Direct synthesis of hBN/MWCNT composite particles using spray pyrolysis

A spray-pyrolysis technique for the direct synthesis of multi-wall carbon nanotubes (MWCNTs) on a hexagonal boron nitride (hBN) matrix has been developed. Cobalt palladium (CoPd) nanoparticles, hBN nanoparticles, and ethanol were used as the catalyst, matrix, and carbon source, respectively. The materials were mixed by ultrasonication and then sprayed into a vertical tubular reactor at 900 °C under an argon flow of 2 L/min. As the aerosol passed through the reactor, the following processes occurred sequentially: solvent evaporation; formation of spherical particles composed of hBN and CoPd nanoparticles; catalytic decomposition of ethanol; and CNT growth on the surface of the CoPd nanoparticles. As a result, spherical-hairy particles were obtained, and both the hBN hexagonal phase and primary particle diameter were maintained during the reaction pathway because of the short residence time (1 s). The results showed that the spray-dried particle size and population of MWCNTs depended on the residence time within the heating zone and on the initial CoPd concentration. The novel synthesis technique described in this paper can be broadly applied to the production of various types of functional inorganic material/CNT composite particles.