LIANG Chenghao
Electromechanics and Materials Engineering College,
Dalian Maritime University,
Dalian 116026, China

School of Chemical Engineering,
Dalian University of Technology,
Dalian 116012, China

HUANG Naibao
Electromechanics and Materials Engineering College,
Dalian Maritime University,
Dalian 116026, China

GUO Jianwei
Institute of Nuclear and New
Energy Technology,
Tsinghua University,
Beijing 100084, China

HU Xianqi
School of Chemical Engineering,
Dalian University of Technology,
Dalian 116012, China

Abstract: Electrochemical measurement and chemical immersion test are employed to investigate the inhibition mechanism of Na₂ MoO₄ for carbon steel, which is studied in 55%LiBr+ 0.07mol/L LiOH solution at high temperature. Testing results indicate that the passive film on carbon steel surface is mainly composed of Fe₃O₄,and Mo is involved in the process of film forming, in a form of MoO3 and MoO₂ . The parametric analysis of the evolving potential and the blend potential of MoO₂ shows that Mo mainly exists as MoO₂ in passive film when the concentration of Na₂ MoO₄ is lower than 150 mg/L. While its concentration is greater than 150 mg/L, it mainly exists as MoO3 inside the film and exists as MoO₂ outside the film. MoO₄ ^{2 −} is deoxidized as MoO₂ on the surface of carbon steel, which may impede the corrosion of active-site and raise the blend potential of carbon steel, and then MoO₄ ²⁻ adsorbs onto the defects of the passive film and decompounds as MoO3 during the process of film forming. The electric field caused by different valence of Mo in passive film may retard the dissolution of carbon steel and lead to an increase in the polarization impedance and a decrease in hydrogen evolution. As a result, heavy concentrated Na2MoO₄ solution (greater than 150 mg/L) has excellent inhibition effect on carbon steel in LiBr solution.

Key words: LiBr solution Carbon steel Anticorrosion Na₂MoO₄