Chromium-iron alloys Flade

As the chromium content in the alloy increases from 8% to 13%, the corrosion rate of iron decreases from 0.08 mm/year to very low values [9]. The Flade potentials of chromium-iron alloys in 4% NaCl solutions increases from —0.57 V (vs. SHE) in the absence of chromium to +0.17 V (vs. SHE) for the ahoy with 12% chromium [7,10]. The critical current density for the passivation of Cr-Fe aUoys at pH = 7 reaches a... 

Figure 6.4. Standard Flade potentials for chromium-iron alloys and chromium [7-9].

The addition of a more passive metal to a less passive metal normally increases the ease of passivation and lowers the Flade potential, as in the alloying of iron and chromium in 10 wt. % sulphuric acid (Table 10.31) . Tramp copper levels in carbon steels have been found to reduce the corrosion in sulphuric acid. Similarly 0 -1 palladium in titanium was beneficial in pro-... 

Table 10.31 Effect on critical current density and Flade potential of chromium content for iron-chromium alloys in lOwt.% sulphuric acid (after West )...

This reproducible Flade potential and its 0.059 pH dependence is characteristic of the passive film on iron. A similar potential-pH relation is found for the passive film on chromium, for Cr-Fe alloys, and for nickel, for which the stan-... 

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