Processings of iron oxides at room temperature. II. Mechanochemical reaction effects on the structure and surface of pure, synthetic lepidocrocite

• Published in: Materials research bulletin 1982, Vol.17 (8), p.1017-1023
• Main Authors: Mendelovici, E., Sagarzazu, A., Villalba, R.
• Format: Article
• Language: English
• ISSN: 0025-5408; 1873-4227
• DOI: 10.1016/0025-5408(82)90127-1

The gradual transformation, at ambient temperature, of synthetic crystalline γ-FeOOH during several dry grinding periods in an automatic mortar, has been followed by IR, XRD and surface area analysis. This study shows that as grinding proceeds, parallel to the progressive disappearence of γ-FeOOH, a distinct α-Fe 2O 3 phase is developing. This mechanochemical reaction is completed at 32 hr grinding, when γ-FeOOH is no further detected by IR spectroscopy nor by X-ray powder diffraction. The surface area (So) measurements indicate a decrease of the γ-FeOOH particles size during the early stages of grinding (24 hr); thereafter the So profile is ruled by the surface energy of the formed α-Fe 2O 3 particles. XRD suggests that broadening affects in a non uniform way the peaks describing the α-Fe 2O 3 diffraction planes, the typical 024 plane being the most affected. By analogy with α-FeOOH dry grinding, variations in size, color and eventually in water content are gradually observed during this γ-FeOOH → defect α-Fe 2O 3 mechanochemical decomposition, The latter's mechanism is discussed.