1 Copyright © 2012 by ASME SYNTHESIS OF CARBON NANOSTRUCTURES BY THERMO-MECHANICAL MEANS David Barber University of Houston, College of Technology Houston, TX USA 77204-4020 H. A. Calderón ESFM-Instituto Politécnico Nacionál Mexico City, Mexico Julio Quintero University of Houston, College of Technology Houston, TX USA 77204-4020 Francisco C. Robles Hernandez University of Houston, College of Technology Houston, TX USA 77204-4020 ABSTRACT Different C phases have been developed by mechanical milling, conventional heat treatments and Spark Plasma Sintering of C soot and transition metals (Fe or Ni). Transition metals are known to catalyze the development of different C phases. The energy input involved in such a processing method has been used to develop composite and ceramic materials made of transition metals and fullerenes and C soot. The as milled samples as well as the sintered composites show various dispersions of diamonds, fullerenes, carbon nanotubes, graphitic carbon, graphenes, among other nanostructures. Thus milling, heat treatment or sintering of quasi-amorphous carbon nanostructures with different transition metals under various conditions can be a simple route to synthesize the above mentioned phases in solid state. Results of electron (scanning and transmission) microscopy, Raman spectroscopy, XRD and nanohardness are presented and discussed accordingly. INTRODUCTION Discovered by Harry Kroto and Richard Smalley in 1985 by vaporizing graphite with a laser [1], the Fullerene containing 60 C atoms structured in a circular fashion has changed the idea of strengthening materials. Mechanical properties of fullerene and other carbon nanostructures (e.g. nanotubes) are up to three orders of magnitude higher than those observed in conventional materials. This is one of the centers of attention for materials scientist to develop the next generation of advanced materials (Harris, 1999). The synthesis of carbon nanostructures is usually conducted by evaporating carbon having a good control of their nucleation and growth [2]. This work looks into the idea of using soot and transforming it into other forms of carbon using a solid state approach by means of mechanical milling and sintering. Cost effectiveness of the transformation was an important piece to this work. Mechanical milling was used to transform the purchased material into other carbon structures and even going further this worked looked at the as milled material after heat treatments were applied to some samples and other samples that were sintered. The in situ synthesized carbon structures include: multiwall carbon nanotubes, fullerene, diamonds and nano-onions [3-5]. Traces of Fe and Ni were used as a catalyst to synthesize the carbon nanostructures. The sintering as conducted by Spark plasma sintering that was reported previously to be efficient to promote phase changes [6]. Material characterization was performed using Raman spectroscopy, x-ray diffraction (XRD), and electron microscopy (scanning (SEM) and transmission (TEM) including high resolution (HRTEM)). METHODS Samples for the milling were prepared using commercially available Fullerene Soot purchased from SERES. Samples of 1 g of carbon and 1-50 wt% of Iron (Fe) or Nickel (Ni) were mixed and milled in a SPEX 8000 M mill using a 20:1ratio milling media to sample. The samples were milled from 0.5 to 50 h. The milled samples were heat treated in a conventional furnace in a protective atmosphere (He) or spark plasma sintering method (SPS). Raman was conducted on a Horiba/Xplora spectrometer equipped with a 638nm laser and 0.5m spot size. XRD was carried on a Siemens D5000 apparatus operated at 30 kV and 40A, using Cu-K  radiation with a wavelength (λ) of 0.15418 nm. The HRTEM was conducted on the TEAM-05 microscope with a resolution of 0.05nm. Additionally, a transmission electron microscope (TEM) with a resolution of 0.2nm was also used. Prior to TEM/HRTEM the samples were acid washed to remove metals. RESULTS AND DISCUSSION Raman spectroscopy shows the synthesis of graphene-like and graphitic carbon structures. Figure 1 shows the change taking place with the movement of the D band toward peaks in the area of 1335 cm -1 and toward 1580 cm -1 for the G band [7]. The Raman spectra (Fig. 1b) shows a well resolved D (1318 cm -1 ), G (1578 cm -1 ) and 2D (2660 cm -1 ) bands that are characteristic of carbon structures such as graphitic (sp2) carbon (2D band). The D band peak shifts with increased milling time from 1318 cm -1 to 1326 cm -1 and to 1334 cm -1 . The red shift in the D band indicates the presence of sp3 bonds. Proceedings of the ASME 2012 International Mechanical Engineering Congress & Exposition IMECE2012 November 9-15, 2012, Houston, Texas, USA IMECE2012-89866 Downloaded from https://asmedigitalcollection.asme.org/IMECE/proceedings-pdf/IMECE2012/45196/599/4512369/599_1.pdf by University of Houston user on 31 October 2019