Investigation of Structural, Optical Properties of Graphite Nanoparticles and Thermal Conductivity of Graphite -Water, Ethylene Glycol Nanofluids

Graphite nanopowders can be prepared by several techniques including graphitization of diamond powder in an inert atmosphere, Chemical Vapour Deposition, Chemical synthesis, etc. In the present work, we present a very economical, simple, less toxic technique for preparing graphite nanoparticles. Graphite nanoparticles were prepared from the graphite present in pencil by hand milling technique using a motor and a pestle. The prepared graphite nanoparticles were used to prepare graphite nanofluids by a two-step method. Nanofluids were prepared by ultrasonication at 42KHz for 20 mins. The hand-milled raw graphite nanopowder was further heat treated at 150 degrees C, 300 degrees C, and 450 degrees C to investigate the effect of temperature on nanosize and dislocation density. The heat-treated nanoparticles were characterized by X-Ray Diffraction studies (XRD) for structural features & UV-Vis spectroscopy for band gap determination. The average size of the nanoparticles varied from 42nm-56nm. The dislocation density of the nanopowders varied from 3.18x10(14)/m(3) to 5.66x10(14)/m(3). The graphite particles heat treated at 450 degrees C had a size of 52nm and there was no effect on particle size till 300 degrees C. The band gap of heat-treated nanoparticles varied from 1.18eV at 150 degrees C to 1.55eV at 450 degrees C. 0.1 vol% Graphite nanofluids were prepared with water and ethylene glycol as base fluid. Nanofluids prepared from graphite nanoparticles that were heat treated at 450 degrees C showed the highest stability in comparison to other nanofluids which contain nanoparticles heat treated at 150 degrees C & 300 degrees C. The thermal conductivity of nanofluids increased with the heat treatment temperature of nanoparticles from 0.431 W/m-K to 0.436W/m-K for the same volume fraction of nanoparticle (0.1%). This is due to the enhanced surface area of heat-treated nanoparticles evident through XRD studies.