Brass

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Brass is the name given to the most common copper-zinc alloy. Due to its properties and performance, it is widely used in mechanic and electric devices, as well as many common objects and installations.

Composition

Common brass alloys are comprised of 55-80% copper and 45-15% zinc, with the rest being either lead, aluminium or silicon. Nickel and tin brasses are sometimes encountered. Nickel-containing brass (NOT nickel-plated) is easy to tell apart from normal brass, as it's slightly magnetic.

Properties

Copper-zinc system phase diagram.

Brass is a straw-yellow metallic alloy, with a density between 8.4 - 8.73 g/cm3 and a melting point of 900 to 940 °C, both of these properties depend on the alloy. Brass is malleable, though this property is heavily influenced by its composition.

Brass will form a protective coating of zinc oxide/carbonate which protects it from further oxidation. Presence of aluminium in brass will improve the passivation.

Similar to copper, brass does not spark when struck or cut with an angle grinder, making it useful in applications where fire can be a hazard.

Brass is slowly attacked by ammonia, forming a deep blue solution of tetraamine copper complex.

Many acids, such as hydrochloric acid or sulfuric acid will only dissolve the zinc from the brass, exposing the copper. Strong bases will achieve a similar effect. Oxidizers like diluted nitric acid will dissolve both the copper and zinc from brass.

Elemental mercury will attack brass by forming an amalgam with zinc.

Availability

Brass is available in all hardware stores in a variety of forms, such as pipes, fittings, tools, toys, decorations, handles, etc.

Scrap brass can be obtained from discarded or damaged items, such as fittings, pipes, old door handles, water taps, padlocks, various musical instruments, heating element shells, old light bulb screw head connectors, etc. It can also be salvaged from various old electronic components, such as: heat sinks, pin connectors, device frames, bolts and screws, sockets, electric contact supports, etc.

If you live in US or have access to a shooting range, empty brass shells are also a good source.

Due to its price, scrap brass is preferable, though if you need a specific brass alloy, you will have to purchase it.

Melting brass is a bit more difficult than melting aluminium, lead or zinc in a makeshift foundry due to its high melting point, but it's perfectly possible to melt brass at home using a homemade furnace.

Preparation

Brass can be made by melting together zinc with copper in the desired proportions. This is complicated by the fact that zinc's boiling point (907 °C) is lower than copper's melting point (1085 °C). Thus, the copper must first be melted and the zinc then added. Some of the zinc will immediately boil, resulting in a "flare-up" with green fire and white zinc oxide smoke, and some will alloy into the copper. It is necessary to add excess zinc to account for such losses. Once alloyed, the zinc is much more stable (but will still fume off somewhat). The alloy should then be vigorously stirred to homogenize the metal.

To limit zinc boil-off, careful temperature control is beneficial. Adding zinc just after the copper has melted seems to limit boiling considerably. Use of a cover flux (such as borax) may also be helpful.

Projects

  • Cast good looking metal objects
  • Make objects resistant to sea water
  • Source of copper and zinc

Handling

Safety

Being a copper alloy, brass has antimicrobial properties, though the passivation layer it produces reduces its effectiveness.

Old types of brass tended to have lead, which is harmful.

When brass is molten, such as when making brass alloys from scratch or casting scrap brass, white fumes of zinc oxide are released. These can cause metal fume fever, a flu-like condition that may last several days. NIOSH recommends at least an N95 particulate respirator for zinc oxide fumes.[1] This should be worn in addition to any heat protection equipment when working with molten metals.

Storage

Brass objects should be kept away from acids and ammonia.

Disposal

Brass is best recycled.

See also

References

Relevant Sciencemadness threads