Other
Scientific paper
Mar 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996lpi....27.1361v&link_type=abstract
Lunar and Planetary Science, volume 27, page 1361
Other
Diamond, Grains: Interstellar, Isotopes, Nitrogen, Noble Gases
Scientific paper
The carrier of the P3 noble gas component in nanometre diamonds from primitive meteorites is still enigmatic. On the one hand it was found to be closely associated with the HL carrier: for P3 rich samples Xe-P3/Xe-HL ratio is remarkably constant. As might be expected, these two components are not separable during laboratory chemical treatment, although they are easily resolved by stepped heating. The fact that P3 noble gases are released at low temperature (300-800 degrees C) during pyrolysis led to the suggestion that they are located near diamond surface. Moreover the association of P3 noble gases released with chemically active gases in the same temperature range can be interpreted to indicate that P3 gases are evolved as a result of chemical reactions destroying diamond surface. At the present time it is not absolutely clear what is happening at the diamond surface during stepped pyrolysis. With no added oxygen, we observe CO + CO2 in the low temperature products in amounts corresponding to 10-15% of the total carbon: we therefore have argued that surface absorbed oxygen is responsible for the reactions. Huss and Lewis supposed that a reaction with hydrogen, also present on the diamond surface, might take place to induce restructuring of the outermost layers during pyrolysis. In our experience, destruction of diamond surface rather than modification is a real fact but how it relates to the release of P3 gases is not quite clear. Incidentally, the release of chemically active gases is observed irrespective of whether or not the P3 component is present in diamond. The same is true for the presence of surface bonded hydrogen and oxygen. Thus, if the mechanism of P3 gas loss under natural conditions is the same as that in the laboratory experiments, then later on the diamond surface acquires a new layer of oxygen and/or hydrogen. In other words the extraneous elements could act as agent(s) for release of P3 noble gases and need not represent a common constituent(s) of the carrier.
Pillinger Colin T.
Verchovsky Alexander B.
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