984
- DOI:
- 10.1029/GL011i003p00161
- Bibcode:
- 1984GeoRL..11..161O
- Keywords:
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- Geomagnetism and Paleomagnetism: General or miscellaneous;
- Physical Properties of Rocks: Magnetic and electrical properties