输水条件下内衬矿渣-水泥砂浆球墨铸铁管腐蚀过程的电化学测试研究

Electrochemical Measurements of Corrosion Process of Slag and Cement Mortar-lined Ductile Cast Iron Pipe for Water Supply

针对输水条件下内衬矿渣-水泥砂浆球墨铸铁管的腐蚀问题,设计制作了内衬矿渣-水泥砂浆球墨铸铁管环试件,开展了扰动普通纯净水和6 mol/L氯化铵溶液腐蚀过程中内衬矿渣-水泥砂浆球墨铸铁管环试件的线性极化(LPR)和电化学阻抗谱(EIS)测试,分析了两种腐蚀溶液中试件的极化电阻、腐蚀电流密度和双电层电容等电化学参数随腐蚀时间的变化规律,并评估了试件的腐蚀程度。结果表明,在120 d的腐蚀时间内,普通纯净水中的矿渣-水泥砂浆球墨铸铁管环试件砂浆层电阻和球墨铸铁表面电荷转移电阻降低幅度很小,且腐蚀电流密度未达到钝化膜脱钝临界值,试件的腐蚀程度较小;而6 mol/L氯化铵溶液中,试件砂浆层电阻和球墨铸铁表面电荷转移电阻均明显降低,其腐蚀电流密度远超过钝化膜脱钝临界值,试件腐蚀程度严重;此外,运用LPR和EIS这两种测试方法所评估的腐蚀程度一致。

Corrosion behavior of ring-shaped segment of ductile cast iron pipe with liner of slag and cement mortar was monitored by means of linear polarization resistance（LPR） and electrochemical impedance spectroscopy（EIS） measurements in disturbed ordinary purified water and 6 mol/L ammonium chloride solution, respectively. The change of polarization resistance, corrosion current density and double-electric-layer capacitance with the corrosion time is acquired, and then the corrosion degree of the test specimen is evaluated. Results show that, the resistance of the slag and cement mortar liner and the charge transfer resistance of the ductile cast iron surface all show a little decrease, while its corrosion current density is far less than the critical value for depassivation for the specimen being immersed in the disturbed purified water for 120 d, so the specimen is almost no corroded. However, the related parameters all show obvious decrease for the specimen being immersed in the disturbed 6 mol/L ammonium chloride solution for the same period, while its corrosion current density is far greater than the critical value for depassivation, thus, the specimen suffers from heavey corrosion. In addition, the corrosion degree of the specimens evaluated by LPR is basically in agreement with that obtained by EIS.