Phosphor bronze

Phosphor bronze propeller salvaged from 1940s American warship.

Phosphor bronze is an alloy of copper with 3.5 to 10% of tin and a significant phosphorus content of up to 1%. The phosphorus is added as deoxidizing agent during melting.

These alloys are notable for their toughness, strength, low coefficient of friction, and fine grain. The phosphorus also improves the fluidity of the molten metal and thereby improves the castability, and improves mechanical properties by cleaning up the grain boundaries.

Industrial uses

Phosphor bronze is used for springs, bolts and various other items used in situations where resistance to fatigue, wear and chemical corrosion are required (e.g., a ship's propellers in a marine environment). The alloy is also used in some dental bridges.

Grades A, C and E – C51000, 52100, 50700 are commonly used nonferrous spring alloys. The combination of good physical properties, fair electrical conductivity and moderate cost make Phosphor Bronze round, square, flat and special shaped wire desirable for many springs and electrical contacts and a wide variety of wire forms where cost of properties does not prescribe Beryllium copper.

Phosphor Bronze (94.8% copper, 5% tin, 0.2% phosphorus) is also used in cryogenics. In this case the combination of a fair electrical conductivity, and a low thermal conductivity allows to make electrical connection to devices at ultra low temperature without adding an excessive heat load.

Spent nuclear fuel overpack

The CuOFP capsule used as overpack for spent nuclear fuel disposal in the KBS-3 concept (Finnish version).

Oxygen-free copper can be alloyed with phosphorus (CuOFP alloy) to better withstand oxidizing conditions. This alloy has application as thick corrosion-resistant overpack for spent nuclear fuel disposal in deep crystalline rocks.

Musical instruments

Phosphor bronze tenor and soprano saxophones

Acoustic guitar string wrapped with phosphor bronze

Phosphor bronze is used in some metal wind instruments (e.g., the A992 alto saxophone manufactured by Yanagisawa). A saxophone made from phosphor bronze is heavier than one made from brass, due to its higher copper content, which gives greater mass. Phosphor bronze saxophones have distinctive, reddish-orange hues, which look different to the yellow-gold color of standard lacquered brass. In addition to being more robust, phosphor bronze gives musical instruments tonal qualities which are slightly different to those made from the usual brass alloys. For example, although their designs are identical in every way apart from the metal used, the Yanagisawa A992 and T992 (phosphor bronze) alto and tenor saxophones sound noticeably "darker" than the A991 and T991 (brass) versions. However, other variables may affect an instrument's tone colors (e.g., mouthpiece design and physical characteristics of the player).

Additionally, phosphor bronze is sometimes used in brass instruments (e.g., Flugelhorns), plus percussion instruments such as cymbals and snare drums. Some acoustic instrument strings for acoustic guitars, mandolins and violins are wrapped with this metal. Some harmonica reeds are made of phosphor bronze, such as those by the Suzuki Musical Instrument Corporation.

Variants

Further increasing the phosphorus content leads to formation of a very hard compound Cu₃P (copper phosphide), resulting in a brittle form of phosphor bronze, which has a narrow range of applications.

Around 2001, the Olin Corporation developed another phosphor bronze alloy comprising:

• Zinc – 9.9%
• Tin – 2.2%
• Iron – 1.9%
• Phosphorus – 0.03%
• Copper – 85.97%

Olin developed this new alloy for use in electrical and electronic connectors. When assessed in strictly metallurgical terms it is not true phosphor bronze, but a form of iron-modified tin brass.

External links

• Copper and copper alloy microstructures: Phosphor bronze
• Phosphor Bronze: Teaching an Old Dog New Tricks
• National Pollutant Inventory - Copper and compounds fact sheet
• Bauhaus Chinese Saxophones