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bismuth bronze
Bismuth bronze or "Bismuth brass" is a copper alloy which typically contains 1-3% Bismuth by weight, although some alloys contain over 6% Bi. This bronze alloy is very corrosion-resistant, a property which makes it suitable for use in environments such as the ocean. Bismuth bronzes and brasses are more malleable, thermally conductive, and polish better than regular brasses. The most common industrial application of these metals are as bearings, however the material has been in use since the late nineteenth century as kitchenware and mirrors. Bismuth bronze was also found in ceremonial Inca knives at Machu Picchu. Recently, pressure for the substitution of hazardous metals has increased and with it bismuth bronze is being marketed as a green alternative to leaded bronze bearings and bushes.
==History==
The earliest known artifact containing bismuth bronze is an Inca knife from Peru, found in 1912. Whether the alloy was chosen because of metallurgical properties which facilitated casting or because of its whiter, more lustrous finish is a matter of conjecture. It is unlikely that the inclusion of the bismuth was accidental, as was likely the case for most other early bronzes which contained bismuth, which makes this the earliest evidence of intentional addition of Bismuth to an alloy.〔
Bismuth bronze was rediscovered in the 1880s by James Webster for telegraph wires. Webster developed two bismuth-tin-bronze alloys. One alloy was developed as an early attempt at producing corrosion-resistant bronze, and was described as "hard, tough, and sonorous." Webster also indicated that this particular alloy was also well suited to piano wires. Another early Webster alloy was described as "durable and bright" and later used in kitchenware due to its luster and slow tarnishing. This particular alloy's ability to hold polish made it useful as a light reflector or mirror material as well, which it continued to be used for into the twentieth century
In the 1990s, autoparts manufacturer Federal Mogul began developing Bismuth Bronzes as an alternative to lead-containing bronzes because of increasing pressure on the removal of lead from both consumer and industrial applications. Bismuth is a non-toxic heavy metal, and as legislation such as the EU Restriction of Hazardous Substances or the American Reduction of Lead in Drinking Water Act continue to regulate the amount of lead that can be in a product or environment, more lead-free alternative materials have been developed which maintain properties of their lead predecessors without containing Pb. Bismuth is an especially appropriate replacement for lead leaded bronze bearings because, like lead, Bi is insoluble in copper and forms similar micro-globules that mimic lead.
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