Why does aluminum leech into a water bottle, but stainless steel does not?

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Main Question or Discussion Point

Why does aluminum "leech" into a water bottle, but stainless steel does not?

My professor was saying that using aluminum water bottles will result in a small amount of aluminum ions dispersing into the water. Stainless steel, however, does not have this problem.

Is this true? Why? I'm curious about the chemical/physical differences that would cause these effects.
 

Answers and Replies

  • #2
AGNuke
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Aluminium is quite reactive, while stainless steel is an alloy composed of Iron, Nickel, Carbon, etc. making it more inert than aluminium.
 
  • #3
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Aluminium is quite reactive, while stainless steel is an alloy composed of Iron, Nickel, Carbon, etc. making it more inert than aluminium.
I know that i's more reactive. I'm wondering about a physical explanation for why?
 
  • #4
AGNuke
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Physical Explanation? What do you mean by that? This is not a physical phenomena, its a chemical reaction going on, so what physical explanation are you expecting?
 
  • #5
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The good news is that your professor was probably quite wrong. There will be no significant leeching of aluminium unless the pH of the water goes outside the range from 4 to 10. Aluminium is covered with a strongly adherent layer of oxide that makes it "passive" to chemical attack from most reagents. Check out a "pourbaix diagram" for aluminium.

You can quite safely use an aluminium water bottle without ingesting any toxic aluminium compounds. However, do not use it for Cola drinks or fruit juices!
 
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The good news is that your professor was probably quite wrong. There will be no significant leeching of aluminium unless the pH of the water goes outside the range from 4 to 10. Aluminium is covered with a strongly adherent layer of oxide that makes it "passive" to chemical attack from most reagents. Check out a "pourbaix diagram" for aluminium.

You can quite safely use an aluminium water bottle without ingesting any toxic aluminium compounds. However, do not use it for Cola drinks or fruit juices!
Ah no this is exactly what he was saying. That aluminum will leech with low ph liquids. And that they often coat it in bpa to avoid this, and that is why aluminum bottles are no better than more common plastic bottles.

Still, what is the chemical explanation for aluminum alloys being more reactive than steel alloys?
 
  • #7
AGNuke
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Aluminium bottles are not used because aluminium in not a cheap metal to purchase, even in comparison to some other metals.

And as for leeching, food is prepared in aluminium vessels in my house for past 15-20 years and still the vessels are in good shape, so it is not that water and spices and salts are eating my vessel.

As for the chemical reaction, it is the simple oxidation of aluminium to aluminium oxide.
 
  • #8
Borek
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Mechanism of resistance is in both cases identical - passivation with oxide, but chromium oxide is much more resistant to low pH solutions than aluminum oxide is.
 
  • #9
Borek
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Aluminium bottles are not used
Really?

And as for leeching, food is prepared in aluminium vessels in my house for past 15-20 years and still the vessels are in good shape, so it is not that water and spices and salts are eating my vessel.
Have you checked how much their mass have changed?

As for the chemical reaction, it is the simple oxidation of aluminium to aluminium oxide.
This is a non-answer - question was "why are aluminum alloys more reactive".
 
  • #10
chemisttree
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You are all overthinking this problem. The professor said that aluminum leaches into water from aluminum containers, and it does. Stainless steel doesn't have this problem because...

IT'S NOT MADE OF ALUMINUM! It's made from iron, chromium, nickel.:biggrin:
 
  • #11
AGNuke
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Really?
You took my statement too much close to heart. I mean, who uses them as commonly as plastic bottles. I don't remember anyone using aluminium bottles.


Have you checked how much their mass have changed?
15-20 years are good enough to leech vessels, considering you cook Indian in them 3 times in day. And these utensils are even older than me. I am not even 20.


This is a non-answer - question was "why are aluminum alloys more reactive".
 
  • #12
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You took my statement too much close to heart. I mean, who uses them as commonly as plastic bottles. I don't remember anyone using aluminium bottles.



15-20 years are good enough to leech vessels, considering you cook Indian in them 3 times in day. And these utensils are even older than me. I am not even 20.
Aluminium bottles -- about 500 mL with a thermos type screw top -- commonly used as bushwalking water bottles around here. Do not leach Al unless used for fruit juice instead -- not recommended at all. (Time to get the right word -- leech refers to quite a different hazard of bushwalking.)

Aluminium vessels will lose mass if used around the kitchen only if
(1) used for very acidic brews, or
(2) cleaned up in very alkaline automatic dishwasher environment.
 
  • #13
AGNuke
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Aluminium vessels will lose mass if used around the kitchen only if
(1) used for very acidic brews
Don't know about that. Never checked whether the broth is acidic.
(2) cleaned up in very alkaline automatic dishwasher environment.
Manual washing, so not an issue.
 

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