Stainless Steel-on-Aluminum: A Question

[frigilux]

It has been pointed out that stainless steel should not come in contact with aluminum, as corrosion is the outcome; I'm referring to the spider on the back of front-loading washers.

My question: My cookware consists of a layer of aluminum sandwiched between two layers of stainless steel. Why doesn't it corrode over time? Is it because there's no exposure to air/moisture?

Thanks in advance to all lovable Brainiacs who respond.

 

[iheartmaytag]

I would assume

Because they are Sandwiched, they are hence sealed thus not exposed to air and able to oxidize. Whereas the spider at the back of the wash tub is exposed to both air and cleaing agents with lots of water.

This is just my hopothisis. Others may have the correct answer for you.

 

[bernina]

OK, I 've just cut and pasted this... but I think I unde

Galvanic corrosion (some times called dissimilar metal corrosion) is the process by which the materials in contact with each other oxidizes or corrodes.

There are three conditions that must exist for galvanic corrosion to occur.

First there must be two electrochemically dissimilar metals present.

Second, there must be an electrically conductive path between the two metals.

And third, there must be a conductive path for the metal ions to move from the more anodic metal to the more cathodic metal.

If any one of these three conditions does not exist, galvanic corrosion will not occur.

Often when design requires that dissimilar metals come in contact, the galvanic compatibility is managed by finishes and plating.

The finishing and plating selected facilitate the dissimilar materials being in contact and protect the base materials from corrosion.

 

[danemodsandy]

The Corrosion:

Needs a couple of specific conditions to take place. First, there needs to be fairly frequent, or even constant, exposure to moisture. Unless cookware spends a lot of its life soaking in the sink (which isn't unheard-of, trust me) it's not that big a factor.

The other thing needed is air. The sandwiching cuts off the air supply, except at the edges, where some corrosion could take place if the piece was kept wet. On vintage Farberware, the aluminium bottom does not corrode because the side of it next to the stainless is sealed off from air, and the bottom side is not in contact with the stainless. It is fairly common to see very, very minor corrosion at the edge of the aluminium layer on vintage Farberware, since a lot of consumers do soak dirty pots and pans for extended periods.

Hope that helps.

 

[sudsmaster]

Above all true about galvanic corrosion.

With regard to the front loader aluminum spider... It's possible that an anodized finish on the spider inhibits corrosion. Another possibility is that the spider is electrically insulated from direct contact with the stainless drum, via plastic bushings/pads/washers. Third, it may be that the overall exposure time of the aluminum metal junction to water is relatively brief (as compared to that in a water pipe) and therefore the corrosion takes a long time to get to the point where it is of concern.

 

[westtexman]

Funny that you mention this . . .

I actually logged in this evening to ask a question about aluminum and SS. I just purchased a new dishwasher (Maytag JetClean Plus Tall Tub - Model # MDBH979AWW). I ordered it just before Thanksgiving and got a GREAT deal on it.

While I really love this dishwasher, I've had a couple of aluminum pieces that have come out really oxidized! Tonight I pulled out my half sheet pan and it looked terrible. I never had a problem washing it in my old dishwasher (builder's grade Hotpoint), but I will certainly never put it in my new dishwasher again. The chemicals I used haven't changed, so I assumed it might be the SS tub reacting with the pan? Strange.

Anyway, after 30 minutes of scrubbing with Bar Keeper's Friend, my pan is back to normal. I expect my hands will regain their original color in a couple of days!

What in the world?!?!?

 

[danemodsandy]

Actually...

...Your chemicals may have changed without your realising it. Phosphates are being eliminated from a lot of brands right now (all of them in some areas), and part of phosphate's job in a DW detergent is to protect metals.

So, it could be that what you're seeing is your detergent; the timing may just be making it look like it's the DW.

 

[westtexman]

I considered that, but I am still using the same container of Cascade Action Packs that I've had for months now. I also use Jet Dry as the rinse agent.

We're not just talking white spots here. While there were some of those, the pan turned a very dark grey and only after 30 minutes of scrubbing with BKF did the color return (and transfer to my hands)!

 

[sudsmaster]

Um, I've never heard that phosphates protect metals. Sodium metasilicate is the chemical that is added protect metals.

Phosphates will attack aluminum.

Aluminum objects should not be put into the dishwasher, unless you want them to discolor.

 

[danemodsandy]

My Impression Is...

That phosphates do have a protective effect. Complaints about phosphate-free DW detergents ruining metalware are becoming pretty easy to find on the Internet:

Phosphate-free dishwasher detergent: Need an alternative to the "alternative"

www.freerepublic.com

 

[alr2903]

I have wondered about this before, Why is there seldom/never a spider issue with the restorations of the old westy laundromats, and bendix machines? I realize they both had porcealain drums. My question is what was the spider made of? and was it porcelain coated. It just seems strange that this part fails in modern machines and seems to be of little or no issue in these fun old 40's and 50's machines. thanks alr2903

 

[bernina]

what's old is new agian

Check out this page in automaticwasher.com's "Vintage Consumer Article Library"

Second paragraph on pg 24 begins the discussion about the "particular difficulty" associated with "corrosion of aluminum washing machine parts."

I actually happen to have a few of these very first Consumer Reports magazines, including your May 1937 "Washing Machines" article. I was very happy to see it (and more) on this website!

At first I had thought reading 70-year-old consumer magazines would just be a pleasant diversion, but was amazed to find (time after time) topics that were completely relevant today.

Sadly, one of the articles discusses the problem of "lead in children's toys."

http://www.automaticwasher.org/RATE%20PAGES/LIST-INDEX.htm

 

[panthera]

This particular problem

in, for instance the Electrolux FLs sent to the US before roughly 2000, was dramatically (and usually terminally) caused by the use of chlorine bleach.

Yes, those washers had a "bleach" drawer, no, they still weren't designed for chlorine bleach.

It caused the aluminium spider to fail very fast.

My Miele with stainless steel everything and German dishwashing detergent with 28%+ phosphates will attack aluminium even in one washload to the point it is nearly hopeless to restore. I assume this new Maytag is similar, you've got all three conditions met for great galvanic action, not to mention that the protective oxide layer on aluminium is stripped by chlorine bleach as well as by such high levels of phosphate...

Anyone with gold crowns who has ever got a really thin piece of aluminium stuck to a chocolate knows exactly what galvanic action is all about.

Yee-Haw!

 

[stopmeister72]

have had the same issues

I think there are more factors than that which contribute to the oxidation. Here is the deal - I have a Hobart WM5H commercial undercounter dishwasher. (150 degree wash -180 degree rinse) If I use Cascade or other dw detergent on my aluminum sheet pans ($5 buck ones from superior products) they get oxided pretty quickly and get the grey coating.
Same thing happens to the burnished aluminum Kitchenaid attachments. Think the temp of the water also has something to do with it, not the stainless steel tub. I use a special commerical detergent for aluminum pans etc and it doesn't get the gray coating which is not fun to get off.
Also, the quality of the aluminum - have an old k5a paddle that can go in and doesn't really get eaten up, but the new ones - watch out. Same with a genuine Hobart paddle. I have run those through with regular detergent and they will oxidize a little; not near as much as the generic paddle I bought- must be made of a lower quality aluminum or something. My mom can run her sheet pan through her Kenmore with casade and it doesn't turn - so thinking the quality of the water might have something to do with it as well. Lots of variables here. Ordered the detergent from Kommerical Kitchens - will have to check out what it is specifially, they carry different kinds and post when I get home.

 

[stopmeister72]

high temp detergent

The detergent I use that doesn't turn aluminum is called "high temp detergent" from Kommercial Kitchens 800 -962-1555. The only numbers on the bottle is the patent 5,577,527 and SEA13826. I don't see it on their website any more but maybe they still carry it. Says it is low chlorine for medium soil loads and medium hard water. Oh wait - there is a label on top of the lid with - 47569. I have also ordered a box of full sheet pan parchment from them.

KOMMERCIAL KITCHENS

www.kommercialkitchens.com

 

[sudsmaster]

Chemistry is complex

Complex or polyphosphates corrode aluminum and other metals like brass and copper.

Sodium metasilicate inhibits corrosion of metal components by complex phosphates and other alkaline components. Virtually all dishwasher and

Aluminum phosphate compounds which are not the same as complex phosphates, may paradoxically have a protective effect on ferrous metals. But I doubt that dishwashing detergents contain much if any aluminum phosphate.

 

[sudsmaster]

PS

STPP is less alkaline than, say, sodium carbonate, and therefore MIGHT buffer a dishwashing solution somewhat. So a phosphate free dishwashing detergent might result in a higher pH than a phosphated detergent. In turn, since high alkalinity attacks metals like aluminum, the phosphate free detergent might result in increased metal corrosion if insufficient sodium metasilicate is not present in the detergent as well. But the phosphate isn't really protecting the metal, it's just lowering the pH somewhat (theoretically) which in turn could result in less corrosion.

In any case, most makers of aluminum cookware advise against putting the cookware in a dishwasher regardless of phosphate content of the detergent.