Here we demonstrate an oven-free and mold-free heating route to convert preceramic polymers to silicon carbide using carbon nanomaterials as susceptors. Silicon carbide is prized for its high thermal stability and low density and could be produced via slow oven heating of polycarbosilane (PCS). We show that addition of multiwalled carbon nanotubes (MWCNT) as susceptors to polycarbosilane results in rapid and volumetric heating upon exposure to microwaves and radio frequency. We assess microwave heating of polycarbosilane-MWCNT composites; this process is capable of reaching pyrolysis temperatures, and the resulting crystal structure is cubic (-SiC). We measure dielectric properties of these composites in the radio frequency range. We cure these composites using RF, and thermogravimetric data shows that the extent of cure for these samples is around 95 %. We demonstrate the applicability of this study for 3D printing silicon carbides by successive iterations of layer deposition and rapid RF curing. We performed on the fly measurements of dielectric values of the 3D printing ink at different temperature while curing it.We have also shown that these volumetric heating methods can rapidly cure polycarbosilane fibers to make silicon carbide fibers without melting them before crosslinking.
Silicon carbide (SiC) fibers are widely used as a reinforcement
in ceramic matrix composites due to their high mechanical strength
and superior thermal resistance. Here, we investigate the rapid radio
frequency (RF) heating response of two types of SiC fibers (Hi-Nicalon and Sylramic) in the 1–200
MHz frequency range. Hi-Nicalon fibers exhibit a surprisingly rapid
RF heating response of 240 °C/s in the perpendicular orientation,
and this property could be exploited for oven-free and noncontact
processing of composites with SiC fibers. The presence of excess carbon
on the surface of Hi-Nicalon fibers is most likely responsible for
the RF heating response and significantly higher temperatures in the
parallel as compared to perpendicular alignment of fibers to the electric
field. The RF heating response of Hi-Nicalon SiC fibers was utilized
to heat preceramic polymers (polycarbosilanes) infiltrated in SiC
fibers and cure them to ceramic matrix composites (CMCs) using RF
applicators. A noncontact RF heating setup to pyrolyze the precursor
polymers under inert conditions and make SiC/SiC composites is also
developed.
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