A set of 45 dust envelopes of carbon stars has been modeled. Among them, 34were selected according to their dust envelope class (as suggested by Sloan,Little-Marenin & Price, 1998) and 11 are extreme carbon stars. The models wereperformed using a code that describes the radiative transfer in dust envelopesconsidering core/mantle grains composed by an alpha-SiC core and an amorphouscarbon (A.C.) mantle. In addition, we have also computed models with a codethat considers two kinds of grains - alpha-SiC and A.C. - simultaneously.Core-mantle grains seem to fit dust envelopes of evolved carbon stars, whiletwo homogeneous grains are more able to reproduce thinner dust envelopes. Ourresults suggest that there exists an evolution of dust grains in the carbonstar sequence. In the beginning of the sequence, grains are mainly composed ofSiC and amorphous carbon; with dust envelope evolution, carbon grains arecoated in SiC. This phenomena could perhaps explain the small quantity of SiCgrains observed in the interstellar medium. However, in this work we consideronly alpha-SiC grains, and the inclusion of beta-SiC grains can perhaps changesome of there results.
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