Carbon nanotubes functionalization process for developing ceramic matrix nanocomposites

The carbon nanotubes (CNTs) functionalization for developing ceramic matrix composites with an optimum interface between the matrix and nanotubes is presented. The functionalization processes were successfully performed by means of oxidation and boron nitride and silicon oxide coatings, which were characterized, among others, by O2/N2 adsorption-desorption method, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. In all cases, the functionalized CNTs exhibited an enhanced thermal stability compared to the original nanotubes. Silicon nitride (Si3N4) nanocomposites having 5.3 vol% of multi-walled CNTs, both pristine and functionalized, were developed. Dense nanocomposites having well dispersed nanotubes were attained under all circumstances, although the nanocomposites containing the coated CNTs required the use of a dispersant agent to prevent nanotubes agglomeration. Besides, slightly higher sintering temperatures were needed to densify the composites containing the coated CNTs. A stronger mechanical interlocking between the matrix and the nanotubes was achieved by the functionalization processes, which led to some improvement of the mechanical properties of these nanocomposites, compared to those containing pristine CNTs; and actually values that were close or even higher than those measured for the blank Si3N4 were achieved.