Inferred time- and temperature-dependent cation ordering in natural titanomagnetites

Abstract

Despite years of efforts to quantify cation distribution as a function of composition in the magnetite-ulvöspinel solid solution, important uncertainties remain about the dependence of cation ordering on temperature and cooling rate. Here we demonstrate that Curie temperature in a set of natural titanomagnetites (with some Mg and Al substitution) is strongly influenced by prior thermal history at temperatures just above or below Curie temperature. Annealing for 10 À 1 to 10 3 h at 350-400°C produces large and reversible changes in Curie temperature (up to 150°C). By ruling out oxidation/reduction and compositional unmixing, we infer that the variation in Curie temperature arises from cation reordering, and Mössbauer spectroscopy supports this interpretation. Curie temperature is therefore an inaccurate proxy for composition in many natural titanomagnetites, but the cation reordering process may provide a means of constraining thermal histories of titanomagnetite-bearing rocks. Further, our theoretical understanding of thermoremanence requires fundamental revision when Curie temperature is itself a function of thermal history.

Thermomagnetic Behavior of Magnetic Susceptibility—Heating Rate and Sample Size Effects

“…Lowering of Curie temperature on cooling may be explained by redistribution and change of valence state of Mn and Fe cations with increasing temperature (Zhang et al, 1998). The effect of cation reordering in magnesioferrites, titanomagnetites and magnetite has been extensively studied Putnis, 1996, 1999;Bartelt et al, 2013;Bowles et al, 2013). Similar effect could be evoked for the observed lowering of Tc on the cooling curves ( Figure 5).…”

“…The shape and the observed peaks on the heating and cooling curves of k-T cycles are interpreted as a reflection of different environmental processes [e.g., degree of soil formation and synthesis of pedogenic strongly magnetic fraction; presence of substitutions; reactions of Fe minerals with organic matter; destruction of thermally unstable minerals such as carbonates, organic matter, clay minerals (Liu et al, 2005;Hanesch et al, 2006;Jiang et al, 2015)]. Thermomagnetic analysis of magnetic susceptibility is a powerful tool in studies of time-and temperature dependent cation ordering in titanomagnetites, magnesioferrites, and magnetite-spinel solid solutions (Harrison and Putnis, 1999;Lattard et al, 2006;Bowles et al, 2013).…”

Gaseous Reduction of Titania-ferrous Solution Ore by H₂–Ar Mixture

“…9. Formulas [1] and [2] are indicating the reduction equations of ingredients in TTM and TTH, where x and y mean the solid solution ratio of And finally, Fe was completely reduced and separated with titanium oxide when the δ and ε were getting to 2x and y.…”

“…1) Due to the shortage of high-quality hematite resource, TFSO have been widely investigated as an alternative source of conventional iron ore. [2][3][4][5][6][7] The advantages of TFSO in large deposit, low mining cost, available iron grades, among others, caused industrial utilize ways of TFSO becoming focusing subjects such as the aspects in beneficiation, 8,9) sintering, [10][11][12][13] pelletizing, [14][15][16] particularly the gaseous reduction in hydrogen which is beneficial to improve the dynamic condition and lower the adverse impact on environment at the same time. [17][18][19][20][21][22][23][24][25][26] Eungyeul P 27) studied the influences of temperature and hydrogen contents on TFSO reduction at the constant condition of 25vol%H 2 -Ar and 1 173 K respectively.…”

Magnetic force microscopy reveals meta-stable magnetic domain states that prevent reliable absolute palaeointensity experiments

“…This may hint to an increase of internal stress, whereby more distinct, stress-dominated domain structures with fewer surface closure domains are formed. The observed processes after heating the sample to 450°C may be akin to the irreversible thermomagnetic behaviour as observed by Bowles et al 42 , and attributed to cation reordering in titanomagnetites induced by heating.…”