电沉积Zn-Fe-SiO₂复合镀层的工艺及机理研究

【作者】 范云鹰；

【导师】 张英杰；

【作者基本信息】 昆明理工大学 ， 冶金物理化学， 2003， 硕士

【摘要】 本文研究了电沉积Zn-Fe-SiO₂复合镀层的工艺和机理，主要包括以下几个方面： 绘制了Zn-H-2O系和Pe-H₂O系的电位-pH图，并对其进行了热力学分析，结果表明，锌和铁发生共沉积的区域很大，这就对电沉积Zn-Fe合金的可能性提供了理论依据，但是锌和铁的平衡电位差别较大，所以，必须在镀液中添入一定量的配合剂才能使锌铁产生共沉积。 确定了Zn-Fe-SiO₂复合镀层的电沉积工艺，其工艺条件为：FeSO₄·7H₂O120～200g／L、ZnSO₄·7H₂O 30～70g／L、（NH₄）₂SO₄ 80～120g／L、C₆H₈O₇·H₂O30～50g／L、H₃BO₃ 30g／L、抗坏血酸1g／L、SiO₂ 20～60g／L、添加剂适量、pH值2～4、施镀时间60min、电流密度Dk 4～8A／dm²、镀液温度15～25℃、搅拌速度200rpm。 电沉积Zn-Fe-SiO₂复合镀层的工艺研究表明，通过采用不同的工艺条件，可以获得成分不同的复合镀层。主盐浓度是影响Zn-Fe-SiO₂复合镀层铁含量最主要的因素，FeSO₄·7H₂O的添加有利于提高镀层铁含量，而ZnSO₄·7H₂O的添加有利于降低铁含量。导电盐（NH₄）₂SO₄的添加有利于提高镀层的铁含量，配合剂C₆H₈O₇·H₂O的添加有利于降低镀层的铁含量，但它们的影响比较小。温度对镀层铁含量的影响比较小，而且没有规律性。镀液pH值上升，可以导致镀层铁含量下降，但有利于提高SiO₂含量。电流密度对镀层成分的影响很大，铁含量在电流密度为6A／dm²时最低，而SiO₂含量在电流密度为6A／dm²时最高。SiO₂的添加在一定限度内有利于提高镀层的SiO₂含量，但基本上不影响锌铁的含量。 研究了Zn-Fe-SiO₂复合镀层（Pe 7.20～12.09％、SiO₂ 0.40～0.51％）的耐蚀性，结果表明，Zn-Fe-SiO₂复合镀层无需钝化即具有较高的耐蚀性。在稀HC1溶液中，该复合镀层的耐蚀性与，Zn-Fe合金镀层相当，其耐蚀性的好坏主要决定于镀层中的铁含量，铁含量越大，镀层的耐蚀性就越好，在所掺杂含量的范围内，SiO₂的含量对镀层耐蚀性的影响不大；在5％NaCl溶液中，Zn-Fe-SiO₂复合镀层的耐蚀性要好于Zn-Fe合金镀层，大约为Zn-Fe合金镀层的1.5～4倍，更远远好于Zn镀层，大约为Zn镀层的3～20倍，并且Zn-Fe-SiO₂复合镀层的耐蚀性会随着铁含量的增大而降低，随着SiO₂含量的增大而提高。昆明理工大学硕士学位论文摘要 首次提出了微双电层的概念，并从510:微粒表面微双电层、界面场强、阴极极化等方面对510:微粒与Zn一Fe合金的共沉积过程进行了机理研究。结果表明，510:微粒在镀液中可以吸附一定量的阳离子而显正电，这有利于它输送到并吸附在阴极上与基质金属共沉积;界面场强对复合电沉积的影响较大，这种影响可以通过电流密度对复合镀层中微粒含量的影响体现;Zn一Fe合金共沉积时，Zn的存在使得Fe的沉积电位负移，Fe的存在使得Zn的沉积电位正移，而且本来电位较负的Zn首先沉积，因此Zn一Fe合金共沉积属于异常共沉积;5102微粒的加入对Zn一Fe合金共沉积的阴极电化学行为影响不大。更多还原

【Abstract】 Process and mechanism of electrodeposited Zn-Fe-Si02 composite coatings were studied, including some contents as follow:Potential-pH plots of Zn-H2O and Fe-H2O systems were drawn, and the thermomechanical analysis was made. Results showed that the region of zinc and iron’s codeposition was wide, which provided theoretic basis for electrodepositing Zn-Fe alloy. But the balance potential of zinc was greatly different from iron’s, so in order to make zinc and iron codepositing, some complexant must be added into electroplating solution.The technics of electrodepositing Zn-Fe-SiO2 composite coatings was confirmed: FeSO4-7H2O 120~200g/L, ZnSO4-7H2O 30~70g/L, (NH4)2SO4 80~120g/L, C6H8O7-H2O 30~50g/L, H3BO3 30g/L, ascorbic acid Ig/L, SiO2 20~60g/L, addition propriety, value of pH 2~4, time of electroplating 60min, current density 4~8A/dm2, temperature 15~25 , intensity of agitation 200rpm.Researches on the process of electrodeposited Zn-Fe-SiO2 composite coatings indicated that composite coatings with different contents could be obtained by means of appropriate parameters. The concentration of main-salt was the primary influence on the content of iron in the composite coatings, and the adding of FeSO4-7H2O could help to increase the content of iron, while the adding of ZnSO4-7H2O helping to reduce the content of iron. The adding of (NH4)2SO4 could help to increase the content of iron, while the adding of C6H8O7-H2O helping to reduce the content of iron, but both of the two influence were weak. Temperature had little and irregular effect on the content of iron. Increasing the value of pH could decrease the content of iron, while helped to increase the content of SiO2. Current density influenced the component! of composite coatings greatly. When current density was 6A/dm2, the content of iron was at the lowest level, while the content of SiO2 was maximal. The adding of SiO2 could help to increase the content of SiO2 to some extent, but which had little effect on the contents of zinc and iron.The corrosion resistance of Zn-Fe-SiO2 composite coatings (Fe7. 20-12. 09%.SiO20. 40-0.51%) were studied, and the result showed that Zn-Fe-SiO2 composite coatings had high corrosion resistance without passivation. In diluent HC1 solution, the corrosion resistance of composite coatings was equal to Zn-Fe coatings, and it was determined mainly by the content of iron, being raised with increasing the content of iron, but the content of SiO2 had little effect on this. In 5%NaCl solution, the corrosion resistance of composite coatings was better than that of Zn-Fe coatings, being about 1.5-4 times of that of Zn-Fe coatings, and it was much better than that of zinc coatings, being about 3-20 times of that of zinc coatings. The corrosion resistance in 5%NaCl solution decreased with the increasing of content of iron and increased with SiO2 .The conception of micro-double-electric layer was brought forward for the first time, and theory of the process of SiO2 particle’s codeposition with Zn-Fe alloy was studied from the points of micro-double-electric layer on the surface of SiO2 particle, electric field’s intensity between the cathode and solution, and cathodic polarization. The results showed that SiO2 particle could show electropositive with adsorbing some cations, this helped it to be transported and adhered to cathode and codeposite with the basic metal. Electric field’s intensity between the cathode and solution influenced the composite codeposition greatly, and this influence could be embodied by current density. When zinc and iron codepositing, the existing of zinc made iron’s deposition potential lower, and the existing of iron made zinc’s deposition potential higher, this led to zinc, which had lower potential originally, deposited first, so a conclusion could be drawn that Zn-Fe’s codeposition belonged to abnormal codeposition. Si02 particle had little effect on the electrochemical process of Zn-Fe’s codepositing at the cathode.更多还原