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Journal of Geophysical Research: Solid Earth

Curie temperature and lattice constant reference contours for synthetic titanomaghemites

Authors

  • Charles M. Keefer,

  • Peter N. Shive


Abstract

Curie point and lattice parameter measurements were made on 57 titanomaghemite samples produced from sintered titanomagnetites with x (mole fraction ulvospinel) values of 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0. Oxidation was carried out in various atmospheres at temperatures as low as 113°C for durations of about 24 hours. The oxidation process was successful in producing homogeneous titanomaghemites with z (oxidation parameter) values between 0.0 and 1.0. Spinels with z < 0.6 are generally single phase, but the necessity of using temperatures greater than 300°C to produce strongly oxidized phases resulted in spinel oxidation in the presence of a rhombohedral phase. Curie temperature and lattice constant data are significantly different from results presented by Ozima and Sakamoto (1971), Readman and O'Reilly (1972), and Nishitani (1979). Although some of these differences may be due to unmixing (inversion), most of them apparently result from differences in techniques of titanomaghemite preparation and oxidation.

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