摘要
热法蒸发技术在废水处理方面得到广泛应用,且随着废水不断蒸发浓缩,溶液中的Cl^(−)含量成倍增加,导致用于蒸发设备的材料也因此快速腐蚀而失效。2507钢是一种Cr、Mo元素含量高的双相不锈钢,结合了铁素体和奥氏体不锈钢共同优点,因此具有极好的耐点蚀性能。为研究2507双相不锈钢在酸性高氯环境中的腐蚀情况,采用动电位极化、电化学阻抗谱、Mott-Schottky曲线以及动态浸泡试验等方法进行测试,利用光学显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)以及3D显微镜对浸泡腐蚀后的试样性能进行表征。研究结果显示,随Cl浓度增加,腐蚀电位E_(corr)负移,腐蚀电流密度I_(corr)增加,极化电阻Rp减小,且施主密度ND和受主密度NA增加,材料的耐蚀性降低。2507双相不锈钢在酸性高氯(pH为3、120 g/L)腐蚀液中浸泡35 d的平均腐蚀速率为2.51μm/a。试样表面蚀孔数量较少,蚀孔外径在70~100μm,平均点蚀深度为20.493μm,最大点蚀速率为0.275 mm/a,属于轻度腐蚀,体现了不锈钢在酸性高氯环境中良好的耐蚀性。由于目前关于高氯废水蒸发设备材料的腐蚀数据非常缺乏,因此2507双相不锈钢的腐蚀情况可以为选材提供数据支撑。
Thermal evaporation technology is widely used in wastewater treatment.With the continuous evaporation and concentration of wastewater,the Cl^(−)content in the solution increases exponentially,resulting in rapid corrosion and failure of the materials used for evaporation equipment.2507 duplex stainless steel is often utilized due to its high content of Cr and Mo elements.This material combines the advantages of both ferrite and austenitic stainless steels,resulting in excellent resistance to pitting corrosion.To investigate the corrosion of 2507 duplex stainless steel in acidic and highly chlorinated environments,dynamic potential polarization,electrochemical impedance,Mott-Schottky curves,and dynamic immersion experiments were used.The electrochemical tests were performed in an acidic solution(pH 3)containing fluorine(F−300 mg/L)and varying concentrations of Cl^(−)(20,60,90,120,150 g/L)at a temperature of 60℃.The stainless steel was subjected to an immersion test in a corrosive solution with 120 g/L of Cl^(−),300 mg/L of F−,and pH 3 at 80℃for 35 d.Dynamic stirring was employed at a linear velocity of 2 m/s,and the solution was renewed every 7 d.Three parallel samples were taken,and the properties of the specimens were characterized using metallographic microscopy,scanning electron microscopy(SEM),energy spectrometry(EDS),and 3D microscopy.The study investigated the corrosive effect of chloride ion concentration on 2507 duplex stainless steel through electrochemical tests,and immersion corrosion tests were conducted to examine the corrosion conditions of stainless steel in a highly chlorinated environment.The results indicate that in various electrochemical tests,the corrosion potential E_(corr)in the polarization curve shifts towards the negative direction,and the corrosion current density I_(corr)gradually increases with the rise in chloride ion solubility.Thermodynamically,the more negative the corrosion potential E_(corr),the higher the tendency of the material to corrode;kinetically,the larger the corrosion current density I_(corr),the poorer the corrosion resistance of the material.The higher the pitting potential Eb,the stronger the corrosion resistance of the material.The test results indicate that an increase in the chloride ion concentration accelerates the corrosion of the material.In addition,the impedance spectrum shows a decrease in the capacitive arc radius as the concentration of chloride ions increases.A larger capacitive arc radius indicates greater resistance to charge transfer at the interface between the metal and solution,which in turn suggests stronger corrosion resistance of the material.The polarization resistance Rp reflects the state of the surface passivation film and is crucial in evaluating the corrosion resistance.The Rp value decreases as the concentration of chloride ions increases.The Mott-Schottky curve shows an increase in both donor density ND and acceptor density NA with an increase in Cl^(−)concentration,indicating an increase in point defects within the passivation film and a reduction in the corrosion resistance of the material.The metallographic analysis of stainless steel after 35 d of immersion in the corrosive solution revealed that pitting corrosion primarily occurs in the boundary region of theα-phase andγ-phase or in theγ-phase zone.This suggests that in the duplex stainless steel,theα-phase is more corrosion-resistant than theγ-phase.The average corrosion rate of the material was 2.51μm/a,as measured by the weightlessness method.The SEM morphology revealed a small number of etching holes on the surface of the specimen,with an outer diameter of approximately 70–100μm.The average pitting depth of the alloy after corrosion was 20.493μm,and the maximum pitting rate was 0.275 mm/a as measured by 3D microscope.These results indicate mild corrosion and reflect the good corrosion resistance of stainless steel in acidic and highly chlorinated environments.Due to the lack of corrosion data on the materials used in perchlorinated wastewater evaporation equipment,the corrosion of 2507 duplex stainless steel can provide data support for material selection.
作者
李玉
刘光明
李富天
刘晨辉
杨淑莉
董猛
LI Yu;LIU Guangming;LI Futian;LIU Chenhui;YANG Shuli;DONG Meng(School of Materials Science and Engineering,Nanchang Hangkong University,Nanchang 330063,China;Dongfang Electric Group Dongfang Boiler Co.,Ltd.,Zigong 643001,China)
出处
《中国表面工程》
EI
CAS
CSCD
北大核心
2024年第2期91-100,共10页
China Surface Engineering
基金
国家自然科学基金(51961028)。
关键词
高氯腐蚀
点蚀
电化学测试
动态浸泡腐蚀
perchloric corrosion
pitting
electrochemical testing
dynamic immersion corrosion
