Dissociation of thorium oxide on the surface of free surface tungsten

摘要

THO_2 doped W is commonly used substance for cathodes of light sources. ThO_2 is present in the bulk, in the grain boundaries and on the free surface of W in form of small particles. In lamp manufacturing various heat treatments in various atmospheres are used affecting the concentration of these particles on the surface. In this paper we studied the dissociation kinetics of ThO_2 on free surface. The novel in situ studies on the cathode performance in high pressure discharge lamps prompted us to re-asses the models explaining the ThO_2 dissociation in thoriated tungsten, by taking into account both the numerical modeling of Selverian and the recent development in modeling of internal oxidation and internal reduction.