Thermal stability of carbon nanotubes, fullerene and graphite under spark plasma sintering

Abstract

a b s t r a c tThe thermal stabilities of carbon nanotubes, fullerene and graphite were investigated under spark plasma sintering (SPS). Results were compared with data from synchrotron radiation in situ high temperature X-ray diffraction of these materials. Part of the nanotubes and fullerene transformed into diamond under SPS, but graphite kept stable. There was no diamond conversion in the in situ X-ray diffraction experiments under the same condition. Their phase transitional mechanism indicated the presence of plasmas during the SPS operation.

Synthesis of Diamond Using Spark Plasma Sintering

“…After SPS processing, the MWCNTs diffraction peaks are still present in the sintered MWCNTs compacts, but the peaks of the CNTs (002), (100) and (004) are stronger than those in the raw MWCNTs. It indicates that the SPS process improved the crystallinity of the MWCNTs (Zhang, Mihoc et al, 2011). Additionally, new peaks were detected in the sample centered at 2.05, 1.23, 1.06 and 1.76 Å corresponding to the cubic diamond (ICDD No.…”

“…The n-diamond is a new kind of carbon allotrope, which is a metallic form of carbon with face-centred cubic structure. It is a metastable and intermediate phase, can decompose slowly at room temperature, and has been synthesized accidentally by various processes (Zhang, Mihoc et al, 2011). It is noted that the n-diamond can also be synthesized by the SPS process.…”

“…The process typically uses moderate uniaxial pressures usually below 100 MPa in combination with a pulsing on-off DC current during its operation. There are many mechanisms proposed to account for the enhanced sintering abilities of the SPS process; for example, field assisted diffusion, spark impact pressure, plasma cleaning of particle surfaces, Joule's heating, local melting and evaporation especially in metallic systems, surface activation on particles and electron wind force (Zhang, Mihoc et al, 2011). The one that draws the most controversy of these mechanisms involves the presence of momentary plasma.…”

Growth of diamond from fullerene C60 by spark plasma sintering

“…Our researches have shown that carbon nanotubes are unstable and can be converted into diamond without [8][9][10] or with metallic catalysts [11] under the pulsed electric field of the SPS. Our recent work has shown that C60 can be converted into diamond under the same SPS conditions as carbon nanotubes are converted to diamond (1500 1C, 80 MPa) [12]. Since the C60 has a higher sp 3 hybridization fraction than that of carbon nanotubes, it makes the transformation of C60 into diamond easier.…”

Metallurgical Challenges in Carbon Nanotube-Reinforced Metal Matrix Nanocomposites

“…[127] In summary, CNTs may transform into other thermodynamically stable allotropes during the heat treatment process. Among these allotropes, cubic diamond [105], n-diamond [122], mono/multi-layer graphene [106], and graphite sheets [107] are the most extensively reported. However, the way these allotropes can affect the final properties are highly contradictory.…”