Kinetic, Solution, and Interfacial Aspects of Iron Corrosion in Heavy Brine Solutions

The corrosion rates of iron at temperatures between 60 and 120°C have been determined in very concentrated zinc halide solutions. The effects of calcium halide were investigated. The corrosion rates were lower in bromide-containing solutions than in chloride solutions. On the other hand, lower corrosion rates were observed with calcium-containing halides solutions than in zinc halide solutions. In zinc halide solutions, the cathodic reaction is under diffusion control with higher currents obtained with the chloride solutions. The nature of complexation in the zinc halide solutions is discussed in detail. The structure of the hydrogen bonding in the water was greatly decreased in the presence of the halides, and a maximum decrease in hydrogen-bonded species appeared to take place in the presence of calcium halide solutions. The structure of the iron interface was determined after immersion of iron in concentrated zinc halide solutions at 120°C for two weeks. In pure zinc chloride solutions, the surface became covered with zinc hydroxide. In calcium chloride + zinc chloride solution and zinc bromide solution, a large amount of Fe₂O₃ was identified on the sample surface.