CORROSION OF CARBON-STEEL IN AQUEOUS LITHIUM HYDROXIDE

The corrosion behavior of carbon steel in 3 and 5 mol/L aqueous solutions of lithium hydroxide at 95-degrees-C under a hydrogen atmosphere was investigated in immersion tests lasting 10 days. Corrosion rates were determined by weight loss, and the corrosion products were characterized by bulk chemical analysis, by light and electron microscopy, and by powder x-ray diffraction. Corrosion was uniform and the corrosion rates were moderately high (0.42 mm/y in 3 mol/L and 0.56 mm/y in 5 mol/L). The corrosion products consisted of a mixture of well-formed, octahedral crystals, and poorly crystallized masses and spherules that formed by precipitation from solution. These products formed a scale on the metal surface that continually sloughed off and afforded only minor protection. Both phases were identified as lithium iron oxides, each possessing a disordered, nonstoichiometric structure. The predominant phase was a magnetic spinel LiFe5O8 and the minor phase was LiFeO2. The alteration of these metastable phases after deposition produce cracks and porosity that weaken the scale and lead to sloughing. A corrosion mechanism is outlined.