Nucleation behavior of silicon carbide whiskers grown by chemical vapor deposition

Silicon carbide (SiC) whiskers as a kind of high strength fibrous material are commonly used as an effective reinforcing element for composite materials. The preparation and characterization of such high aspect ratio materials are of great importance to the understanding of fundamental properties and potential industrial applications of whisker materials. In this study the growth of SiC whiskers by chemical vapor deposition (CVD) from the thermal decomposition of methyltrichlorosilane was performed on Ni-coated graphite substrates in a hot wall reactor with an emphasis on the study of the fundamental nucleation and growth characteristics of the whiskers. Since vapor-liquid-solid mechanism is found to be responsible for the growth of whiskers, the formation of the Ni catalyst and its subsequent evolution on whisker nucleation and growth is a subject of extensive research. Scanning electron microscope is employed to characterize the nucleation and growth of SiC whiskers. It is found that the incubation period for whisker nucleation and growth to noticeable dimension depends on the size of the Ni particles. It takes about 3 min for the first whisker to appear and about 8 min to complete the whole nucleation stage for the case of Ni-coating thickness of about 2.5 mum under the CVD parameters employed in the present study. Besides, due to the balance between the volume and the curvature effect of the liquid droplet of Ni catalyst formed on the graphite substrate during CVD process, the shortest incubation time for SiC whisker nucleation was found for droplets of 2 mum in diameter, instead of those with larger or smaller dimensions. (C) 2002 Elsevier Science B.V. All rights reserved.