電鍍鋅鋼板的複合型三價鉻鈍化處理

Composite Trivalent Chromium Conversion Coating on Electrogalvanized Sheet Steel

楊育銓(Yu-Chuan Yang)

指導教授 ： 林招松

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.01573

摘要

電鍍鋅常用來改善鋼鐵工件的抗蝕性，經過六價鉻鈍化處理的鍍鋅鋼件具有優異的抗蝕性，同時亦提昇塗裝層的附著性。然而，六價鉻物質會嚴重污染環境和人體健康，因此，因應國際環保法規對於危害物質限用指令的實施，發展替代六價鉻鈍化處理製程的技術刻不容緩。本研究旨在開發複合性三價鉻鈍化處理系統，著重於添加六氟矽酸在鈍化液中，使其解離的二氧化矽奈米級微粒與三價鉻鈍化膜同時披覆於鍍鋅基材上，並針對複合型三價鉻鈍化膜進行化學組成分析、微結構解析、電化學測試與抗蝕性鹽霧試驗。研究結果顯示複合型三價鉻鈍化膜是由Cr(III)與Zn(II)的氧化物/氫氧化物、二氧化矽、氟化鉻及氟化鋅組成，複合型三價鉻鈍化膜微結構較單純三價鉻鈍化膜緻密，尤其添加2.5×10-2 M六氟矽酸所製作的鈍化膜具有雙層以及較緻密的結構。利用XPS的縱深分析以及橫截面TEM微結構的觀察，有助於推導出複合型三價鉻鈍化膜的成膜機制。168小時鹽霧試驗的結果顯示三價鉻鈍化液中添加2.5×10-2 M六氟矽酸所製作的鈍化膜具有最優異的抗蝕能力。另外，交流阻抗分析與極化曲線也都顯示添加六氟矽酸的複合型三價鉻鈍化膜比未添加的鈍化膜具有更優異的抗蝕性。

關鍵字

電鍍鋅鋼件 ； 六價鉻鈍化 ； 複合型三價鉻鈍化 ； 鹽霧試驗 ； 交流阻抗 ； 極化曲線

並列摘要

Electrogalvanized zinc has been widely used to improve the corrosion resistance of steel, but its active chemical property may cause other corrosion problems although the steel beneath is protected. Hexavalent chromium passivation treatment has generally been used to further improve the corrosion resistance of the electrogalvanized steel and the adhesion between the substrate and painting layer. However, hexavalent chromium is highly toxic and severely endangers ecological environment and operators’ health. Since several international regulations have limited the use of hexavalent chromium, the development of alternatives to the hexavalent chromium passivation treatment is now an urgent necessity. Trivalent chromium compounds possess chemical properties similar to hexavalent chromium ones and are not toxic, so recently they have been used as one of the alternatives for the passivation treatment on electrogalvanized steel. In this study, hexafluorosilicic acid, which can dissociate into silicon dioxide nanoparticles in the solution, is added in a trivalent chromium conversion bath to form the composite trivalent chromium conversion coating. Chemical compositions, microstructure characterization, and corrosion resistance of the composite trivalent chromium conversion coating are discussed firstly. Experimental results showed that the composite trivalent chromium coating consisted of trivalent chromium and zinc oxide/hydroxides, silicon dioxide, trivalent chromium fluoride, and zinc fluoride. From the cross-sectional TEM observation, the composite trivalent chromium conversion coating was denser than the traditional trivalent chromium conversion coating. Especially, the coating fabricated by adding 2.5×10-2 M hexafluorosilicic acid in the conversion bath presented a double-layer structure with enhanced compactness. After 168 h of the salt spray test, the conversion coating formed in the bath with the addition of 2.5×10-2 M hexafluorosilicic acid showed the best corrosion resistance. Moreover, the electrochemical analyses, including EIS and potentiodynamic polarization curves, also indicated that the presence of hexafluorosilicic acid in the trivalent chromium bath indeed improved the corrosion resistance of the composite trivalent chromium conversion coating.

並列關鍵字

electrogalvanized steel ； hexavalent chromium passivation ； composite trivalent chromium passivation ； salt spray test ； EIS ； potentiodynamic polarization curves

參考文獻

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