Oxidation Behavior of Zirconium Diboride Nanoparticles

The products of oxidation of ZrB 2 powders with average particle sizes of ~100 and ~30 nm by atmospheric oxygen under isothermal conditions and during heating have been characterized by thermal analysis, X-ray diffraction, scanning electron microscopy, IR frustrated total internal reflection spectroscopy, energy dispersive X-ray analysis, and elemental analysis. The oxidation onset has been observed at 594 and 396°C, respectively. Oxidation at temperatures of ≥800°C leads to the formation of boron oxide and monoclinic ZrO 2 , independent of the particle size of ZrB 2 . The reaction rate constants for the oxidation of ZrB 2 nanoparticles ~100 and ~30 nm in size have been determined to be 0.03, 0.15, and 0.31 h –1 at 600, 650, and 700°C and 0.11, 0.35, and 0.81 h –1 at 500, 600, and 700°C, respectively. The apparent activation energies for the oxidation of the ZrB 2 nanoparticles ~100 and ~30 nm in size are 161 ± 4 and 62 ± 3 kJ/mol, respectively, as evaluated from the temperature dependence of the rate constants at the above temperatures.