Open AccessLow Temperature Oxidation of Ferro‐Magnesian Olivines—A Gravimetric and Magnetic Study
Author(s) -
Hoye G. S.,
O'Reilly W.
Publication year - 1973
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1973.tb03416.x
Subject(s) - magnetite , spinel , gravimetric analysis , ferrite (magnet) , mineralogy , magnesium , metallurgy , materials science , analytical chemistry (journal) , chemistry , composite material , environmental chemistry , organic chemistry
Summary The oxidation of finely divided (≲ 1000 Å) synthetic ferromagnesian olivines (Fe x Mg 1 ‐x ) 2 SiO 4 has been studied using gravimetric and magnetic techniques. It is found that olivines oxidize in air at temperatures appreciably lower than formerly thought possible. Magnetite, Fe 3 O 4 , is produced at temperatures ≲ 300°C. At higher temperatures this oxidizes to haematite, α– Fe 2 O 3 . Above 550°C a second spinel phase, magnesium ferrite, MgFe 2 O 4 , is produced together with further quantities of haematite. The kinetics of the magnetite production have been studied gravimetrically and magnetically in the temperature range 300°–420°C yielding values for the activation energy (1.6–1.9 eV mole –1 ) typical of binding energies of cations in oxides. The development of CRM at 345°C has been observed in the magnetite, showing the characteristic transitions from superparamagnetism to the stable monodomain and to the multidomain state.