Comportement à 700°C de métaux et alliages soumis à NbCl₅ gazeux^*

Corrosion at 700°C of metals and alloys exposed to NbCl₅ vapor

Centre d'Études de Chimie Métallurgique, CNRS, Vitry-sur-Seine

Abstract

The electrochemical reduction of NbCl₅ performed at 700°C in a molten salt bath for obtaining niobium has shown that all metallic elements present in the cell are corroded. In such conditions the electrolysis produces only a Ni₃Nb alloy and never pure metallic niobium. To determine the effect of NbCl₅, we have studied the oxidation of metals (M = Ni, Cr, Nb, Fe, Ti) and alloys (NSMC-NS21C-NS22S-NS30-Inconel 600) put in vapors of niobium pentachloride. For the pure metal M this corrosion is limited by the formation of pure or mixed dichloride (M, Nb)Cl₂. Nickel and chromium are the most resistant in this atmosphere. The alloys with melai M as the main component show a much more important corrosion than pure metal. More ever the amount of corrosion is always too weak to explain the big production of NiCl₂ that appears when a cell is continously feed with NbCl₅.

We study now the same metals and alloys put in a molten salt bath having differents concentrations in NbCl₅.