10
$\begingroup$

These will melt - metal zip tags and belt buckles

Metal zipper tags and belt buckles melt very easily and can be melted by heating it in the stove for 5 minutes. But other metals like aluminium refuse to melt even after hours.

If you leave it overnight, it dissolves pretty well in vinegar. I am sure they are made of metal, as I've melted it and cast some metal cookies. The metal is denser than aluminium, shiny when molten and cast, but surface tarnishes after 1-2 hours. I'm guessing it is some type of a zinc alloy.

The metal of the zip tag has the following characterisitics:

  • silvery
  • tarnishes into a dark gray
  • does not colour a flame in odd colours (like red , crimson , green etc.)
  • malleable (easy to bend a 5 mm thick square just by using leverage of hands and a surface to press down on)
  • brittle if bent a couple of times.
  • melts in a few minutes

So, what alloy or metal are they made of?

$\endgroup$
1
  • 1
    $\begingroup$ Possibly Woods Metal which is one of several low melting point alloys, see Wikipedia. $\endgroup$
    – porphyrin
    May 9, 2018 at 10:00

1 Answer 1

5
$\begingroup$

You were right, these are zinc alloys commonly used for making zips and stuff. It is called Zamak which contains:

Zinc (Zn): Around 90% by weight
Aluminum (Al): Around 4% by weight
Magnesium (Mg): Around 4% by weight
Copper (Cu): Around 2% by weight

It is used because it is resistant to corrosion, cost effective, as you've mentioned malleability (can be moulded into shapes for designs) and last but not the least it can be coated with other metals like nickel and chrome for shine, antimicrobial properties etc.

As you have mentioned Zamak whose melting point is at around 385-410°C (725-770°F), which is relatively less for metal alloys.

Now coming to the tarnishing part, it is said to tarnish into a dark grey colour within a couple hours in contact with atmosphere due to the reaction between atmospheric oxygen and zinc present in the alloy.

2Zn + O2 → 2ZnO [dark grey]

But based on the specific environmental conditions, there can be formation of zinc hydroxide (Zn(OH)2) and zinc carbonate (ZnCO3), which can contribute to the overall tarnishing of the alloy.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.