Analysis of the acid, base and air oxidized carbon microspheres synthesized in a single step from waste engine oil

Carbon microsphere (C-μS) ball bearings are prone to corrode after long exposure to oxidizing environments. ∼4.2 μm diameter C-μSs synthesized from waste engine oil (at 600 and 900 °C) by dry autoclaving, were exposed to nitric acid (30 and 60 vol.%), piranha (H2SO4:H2O2 60:40 and 90:10), base (NH4OH:H2O2 15:30 and 30:15) and air oxidation at 300 and 450 °C for 12-48 h. The oxidation processes were monitored by weight loss analyses, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, chemical functionalization and electrical conductivity measurements. Crystallinity and higher graphitic content in the C-μSs results in better resistance to oxidation.