不鏽鋼跟鋁接面間的繡蝕
Corrosion Between Stainless Steel and Aluminum Interface
在工地現場
年輕工程師: “聽說不同材質的金屬相接，久了會有腐蝕的狀況發生。我們這次是不鏽鋼跟鋁互相鎖在一起，會不會有這種狀況啊?”
老工程師: “這是個好意見。但這個工程十幾年前就是用不鏽鋼跟鋁互相鎖在一起，你剛剛來時，有看到繡蝕嗎? 而且，你剛剛為了拆除這些相接處，不是嫌鎖太緊，後來還使用砂輪機磨掉。要是有發生嚴重鏽蝕，早就都已經鬆脫了，只要用手隨便扳一下就開了，那輪得到砂輪機。”
背景知識
不同的金屬相接觸，若有電流通過其中，有可能會產生電化學效應，造成金屬腐蝕。這現象稱為”伽凡尼腐蝕”。經典案例為紐約自由女神像。
由於自由女神像採用了金屬銅作為外觀表皮、金屬不鏽鋼作為內骨架建造而成。兩種金屬材料長期接觸，並且潮濕空氣、雨水、鹽分等成分，形成天然的電解液，使得自由女神像變成一個大型”伏打電池”，而長時間的放電則會造成金屬接面間腐蝕，稱為”伽凡尼腐蝕”。
At the construction site
Young engineer: “I heard that when metals of different materials are connected, corrosion will occur over time. This time, we have stainless steel and aluminum locked together. Will this happen?”
Senior engineer: “That’s a good idea. However, this project used stainless steel and aluminum to be interlocked more than ten years ago. Did you see corrosion when you first came here? Moreover, you just removed these joints, didn’t you? You thought the lock was too tight, so you used a grinder to remove it. If there had been serious corrosion, it would have loosened long ago. Just pull it with your hand, and it will open. No need for grinder.”
Background knowledge
When different metals come into contact, if current passes through them, electrochemical effects may occur, causing metal corrosion. This phenomenon is called “Galvanic corrosion.” A classic example is the Statue of Liberty in New York.
The Statue of Liberty is built using metallic copper as the exterior skin and metallic stainless steel as the inner frame. The two metal materials are in long-term contact, and moist air, rain, salt, and other ingredients form a natural electrolyte, turning the Statue of Liberty into a large “Voltaic pile.” Long-term discharge will cause corrosion between the metal interfaces, called “Galvanic corrosion.”
REF:
- Wikipedia: Conservation-restoration of the Statue of Liberty
- National Park Service: Restoring the Statue
- Wikipedia: Voltaic pile
- Galvanic corrosion
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