Deposition and Study of Nobium Coating on Iron and Copper Substrates from Reduction of NbCl₅ by Hydrogen or Vapors of Zinc

Abstract
The chemical vapor deposition technique is used to form niobium deposits on Armco iron or copper substrate. A thermodynamic study confirms the possibility of reducing pentachloride of niobium (NbCl₅) by hydrogen (at a temperature superior to 750°C) or by vapor of zinc (at approximately 500°C). The influence of the substrates on the reaction is shown. The kinetics of the deposit is studied. The resulting coatings are very adherent. A folding (superior to 90°C) does not cause any cracking. Microhardness tests, X-ray diffraction, Glow discharge analysis, SIMS, ..., as well as observations by light or scanning microscopy have made it possible to characterize the formed layers (their nature, composition, thickness, continuity and porosity). The coatings obtained by hydrogenous reduction are thick (deposition rate : 22µm/hr on copper, 50µm/hr on iron). They are constituted of pure niobium, with only a few traces of copper or iron. This technique requires a high temperature treatment (950°C). The reduction treatment by vapor of zinc, made on copper substrate, leads to a deposition rate which does not exceed 5µm/hr. In this case, the layer is composed of a solid solution Nb-Zn (Zn : 8% wt, Cu : 2% wt). On the other hand, this method makes it possible to work at a lower temperature (520°C), which is an asset both on a technical and on an economical point of view.