Corrosion of metals in acids

Reactions with aqueous solutions. Uniform dissolution or corrosion of metals in acid, alkaline or neutral solutions (e.g. dissolution of zinc in hydrochloric acid or in caustic soda solution general corrosion of zinc in water or during atmospheric exposure). Reactions with non-aqueous solution (e.g. dissolution of copper in a solution of ammonium acetate and bromine in alcohol). 

The hydrogen evolution reaction (h.e.r.) is of particular importance in corrosion for a number of reasons. Firstly, the reduction of the HjO ion in acid solutions or the H2O molecule in neutral and alkaline solution is a common cathodic reaction for the corrosion of metals in acid, neutral and alkaline solutions the fact that iron will corrode in neutral water free from dissolved... 

It next became interesting to investigate some chemical processes in which hydrogen overvoltage is intimately involved in order to see whether changes in these processes, produced by variations in the external pressure, are also in the direction predicted by the theory. Three such processes are (1) the corrosion of metals in acid solutions,... 

Andrus, IEC 40, 1946-47 (1948) (Corrosion of metals in acids) 16) Anon, ChemEngrg55,... 

Rust of iron (the most abundant corrosion product), and white rust of zinc are examples of nonprotective oxides. Aluminum and magnesium oxides are more protective than iron and zinc oxides. Patina on copper is protective in certain atmospheres. Stainless steels are passivated and protected, especially in chloride-free aqueous environments due to a very thin passive film of Cr2C>3 on the surface of the steel. Most films having low porosities can control the corrosion rate by diffusion of reactants through the him. In certain cases of uniform general corrosion of metals in acids (e.g., aluminum in hydrochloric acid or iron in reducible acids or alkalis), a thin him of oxide is present on the metal surface. These reactions cannot be considered hlm-free although the him is not a rate-determining one.1... 

To discuss the corrosion of metals in acid solution, we consider the cell shown in Fig. 34.11(a). It consists of a zinc electrode and a hydrogen electrode immersed in a ZnS04 solution that contains sufficient sulfuric acid to prevent the precipitation of Zn(OH)2. If this cell is short-circuited, the reaction... 

Uniform Corrosion of Metals in Acid, Neutral and Alkaline Electrolytes 69... 

The triazole moiety has anticorrosive properties in general. For copper and its alloys, in aqueous medium, benzotriazole is most widely used as a corrosion inhibitor. 5-Aminotriazole is used as such in an anticorrosion lubricating oil composition. The corrosion of metals in acidic solutions is inhibited by adding 0.01-1 wt.% of a pol5mier with a backbone of 1,2,4-triazole. ... 

In practice, cathode reactions 20.7a and 20.7b are particularly important becanse of their frequency. In the corrosion of metals in acid solutions, the reduction of hydrogen ions is the main reaction, whereas oxygen rednction is the main reaction in the corrosion of metals in nentral, aerated electrolyte solntions (salt solntions, seawater, and atmosphere). 

---