Potentiometric Determination of the Concentration of Aggressive Anions That Can Be Tolerated by a Certain Passivator

Abstract

The effect of various additives of Cl−, Br−, and I− on the potential of a passivated steel electrode was established. In solutions of Na2CrO4, Na2HPO4, and Na2WO4, S-shaped relations were obtained between the steady-state potential and the quantity of the aggressive salt added. The resulting active potentials were established after an induction period which decreases with increase in the concentration of the attacking ions and/or decrease in that of the inhibiting anions. The concentration, Cagg, that can be tolerated by a certain concentration of the inhibiting anion, Cinh, is given by logCinh=K+nlogCagg, where K and n are constants. The equation was derived theoretically on the basis of the changes produced in the structure of the double layer caused by specific adsorption of both aggressive and passivating ions. In solutions of KMnO4, NaNO2, and K3[(Fe(CN)6)], the passivating film could not withstand the corroding action of the halide ions.

Inhibition of Pitting Corrosion of Aluminum Bronze in Sodium Chloride Solution

“…The relationship between the E pit and the logarithm of the molar concentrations of chloride ions is illustrated in Figure 2. This relationship usually gives a straight line satisfying the following empirical equation: 17…”

“…However, in the case under consideration, a plot of Figure 2 gives rise to a curve of segmoidal nature in which Equation (1) is obeyed only within a limited range of chloride ion concentrations. [17][18] At lower chloride ion concentrations, the E pit shifts slightly in the negative direction, as the concentration of the chloride ions is increased. This may be caused by the fact that these low concentrations of chloride ions are not sufficient to destroy completely the passive fi lm formed on the electrode surface, or that pits formed are not completely active and may undergo repassivation.…”

“…This may be caused by the fact that these low concentrations of chloride ions are not sufficient to destroy completely the passive fi lm formed on the electrode surface, or that pits formed are not completely active and may undergo repassivation. [17][18] At relatively higher chloride ion concentrations, the E pit varies with log C 1 according to the straight line relationship satisfying Equation (1). In the presence of still higher chloride ion concentrations, which represents the fi nal part of the curve of Figure 2, the pits formed assumed to be nonpassivable active pits, which means that these concentrations of chloride ions are suffi cient to cause a continuous propagation of the pits, already formed.…”

Oxide film growth on manganese in neutral aqueous solutions

“…It is more reasonable to relate this potential to that of the initial value in such a manner that it is common for all curves. Shams El Din and Abd El Haleem 32,33 assumed that pitting corrosion is operative to the same extent in all solutions when enough of the aggressive anion is added to displace the initial potential to the active direction by a constant value. The relation between C agg .…”

Chemical Behavior And Corrosion Inhibition Of Zinc Electrode In Phosphate Solutions Under Open Circuit Conditions

“…Inhibiting agents are added in order to improve the electrochemical behavior of the discharged cell, decrease in the ohmic cell resistance and decrease in the self-discharge rate while the cell is being partially discharged, and to suppress the anodic reaction of zinc, still there is a need to add another component to the electrolyte which is capable of reducing the zinc corrosion in the alkaline media. Both of corrosion and inhibition processes involve a decrease in free energy of the metal/solution interface as any physicochemical process can occur at low free energy between the metal and its environment and the suggesting process that associated with a larger decrease in free energy [10,11]. Organic surfactants and inorganic corrosion-inhibiting agents are commonly added to the zinc anode.…”