結合電化學方法與電子顯微鏡探討鍍鋅鋼板表面塗層之抗蝕研究

Abstract

本研究的目的是結合多樣性電化學方法及掃描式電子顯微鏡探究經過鈍化後鍍鋅鋼板表面性質之差異，就電化學而言，腐蝕電位越大、腐蝕電流越小、極化電阻越大及電荷轉移電阻越大其抗蝕性也就越好，掃描式電子顯微鏡則可幫助我們了解表面結構與元素成分百分比。本實驗將鍍鋅鋼板先經由鋯鈍化處理，形成氧化鋯抗蝕薄膜，再利用氧化矽與氧化鈦複合奈米網狀結構塗層進行表面封孔。本研究分別以6%、8%、10%不同濃度鋯鈍化液進行鈍化，結果發現塗佈6%鋯鈍化液之鋼板具有最佳抗蝕能力，從鹽霧試驗結果也證實從無鋯鈍化之鋼板到鋯鈍化之鋼板，出現白鏽時間從原48小時增加至72小時。我們也試著調整鋯鈍化液pH值進行鈍化，結果為pH5具有最佳鈍化條件。同時也針對高濃度與低濃度環境下水解之氧化矽與氧化鈦複合奈米塗層進行比較，發現低濃度下水解之材料粒徑約在2～5 nm之間且粒徑分布均勻，具有較佳封孔能力。我們也將塗有氧化矽與氧化鈦複合材料塗層之鋼板與傳統之磷酸皮膜鋼板進行比較，發現氧化矽與氧化鈦複合材料塗層鋼板抗蝕性略優於傳統磷酸皮膜鋼板。最後針對鋅鎳合金塗層鋼板與鍍鎳鋼板進行電化學量測，相較於有塗層之鍍鋅鋼板，發現其腐蝕電位較大、腐蝕電流較小、電荷轉移電阻較大，但在48小時鹽霧試驗後，鋅鎳塗層鋼版與鍍鎳鋼板即出現不小的鏽蝕面積，推測原因是鍍鋅鋼板上因為有塗層可延緩腐蝕速率，但鋅鎳與鍍鎳表面並無塗層保護，因此底層鋼材容易遭到腐蝕。我們也觀察到在表面材料差異甚大的情況下，電化學表現與現實抗蝕能力可能並非正相關，但在相同材料系統下我們可以建立資料庫互相進行比較，訂定參考值，並實際應用於產線中進行快速品管。The aim of this study is to investigate the differences in surface properties of galvanized steel plates after passivation using a combination of diverse electrochemical methods and scanning electron microscopy (SEM). In terms of electrochemistry, a higher corrosion potential, lower corrosion current, larger polarization resistance, and larger charge transfer resistance indicate better corrosion resistance. SEM can help us understand surface structures and the percentage of elemental composition.In this experiment, the galvanized steel plates were initially treated with zirconium passivation to form a zirconium oxide corrosion-resistant film. Subsequently, a composite nanostructured coating of silicon oxide and titanium oxide was applied to seal the surface. Three different concentrations (6%, 8%, and 10%) of zirconium passivation solution were used for passivation. The results revealed that the steel plate coated with 6% zirconium passivation solution exhibited the best corrosion resistance. The salt spray test results also confirmed that the white rust occurrence time increased from 48 hours for the steel plate without passivation to 72 hours for the zirconium passivated steel plate. We also attempted to adjust the pH value of the zirconium passivation solution for passivation and found that pH 5 provided the optimal passivation conditions. Furthermore, a comparison was made between silicon oxide and titanium oxide composite coatings hydrolyzed under high and low concentration environments, indicating that the material hydrolyzed under low concentration had particle sizes ranging from 2 to 5 nm with a uniform size distribution, thereby exhibiting better sealing capability.Additionally, the steel plate coated with the composite material of silicon oxide and titanium oxide was compared with traditionally phosphoric acid coated steel plates, revealing slightly better corrosion resistance for the former.Finally, electrochemical measurements were conducted on zinc-nickel alloy coated steel plates and nickel-plated steel plates. Compared to the coated galvanized steel plates, it was found that the zinc-nickel alloy coated steel plates exhibited a higher corrosion potential, lower corrosion current, and larger charge transfer resistance. However, after a 48-hour salt spray test, significant rust areas were observed on the zinc-nickel coated and nickel-plated steel plates. This may be attributed to the delayed corrosion rate due to the presence of coatings on the galvanized steel plates, whereas the zinc-nickel and nickel surfaces were not protected by a coating, making the underlying steel susceptible to corrosion.Furthermore, it was observed that under significant surface material differences, the electrochemical performance may not necessarily correlate directly with real-world corrosion resistance. However, within the same material system, we can establish a database for comparison, set reference values, and apply them in actual production lines for rapid quality control.