Wood's metal
Encyclopedia
Wood's metal, also known as Lipowitz's alloy or by the commercial names cerrobend, bendalloy, pewtalloy or MCP 158, is a eutectic, fusible
alloy
with a melting point
of approximately 70 °C (158 °F). It is a eutectic alloy of 50% bismuth
, 26.7% lead
, 13.3% tin
, and 10% cadmium
by weight. It is named after American metallurgist B. Wood.
, low-temperature casting metal, high temperature coupling fluid in heat baths, and as a fire-melted valve element in fire sprinkler
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 common use is as a filler when bending thin-walled metal tubes
. For this use the tubing is filled with molten Wood's metal. After the filler solidifies the tubing is bent, and the filler prevents collapse of the tubing. The Wood's metal is then removed by heating, often by boiling in water.
Other uses include making custom-shaped apertures and blocks (for example, electron-beam cutouts and lung blocks) for medical radiation treatment, and making metal inlay
s in wood.
Wood's metal is also useful for repairing antiques. For example, a bent piece of sheet metal
may be repaired by casting a Wood's metal die
from a good example. The low melting temperature of Wood's metal makes it unlikely this will harm the original. 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 is also used in the making of extracellular electrode 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 220 °C.
carries the risk 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.
A similar alloy is called cerrosafe. This non-eutectic
alloy melts at 165 °F (74 °C). It is mainly used by gunsmith
s for making a reference casting of the chamber of a firearm
. When it solidifies it first shrinks, allowing easy removal from the chamber. When it cools it expands back to the exact size of the chamber. The casting can then be directly measured with calipers or a micrometer
to determine the dimension of the weapon's chamber, which is important for safety.
Their compositions are as follows:
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....
alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
with a melting point
Melting point
The melting point of a solid 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 depends on pressure and is usually specified at standard atmospheric pressure...
of approximately 70 °C (158 °F). It is a eutectic alloy of 50% bismuth
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
, 26.7% lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, 13.3% tin
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
, and 10% cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
by weight. It is named after American metallurgist B. Wood.
Applications
Wood's metal is useful as a low-melting solderSolder
Solder is a fusible metal alloy used to join together metal workpieces and having a melting point below that of the workpiece.Soft solder is what is most often thought of when solder or soldering are mentioned and it typically has a melting range of . It is commonly used in electronics and...
, low-temperature casting metal, high temperature coupling fluid in heat baths, and as a fire-melted valve element in fire sprinkler
Fire sprinkler
A fire sprinkler system is an active fire protection measure, consisting of a water supply system, providing adequate pressure and flowrate to a water distribution piping system, onto which fire sprinklers are connected...
systems in buildings. Medical gas cylinders in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
have a Wood's metal seal which melts in fire, allowing the gas to escape and reducing the risk of gas explosion
Gas explosion
A gas explosion is an explosion resulting from a gas leak in the presence of an ignition source. The principal explosive gases are natural gas, methane, propane and butane, because they are widely used for heating purposes. However, many other gases like hydrogen, are combustible and have caused...
.
A common use is as a filler when bending thin-walled metal tubes
Tubing
Tubing may refer to:* Tubing , flexible hose or pipe * Tubing , the act of riding an inner tube* Structural tubing* Plumbing tube used in domestic water systems* Inserting a tube* Brass instrument tubing...
. For this use the tubing is filled with molten Wood's metal. After the filler solidifies the tubing is bent, and the filler prevents collapse of the tubing. The Wood's metal is then removed by heating, often by boiling in water.
Other uses include making custom-shaped apertures and blocks (for example, electron-beam cutouts and lung blocks) for medical radiation treatment, and making metal inlay
Inlay
Inlay is a decorative technique of inserting pieces of contrasting, often coloured materials into depressions in a base object to form patterns or pictures that normally are flush with the matrix. In a wood matrix, inlays commonly use wood veneers, but other materials like shells, mother-of-pearl,...
s in wood.
Wood's metal is also useful for repairing antiques. For example, a bent piece of sheet metal
Sheet metal
Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material...
may be repaired by casting a Wood's metal die
Die (manufacturing)
A die is a specialized tool used in manufacturing industries to cut or shape material using a press. Like molds, dies are generally customized to the item they are used to create...
from a good example. The low melting temperature of Wood's metal makes it unlikely this will harm the original. 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 is also used in the making of extracellular electrode for the electro-physiological recording of neural activity.
Like other fusible alloys, e.g. Rose's metal
Rose's metal
Rose's metal, Rose metal or Rose's alloy is a fusible alloy with a low melting point.-Properties:Rose's metal consists of 50% bismuth, 25–28% lead and 22–25% tin; its melting point is . The alloy does not contract on cooling.-Uses:...
, 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 220 °C.
Toxicity
Wood's metal is toxic because it contains lead and cadmium, and therefore contact with the bare skin is thought to be harmful, especially in the molten state. Vapour from cadmium-containing alloys is also known to pose a danger to humans. Cadmium poisoningCadmium poisoning
Cadmium is an extremely toxic metal commonly found in industrial workplaces. Due to its low permissible exposure limit, overexposures may occur even in situations where trace quantities of cadmium are found. Cadmium is used extensively in electroplating, although the nature of the operation does...
carries the risk of cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
, anosmia
Anosmia
Anosmia is a lack of functioning olfaction, or in other words, an inability to perceive odors. Anosmia may be either temporary or permanent. A related term, hyposmia, refers to a decreased ability to smell, while hyperosmia refers to an increased ability to smell. Some people may be anosmic for one...
(loss of sense of smell), and damage to the liver, kidneys, nerves, bones, and respiratory system. Field's metal
Field's metal
Field's metal, or Field's alloy is a fusible alloy that becomes liquid at approximately . It is a eutectic alloy of bismuth, indium, and tin, with the following percentages by weight: 32.5% Bi, 51% In, 16.5% Sn....
is a non-toxic alternative.
The dust may form flammable mixtures with air.
Related alloys
A similar alloy is called cerrosafe. This non-eutectic
Eutectic system
A eutectic system is a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other composition. This composition is known as the eutectic composition and the temperature is known as the eutectic temperature...
alloy melts at 165 °F (74 °C). It is mainly used by gunsmith
Gunsmith
A gunsmith is a person who repairs, modifies, designs, or builds firearms. This occupation is different from an armorer. The armorer primarily maintains weapons and limited repairs involving parts replacement and possibly work involving accurization...
s for making a reference casting of the chamber of a firearm
Firearm
A firearm is a weapon that launches one, or many, projectile at high velocity through confined burning of a propellant. This subsonic burning process is technically known as deflagration, as opposed to supersonic combustion known as a detonation. In older firearms, the propellant was typically...
. When it solidifies it first shrinks, allowing easy removal from the chamber. When it cools it expands back to the exact size of the chamber. The casting can then be directly measured with calipers or a micrometer
Micrometer
A micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...
to determine the dimension of the weapon's chamber, which is important for safety.
Their compositions are as follows:
| Alloy | Melting point | Eutectic? | Bismuth | Lead | Tin | Indium | Cadmium | Thallium |
|---|---|---|---|---|---|---|---|---|
| Rose's metal Rose's metal Rose's metal, Rose metal or Rose's alloy is a fusible alloy with a low melting point.-Properties:Rose's metal consists of 50% bismuth, 25–28% lead and 22–25% tin; its melting point is . The alloy does not contract on cooling.-Uses:... |
98 °C (208 °F) | no | 50% | 25 % | 25% | – | – | – |
| Cerrosafe | 74 °C (165 °F) | no | 49% | 37.7% | 11.3% | – | 8.5% | – |
| Wood's metal | 70 °C (158 °F) | yes | 50% | 26.7% | 13.3% | – | 10% | – |
| Field's metal Field's metal Field's metal, or Field's alloy is a fusible alloy that becomes liquid at approximately . It is a eutectic alloy of bismuth, indium, and tin, with the following percentages by weight: 32.5% Bi, 51% In, 16.5% Sn.... |
62 °C (144 °F) | yes | 32.5% | – | 16.5% | 51% | – | – |
| Cerrolow 136 | 58 °C (136 °F) | yes | 49% | 18% | 12% | 21% | – | – |
| Cerrolow 117 | 47.2 °C (117 °F) | yes | 44.7% | 22.6% | 8.3% | 19.1% | 5.3% | – |
| Bi-Pb-Sn-Cd-In-Tl | 41.5 °C (107 °F) | yes | 40.3 % | 22.2% | 10.7% | 17.7 % | 8.1% | 1.1 % |
External links
- Making your own low-melting point eutectic: Science Toys: A metal that melts in hot water
- Examples of chamber casts using low-temp metal