Bronze

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A bronze disc from a machine part and a poorly cast bronze eagle

Bronze is an alloy consisting primarily of copper alloyed with about 12% tin. Like brass, it is widely used in the construction of various metallic items and machine parts.

Composition

Bronze consists of 88-90% copper and 10-12% tin. Bronze are often alloyed with other elements, such as metals (aluminium, beryllium, lead, manganese, nickel, zinc) and sometimes non-metals or metalloids (arsenic, phosphorus, silicon).

Properties

Bronze is a reddish-brown metallic alloy with a dark luster, hard and brittle. It has a density between 7.4 - 8.9 g/cm3 depending on the tin content and other elements present. It melts between 900-950 °C, temperature low enough that it allows it to be cast in a home backyard. Bronze is non-magnetic, though nickel bronze is magnetic and is easy to tell apart from other bronze alloys by using a magnet.

Like brass, bronze is resistant to air oxidation and sea water attack by forming a protective oxide coating which prevents further corrosion. Hydrohalic acids attack bronze in the presence of oxygen, while sulfuric acid attacks it slowly. Bronze is readily attacked by nitric and perchloric acids. Elemental mercury attacks bronze.

Availability

Bronze items can be salvaged from various machine parts, such as bearings, frames, electric contact stems, boat parts, or more common items, such as bells, fittings, musical instruments, valves, zippers (not all bronze-colored though!), etc. Some old kids toys, such as some Kinder metal figurines are made of bronze.

Bronze bars and ingots can also be purchased from various metal suppliers, though being a copper alloy, bronze can be quite pricey.

Powdered bronze is available in most hardware stores as suspension in lacquer. Removal of liquid is difficult, but not impossible. It is also sold by many art hobby stores, without solvent. Make sure to check if the powder is metallic bronze, as some may be cheap imitation.

Projects

  • Cast bronze objects
  • Source of elemental copper
  • Make flash powders (powder)

Handling

Safety

Being a copper alloy, bronze displays anti-bacterial effects, though the presence of the passivation layer limits its potency.

Arsenic bronze is irritant to touch and inhaling its powdered form may lead to arsenic poisoning.

Storage

Bronze items should be kept away from corrosive vapors.

Disposal

Bronze should be taken to metal recycling centers. Bronze leftovers aren't toxic and can be discarded with normal trash. Avoid dumping arsenic bronze though.

See also

References

Relevant Sciencenamdenss threads