1.
Science
; 296(5574): 1852-5, 2002 Jun 07.
Artigo
em Inglês
| MEDLINE
| ID: mdl-12052956
RESUMO
The inferred crystallographic class of circumstellar silicon carbide based on astronomical infrared spectra is controversial. We have directly determined the polytype distribution of circumstellar SiC from transmission electron microscopy of presolar silicon carbide from the Murchison carbonaceous meteorite. Only two polytypes (of a possible several hundred) were observed: cubic 3C and hexagonal 2H silicon carbide and their intergrowths. We conclude that this structural simplicity is a direct consequence of the low pressures in circumstellar outflows and the corresponding low silicon carbide condensation temperatures.
Assuntos
Astronomia , Compostos Inorgânicos de Carbono/análise , Meteoroides , Compostos de Silício/análise , Fenômenos Astronômicos , Microscopia Eletrônica , Pressão , Temperatura
2.