Wood's metal, also known as Lipowitz's alloy or by the commercial names Cerrobend, Bendalloy, Pewtalloy and MCP 158, is a metal alloy that is useful for soldering and making custom metal parts, but which is toxic to touch or breathe vapors from. The alloy is named for

Barnabas Wood Barnabas Wood (May 17, 1819 in Guilderland, New York – May 30, 1875 in Albany, New York) was an American dentist and inventor best known for his discovery of the fusible alloy known as Wood's metal. It is a eutectic,

fusible alloy A fusible alloy is a metal alloy capable of being easily fused, i.e. easily meltable, at relatively low temperatures. Fusible alloys are commonly, but not necessarily, eutectic alloys. Sometimes the term "fusible alloy" is used to describe alloys ...

of 50%

bismuth Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs ...

, 26.7%

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

, 13.3%

tin Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal. Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...

, and 10%

cadmium Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...

by mass. It has a

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...

of approximately .

Applications

Wood's metal is useful as a low-melting

solder Solder (; NA: ) is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable ...

, low-temperature

casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...

metal, high-temperature coupling fluid in

heat bath In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...

s, and as a fire-melted valve element in

fire sprinkler A fire sprinkler or sprinkler head is the component of a fire sprinkler system that discharges water when the effects of a fire have been detected, such as when a predetermined temperature has been exceeded. Fire sprinklers are extensively use ...

systems in buildings. Medical gas cylinders in the United Kingdom have a Wood's metal seal, which melts in fire, allowing the gas to escape and reducing the risk of

gas explosion A gas explosion is an explosion resulting from mixing a gas, typically from a gas leak, with air in the presence of an ignition source. In household accidents, the principal explosive gases are those used for heating or cooking purposes such as n ...

. Wood's metal is commonly used as a filler when bending thin-walled metal

tubes Tube or tubes may refer to: * ''Tube'' (2003 film), a 2003 Korean film * ''The Tube'' (TV series), a music related TV series by Channel 4 in the United Kingdom * "Tubes" (Peter Dale), performer on the Soccer AM television show * Tube (band), a ...

. For this use the tubing is filled with molten Wood's metal. After this filler solidifies, the tubing is bent. The filler prevents the tube collapsing. The Wood's metal is then removed by heating, often by immersion in boiling water. Other uses include making custom-shaped apertures and blocks (for example, electron-beam cutouts and lung blocks) for medical radiation treatment, making casts of keys that are hard to duplicate otherwise and making metal

inlay Inlay covers a range of techniques in sculpture and the decorative arts for inserting pieces of contrasting, often colored materials into depressions in a base object to form Ornament (art), ornament or pictures that normally are flush with th ...

s in wood. Wood's metal is useful in machine shops and technical laboratories when alternative means of holding delicate parts become necessary. It is used as an additional hardened layer to allow the proper gripping and machining of an object. The object is immersed in melted Wood's metal to completely or partially coat it, forming a layer from a few millimeters up to few centimeters thick, depending on how the object will be held in place. After cooling, the new assembly is clamped by conventional means. This method is most useful for one-off or limited-production workpieces, when construction of a special clamping or holding jig would neither be cost-effective nor offer maximum holding capability. Wood's metal is also useful for repairing antiques. For example, a bent piece of

sheet metal Sheet metal is metal formed into thin, flat pieces, usually by an industrial process. Sheet metal is one of the fundamental forms used in metalworking, and it can be cut and bent into a variety of shapes. Thicknesses can vary significantly; ex ...

may be repaired by casting a Wood's metal die from an intact example: The low melting temperature of Wood's metal makes it unlikely to harm the original, and the damaged piece can then be clamped in the die and slowly tightened to form it back into shape. Wood's metal has long been used by model railroad enthusiasts to add weight to locomotives, increasing traction and the number of cars that can be pulled. Wood’s metal was used for many years in the 1950’s and 1960’s to make gag flatware spoons as a novelty, and used as a practical joke. Given to an unsuspecting diner, the bowl of the spoon, when immersed in hot coffee or other hot drinks, melted and fell into the liquid, much to the amusement of all. Wood's metal is also used in the making of extracellular electrodes for the electro-physiological recording of neural activity. 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 in routine use but are employed for temperatures above . Wood's metal has a

modulus of elasticity An elastic modulus (also known as modulus of elasticity) is the unit of measurement of an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The elastic modulus of an object is ...

of 12.7 GPa and a

yield strength In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and ...

of 26.2 MPa.

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.

Cadmium poisoning Cadmium is a naturally occurring toxic metal with common exposure in industrial workplaces, plant soils, and from smoking. Due to its low permissible exposure in humans, overexposure may occur even in situations where trace quantities of cadmium ...

carries the risk of

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

anosmia Anosmia, also known as smell blindness, is the loss of the ability to detect one or more smells. Anosmia may be temporary or permanent. It differs from hyposmia, which is a decreased sensitivity to some or all smells. Anosmia can be due to a nu ...

(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.

Related alloys

Several other alloys with similar low melting points are listed here.

References

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
{{DEFAULTSORT:Wood's Metal Fusible alloys