Studies of the oxidation of nanocrystalline iron with oxygen by means of TG, MS, and XRD methods

The oxidation of the nanocrystalline iron containing small amounts of structural promoters-such as aluminum, calcium, and potassium oxides-has been studied. The oxidation processes were carried out under atmospheric pressure at pure oxygen atmosphere at various temperatures in the range of 573-773 K, in the differential tubular reactor with thermogravimetric (TG) measurement. Nanocrystalline promoted iron did not reveal the pyrophority under pure oxygen atmosphere at temperatures higher than 573 K. The oxide layer stable at a given temperature was formed and protected the iron against further oxidation. The higher oxidation temperature. the thinner was the oxide layer. X-ray diffraction analysis (XRD) and Mossbauer spectroscopy (MS) were used to characterize the oxidized samples in order to determine the structure of formed oxides. The XRD analysis proved the magnetite structure of obtained iron oxides. The Mossbauer studies revealed that magnetite layer formed at temperatures higher than 573 K had got the disturbed structure, derived from aluminum tons incorporation into the tetrahedral sites of magnetite's lattice. The ratio of the number of iron atoms to the number of aluminum atoms located in tetrahedral sites was 2:1 whereas the ratio of the number of iron atoms located in tetrahedral sites to the number of iron atom located in octahedral sites was 1:3.