Journal of Materials Science, Vol.38, No.3, 565-573, 2003
An investigation of oxidation effects on hysteresis heating of nickel particles
The oxidation kinetics of nickel particles with approximate diameters of 79 nm, 0.7 micron, and 3 micron, at temperatures between 250degreesC and 350degreesC in air were investigated. Thermogravimetric measurements indicated a diffusion-controlled mechanism for the oxidation of spherical metal particles. Deviation of the oxidation kinetic rate from the diffusion-limited model was found in the case of Ni 3 micron and Ni 79 nm. The oxidation rate constant is governed by an Arrhenius equation as expected. Apparent activation energies are approximately 1.55 eV, 1.32 eV and 1.12 eV for Ni 79 nm, Ni 0.7 mum and Ni 3 mum, respectively. The exponential factor is found to be a function of particle size. Oxidation maps were constructed to relate the degree of oxidation to time and temperature. The oxide formed on the surface of the particles significantly modified the magnetic properties of the nickel particles by changing both the magnetization and the coercivity. The measured properties of oxidized particles were used to construct magnetic property maps to help determine appropriate processing conditions and predict oxidation effects on hysteresis heating performance. (C) 2003 Kluwer Academic Publishers.