Core–shell composite of SiCN and multiwalled carbon nanotubes from toluene dispersion

Carbon nanotubes are known to have high thermal conductivity, and in bulk form, a topology that could constitute the matrix of an inhomogeneous solid [1]. Among the promised applications of carbon nanotubes is a composite material that is practical for thermal management and suitable for commercial products that behave as thermal emitters, absorbers, and interfaces. However, carbon nanotubes are known to oxidize in the temperature range of 400 to 600 C, which limits the options for forming the composite and the applicability for high-temperature environments where such a composite is needed. A variety of polymer, metal, and ceramic composites bearing carbon nanotubes have been reviewed [2, 3]. More recently, Francis and Riedel [4] reported the use of polyureasilazane as a route to form a shell–core composite containing nanotubes. In their work, the SiCN shell is derived from polyureasilazane. However, the polyureasilazane is a viscous liquid in which nanotubes do not readily disperse. Francis and Riedel were able to report a multiple-step process that includes cross-linking (at 280 C), pressing, mixing, ball milling, and baking again at higher temperature. We have found an alternate route of forming a similar composite that is facilitated by dispersing the nanotubes in toluene and then mixing with polyureasilazane. A single episode of baking forms a core–shell structure of amorphous SiCN surrounding MWCNTs (abbreviated hereafter as SiCN/MWCNT). Our primary application is that of coating thermal detectors and other surfaces intended to absorb and thermalize laser radiation. The challenge is shared by other applications that demand heat dissipation without oxidation and melting. Before now, we have pursued nanotubes (single-walled and multi-walled) applied from a volatile suspension, grown vertically aligned, and bound in potassium silicate [5–7]. Here we report on the method of preparation and some aspects of surface chemistry that distinguish the shell–core composite from its constituents.