Primordial Mineral Growth in a Plasma

Details Primordial Mineral Growth in a Plasma Primordial Mineral Growth in a Plasma

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.335c&link_type=abstract

Meteoritics, vol. 28, no. 3, volume 28, page 335

Other

Condensation, Diamonds, Dust, Interplanetary, Plasma

Scientific paper

Diamonds, SiC, TiC, corundum, and graphite have been found in primitive meteorites [1] as crystalline components existing with, but far removed from equilibrium with, lower-temperature minerals and, in some cases, hydrocarbons. From anomalous isotopic ratios there is a presumption that the grains, many of them submicroscopic in size, had an extra-solar system origin [1] and may have formed within stellar atmospheres. If that were true, their environment of formation was a plasma. A plasma is an electrically neutral gas containing a high proportion of its component molecules in the ionized state, with charge balance satisfied by the presence of free electrons; it has been described as a fourth state of matter. The exact way in which the presence of a plasma would affect the Gibbs Phase Rule and alter the laws of thermodynamics is not understood, and condensation and vaporization in the presence of a plasma is affected in ways that cannot now be predicted. A good example of the truth of this assertion is the commercial process of growing diamonds in a plasma, where diamonds grow very rapidly in an atmosphere whose components before dissociation were 99.5% H2 + 0.5% CH4, at pressures ranging from 40 to 65 millibars and substrate temperatures ranging between 800 and 1000 degrees C. These P-T conditions, particularly the pressures, are very different from those necessary for equilibrium growth of diamond in the absence of a plasma. If non-shock meteoritic diamonds grew "metastably" in a plasma, perhaps other meteoritic minerals would also grow in such an environment: silicates, for example, have been detected in interstellar clouds. Such minerals might be incorporated later, along with diamonds, as minor constituents in the matrix of forming meteoroidal objects, and be unrecognized because of their similarities to the much more abundant intrasolar system minerals making up the bulk of primitive meteorites. References: [1] Nittler L. R. et al. (1993) LPS XXIV, 1087-1088.

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