Preparation And Characterization Of Micro-nano Graphite Spheres

Carbon materials with the sizes of nanometer and micron possess the structural diversity, such as carbon nanotubes, carbon onions, fullerene, graphene, carbon sphere and treelike carbon etc. Graphite spheres have been potential candidate materials, widely used for physical, chemical, medical and biological fields due to unique highly ordered concentric spherical shell structure and excellent physical and chemical properties, and always received great concerns. Graphite shells with anti-corrosive characteristics can be used to synthesize carbon-encapsulated magnetic materials to resist the corrosion or oxidation of external environment. These composite materials not only can maintain graphitic properties but also possess magnetic function, which can be widely used in the fields of magnetic recording materials, medical drug delivery, and anode material for lithium-ion. Moreover, the composite materials have low density and good absorbing capacity, and can be expected to make novel microwave absorbing materials. Therefore, it can be urgent to explore a cheap and simple method of large-scale preparation of carbon spheres for meeting the business needs.Currently, the methods of preparation of carbon spheres mainly involve chemical vapor deposition, pyrolysis of carbon source, catalytic reduction and solvothermal, etc. These methods are based on the chemical reaction, which will inevitably produce by-products difficult to purify, and need appropriate catalyst, harsh reaction conditions (such as high temperature and pressure), and other complex operations, etc. In this paper, a novel method of preparation of carbon spheres has been explored according to the growth of graphite spheres in the liquid metal melt (Ni, Fe). The research has found that firstly, the graphite morphology will change by means of a single roller melt spinning apparatus and nodularizing inoculation treatment process, and then the graphite spheres with uniform morphology have been obtained with acid corrosion of metal substrates (Fe and Ni). The specific contents are as follows:(1) The Ni-C alloy with eutectic composition firstly has been blown into many ribbons with a single roller melt spinning apparatus, then corroded with concentrated HC1. and collected to obtain graphite spheres. Flake graphite has been found to transform into spherical graphite in a liquid nickel catalyst; the internal structures of graphite spheres with ball concentric structure are composed of loose disordered center and ordered graphite shells from interior to exterior; the spontaneous curling of graphene has been simulated by Molecular Dynamics to explain the growth mechanism of graphite spheres.(2) The Fe-C alloy with certain components fistly has been melted in the alkaline medium frequency induction melting furnace with 25kg, and prepared by nodularizing inoculation treatment process. Graphite spheres have been obtained by acid corrosion Fe-C alloy with hydrochloric acid and hydrofluoric acid, respectively. The results show that graphite spheres possess ferromagnetic properties and smaller specific surface area; the thickness of graphite layer is about 10-15μm, and non-porous graphite layer can better protect the inner magnetic particles from erosion of the external environment; the valuesμ' andμ" of graphite spheres is relatively smaller due to smaller magnetization. Through simulating the micro-wave absorbing curves of samples with different thickness, the results show that the sample with 1.8mm thickness can absorb the high frequency range of 11 GHz to 18GHz band, therefore, the composite materials have competitive advantages of "thin, light weight, the wide absorption band" in high frequency band range.(3) The above Fe-C alloy in (2) step has been blown into many ribbons with a single roller melt spinning apparatus, then corroded with concentrated HCl and HF, respectively, and collected to obtain graphite spheres. Graphite spheres have been fully characterized using XRD, FESEM, Raman spectrum, HRTEM. The results show that compared to graphite spheres with nodularizing inoculation treatment process in (2) step, graphite spheres have loose structure, smaller diameter size, more narrow distribution, more smooth surface, better roundness. Therefore, the cooling rate is the critical factor that graphite transforms into spherical graphite in a liquid metal melt, and the greater cooling rate, the more uniform morphology and the smaller size of graphite spheres.