The Study Of New Inhibitors And The Corrosion Inhibition Mechanism For Carbon Steel In LiBr Absorption Chiller

The development of lithium bromide absorption chiller was restricted by the serious corrosion of metal in LiBr solution. It was important to develop new type corrosion inhibitors used in high concentrated LiBr solution at high temperature. The low solubility of molybdate inhibitors in concentrated LiBr solution leaded to less effective of inhibition. The solubility of molybdate in LiBr solution could be enhanced by some compounds, such as organic phosphonic acid compound A and B. In this paper the complex inhibitors were prepared composed of A, B, Na2MoO4and Na2WO4. The corrosion inhibition effect and mechanism were studied by weight-loss method, electrochemical tests, surface analysis methods and the quantum chemical calculation.The passive film on carbon steel has good protection performance in55%LiBr solution with A-Mo and B-Mo inhibitors, which was composed of Fe3O4, M0O2and MoO3. The corrosion rates of carbon steel at240℃were43.2μm·a-1and44.1μm·a-1, respectively. A-Mo and B-Mo inhibitors improved the electrochemical properties of carbon steel, and carbon steel was stable passive state in55%LiBr solution. The passive film was n-type semiconductor. The donor density ND was decreased, the flat band potential Efb was shifted more negative and the space charge layer thickness increased after adding A-Mo and B-Mo inhibitors, so carbon steel corrosion resistance was improved.During160～240℃, E-A-Mo and E-B-Mo inhibitors exhibited good corrosion inhibition effect for carbon steel in55%LiBr solution with the concentration of900mg·L-1. The corrosion reaction of carbon steel was more difficult because E-A-Mo inhibitor increased the apparent activation energy of corrosion reaction and improved the reactive energy barrier. But the usage cost of E-A-Mo and E-B-Mo inhibitor was high.On the basis of the above, A-Mo-W and B-Mo-W complex inhibitor were prepared. A-Mo-W and B-Mo-W complex inhibitor promoted the formation of the granular passive film of carbon steel by synergistic inhibition effect. The film was even compact which composed of Fe3O4, MoO3, MoO2and Na2WO4. The corrosion rate of carbon steel at240℃were22.1μm·a-1and25.7μm·a-1, respectively. The apparent activation energy of corrosion reaction of carbon steel were28.35kJ-mol"1and26.77kJ-mol-1respectively. The efficiency of A-Mo-W and B-Mo-W complex inhibitors for carbon steel in55%LiBr solution were98.8%and94.4%, respectively. The corrosion inhibition effect of A-Mo-W and B-Mo-W complex inhibitors were better than market Na2MoO4inhibitor and provide theoretical basis for the inhibitor development of triple-effect LiBr absorption chiller.The quantum chemical calculation indicated that N1-026(spacing0.3405nm) and N1-027(spacing0.3412nm) of molecular A and021-022(spacing0.3386nm) of molecular B could adsorption neighboring Na+(spacing0.3427nm) of Na2MoO4growth face by electrostatic interactions. It could inhibit the growth and precipitation of Na2MoO4and improved the solubility of Na2MoO4. Molecular A and B formed σ-π coordination bond with Fe, which resulted in the formation of adsorption film on the carbon steel, so they had inhibitive effect. The efficiency of molecular A was better than molecular B.