The active to passive transition in the oxidation of sintered 0~-SiC has been determined by a thermodynamic approach and then experimentally under flowing air at high temperatures (1673-1973 K) and low pressures (oxygen partial pressure from 200-2100 Pa). Then, the physico-chemical behaviour of samples was compared for two different environments such as air-plasma atmosphere generated by microwaves, and a molecular atmosphere. The thermodynamic calculation does not predict any variation of the oxidation transition when changing the chemical state of oxygen (Q2 or O) but experimentally the domain characterized by the formation of a passive layer of silica is extended to lower pressure under atomic oxygen (for the same temperature range) than in the case of molecular oxygen.

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This paper deals with the analytical computation of the magnetic field distribution in a wholly superconducting reluctance motor. The rotor is made with high temperature superconductor bulks which nearly present a diamagnetic behavior under zero-field cooling. The stator consists of superconducting armature windings fed by AC currents of high amplitude. The superconducting stator winding can generate a high rotating magnetic field without the need of ferromagnetic material in the rotor. The electromagnetic torque is obtained by the interaction between the rotating magnetic field created by the superconducting stator windings and the variable reluctance due to the superconducting bulks. The proposed analytical method is based on the resolution of Laplace's equation (by the separation of variables method) for each sub-domain, i.e. rotor shaft, holes between superconducting bulks and air-gap. The global solution is obtained using boundary and continuity conditions. Magnetic field distribution and electromagnetic torque obtained by the analytical method are compared with those obtained from finite element analyses.