有沒有發現不鏽鋼周圍的鐵板比較容易生鏽?
文章目錄
不鏽鋼本身雖然耐蝕，但當它與碳鋼（鐵）接觸時，在潮濕或導電環境下，會產生「電位差腐蝕」（galvanic corrosion），這就是為什麼不鏽鋼周圍的鐵板反而「更容易生鏽」。
① 為什麼會這樣？
不同金屬在電化學序列上有不同的電極電位，當兩種金屬接觸、再加上水氣或鹽霧（形成電解質環境），就會變成一個「小型電池」。
- 電位較低的金屬 → 成為 陽極 → 被犧牲、開始腐蝕
- 電位較高的金屬 → 成為 陰極 → 保持穩定，不腐蝕
👉 不鏽鋼的電位比碳鋼高
👉 所以碳鋼變成「陽極」
👉 碳鋼開始優先生鏽
② 電位差腐蝕的形成條件
- 兩種不同金屬（例如：不鏽鋼 + 鐵）
- 有電解質（例如：雨水、潮濕空氣、鹽霧）
- 金屬間有導電接觸
📌 三個條件一旦同時存在 → 電化學反應就開始了。
③ 為什麼不鏽鋼不生鏽，反而旁邊的鐵板鏽得更快？
- 不鏽鋼在這個電化學反應中成為 陰極，它幾乎不被破壞。
- 鐵板成為 陽極，電子不斷流出，氧化反應發生，鏽蝕速度加快。
- 加上不鏽鋼本身的表面平滑，水氣容易集中在接縫，造成局部腐蝕更劇烈。
📌 這種現象在：
- 屋頂板與不鏽鋼螺絲結合
- 水塔支架
-
戶外鋼構螺接點
非常常見 ⚠️
④ 預防與解決方式
| 方法 | 說明 |
|---|---|
| 絕緣墊片／塗層隔離 | 切斷金屬直接接觸，避免電偶形成 |
| 選用相近電位的金屬組合 | 例如：不鏽鋼搭配不鏽鋼、鋁配鋁 |
| 加上防鏽塗層或鍍層 | 降低陽極金屬（鐵板）的裸露面積 |
| 陰極保護 | 以「犧牲陽極」方式，保護主體結構 |
| 定期檢修 | 在潮濕環境尤其重要 |
📌 工程重點總結
| 項目 | 說明 |
|---|---|
| 不鏽鋼不生鏽 ≠ 不會造成鏽 | 它反而會讓鄰近鐵板更快生鏽 |
| 問題根源 | 電位差形成的電偶腐蝕 |
| 預防方式 | 隔離、塗層、防鏽、材料匹配 |
👉 所以在設計螺絲與板材搭配時，不只要看「強度」與「外觀」，還要考慮電化學相容性。
👉 否則螺絲沒壞，板子先鏽光。
why steel plates around stainless steel tend to rust faster — this is a classic case of galvanic corrosion caused by potential difference ⚡️
① Why this happens
When two different metals come into contact and there’s moisture or salt in the air, they form a small galvanic cell (battery).
- The less noble metal (lower potential) becomes the anode → it corrodes first.
- The more noble metal (higher potential) becomes the cathode → it is protected.
👉 Stainless steel has a higher electrode potential than carbon steel.
👉 Carbon steel becomes the sacrificial anode.
👉 The steel plate corrodes faster.
② Conditions required for galvanic corrosion
- Two different metals (e.g., stainless steel + carbon steel)
- An electrolyte (e.g., rainwater, humidity, salt spray)
- Direct electrical contact between the metals
Once these three conditions are met → corrosion starts.
③ Why stainless steel stays clean while the steel plate rusts
- Stainless steel acts as the cathode, so it does not corrode.
- Carbon steel acts as the anode, and corrosion is accelerated.
- Because stainless steel is smooth and doesn’t corrode itself, the surrounding area concentrates moisture, making the steel plate even more vulnerable.
⚠️ Common places where this happens:
- Roofing panels fastened with stainless screws
- Water tank brackets
- Outdoor steel structures
④ How to prevent galvanic corrosion
| Method | Description |
|---|---|
| Use insulating washers/coatings | Break the direct metal-to-metal contact |
| Choose similar metal combinations | e.g., stainless with stainless, aluminum with aluminum |
| Apply protective coatings | Reduce exposed anode area |
| Cathodic protection | Use sacrificial anodes to protect the structure |
| Regular maintenance | Especially important in humid or marine environments |
⑤ Key takeaway
| Misconception | Reality |
|---|---|
| Stainless steel won’t rust = no corrosion | ❌ It can make nearby steel rust faster |
| Problem is the screw itself | ⚡ The real issue is potential difference corrosion |
| No special design needed | ✅ Material compatibility and insulation are crucial |
👉 So when designing fastener + metal sheet combinations, it’s not enough to only consider mechanical strength —
you must also consider electrochemical compatibility to avoid premature failure.