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This work reported an experimental investigation of complete oxidation of nickel nanoparticles using simultaneous thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). Nickel nanoparticles and their elemental compositions were characterized by Brunauer-Emmett-Teller (BET) analysis, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The oxidation experiments were performed under isoconversion conditions for seven heating rates, varying from 2 to 20 K min(-1), with temperatures up to 1000 degrees C. The experiments revealed unique oxidation behaviour of nickel at the nanometre scale, such as early oxidation and melting phenomena, variable activation energies and different oxidation kinetics between low and high conversion ratios. Unlike its bulk counterpart where the activation energy is a constant, the activation energy of nickel nanoparticles depended on the conversion ratio, ranging between 1.4 and 1.8 eV. The oxidation kinetics of nickel nanoparticles changed from the classical diffusion controlled mechanism to a pseudo-homogeneous reaction as conversion ratios were over 50%. The oxidation mechanisms of nickel nanoparticles were further discussed and future studies to enhance understanding were identified.

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In this paper, the electromagnetic torque, reluctance torque, inductance, and back-EMF are analytically calculated for brushless slotless machines with surface inset magnets. The calculations are based on the 2-D analytical magnetic field distributions. Although the expressions can be used for any magnetization patterns, the effects of three different magnetization patterns, i.e., radial, parallel, and Halbach, on the developed torque, back-EMF and inductances are examined. Besides, the influences of three types of armature current waveforms (sinusoidal, ideal rectangular, and six-step rectangular) on the mentioned quantities are investigated. The effects of pole arc per pole pitch ratio on the performance of slotless brushless machines are also studied. To evaluate the proposed 2-D analytical expressions, the analytical results are compared with those obtained by finite element analyses.Index Terms-Brushless direct current (dc) machine, Halbach, magnetic field, magnetization, permanent magnet (PM), synchronous machine.