Wood's metal

Wood's metal (in an ampoule)

Wood's metal, also known as Lipowitz's alloy or by the commercial names Cerrobend, Bendalloy, Pewtalloy and MCP 158, is a fusible metal alloy (having a low melting point) that is useful for soldering and making custom metal parts.<ref name="Moody">Template:Cite book</ref> The alloy is named for Barnabas Wood, who invented and patented the alloy in 1860.<ref>Template:Cite journal</ref><ref name="SCOUT-Wood-papers">Template:Cite web</ref> It is a eutectic alloy of 50% bismuth, 26.7% lead, 13.3% tin, and 10% cadmium by mass. <ref name="Moody" /> It has a melting point of approximately Template:Convert.<ref name="CSTN" >Template:Cite book</ref><ref name="Khan5e" >Template:Cite web</ref> Its fumes are toxic, as well as being toxic on skin exposure.

Applications

Wood's metal (in a visibly solid state)

As suggested by the trade names, Wood's metal is used to fill thin-walled tube so that it can be bent to a radius without kinking or collapsing. The filling is easily melted and run out of the tube after bending is completed. The low melting point and lack of contraction on freezing make Wood's metal suitable for this purpose.

Wood's Metal is also used for making fusible links in the sprinkler heads of commercial building automatic fire sprinkler systems.<ref name="Moody" /> Due to the fire, ambient temperature increases enough to melt the link, releasing the water. A similar use is fusible plugs in boilers.<ref name="Moody" />

Uses also include making custom-shaped apertures and blocks (for example, electron-beam cutouts and lung blocks) for medical radiation treatment, and making casts of keys that are hard to otherwise duplicate.<ref>Template:CitationTemplate:Cbignore</ref><ref>Template:CitationTemplate:Cbignore</ref>

Like other fusible alloys, e.g. Rose's metal, Wood's metal can be used as a heat-transfer medium in hot baths. Hot baths with Rose's and Wood's metals are not used routinely but are employed at temperatures above Template:Convert.<ref>Template:Cite book</ref>

At room temperature, Wood's metal has a modulus of elasticity of 12.7 GPa and a yield strength of 26.2 MPa.<ref>Template:Cite journal</ref>

Toxicity

Wood's metal is toxic because it contains lead and cadmium, and contamination of bare skin is considered harmful. Vapour from cadmium-containing alloys is also known to pose a danger to humans.<ref name="Flinn_SDS"/> Cadmium poisoning carries the risk<ref>Template:Cite journal</ref> of cancer, anosmia (loss of sense of smell), and damage to the liver, kidneys, nerves, bones, and respiratory system. Field's metal is a non-toxic alternative.

The dust may form flammable mixtures with air.<ref name="Flinn_SDS">Template:Cite web</ref>

Bibliography

• Birchon's Dictionary of Metallurgy, London, 1965
• Experimental techniques in low-temperature physics, G. K. White, Oxford University Press, Third Edition

External links

• Making your own low-melting point eutectic: Science Toys: A metal that melts in hot water
• Burdakin et al., "Melting points of gallium and of binary eutectics with gallium", Metrologia, 2008