# Metal combinations that cause corrosion **URL:** \ **Category:** Factual Questions\ **Created:** [November 16, 2001, 6:50pm UTC](https://boards.straightdope.com/t/metal-combinations-that-cause-corrosion/93782 "2001-11-16T18:50:39Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![El\_Zagna](https://avatars.discourse-cdn.com/v4/letter/e/d2c977/32.png) [@El\_Zagna](https://boards.straightdope.com/u/El_Zagna)\ **Post date:** [November 16, 2001, 6:50pm UTC](https://boards.straightdope.com/t/metal-combinations-that-cause-corrosion/93782/1 "2001-11-16T18:50:39Z")
I know - at least I think I know - that certain metals when in contact with each other will cause one or the other to corrode rapidly. Which combinations are problematic? In particular, will iron and lead react? The reason I’m asking this - just in case anyone is interested - is that I need to add some additional weight to some old window sash weights. ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [November 16, 2001, 6:56pm UTC](https://boards.straightdope.com/t/metal-combinations-that-cause-corrosion/93782/2 "2001-11-16T18:56:41Z")
I really wouldn’t use mercury as a window sash weight if parts of your window are made from aluminum. That would be a really bad idea and probably wouldn’t work that well anyway. 😃 I think lead and iron are OK though. ---
**Author:** ![Ich\_Bin\_s](https://avatars.discourse-cdn.com/v4/letter/i/e9c0ed/32.png) [@Ich\_Bin\_s](https://boards.straightdope.com/u/Ich_Bin_s)\ **Post date:** [November 16, 2001, 7:06pm UTC](https://boards.straightdope.com/t/metal-combinations-that-cause-corrosion/93782/3 "2001-11-16T19:06:09Z")
Probably more info than you need. But the answer is, they’re probably okay, but matching the metal would be better. This is the galvanic series of metals. The further apart two metals are on the scale, the greater the corrosion of the less noble materials. Anodes, the least noble, are at the top. Cathode, the most noble, are at the bottom. I’ve highlighted lead and iron Magnesium Zinc Aluuminum Cadmium Alluminum, 2024 T4 alloy **Iron or carbon steel** Chromium steel Ferritic Stainless steel Austenitic stainless steel **Lead** Tin Nickel (active) Brass Copper Bronze Monel Silver Solder Nickel (Passive) Ferritic Stainless steel Austinitic Stainless steel Silver Titanium Graphite Gold Platinum ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [November 16, 2001, 7:23pm UTC](https://boards.straightdope.com/t/metal-combinations-that-cause-corrosion/93782/4 "2001-11-16T19:23:43Z")
Do you live under water? Are your sash weights submerged in salt water? If not, in normal circumstances, you are OK. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 16, 2001, 7:43pm UTC](https://boards.straightdope.com/t/metal-combinations-that-cause-corrosion/93782/5 "2001-11-16T19:43:42Z")
**Ich Bin’s** , you have Ferritic Stainless steel and Austenitic stainless steel on your list twice. Was that error or not? And how come graphite is on the list? It’s not a metal. Does it cause corrosion in metals it comes into contact with? ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [November 16, 2001, 7:57pm UTC](https://boards.straightdope.com/t/metal-combinations-that-cause-corrosion/93782/6 "2001-11-16T19:57:07Z")
steel alloys, like aluminum and other alloys have a wide range depending on the specific alloy. I guess those may be the upper and lower limits? ---
**Author:** ![Ich\_Bin\_s](https://avatars.discourse-cdn.com/v4/letter/i/e9c0ed/32.png) [@Ich\_Bin\_s](https://boards.straightdope.com/u/Ich_Bin_s)\ **Post date:** [November 16, 2001, 8:46pm UTC](https://boards.straightdope.com/t/metal-combinations-that-cause-corrosion/93782/7 "2001-11-16T20:46:05Z")
Sailor’s right. The first ferritic and stainless steel should be 400 series (active) and 18-8 series (active) respectively, while the later are passive. I’ll have to come back to the graphite question, dtilque, sorry. But that’s a good question! ---
**Author:** ![Bob\_Scene](https://avatars.discourse-cdn.com/v4/letter/b/e19adc/32.png) [@Bob\_Scene](https://boards.straightdope.com/u/Bob_Scene)\ **Post date:** [November 16, 2001, 9:28pm UTC](https://boards.straightdope.com/t/metal-combinations-that-cause-corrosion/93782/8 "2001-11-16T21:28:22Z")
Graphite’s not a metal, but it’s a reasonably good conductor of electricity. The corrosion problem is related to electrons flowing from the less noble metals to the more noble ones they’re in contact with, which promotes the formation of positive ions from the less noble metal, which is part of the corrosion process. So it makes sense that graphite could promote corrosion in the metals above it on the list, but I don’t know what happens to graphite in contact with gold or platinum. ---
**Author:** ![manhattan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/manhattan/32/7_2.png) [@manhattan](https://boards.straightdope.com/u/manhattan)\ **Post date:** [November 16, 2001, 11:01pm UTC](https://boards.straightdope.com/t/metal-combinations-that-cause-corrosion/93782/9 "2001-11-16T23:01:25Z")
> [@](#): > > \*Originally posted by Ich Bin’s \* > \*\*Probably more info than you need. But the answer is, they’re probably okay, but matching the metal would be better. > > This is the galvanic series of metals. The further apart two metals are on the scale, the greater the corrosion of the less noble materials. Anodes, the least noble, are at the top. Cathode, the most noble, are at the bottom. I’ve highlighted lead and iron > > Magnesium > . > . > . > . > . > . > . > . > . > . > . > . > . > . > . > . > . > . > . > . > . > . > . > Platinum \*\* So much for that magnesium catylitic converter that was going to make me rich. On to the next idea. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [November 17, 2001, 4:03am UTC](https://boards.straightdope.com/t/metal-combinations-that-cause-corrosion/93782/10 "2001-11-17T04:03:10Z")
I recall from my Materials curs way-y-y-y-y back in my Freshman year, in the Paleolithic era, that you don’t even need dissimilar metals. You can get corrosion on a block of uniform metal if you restrict access to the surface. A block of steel with a rubber band wrapped around it and immersed in salt water will show a galvanic difference between th part under the rubber band and the part that isn’t, leading to corrosion where the rubber band is. Something about dissolved oxygen not having equal access o all parts. In fact, “high energy” areas like Grain Boundaries will tend to be more reactive (which is why you can “etch” the surface of a metal to see them), s you don’t even need that rubber band. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [November 17, 2001, 10:03am UTC](https://boards.straightdope.com/t/metal-combinations-that-cause-corrosion/93782/11 "2001-11-17T10:03:39Z")
The “immersed in salt water” part is of the essence. I own plenty of objects, including one (1) vehicle, made in Japan, made with plenty of separate parts themselves made of dissimilar metals and they are not corroding. I do take care not to immerse it in salt water though. I guess if I were in the habit of parking it underwater it might not have lasted so long though, notwithstanding the fine quality and workmanship in Japanese products.