discuss the chemical kinetic off corrosion
Answers
Activation energy control occurs when the electrode kinetics or corrosion rate is controlled by a slow electrochemical step. ... An anodic control corrosion system. Mass transport control occurs when the corrosion rate is limited by a diffusion or mass transport process involving the reactant at the electrode surface.
Explanation:
Thermodynamics gives an indication of the tendency of electrode reactions to occur, whereas electrode kinetics addresses the rates of such reactions. The reactions of concern are mainly corrosion reactions, hence, it is more appropriate to call the kinetics of such reactions as corrosion kinetics. In order to understand the theory of aqueous corrosion, it is important to develop a complete understanding of the kinetics of reaction proceeding on an electrode surface in contact with an aqueous electrolyte. Methods which are used to study the rate of a reaction involve the determination of the amount of reactants remaining in products after a given time. In aqueous corrosion, it is very important to appreciate the nature of irreversible reactions which take place on the electrode surface during corrosion.
3.2.1 ANODIC AND CATHODIC REACTIONS
Consider a piece of iron corroding in an acid solution. The following are the basic reactions:
(3.11)Fe⇄Fe2++2e (anodic)
(3.12)H2⇄2H++2e (cathodic)
The overall reaction which takes place in the iron surface is
(3.13)Fe+2H+→Fe2++H2
The above process is illustrated in Fig. 3.1. The anodic reaction shown above involves the transfer of a metal atom from a metal lattice to the aqueous solution at the electrode/electrolyte interface. The reactions (3.11) and (3.12) shown above are called charge transfer reactions as they proceed by transfer of charge (electrons).