Cleavage and size reduction of graphite crystal using ultrasound radiation

Abstract

The influence of ultrasound radiation on graphite structure was studied by laser light scattering, X-ray diffraction, Raman spectroscopy and Transmission Electron Microscopy. Irradiations of polycrystalline graphite powder suspensions at frequencies of 20kHz and 500kHz, were carried out in three different solvents: water (as the best medium for cavitation), a surfactant (OMImBr) aqueous solution and also a mixture of sulfuric and nitric acids which caused the exfoliation by intercalation. The average basal particle size of 168μm was reduced to 4μm after ultrasonication delivering a huge energy density up to 1.2MW/m2. Change of the sonication time and the nature of the solvents produced different reduction of the graphite crystals dimensions, affecting the out of plane thickness and the basal width as well. The ultrasonication promoted the disordering of the graphite tridimensional stacking for all solvents used, with the strongest effect in acidic medium. Turbostratic structures formation and exfoliation of graphene flakes have been observed after the use of surfactant for sonication medium. Intercalation in acid medium prior to the ultrasound treatment produced similar effects.