The kinetics and mechanisms involved in the siliconization of Nb and the oxidation of niobium silicides at low pressures and high temperatures

The silicidation of niobium ribbons by heterogeneous decomposition of SiH4 results from a competition between the supply of silicon at the surface and its diffusion into the metal. The kinetics of SiH4 decomposition on silicon and on silicides were studied, as well as the evolution of the surface during silicidation. By heating silicidated ribbons or those coated with silicon in the presence of oxygen, a sudden transition from the passivation state of the metal, protected by a SiO2 layer, to a steady-state regime of rapid combustion of silicon, resulting from the vaporization of SiO oxide, was highlighted; in the case of ribbons consisting of a solid solution of silicon in niobium, the reaction kinetics of oxygen on the non-volatile niobium oxide layer formed at the surface was determined.