Structure Characteristic Of Micro/nano Carbon Spheres(Tubes) Via CaC₂-CHCl₃(CCl₄) Systems

Micro/nano carbon spheres have low density (<2.26g/cm³), stable physico-chemical properties, special structure, big specific surface area, excellent electromagnetic properties and good biocompatibility. Therefore, carbon spheres are potential candidates in cathode material of Li-ion batteries, carrier of catalysts, enforcement of composites and drug capsules, and are probably applied in advanced materials of high-tech fields. Carbon spheres are another hot of novel carbon nanomaterials after fullerenes and carbon nanotubes, and are absorbing more and more attentions all over the world. In this study, the structures of carbon spheres (tubes) via oxidation reduction reaction are characterized, and their growth models are proposed. Furtheremore, carbon spheres as negative electrodes of Li-ion batteries are also primarily accessedCalsulm carbide-chloroalkane is proposed to fabricate micro/nano carbon spheres (tubes) by oxidation reduction reaction under different process conditions. The advantages of this metheod are simple, quick and high carbon yield.Gibbs energies and heat effects of CaC₂-CCl₄ system and CaC₂-CHCl₃ system were calculated based on thermodynamics data. These two systems are all intensely exothermix and spontaneous, and graphite, diamond and C₃ (atom gas) can be produced through these systems under lower temperature. According to isobaric reaction condition, the thermodynamics of two reaction systems can accord with the synthesis conditions of micro/nano carbon spheres (tubes).Effects of process factors on carbon spheres (tubes) through CaC₂-CHCl₃ system were systematically investigated. With no-catalyst condition, carbon spheres with diameter about 200nm, low agregation degree and better crystallinity were synthezied. With ferrocene, iron chloride and iron oxide as catalysts, fluffy carbon spheres with diameters approximate 150nm and amorphous carbon, Brooks-Taylor carbon spheres with diamemters between 100-200nm and carbon spheres with diameters 70-135nm were fabricated, repectively. When the autolave was filled with 1.0MPa Ar gas, four hollow carbons with diameters between 12-200nm were formed, including fluffy hollow carbon spheres, hollow carbon nanohorns, smooth hollow carbon spheres/rods and hollow carbon polyhedrons. With the increase of reaction contents, the crystallization degree carbon spheres (tubes) increases, but is not effective to the diameters. With bulk CaC₂ as reactants, submicro-carbon tubes with directional growth, uniform diameter (external diameter: 160-200nm, wall thichness:70nm) were synthesized. Hollow carbon speres and hollow cones were formed while absolute acohol as reaction buffer.Effects of different catalyst on smooth carbon spheres (tubes) by CaC₂-CCl₄ systems were studied. Under no-catalyst condition, t diameter about 200nm and low agreegation were studied. While ferrocene, iron chloride and iron oxide as catalysts, porous carbon spheres (diameters :60-200nm), fluffy hollow carbon spheres with amorphous structure (diameters: 0.3-1.8μm), and well-distributed carbon spheres (diameters: approximate 150nm) and carbon tree (height: 750nm) were formed.The substrate catalysis growth model of carbon spheres by CaC₂-CHCl₃ system was proposed. Fluffy carbon spheres with filamentous and scattering structure cause from the substracte catalysis of iron atoms pyrolyzed from ferrocene.The droplet model substrate growth models of hollow spherical carbon of pressure ferrocene catalyzed CaC₂-CHCl₃ system and FeCl₃ catalyzed CaC₂-CCl₄ system were proposed, respectively. During the reaction process, CHCl₃ and CCl₄ droplets by atomization are the key fators to form hollow carbon strutures.Effect of high temperature treatment on morphology and structure of carbon spheres were studied. The transformation mechanism of carbon spheres to hollow carbon polyhedrons was discussed.The electrochemical properties of carbon spheres as negative electrodes of Li-ion batteries using constant current discharge were studied. Though 2100℃heat treatment, the reversible capacity of carbon spheres of CaC₂-CHCl₃ system after 5 cycles is 280mAh/g with coulomb efficiency of above 97% after 11 cycles. The reversible capacity and coulomb efficiency of carbon spheres of CaC₂-CCl₄ system after 15 cycles is 190mAh/g and near 100%, respectively. Carbon spheres of these two systems through high temperature heat treatment are candidate materials of negative electrodes of Li-ion batteries.