Lithium Hydroxide Effects in the Potentiostatic Passivation of Mild Steel at 300 C

The Electrochemistry of Iron in lM Lithium Hydroxide Solution at 22° and 200°C

“…Fe + 3 OH-----Fe(OH)z + 3e- [4] Reaction [4] has an equilibrium potential at pH ----14 of --1380 mV (27) which therefore satisfies Eq.…”

“…[2], mm Hg log mean vapor pressure of water in Eq. [2], mm Hg water vapor loss rate, g/yr Fe + 3 OH--+ HFeOz-+ H~O + 2e- [1] 3Fe + 8 OH-...* FesO4 + 4H20 -I--8e- [2] 3HFeO2-~ FesO4 "-I-HsO -I-OH--}-2e- [3] Li + -{-HFeOz--* LiFeO~ W H + W e- [4] where process [1] accounts for active dissolution of iron, [2] for the direct formation of the base oxide layer from the metal, and [3] and [4] for the nucleation and growth of the "upper-layer" oxide crystals. [2], mm Hg water vapor loss rate, g/yr Fe + 3 OH--+ HFeOz-+ H~O + 2e- [1] 3Fe + 8 OH-...* FesO4 + 4H20 -I--8e- [2] 3HFeO2-~ FesO4 "-I-HsO -I-OH--}-2e- [3] Li + -{-HFeOz--* LiFeO~ W H + W e- [4] where process [1] accounts for active dissolution of iron, [2] for the direct formation of the base oxide layer from the metal, and [3] and [4] for the nucleation and growth of the "upper-layer" oxide crystals.…”

“…This alkalizing agent is of fundamental interest, since a number of studies (1)(2)(3)(4) have suggested that the corrosion mechanism of mild steel in LiOH solution at elevated temperatures is dis-tinctly different from that in NaOH under the same conditions. Lithium hydroxide is the most commonly used alkalizing agent in nuclear reactors, since lithium gives rise to fewer radiation problems than other alkali ions.…”

“…3Fe + 8 OH-...* FesO4 + 4H20 -I--8e- [2] 3HFeO2-~ FesO4 "-I-HsO -I-OH--}-2e- [3] Li + -{-HFeOz--* LiFeO~ W H + W e- [4] where process [1] accounts for active dissolution of iron, [2] for the direct formation of the base oxide layer from the metal, and [3] and [4] for the nucleation and growth of the "upper-layer" oxide crystals.…”

“…The use of lithium hydroxide has also been suggested by Bloom (1) as a means of avoiding boiler pitting due to localized concentration of the feed water alkali. This alkalizing agent is of fundamental interest, since a number of studies (1)(2)(3)(4) have suggested that the corrosion mechanism of mild steel in LiOH solution at elevated temperatures is dis-tinctly different from that in NaOH under the same conditions.…”