The anodic dissolution of iron—V. Some observations regarding the influence of cold working and of annealing on the two anodic reactions of the metal

Under conditions, where two anodic current regions, I₂ and I₂, were distinct in the Tafel plots of the iron electrode, the reaction orders with respect to pH were determined. In solutions containing chloride or bromid, pH ca 3–5, the reaction order for I₁(p_1,pH) was close to 1, while that for I₂(p_2,pH) assumed positive or negative values or even values changing from positive to negative over the pH-range. The numerical values were small, 0·2–0·3. Only lightly cold-worked iron was used in this group of experiments.

In another group of experiments only involving acetate containing solutions both cold-worked and annealed electrodes were employed. Until the influence of acetate became negligible at low pH, the effect of the treatment was largely limited to dissolution rates. The characteristic parameters at pH ca 4 were: for the I₁ reaction: b₁ = 30 mV, p_1,pH = 1·7 and p_1,Ac¹ (the reaction order for Ac) = −0·7; for the p₂ reaction: b₂ = 110 to 130 mV, p_2,pH = 0·2 and p_2,Ac = −0·2 to −0·3.

At lower pH the influence of acetate gradually disappeared, and higher values of b₁ and lower values of p_1,pH were then noted for the annealed metal. The I₂ reaction could not be followed here.

The transition between the I₁ and the I₂ reaction was studied at pH ca 4, and some deviation from earlier experience was noted for strongly cold-worked iron.