Low- and high-temperature oxidation of titanomagnetite in relation to irreversible changes in the magnetic properties of submarine basalts
Abstract
Re-examination of the sintering process of Akimoto, Katsura, and Yoshida indicates that titanomagnetite made according to this process does not undergo low-temperature oxidation to a single-phase cation-deficient spinel (γ-titanomaghemite) but instead oxidizes and unmixes to Mtss and Ilss at about 350-400°C, and Mtss, Ht, rutile, and pseudobrookite at about 600°C. Since this unmixing (high-temperature oxidation) reduces the Ti content in the spinel phase, the saturation magnetization Js and Curie point increase up to 4 μB (Bohr magnetons at 0°K) and 580°C, respectively, and the lattice parameter decreases down to 8.39 A. From experimental results on synthesized titanomagnetite and titanomaghemite, we conclude that the irreversible increase in Js and Curie point of some submarine basalts during heating in air or in vacuo is the result of unmixing of Ti-rich titanomagnetite and/or breakdown of γ-titanomaghemite into Mtss, Ht, pseudobrookite, and rutile. This conclusion is supported by microscopic obervation and chemical and X-ray analysis.
- Publication:
-
Journal of Geophysical Research
- Pub Date:
- February 1970
- DOI:
- 10.1029/JB075i005p01003
- Bibcode:
- 1970JGR....75.1003O
- Keywords:
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- Geochemistry: Chemistry of the solid Earth;
- Mineralogy;
- Petrology;
- and Physical Properties of Rocks: Magnetic and electrical properties