Superparamagnetic Fe 3 O 4 particles formed by oxidation of pyrite heated in an anoxic atmosphere
As a follow-up to previous gas analysis experiments in which pyrite was heated to 681 K in an anoxic (oxygen starved) atmosphere, the first oxidation product, FeSO 4 , was studied as a bulk material. No decomposition of FeSO 4 to Fe 3 O 4 was observed in the temperature range studied. The lack of decomposition of bulk FeSO 4 to Fe 3 O 4 suggests that FeS 2 oxidizes directly to Fe 3 O 4 , or that FeSO 4 , FeS 2 and O 2 react together to form Fe 3 O 4 . Magnetic susceptibility and magnetization measurements, along with magnetic hysteresis curves, show that small particles of Fe 3 O 4 form on the pyrite surface, rather than a continuous layer of bulk Fe 3 O 4 . A working model describing the oxidation steps is presented.
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