Corrosion behavior of niobium, tantalum and their alloys in hot hydrochloric and phosphoric acid solutions

The corrosion resistance of niobium, tantalum and Nb-20, 40, 60 and 80 wt% Ta alloys in 5, 10, 15 and 20 wt% HCl and 20, 40, 60 and 80 wt%, H3PO4 solutions at boiling point, 150 degrees C and 200 degrees C is evaluated using the mass-loss technique. The corrosion rates of all materials increase with acid concentration and temperature. At boiling point the corrosion rates diminish with time but for long exposure time, they tend to stabilize due to the formation of superficial oxides. The corrosion resistance increases with tantalum content. The iso-corrosion curves of niobium, tantalum and Nb-Ta alloys in 5-20 wt% HCl and 20-80 wt% H3PO4 up to 200 degrees C are drawn from interpolation of the measured corrosion rates. (C) 2000 Elsevier Science Ltd. All rights reserved.