LiNO_3对高温高浓度LiBr溶液中碳钢的缓蚀机理

INHIBITION EFFECT OF LITHIUM NITRATE ON CARBON STEEL CORROSION IN HIGH CONCENTRATION LITHIUM BROMIDE SOLUTION AT 173℃

采用电化学法和化学浸泡法研究了高温 65 %LiBr+0 .0 7mol/LLiOH溶液中 ,LiNO3对碳钢腐蚀的影响 .结果表明 ,随LiNO3浓度增加碳钢腐蚀速率降低 ,复合添加 1 50mg/LNa2 MoO4 后 ,碳钢在 1 0 0mg/LLiNO3时腐蚀速率出现最小值 .通过计算NO- 3和MoO2 - 4还原平衡电极电位 ,发现NO- 3优先还原形成以Fe的氧化物为主的内层膜是由于NO- 3具有较高的还原电极电位 .LiNO3小于 1 0 0mg/L时 ,复合添加的MoO2 - 4在外层得以还原形成缺氧型MoO2 ,建立起稳定的双层膜结构 .当LiNO3浓度大于 1 0 0mg/L后 ,NO- 3对膜层中MoO3优先侵蚀 ,加速Br- “楔入”钝化膜历程 。

By means of electrochemical measurements and chemical immersion experiments,this paper investigates the inhibition effect of lithium nitrate on corrosion of carbon steel in 65%LiBr +0.07mol/L LiOH solution at 173℃.The results show that,the corrosion rate of carbon steel decreases with increase of LiNO 3 concentration.Combined with 150 mg/L Na 2MoO 4 in this solution,the corrosion rate shows a minimum at 100mg/L LiNO 3.Through calculation of the equilibrium potentials of the reduction electrodes for NO - 3 and MoO 2- 4,it is revealed that NO - 3 possessed higher reduction electrode potential,therewith,NO - 3 was reduced firstly,which is favior to the formation of an inner film with ferric oxide as its main component.In addition,an oxygen-deficient MoO 2 as outer-layer is formed by reduction of MoO 2- 4 when LiNO 3 is less than 100 mg/L,and then a stable double film is built up.However,when LiNO 3 is more than 100 mg/L,NO - 3 reacts with MoO 3 preferentially and results in Br - coupling in the formed passive film,which further damages the double film and thus increases the corrosion rate to a large extent.