無鉻熱浸鍍鋅鈍化膜之微觀研究

Study of Microstructure for Chromium-Free Passivating Coating on Hot-Dipped Galvanized Steel

傳統六價鉻表面處理因環保法規限制，已逐漸取代成環境友善型表面處理。中鋼實驗室成功開發釩鹽／酸性系統為主之無鉻鈍化系統，該系列塗料應用於鍍鋅產品上可符合一般耐蝕、上漆附著性、耐黑變等要求。耐蝕性評估以鹽霧測試及電化學評估為主；上漆附著性評估烤漆層百格試驗後之脫膜水準；耐黑變性於高溫、高濕條件下模擬鋼捲表面狀況。塗膜組成及分布藉由GDS、XPS、TEM等探討塗膜微結構；上述塗膜優異性質與塗膜組成關聯性可解釋為：（a）塗膜中V-P複合物可提供屏蔽效果以減緩腐蝕因子滲入，繼而改善耐蝕性；（b）塗膜／鍍鋅層界面處P-O-Zn、Si-O-Zn鍵結形式改善塗膜上漆附著性。

Chromate conversion coatings with hexavalent chromium are currently being replaced by eco-friendly surface treatments due to environmental legislation. A novel chromium free passivating coating based on vanadium compound in an acidic system has been successfully synthesized. This new coating for galvanized steel meets the general standards such as those for corrosion resistance, adherence, and black tarnish resistance. The corrosion resistance of the new coating was evaluated by salt spray test and polarization curves. The adherence of the coating was evaluated by cross-cut and erichsen test after acrylic or alkyd resin coated. The distribution of the elemental composition of the new coating was studied by glow discharge spectrometer (GDS), Xray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) to investigate the microstructure. The superiority of the new coating can be characterized by the following aspects: (a) vanadyl-phosphate complexes in the coating can enhance the barrier effect which suppresses diffusion of corrosive elements and improve corrosion resistance; and (b) P-O-Zn and Si-O-Zn bonds formed in the coating/zinc interface enhance the adherence of the coating film.