The passivation behavior of sputter-deposited W-Ta alloys in 12M HCl

A series of nanocrystalline or amorphous single solid solutions of W-Ta alloys are prepared by D.C. magnetron sputtering. The passivation behavior of these alloys is studied by immersion test, electrochemical measurements and X-ray photoelectron spectroscopy (XPS) analysis. The W-Ta alloys are passivated spontaneously and show significantly high corrosion resistance in 12 M HCl at 30 degrees C. Their corrosion rates are about two orders of magnitude lower than that of sputter-deposited tungsten and are lower than that of sputter-deposited tantalum. XPS analysis shows that tantalum is concentrated in both the air-formed films and the passive films formed spontaneously on the alloys after long time immersion in 12 M HCl. The surface films are composed of double oxyhydroxides of Ta5+ and W4+ ions. The formation of spontaneous passive film composed of a double oxyhydroxide of tungsten and tantalum ions is responsible for high corrosion resistance of the W-Ta alloys in concentrated hydrochloric acid solution. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.