Self-diffusion and impurity diffusion in oxides

Freer, Robert

doi:10.1007/bf00552089

Cited by 183 publications

(55 citation statements)

References 19 publications

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“…The values obtained by Dieckmann and Schmalzfled are in good agreement with those obtained in previous studies of cation diffusion in spinels (Freer, 1980). Freer and Hauptman (1978) performed a series of interdiffusion experiments on couples of stoichiometric magnetite and titanomagnetite (Fe2.aTi0.204).…”

supporting

confidence: 88%

Diffusion in the titanomagnetite solid solution series

Price¹

1981

Mineral. mag.

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ABSTRACT. In order to be able to use the nature and scale of the exsotution microstructures developed in titanomagnetites as quantitative indicators of thermal history, it is necessary to have available accurate diffusion data for the system. Diffusion data for pure magnetite and Ti-poor titanomagnetites are available, but no data for diffusion in the centre of the solid-solution series exist. In order to obtain values for the activation energy (AE) and the pre-exponential factor (Do) for the interdiffusion of Fe and Ti in ulvrspinel-rich titanomagnetites, the natural microstructures developed in titanomagnetites from the Taberg intrusion, Sweden, were homogenized over a range of temperatures from 490 to 730 ~ From the model describing homogenization, values of 49.8 kcal mole-1 and 2.38 • 10-3 ClTI2 S-X were calculated for AE and D o respectively. Although the results obtained from these homogenization experiments are slightly less accurate than those which could be obtained by more conventional methods, the homogenization technique has several advantages which outweigh this drawback, namely the ease with which the experiment can be performed and the fact that the diffusion data can be obtained at significantly lower temperatures than is usually possible with more conventional methods.DIFFUSION is generally an extremely important process in all crystalline materials at temperatures above approximately one-third of their absolute melting-point. Understanding the laws of diffusion is indispensible, therefore, in describing such geologically important phenomena as exsolution, phase transformation kinetics, recrystallization, high-temperature flow, and, in general, all igneous and high-grade metamorphic events. In particular, if sufficient kinetic data were available for mineral systems, transformation-process theory (McConnell, 1975) could be used to give quantitative information on the time-temperature-pressure history of rocks from the scale and nature of the microstructures exhibited by their constituent minerals. This study is concerned with diffusion in titanomagnetites, with particular reference to the effect * Present address, Dept. of the Geophysical Sciences, University of Chicago, 5734 S. Ellis Ave., Chicago, Illinois 60637.t~ Copyright the Mineralogical Society of diffusion on the development of exsolution microstructures. Accurate diffusion data for the system are required in order to be able to use these exsolution textures as indicators of thermal history. In this paper the results of some homogenization experiments, performed on natural, inhomogeneous titanomagnetites, are presented, and the resulting values calculated for the diffusion parameters are discussed.Previous studies of diffusion in titanomagnetites. Several studies of diffusion in titanomagnetites have been published. The earlier studies of diffusion in titanomagnetites were based upon the rate of production of non-magnetic iron oxides from titanomagnetite during oxidation (Creer et al., 1970;Petersen, 1970;Ozima and Ozima, 1972). However...

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confidence: 88%

Diffusion in the titanomagnetite solid solution series

Price¹

1981

Mineral. mag.

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“…We assume that the composition of magnesiowastite in chemical equilibrium with the liquid metal is that at the interface with the metal. This assumption of local equilibrium is reasonable as diffusion rates in the liquid metal are > 104 faster than those of Fe in magnesiowastite (magnesiowastite diffusion data are summarized by Freer [1980]). This interface composition was obtained as follows.…”

Section: Electron Microprobe Analysismentioning

confidence: 95%

Oxide‐metal equilibria to 2500°C and 25 GPa: Implications for core formation and the light component in the Earth's core

O’Neill¹,

Canil²,

Rubie³

1998

J. Geophys. Res.

111

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also recent reviews by Palme and 0 'Neill [ 1996] and O'Neill and Palme [1997]). Generally, the abundances of the moderately and highly siderophile elements are greater than predicted from low pressure metal/silicate partition coefficients, but two elements (Cr and V), which are just barely siderophile, are more depleted than would be predicted. This is the siderophile element anomaly. There are two explanations for this anomaly (not necessarily mutually exclusive): (1) the metal/silicate segregation occurred at high pressures, which may alter metal/silicate partitioning relationships sufficiently, or (2) the Earth accreted heterogeneously, with the core forming in a number of episodes of accretion and metal segregation. Heterogenous accretion/core formation implies that the present composition of the mantle is a mixture that was never in equilibrium with a single metal composition. Since Occam's razor favors the conceptually simpler equilibrium type of model, the chemical effects of core formation at high pressure need to be evaluated before the heterogenous accretion class of model is accepted. In this study we investigate the partitioning of five key elements (Fe, Ni, Co, Cr, and Ti) between liquid Fe-rich metal and magnesiowastite solid solution to pressures corresponding to the top of the lower mantle and to near-liquidus temperatures. e Experimental Methodology Experimental StrategyThere are two critical experimental problems to face in attempting to study the equilibrium between superliquidus, Ferich metal and possible mantle compositions at very high temperatures and high pressures. First, it is necessary to find a suitable capsule material, which ideally should contain the experimental charge without reacting chemically with it. No such material has yet been found. Here we attempt to circumvent the capsule problem by reacting the initial capsule material to one of the phases partaking in the investigated equilibrium itself; clearly, this approach is only viable if there is a solid phase which can be used as the capsule. For this reason, we have chosen magnesiowastite, (Mg,Fe)O, both as the representative of the Earth's mantle and as the capsule material in our experiments. Magnesiowastite is a principle phase in a mantle of peridotitic composition at depths below the 670 km seismic discontinuity and is therefore an appropriate choice for the direct investigation of mantle/metal equilibria at such pressures. At lower pressures, its use yields results that can be extrapolated to real mantle compositions with some simple thermodynamic manipulation. In this study, the high melting temperature of Mg-rich magnesiowastite has permitted experiments up to 2500øC at 5 to 25 GPa.The second difficulty with very high temperature, superliquidus experiments is that the high-temperature phase relations are not well preserved during quenching but need to be reconstructed from the quenched experimental run products.Problems of this kind are well known from the literature on the experimental petrology of peridotite melti...

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“…The absence of hematite on the surface in combination with the microstructure of the inward growing scale may explain this. Diffusion through magnetite is known to be faster than through hematite [44,45]. Also, the microstructural investigation showed that the ratio: reaction zone/fully oxidized spinel oxide, was higher in H 2 ?…”

Section: Influence Of the Formation Of Reactions Zones On Oxidation Pmentioning

confidence: 98%