Another one bites the dust

September 10, 2014 4:50 PM

Instead of hand washing as I clearly should have, I ran two toaster oven pans through the dishwasher (bottom rack.) They were a light metal, probably aluminum. When they came out of the dishwasher they were covered in a fine gray/silver dust that came off on fingers and paper towels. The pans did not seem salvageable because the metal dust just kept coming off them. What happened chemically/physically (other than simply the pans breaking down), and is there going to be Bad Metal Dust hanging out in the dishwasher now?
posted by third rail to Home & Garden (5 answers total)

It's just the aluminum version of corrosion or rust. No big deal. I just scrub with a coarse scrubby.
posted by theora55 at 5:05 PM on September 10, 2014

Ya thats what happens when the seasoning or coating comes off the metal. Just oil it up, should be fine. And don't worry about the dishwasher.
posted by rmless at 6:33 PM on September 10, 2014

Best answer: This link has one particularly interesting answer that gets into the chemistry of the aluminum - dishwasher detergent reaction:

Okay, so here's what's happening:

Your dish-washing detergent contains alkaline phosphates. At high pH, the 'passive' aluminum surface dissolves as Na2Al(OH)4 (sodium aluminate). This reveals 'active' metal underneath, which reacts with the phosphates in the water to form aluminum phosphate. Sodium aluminate reacts with sodium phosphate to form sodium aluminum phosphate. Sodium aluminum phosphates precipitate out of the water, and deposit onto the sites along the surface of the aluminum cookware, leaving these powdery spots.

Sodium aluminum phosphate isn't dangerous if you accidentally consume. It's often used as a leavening agent for baking. If you scrub the surface with a Brillo pad, this should be fine to use again.

In the future, try to clean baking sheets by hand; dishwashers provide a corrosive environment for aluminum.

Robert Kinner
- Toledo, Ohio

posted by gimli at 7:09 PM on September 10, 2014 [2 favorites]

Best answer: Aluminum oxidizes really well.

"Modern composite propellants are heterogeneous powders (mixtures) that use a crystallized or finely ground mineral salt as an oxidizer, often ammonium perchlorate, which constitutes between 60% and 90% of the mass of the propellant. The fuel itself is generally aluminum."

A counterintuitive property is that the readiness with which aluminum oxidizes actually protects the underlying layers from further oxidation. As said above just put a lite coating of oil on the pans and I wouldn't worry about the dishwasher at all but run a cycle to ease your fears if you like.
posted by vapidave at 7:11 PM on September 10, 2014 [1 favorite]

Best answer: PS every time you try to take off that gray stuff, it just exposes a new layer of fresh metal and the process will repeat. Eventually you could scrub, oxidize, scrub, oxidize your way all the way down to a sliver of nothing which I think is kind of cool. That would take a long time though since you are only doing it microns at a time.
Uhhh anyway... the point is that it's all just the metal itself so you'll never get it "fully clean" to where it doesn't oxidize anymore unless it has some other protective coating (like oil) on it.
posted by rmless at 8:09 PM on September 10, 2014 [1 favorite]