Structural characterization of carbon-based materials obtained by spark plasma sintering of non-graphitic carbon with nickel and iron as catalysts and space holders

In this work, carbon-based materials were obtained by graphitization-accompanied sintering of mixtures containing non-graphitic forms of carbon (nanodiamonds or amorphous carbon) and nickel or iron as graphitization catalysts. The mixtures were consolidated by Spark Plasma Sintering (SPS). After sintering, the metals were selectively dissolved from the compacts in hydrochloric acid solution. The structural investigations of the obtained carbon-based materials were conducted using X-ray diffraction, Raman spectroscopy, Scanning and Transmission tlectron Microscopy and specific surface area (SSA) measurements. Selective dissolution of the metals resulted in the formation of carbon-based porous compacts, which retained the shape of the as-sintered composite metal-carbon compacts. The dependences of the phase composition and structural features of the carbon-based materials on the characteristics of the carbon source and sintering conditions were analyzed. It was found that SPS of nanodiamonds in the presence of nickel leads to a dramatic decrease in the SSA of the carbon-based material (measured after nickel has been dissolved) relative to the initial nanodiamond powder. The graphitization degree of the amorphous carbon in the presence of nickel increased with the SPS temperature; however, the SSA values of the obtained carbon-based materials did not follow any discernible trend. The iron-containing mixtures showed the iron carbide Fe₃C phase after the SPS. The products of partial dissolution of iron from the compacts contained carbon that was poorly graphitized and its graphitization degree was not influenced by the sintering temperature.