Influence of silicon and carbon excesses on the aqueous dispersion of SiC nanocrystals for optical application

The dispersion behaviour of laser-synthesized silicon carbide nanoparticles (npSiC) in water is investigated by photon correlation spectroscopy (PCS). With regard to previous studies and due to an application in the processing of optical materials, this paper concerns low npSiC contents (from 0.05 to 10 wt.%). The role played by the particle surface state is be pointed out through the consideration of stochiometric (C/Si=1), carbon-rich (C/Si>1) and silicon-rich (C/Si < 1) nanopowders. Suspensions made from stoichiometric and silicon-rich nanopowders are easily dispersed and stable with time. The PCS measurements reveal in this case more than 95% of isolated nanoparticles, pointing out the key role of the oxidized layer covering the grain of silicon-rich samples. At the opposite, the carbon-rich powders are hardly dispersed in pure water, correlated with the presence of a relatively inert graphitic carbon layer at the grain surface. However, by addition of a commercial polymeric dispersant, all nanopowders induce high quality suspensions. In particular, the carbon-rich samples are easily dispersed, and possible dispersion mechanisms of npSiC in presence of a polymeric surfactant are discussed. The influence of the npSiC loading and the time evolution of the suspension are also presented. By considering stoichiometric, as well as carbon- and silicon-rich samples, this paper demonstrates the possibility to achieve high quality dispersions of SiC nanoparticles, whatever the chemical composition of the powder, as an easy step for optical material processing.