Abstract
In our study on lodine methanol method and electrolytic method performed in order to isolate iron oxides in iron and steel from iron matrix, the behavior of iron oxides during isolation has been made clear.Then the change in the composition and the form of iron oxides in pure iron by heat treatment with application of the isolation technique was alsostudied.
The results are summarized as follows:
(1) In electrolytic method, generally lower values were obtained because Wustite was decomposed electrochemically during electrolysis, even if the electrolyte was neutral (pH=7); however, magnetite was not decomposed but recovered almost completely.On the other hand, in iodine methanol method, both Wustite and magnetite were recovered completely, and oxygen values calculated from iron oxides were in good agreement with those in vacuum fusion method.The oxygen values in these two different methods having been in good accord with each other, it was presumed that oxygen in solid iron exists generally as iron oxides and oxygen in the form of solid solution does not exist or is very little at 1200°C and 500°C.
(2) The composition and the form of iron oxides in iron and steel changed by heat treatment. The process of its change was almost similar to Fe-O diagram, that is, iron oxides. in iron and steel existed as Wustite at the temperature of above approx.570°C, while as magnetite below this temperature.
(3) Iron oxides in pure iron changed from Wustite to magnetite during heating at 500°C for several different hours.The velocity of change from Wustite to magnetite depended on the thermal history of specimen.In the specimen as cast this change finished in 72 hours, while in the specimen which was heat treated with 1200°C×5hr/water quench this change did not finish even in 215 hours.Then from the result of X-ray diffraction or chemical analysis of iron oxides isolated from pure iron which was heat treated at 500°C for several different hours after the heat treatment of 1200°C×5hr/water quench, it was made clear that this reaction occurred in the following order.
(i) FexO→Fe3O4+Fex′O (x<x′)
(ii) FexO→Fe3O4+a·Fe
(iii) FexO→Fex″O+a·Fe(x>x″)
(4) Lattice parameter of Wustite having linear relation with its iron content.the iron content of Wustite could be found by applying X-ray analysis on the residue isolated from iron matrix with the aid of iodine methanol method.
