Metal finishing Q&As since 1989

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Tin Plating or Aluminum

 

We are a small mail order toy company. A new product we are considering is a "tin" plated bakeware set available from one of our German vendors. One of our competing American vendors claims that all "tin" plated products are actually aluminum coated or plated. Is there any truth to this claim. Is there a way to test the plating material; are there any standards (ASTM or otherwise) that we can ask vendors to adhere to; and equally important to us, are there any health risks associated with children using either tin plated items.

William McDonald
Magic Cabin Dolls - Viroqua, Wisconsin

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Tinplate is usually considered to be steel coated with tin. If it is tinplate the metal will almost certainly be magnetic. If it is aluminium, it will not be magnetic unless it is some very expensive bakeware. Electrodepositing tin onto steel is very easy, but aluminium is very difficult. Both metals can be dip coated, where the article is dipped into a vat of molten metal, but again this is usually only done with tin, as it has a lower melting point(232C compared with 657C). If it is tinplate, the tin will slowly migrate into the steel with use at high temperatures and form a dark grey to black film. This is an intermetallic compound (FeSn2) and is harmless. In Europe the majority of bakeware is tinplate or stainless steel because of the high reflectance both metals will (initially) offer. Aluminium, on the other hand, is much more dull.

I am not acquainted with US standards, so I cannot answer your question on that. However, as far as harm to children is concerned, I would consider tinplate to be absolutely safe with the caveat that any soldered joints are done with lead-free solder. In the UK (and I presume Europe) for many years it has been illegal to use leaded solder on any food container that will contain children's or baby food. European food hygiene standards are generally some of the best in the world so I would not be remotely concerned about any harm coming to any children or even adults.

There is a lot of nonsense talked about the effects of metals and aluminium has had its own share of rubbish. Not wanting to start a hare running, but some years ago there was speculation (later almost shown to be almost certainly incorrect) that Alzheimers Disease was associated with increased levels of aluminium in the brain. There was even a brief campaign to avoid using aluminium cookware, but thankfully the follies of this little soiree were quickly seen and ignored. As far as I am aware, there is NO EVIDENCE WHATSOEVER to support the claims against aluminium, but no doubt someone will recall the debate and may even believe it!

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
 

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