Abstract
Two batches of wüstite were produced from a stoichiometric mixture of Fe and Fe2O3 by sealing in steel tubes in vacuum and helium, respectively, and igniting the first tube at 1300° for 21 hours and the second one at 1200° for 34 hours. There were two exothermic peaks on the DTA curves of both samples at 345 and 545 to 700° due to surface oxidation of FeO to Fe3O4 followed by bulk oxidation of FeO to Fe3O4 and of Fe3O4 toα-Fe2O3. The last two reactions gave rise to a dual (or twin) peak for coarse material but one peak in the case of fine material, indicating that the two reactions occurred concurrently for fine material. Similar investigations on both fine and coarse magnetites showed only two exothermic peaks which corresponded to surface and bulk oxidation, respectively. This result confirms the previous observations that coarse magnetite converts toα-Fe2O3 by surface oxidation followed by bulk oxidation.
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