Other
Scientific paper
Nov 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996gecoa..60.4095d&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 60, Issue 21, pp.4095-4106
Other
12
Scientific paper
We have measured the diffusion coefficient of 44 Ca along and perpendicular to c direction in natural Fe-bearing (~2 at.%) diopside single crystals. Specimens were annealed at temperatures ranging from 1000 to 1250°C, with controlled oxygen fugacity. Diffusion profiles were analysed by Rutherford Back-Scattering Spectrometry (RBS) of -particles. The diffusion of Ca is isotropic along c and b directions. In addition, the results clearly show two distinct diffusional regimes for the natural diopside, revealed by silica precipitates occurrence in the diopside matrix when T 1150°C. In this case the oxygen partial pressure p O 2 does not influence the self-diffusion coefficient which is characterized by the activation energy E = 396 ± 38 kJ/mol. For T 1100°C the diffusional process has a lower activation energy ( E = 264 ± 33 kJ/mol) and varies as ( p O 2 ) -0.14±0.01 in the investigated range (from 10 -16 atm to 10 -6 atm). These results are consistent with previously reported results on electrical conductivity (Huebner and Voigt, 1988) and high temperature plastic deformation of natural diopside single crystals (Jaoul and Raterron, 1994). According to the point defects model, elaborated by Jaoul and Raterron (1994), the diffusional mechanism of Ca should be essentially interstitial. Furthermore, this mechanism should be the same for different diopside samples with iron content ranging from 0.4 to 2.42 at.%. Indeed, for Ca diffusion in synthetic diopside (0.4 at.% Fe) the activation enthalpy is very similar (281 ± 26 kJ/mol, Dimanov and Ingrin, 1995). On the other hand, the Fe content indoubtly influences the preexponential factor. The present paper reports Ca self-diffusion in diopside as a function of T , p O 2 crystallographic orientation, and Fe content. In fact, among all diffusion coefficients previously reported in diopside, but Si, D Ca is the lowest. Thereby, Ca should be a kinetically limiting species for diffusion-controlled processes such as plastic deformation and cation exchanges. For instance, Ca self-diffusion controls Ca---Mg exchanges between pyroxenes. Then, our results could be helpful to better understand the closure behaviour (Dodson, 1973, 1976) of the Clinopyroxene-Orthopyroxene geothermometer.
Dimanov Alexandre
Jaoul Olivier
Sautter Violaine
No associations
LandOfFree
Calcium self-diffusion in natural diopside single crystals does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Calcium self-diffusion in natural diopside single crystals, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Calcium self-diffusion in natural diopside single crystals will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1148062