普碳钢表面锌防护层在青岛中港海水中耐蚀与防污损性能对比研究
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Characterization of Seawater Corrosion Interface of Zinc Coated Steel Plate in Zhong-gang Harbor
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通讯作者: 刘欣,E-amil:xliu_neu@126.com,研究方向为海洋金属材料腐蚀与防护
收稿日期: 2020-11-30 修回日期: 2020-12-07 网络出版日期: 2021-07-14
基金资助: |
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Corresponding authors: LIU Xin, E-mail:xliu_neu@126.com
Received: 2020-11-30 Revised: 2020-12-07 Online: 2021-07-14
作者简介 About authors
马士德,男,1938年生,研究员
对普碳钢表面热浸锌、冷镀锌和富锌涂层在青岛中港中进行了5年部分浸入腐蚀实验,对比研究了3种锌防护层耐蚀与防生物污损性能。实海腐蚀实验后进行SEM、EDS、XRD和Fourier红外分析可知,富锌板涂层边角开裂,涂层脱落,防护涂层基本失效;冷镀锌和热浸锌板在相同条件下保持着较好的阻隔性能,表面具有耐腐蚀性能的Zn分布均匀,对基底的防护性能较好,其中热浸锌效果更佳。钢板表面污损生物表征与分析结果表明,3种材料的污损过程从微型生物膜到大型污损生物群落的形成无大差别。综合比较钢板腐蚀和污损情况可知,3种锌涂层对基体的防护作用大小排序为:热浸锌>冷镀锌>富锌涂层。
关键词:
Hot dip galvanized-, cold galvanized- and Zn-rich coating coated-plain carbon steels were exposure in the seawater of Zhong-gang harbor at Qingdao for five years. Then the long-term immersed steels were characterized by means of EDS, XRD and FT-IR, especially in terms of the interface of seawater/steel. It follows that for the steel plate with Zn-rich coating, cracks emerged at edges and conners, and occurrence of coating falling off on the surface could be observed, which indicates that the coating has generally failed; Meanwhile, both the cold-dip galvanized and hot-dip galvanized plates maintain good barrier performance, and the elemental X-ray mapping reveals that there exist Zn of homogeneous distribution on their corroded surface, to which the better protectiveness of the two Zn galvanizing coatings may be ascribed. Among others, the hot-dip galvanizing is the best in corrosion resistance. The results of characterization for fouling organism on the surface of steel plates show that there is no significant difference in the fouling process in the formation of micro biofilm or the large fouling biological community among the three materials. Comprehensive comparison of corrosion and fouling of steel plates show that the corrosion protectiveness of the three coatings may be ranked in the order as follows: hot dip galvanizing>cold galvanizing>zinc rich coating.
Keywords:
本文引用格式
马士德, 刘欣, 王在东, 任亚东, 邰余, 韩文, 段继周.
MA Shide, LIU Xin, WANG Zaidong, REN Yadong, TAI Yu, HAN Wen, DUAN Jizhou.
本研究是在青岛中港进行了普碳钢表面热浸锌、冷镀锌和富锌涂料3种保护层的部分浸入腐蚀试验,进行全过程各阶段海水界面腐蚀产物膜、腐蚀表征及污损生物等分析检测。通过对腐蚀产物的表征分析,明确了腐蚀界面腐蚀产物层的变化,揭示了防腐锌涂层的防腐防污效果及其机理。
1 实验方法
将普碳钢 (M60) 加工成600 mm×60 mm×5 mm (—端打孔,孔径18 mm),分别进行了涂覆富锌涂层 (JR-FX) 以及冷镀锌和热浸锌处理。热浸锌处理时,首先通过抛丸处理去除钢铁试板表面的锈污,处理后试板表层呈银灰色。试板经18% (体积分数) 六次甲基四胺的稀盐酸酸洗后,浸入锌液中,使试板表面均匀附上锌层。所使用锌原料为葫芦岛60号出口锌 (纯度99.99%)。浸锌后的试板用2% (质量分数) NH4Cl溶液进行漂洗。
冷镀锌处理中的镀层锌液为JP1618型,即将锌粉加入JP-SZ-20型树脂液中搅拌均匀,待混胶体可以在刮板上平整形成涂层时,过滤保存。冷镀锌时,先对碳钢试板进行机械除锈,使其光洁度达到Sa2.5 级 (ISO 8501-1:2007)。将配套用稀释剂以0.15∶1的比例加入JP1618型冷镀锌的镀液中,搅匀、过滤并稀释。使用有气喷涂的方法正面均匀喷涂,膜厚约为120 μm。喷涂后的试板需静置7 d,使涂膜实干,再对试板另一面进行喷涂。
富锌涂层的涂覆时,试板表面处理与冷镀锌前处理相同。富锌涂料的双组份按A∶B=9∶1的比例混合,将配套用稀释剂加入富锌涂料中,搅匀、过滤。涂装方法与冷镀锌处理工艺相同。
锌防护层试板均用螺栓紧固到固定装置上,制成实验用的试架。标记冷镀锌挂板为C,富锌挂板为F,热浸锌挂板为H,后文中各试样标号与此一致。每块试板又被均分为6个区域,以便于后续的表征与分析。
2014年4月,将试架投放到青岛中港海中,使各试板的3/4浸入海水中,1/4暴露在大气中。分别在浸海10、17、24、58和89 d后取出,目测和手触摸并照相记录表观状态。2014年7月~2018年7月间共进行了36次月检和4次年检。
从挂件上切取10 mm×10 mm的小试样,利用JSM-6700F扫描电镜 (SEM) 及JSM-6700F能谱分析仪 (EDS) 观察形貌,分析结构及成分。刮取试板表面的腐蚀产物,利用X射线衍射仪 (XRD,D/max-rA) 测试,扫描2θ角为5°~90°,扫描速率为10°/min。采用Fourier变换红外光谱仪 (FTIR,BRUKER TENSOR 27) 进行分子结构分析。其具体参数设置如下:光源光谱范围为500~4000 cm-1,光源波数精度为0.01/2000 cm-1,分辨率参数为0.4~1 cm-1,信噪比参数为4000∶1 (p/p值),吸收精度参数为0.01%T。
此外,还对试板表面产物及试板基体进行了元素能谱分析、金相分析 (金相显微镜,XJP-200) 等表征检测,确定腐蚀产物的形貌、结构、成分及试板的金相组织变化。
2 结果与讨论
2.1 锌防护层钢板宏观腐蚀形貌
图1
图1
3种挂板实海浸入5 a后的正反面照片
Fig.1
Photos of the front (a~c) and back (d~f) sides of cold galvanized (a, d), zinc rich (b, e) and hot dip (c, f) galvanized hanging plates after immersion for 5 a
挂板经自来水进行冲洗,轻微刷除顽固残留生物后,再用去离子水冲洗3遍,放置到鼓风干燥箱之中,60 ℃干燥8 h。待干燥后对挂片进行拍照分析,如图2和3所示。看出,热浸锌挂板和冷镀锌挂板表面锈蚀较轻微,有一层牢固的沉积层;而富锌挂板涂层脱落,碳钢全面腐蚀,干湿交替区腐蚀最严重。
图2
图2
3种挂板海水全浸区正反面照片
Fig.2
Photos of the front (a~c) and back (d~f) sides of the full immersion zones of cold galvanized (a, d), zinc rich (b, e) and hot dip (c, f) galvanized hanging plates after exposure test for 5 a
图3
图3
3种挂板干湿交替区的宏观形貌
Fig.3
Macromorpholgies of the dry-wet alternation zones of zinc rich (a), hot dip galvanized (b) and cold galvanized (c) hanging plates after exposure test for 5 a
2.2 锌防护层钢板腐蚀显微形貌表征与分析
2.2.1 SEM测试分析
图4是对3种不同镀锌层钢板浸入实验后不同位置的SEM分析结果。如图所示,3种不同镀锌钢的表面均发生了严重的点蚀、缝隙腐蚀等局部腐蚀。在1000倍下的SEM图片中可以看到一些生物,而这些生物一般存在于腐蚀坑,表明其对腐蚀进程有影响。从截面的SEM图片可以看出,冷镀锌和热浸锌的镀层内没有明显裂纹,且与基体结合良好;而富锌镀层内有明显裂纹,说明钢基体发生了腐蚀,而且基体与镀层之间存在缝隙,镀层与基体的结合不致密。综上所述,冷镀锌和热浸锌镀层对碳钢基体材料发挥了良好的保护作用,而富锌镀层对钢铁基体的保护性差。
图4
图4
3种挂板正面、背面及横截面的SEM形貌
Fig.4
SEM photographs of the front (a1~c1) and back (a2~c2) sides and cross section (a3~c3) of cold galvanized (a) , zinc rich (b) and hot-dip galvanized (c) panels after exposure test
2.2.2 EDS测试分析
图5
图5
冷镀锌板表面腐蚀形貌及EDS分析
Fig.5
SEM image (a) and EDS elemental mappings of Fe (b), O (c), Ca (d), Zn (e), Cl (f), Na (g) and element contents of the surface (h) of the corrosion product layer formed on cold galvanized plate after exposure test
图6
图6
冷镀锌板断面腐蚀形貌及EDS分析
Fig.6
SEM image (a) and EDS elemental mappings of Fe (b), O (c), Ca (d), Zn (e), Cl (f), Na (g) and element contents (h) of the cross section of the corrosion product layer formed on cold galvanized plate after exposure test
图7
图7
富锌板表面腐蚀形貌及EDS分析
Fig.7
SEM image (a) and EDS elemental mappings of Fe (b), Zn (c), Zr (d), Pt (e) and O (f) of the corrosion product layer formed on zinc rich plate after exposure test
图8
图8
富锌板断面腐蚀形貌,EDS分析及表面腐蚀产物EDS分析
Fig.8
SEM cross-sectional image (a) and EDS elemental mappings of C (b), Fe (c), Zn (d), Na (e), Cl (f), Al (g), O (h) of the corrosion product layer formed on zinc rich plate after exposure test and EDS analysis result of the corrosion products (i)
图9
图9
3种锌板正反面腐蚀产物的XRD谱
Fig.9
XRD patterns of the corrosion products formed on the front and back sides of cold galvanized plate (a) hot dip galvanized plate (b) and zinc rich plate (c)
冷镀锌挂板断面处的EDS分析表明,镀层处Zn仍为主体元素,并伴有Cl、Na、O等,而Fe含量很少,这表明了镀锌层的完整性,且基体未发生明显的氧化腐蚀,导致镀层中Fe的氧化物较少。
热浸锌挂板的EDS测试分析结果与冷镀锌测试结果相近,同样含有O、Zn、K、C、Al、S、Ca、Fe等,且断面EDS的元素分析也观察到了Zn为主的镀层元素分布情况,表明了热浸锌层对于碳钢基体的有效保护。
由图7和8可知,富锌挂板表面的主要元素仍为O、Fe、Zn、C、S、Ca、Na等元素。由其断面的EDS分析结果可以明显看出,镀层内的主体元素为Fe,而Zn的含量低于Fe。可见,富锌镀层在挂件试验期间发生了严重的破损,导致碳钢基体发生了腐蚀。
2.2.3 XRD检测
实验后的冷镀锌板的XRD分析结果如图9a所示。冷镀锌的腐蚀产物比较单一,正反面腐蚀产物相同,均为FeFe2O4。相比富锌板,冷镀锌基体表面仍然存在大量的Zn。结合EDS分析结果,证明涂层的防护作用较好。
实验后的热浸锌板表面的XRD分析结果如图9b所示。可知,正反两面的腐蚀产物基本相同,均为FeFe2O4、Fe2O3和ZnCO3。结合FT-IR和EDS的结果判断,基体表面的热浸锌涂层比较致密、含Zn量大,腐蚀防护效果在3种锌涂层中最佳。
实验后的富锌板表面XRD分析结果如图9c所示。正反两面的腐蚀产物中均有Zn,是刮取腐蚀产物时从镀层中刮下来的。由测试结果可知,正反面的腐蚀产物基本相同,主要为Fe3O4和CuFe2O4。结合FT-IR和EDS的结果判断,基体表面的富锌涂层基本被破坏,涂层已基本失效。
2.2.4 Fourier红外检测
表1 相关红外吸收峰对应的基团
Table 1
Absorption peak / cm-1 | Chemical bondig group |
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3442 | Hydroxyl |
2922、2847、2923、2359 | HCO3- |
1788 | Carbonyl |
1636、1637 | HCO3- |
856 | NO3- |
1439 | CO32- |
1083 | C—O stretching vibration |
1034、1096 | SO42- |
914 | PO43- |
800~1200 | [SiO4] tetrahedron Si—O stretching vibration |
650~1000 | C—H out of plane bending vibration region |
图10
图10
3种不同镀锌板腐蚀产物的FT-IR图谱
Fig.10
FT-IR spectra of the corrosion products of three different galvanized sheets: (a) front of cold galvanized, (b) back of cold galvanized, (c) front of zinc rich, (d) back of zinc rich, (e) front of hot dip galvanized, (f) back of hot dip galvanized
2.3 锌防护层钢板表面污损生物表征与分析
2.3.1 微型污损生物
图11
图11
试片附着硅藻优势种
Fig.11
Dominant species of diatoms attaching on the test sheets e (1 bar=10 μm): (a) Parlibellus berkeleyi, (b) Pseudo-nitzschia cf.cuspidata,(c) Tabulariain-vestiens,(d) Tabularia parva, (e) Cocconeisstauron-eiformis, (f) Proschkinia cf. hyalosirella
图12
图12
显微镜下玻片附着的纤毛虫活体照片
Fig.12
Microscope views of the living ciliates attaching on the slide: (a) Euplotes raikovi; (b). Euplotes harpa, (c) Diophrys scutum, (d) Cohnilembusverminus, (e) Apokeronopsiscarssa, (f) Anteholostichagracilis, (g) Dysteriaprocera, (h) Loxophyllumperihoplophorum, (i) Condylostentorauriculatus, (j) Pseudovorticella sp.
2.3.2 可视污损生物
由月检和年检可知,常见污损生物有绿藻 (石莼和浒苔)、褐藻 (裙带菜、角毛藻和带藻)、褐红藻 (金箔藻和蜈蚣藻) 等植物类,以及藤壶、牡蛎、苔藓动物、蛃海鞘、玻璃海鞘、覆海鞘、海绵动物、贻贝、水螅和石灰虫等动物类。
月检表明12月到次年3月为可视生物的休眠期,8,9,10为生长高峰期。不同年份的月变化不同(图13)。同一年的不同月份以及不同年的同一月变化情况均不同。
图13
图13
不同年份富锌涂料、冷镀锌和热镀锌月变化图
Fig.13
Monthly variations of the surface morphologies of zinc rich coating (a), cold galvanizing (b) and hot galvanizing (c) in different years
3 结论
经过长时间实海部分浸入实验后,富锌板涂层由边角裂缝、局部开裂到全部脱落失效,耐蚀性能较差;冷镀锌和热浸锌板在相同条件下保持着较好的阻隔性能,试板表面Zn仍为主体元素,耐蚀性能较好,且热浸锌防护效果更好些。在该海域,主要微型生物为细菌、单胞藻和原生动物,大型生物有20余种。3种材料在浸海的开始阶段,热浸锌和冷镀锌较富锌底漆有较好的防污性能,约三个月后没有明显差异。3种锌涂层按对基体的腐蚀防护作用大小排序为:热浸锌>冷镀锌>富锌涂层。富锌底漆适用于短期防护,及作为底漆同防污防腐漆配套使用;热浸锌或冷镀锌可用于长期防护,防护中还可以用冷镀锌作为热浸锌的修补。
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