Zamak

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Two wheel weights, the upper one has the inscription "Zk" which is the abbreviation for "Zamak", while the lower weight has the inscription "Zn", which is zinc. However, given that wheel weights aren't specialized items that are thoroughly inspected by proper authorities, many manufacturers may choose to add the cheaper zamac for all zinc-based wheel weights, meaning that the second weight could also be zamac alloy, especially if recycled zinc is used.

Zamak (formerly trademarked as ZAMAK), also known as Zamac is a family of zinc alloys widely used in common everyday items. Zamak is most often than not the "mysterious metal" from zippers, buttons, cases, that loses its luster in air rapidly and is brittle.

If you plan to use zamak as source of zinc for your chemical reactions, expect plenty of side products to appear in the reaction flask, as many zamak alloys may also contain other elements, especially if it's low quality.

Composition

Zamak consists of >96% zinc, <4% aluminium, with other metals like magnesium or copper being added. The most common zamak alloy used in North America is Zamak 3, which has a general composition of >95% Zn, 3.5-4.3% Al, 0.25% Cu, 0.05-0.1% Mg, with traces of iron, tin, lead or cadmium. In Europe, Zamak 5 is instead more widely used. It has a composition of >95% Zn, 3.5-4.3% Al, 0.75-1.25 Cu, 0.03-0.08% Mg and traces of other metals like iron or tin.

Properties

Zamak is a silvery alloy, which gets dull in air over time, with an average density around 6.6 g/cm3. It melts between 381—387 °C, has a thermal conductivity between 104-116 W/m·K and electrical resistivity of 6.3.8-6 μΩ/cm, depending on the alloy composition.

Zamak quickly tarnishes in air and reacts with most acids and bases, as well as halogens.

Availability

Zamak can be found in a variety of everyday objects, like buttons, zippers, toys, jewelries, chains, cases, locks, keys, handles, various die-cast parts. Some wheel weights are also made of Zamak rather than zinc, even though both are labelled "Zn".

To differentiate pure zinc from zamak, you can do a density test (pure Zn has 7.14 g/cm3, while zamak is lighter, 6.6 g/cm3) or dissolve the metal in diluted nitric acid. Aluminium does not dissolve in HNO3 and precipitates as aluminium oxide, while copper dissolves, giving the solution a blueish color. Pure zinc dissolves in nitric acid without forming any precipitate. If no blue color is produced, it's possible that what you have there is just some other zinc-aluminium alloy.

Projects

  • Source of elemental Zn in chemistry
  • Cast objects

Handling

Safety

Zamak has low toxicity, though inhaling zinc alloy dust is harmful, and proper protection should be worn when doing metalworking.

Low quality zamak may contain heavy metals like cadmium or lead, and work should be avoided if possible.

Storage

No special storage is required, although it's best to keep the metal in a dry place, as it corrodes easily in contact with corrosive reagents.

Disposal

Zamak items should be taken to waste metal centers.

See also

References

Relevant Sciencemandess threads