熱浸鍍鋅白銹生成之抑制研究

The Inhibition of the White Rust Formation on Hot Dip Galvanized Products

熱浸鍍鋅表面會生成具良好保護性的碳酸鋅膜，保護鋅材在一般環境中不致腐蝕太快。但是在台灣這種高濕度的環境下，熱浸鍍鋅工廠的鍍件在戶外儲存時，卻遭遇到鍍件在表面上生成的白銹問題。本研究探討生成白銹的環境因子，諸如相對濕度、氯離子、硫酸根離子等的臨界條件。熱浸鍍鋅鍍件上為了防止白銹，一般以鉻酸鹽處理在表面形成保護膜來抑制白銹的生成。但是面對日趨嚴格的環保法規要求，發展對環境汙染度低的轉化膜處理方式就成為現今急需的工作。本研究開發使用非鉻酸鹽溶液的處理方式，以三價鉻代替鉻酸鹽中的六價鉻離子。藉著將處理過後的試片暴露在臨界環境－表面鹽類濃度分佈1.5 µg/cm2 NaCl、相對濕度80%，證實此種非鉻酸鹽轉化膜處理對白銹有成功的抑制效果。

The good corrosion resistance of hot dip galvanized steel products in nature environments is due to the formation of a protective basic zinc carbonate film on the surface of the zinc coatings. However, in Taiwan, we face a severe white rust problem for freshly galvanized works stored in high humidity out-doors environments. This paper investigated the critical factors such as relative humidity, chlorides, sulfates for the formation of white rust. It was recognized that a simple chromate treatment of galvanized products results in the production of a passive film on the surface of zinc coating which inhibits white rust formation. However, in response to upcoming environmental regulations, we should give a considerable amount of resources and time in the development of environmental friendly manufacturing processes, particularly in the areas of chromate compound reduction and environmentally compatible conversion treatments. This work concentrates on non-chromate chemical conversion treatments of galvanized coatings to provide good resistance to the formation of white rust, The present study develops the optimum condition for determining the protective value of non-chromate conversion coating by exposing the zinc specimen contaminated with 1.5 µg/cm2 NaCl particles to 80% RH at room temperature.