化学镀Ni-Cu-P在露点腐蚀防护中的应用

发布时间：2018-08-04 21:34

【摘要】：工业窑炉的省煤器在工业生产中经常会遇到露点腐蚀问题。由于工业燃料中含有S、C、N等元素,烟气中通常含有相应的氧化物,这些氧化物会与烟气中的水蒸气反应生成酸性蒸汽。当酸性蒸汽遇到低于露点温度的省煤器外壁时,就会凝结成酸性液滴,使省煤器外壁产生剧烈腐蚀,导致使用寿命缩短。所以防止露点腐蚀是提高省煤器使用寿命的关键。工业上常用碳钢作为省煤器材料,所以本文以Q235碳钢作为基材,在其表面通过化学镀技术镀覆一层Ni-Cu-P镀层,提高其耐蚀性。利用两步法制备性能更好的镀层,提高镀层对基体起保护作用的时间,并对镀层的腐蚀机理进行研究。本文通过正交试验确定较佳的化学镀配方和工艺条件,通过SEM对镀层表面形貌进行观察,通过EDS镀层表面元素含量进行分析,采用XRD和XPS分析了镀层的结构和表面元素。通过孔隙率测试、硬度测试、接触角测试等测试方法研究了施镀时间对镀层各种性能的影响。利用腐蚀浸泡实验和动电位极化曲线对镀层在80℃C的模拟烟气冷凝液、5%H2SO4、10%H2SO4和20%H2SO4溶液中的腐蚀行为进行了研究。主要研究结果如下:本实验所用的化学镀配方及工艺条件为:NiSO4 25g/L、CuSO40.9g/L、NaH2PO235g/L、Na3C6H5O745g/L、NaCH3COO 15g/L 和硫脲 1mg/L,温度为84℃,镀液pH值为6,施镀时间1.5h。所得镀层中,Ni、Cu和P元素含量分别78.72%、7.56%和13.72%,Cu和P与Ni形成固溶体,使得镀层为非晶体结构,其中P和部分Ni之间交换电子形成共价键,而Cu是以单质形式存在。在Q235碳钢表面化学镀Ni-Cu-P (Ni-Cu-P/Q235)能显著提高Q235碳钢在80℃的模拟烟气冷凝液、5% H2SO4、10% H2SO4和20% H2SO4溶液中的耐蚀性,在上述四种介质中,Ni-Cu-P/Q235的腐蚀速率是分别是Q235碳钢的1/9、1/166、1/165和1/466;耐蚀性也优于ND钢,腐蚀速率分别是为ND钢的1/6、1/136、1/139和1/351;在80℃三种浓度的H2SO4溶液中(5%、10%和20%),腐蚀速率分别是316L不锈钢的1/8、1/10和1/121,耐蚀性也优于316L不锈钢。利用两步法制备四种镀层,其中一级施镀时间为1.5h不变,二级施镀时间分别为0.25h、0.5h、1 h和1.5h,镀液成分和条件同前。两步法能有效延长镀层对基体的保护时间。当二级镀层施镀1.5 h时镀层的性能最好,厚度为43.8 μm,孔隙率接近0,镀层硬度最小(656.1 Hv),在80℃的5%H2SO4溶液中的腐蚀速率最低,镀层发生鼓泡的时间(418h)是一步制备的镀层鼓泡时间(106h)的3.9倍。当二级施镀时间为1.5 h时,镀层在80℃的5%H2SO4溶液中浸泡过程中,镀层先后经历一个由米黄色变为黑色、然后红色、最后为黑色的过程。米黄色为镀层的初始颜色。变为黑色是因为在浸泡过程中,镀层表面Ni选择性溶解所致;当镀层表面Ni继续溶解导致Cu富集后镀层变红色;当二级镀层完全腐蚀掉,一级镀层的Ni开始溶解时镀层又变成黑色。在一级镀层腐蚀掉之前,镀层的腐蚀速率变化平缓,镀层对基体仍起到保护作用。
[Abstract]:The economizer of industrial kiln often meets the problem of dew point corrosion in industrial production. Since industrial fuels contain elements such as Schion N and so on, the flue gas usually contains corresponding oxides, which react with the water vapor in the flue gas to form acid steam. When acid steam encounters the outside wall of economizer which is lower than dew point temperature, it will condense into acid droplets, which will cause severe corrosion on the outside wall of economizer and shorten the service life. So to prevent dew-point corrosion is the key to improve the service life of economizer. Carbon steel is commonly used as economizer material in industry. Therefore, Q235 carbon steel is used as substrate in this paper. The surface of Q235 carbon steel is coated with a layer of Ni-Cu-P coating by electroless plating technology to improve the corrosion resistance of Q235 carbon steel. The coating with better performance was prepared by two-step method to improve the protective time of the coating on the substrate and the corrosion mechanism of the coating was studied. In this paper, the optimum formula and technological conditions of electroless plating were determined by orthogonal test. The surface morphology of the coating was observed by SEM, the surface element content of EDS coating was analyzed, and the structure and surface elements of the coating were analyzed by XRD and XPS. The effect of plating time on the properties of the coating was studied by means of porosity test, hardness test and contact angle test. Corrosion behavior of the coating in simulated flue gas condensate at 80 鈩，

本文编号：2165235