Physics
Scientific paper
Jun 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983gecoa..47.1117o&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 47, Issue 6, pp.1117-1129
Physics
14
Scientific paper
Carbon subsurface concentration profiles in olivine single crystals from San Carlos, Arizona, and the Sergebet Island. Red Sea, containing total carbon between 60-180 wt.-ppm, were analyzed by means of the 12 C(d. p) 13 C nuclear reaction and by x-ray induced photoelectron spectroscopy (XPS) in combination with acid etching and with Ar + ion sputtering respectively, between 200-930 K. The (d, p) analysis reveals equilibrium subsurface C profiles extending 1-2 m or more into the bulk. Their steepness is a function of temperature. Typical mean C concentrations at 300 K in the resolvable layers, 0-0.6, 0.6-1.2, and 1.2-1.8 m. are 1.8, and 0.6 wt.-%, corresponding to enrichment factors over the mean bulk C concentration of the order of 100, 40 and 30 respectively. In the topmost atomic layers analyzed by XPS the carbon is enriched by a factor of the order of 1000, decreasing with increasing temperature. The results suggest that the carbon is in a truly dissolved state and highly mobile, subject to a reversible subsurface segregation. Most probably local lattice strain associated with the solute C species provide the driving force for this diffusional process. The C diffusion coefficient was determined from the (d, p) data below 300 K: D = 10 -13 exp(-7.8/RT) [m 2 · sec -1 ; KJ · mole -1 ] and from XPS data between 450-925 K: D = 10 -14 exp(-6/RT) [m 2 · sec -1 ; KJ · mole -1 ] The estimated error of the preexponential factors is ± one order of magnitude, that of the activation energies ±3.5 and ±2 KJ mole -1 respectively.
Demortier Guy
Freund Friedemann
Gonska Horst
Kathrein Hendrik
Oberheuser Gert
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