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CORROSION TESTING of NIOBIUM in HCL, CONT., P. 3
TABLE 3 - CORROSION RESISTANCE of Nb
HCl % Ferric ppm Temperature 0C Corrosion Rate - mils per year (mpy)
      Nb Nb lZr
15 500 60 .1 .1
15 1000 60 .1 .1
15 1500 60 .2 .1
15 500 100 .4 .4
15 1000 100 .6 .6
15 1500 100 .4 .4
15 15% 93 .2 .3
20 500 60 1.8 1.9
20 1000 60 2.3 2.7
20 1500 60 1.2 1.2
20 500 100 2.2 1.1
20 1000 100 2.2 3.6
20 1500 100 2.6 2.5
20 15% 93 .2 .3
20 2% 93 2.1 2.1
25 500 60 .3 .2
25 1000 60 .2 .2
25 1500 60 .2 .2
25 500 100 12 12.4
25 1000 100 8.5 9
25 1500 100 13 12

The presence of the ferric ion improves Nb's corrosion resistance to higher temperatures. For example, Nb in pure 15% HCl at 100°C corrodes at a rate >20 mpy (from Figure 1). With 500 ppm ferric, the corrosion rate drops below 1 mpy. Even in 20% acid at 100°C, the corrosion rate drops from >50 mpy to <3 mpy. The 5-mpy iso-corrosion curve for the Ti-Pd alloy in HC1 with 125 ppm ferric lies just below the Nb curve in Figure 1. The Ti-Pd curve (with 125 ppm ferric) drops rapidly to room temperature at just over 30% acid, while the Nb line remains above 50°C.

We plan to conduct similar tests at concentrations to 37% acid, since it is expected that the ferric additions will raise the Nb curve in this region to near the boiling point curve.

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INDEX  •  CORROSION RESISTANCE PROPERTIES  •  FABRICATION   
NIOBIUM PRODUCTS   •  SPECIFICATIONS of NIOBIUM   
NIOBIUM ELECTRONICS APPLICATIONS