EFFECT OF MONTMORILLONITE NANOPARTICLES ON THERMAL CONVERSION OF COAL TAR PITCH Maciej Gubernat1*, Wilhelm Frohs2, Janusz Tomala3, Aneta Fraczek – Szczypta1 and Stanislaw Blazewicz1 1
(Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Al.Mickiewicza 30, 30-059 Cracow/Poland) 2 (SGL CARBON GmbH Werner-von-Siemens-Straße 18 86405 Meitingen / Germany) 3 (SGL Carbon Polska S.A. 47-400 Raciborz ul.Piastowska 29/Poland) *(
[email protected])
INTRODUCTION Coal tar pitches (CTP) constitute main binder components in the manufacture of synthetic carbon and graphite materials. The most important properties of CTP- based binders for carbon and graphite products are their appropriate viscosity at molding temperatures, a high carbon yield after carbonization and graphitizability. Carbon products with graphitic structure fulfill the demands for electrode industry i.e., they display a low electrical resistivity and high thermal conductivity. Graphitization is the stage that significantly contributes in the total energy consumption during multi-stage process of the fabrication of graphite materials. Because of that an attempt to reduce graphitization temperature of CTP by using nanoparticles is the aim of this study. METHODOLOGY Two types of CTP (Table 1) were modified by nano montmorillonite (MMT). Prior to mixing deagglomerated nanoparticles
with the CTP MMT powder was sonicated in ethanol
suspension. After mechanical dry mixing ethanol was evaporated in a dryer. To obtain good homogeneity of MMT in CTP matrix, mixing at elevated temperatures was made. Deagglomeration and mixing parameters, i.e. time and the temperatures of the processing were established experimentally by Dynamic Light Scattering (DLS), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM+EDS), viscosity and wettability measurements. Modified CTPs were heat treated at 1000oC and 2000oC. Effect of MMT on microstructure and structure of carbon residues was studied by X-ray Diffraction (XRD), Raman Spectroscopy, Transmission Electron Microscopy (TEM) and SEM+EDS . Modified CTP based binders with MMT nanoparticles were also used for graphitized cathode samples preparation. After the graphitization process Specific Electrical Resistivity (SER),
Thermal Conductivity (TC) and Mechanical Strength of cathodes with modified binders were compared with the reference cathode. RESULTS AND DISCUSSION The study showed that the presence of
nano-MMT in CTP – based binder precursors
influences carbon structure ordering during heat treatment as compared to pure CTP binders. XRD analysis revealed that CTP-based carbons in the presence of MMT after heat treatment to 1000oC perform a complex turbostratic structure containing graphitic phases with well ordered crystallites (d002=0,335nm) (Figure 1). Well ordered phases in the samples of CTPbased carbons were also observed by TEM. The studies also showed that in the presence of MMT carbon nanotubes (CNT) growth occured (Figure 2) . After a subsequent heat treatment to 2000oC further enhancement in the graphitic crystallite sizes was observed. Such a modification allows to obtain graphitic materials with the desired functional properties at lower temperatures in comparison to typical processing conditions related to the graphitization stage of carbon materials. Further study on the impact of other nanoparticles on the CTP graphitization process is conducted. ACKNOWLEDGMENT: This study is supported by the Polish National Centre for Research and Development, project no: PBS2/B5/27/2013 19.19.160.86540
Figure 1 XRD pattern for CTP + MMT after heat treatment at 1000oC Figure 2 SEM for CTP + MMT after heat treatment at 1000oC Table 1 Characteristic of CTP and HCTP Softening Point [oC]
Coking Value [%]
Benzo[a]pyrene content [ppm]
CTP
103,3
54
13273
HCTP
234,5
83
110
