A fusible alloy is a
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...
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 with 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 ...
below . Fusible alloys in this sense are used for
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 ...
.
Introduction
From a practical view, low-melting
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...
s can be divided into the following categories:
*
Mercury-containing alloys
*Only
alkali metal-containing alloys
*
Gallium-containing alloys (but neither alkali metal nor mercury)
*Only
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 ...
,
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 ...
,
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 ...
,
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 ...
,
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
,
indium
Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts ...
, and sometimes
thallium
Thallium is a chemical element with the symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists William Crookes an ...
-containing alloys
*Other alloys (rarely used)
Some reasonably well-known fusible alloys are
Wood's metal,
Field's metal,
Rose metal
Rose's metal, Rose metal or Rose's alloy is a fusible alloy with a low melting point.
Rose's metal consists of 50% bismuth, 25–28% lead and 22–25% tin. Its melting point is between . The alloy does not appreciably contract or expand on solidi ...
,
Galinstan, and
NaK.
Applications
Melted fusible alloys can be used as
coolant
A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosi ...
s as they are stable under heating and can give much higher thermal conductivity than most other coolants; particularly with alloys made with a high
thermal conductivity
The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa.
Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
metal such as
indium
Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts ...
or
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
. Metals with low
neutron cross-section
In nuclear physics, the concept of a neutron cross section is used to express the likelihood of interaction between an incident neutron and a target nucleus. The neutron cross section σ can be defined as the area in cm2 for which the number of ...
are used for cooling
nuclear reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...
s.
Such alloys are used for making the fusible plugs inserted in the furnace crowns of
steam boilers, as a safeguard in the event of the water level being allowed to fall too low. When this happens the plug, being no longer covered with water, is heated to such a temperature that it melts and allows the contents of the boiler to escape into the furnace. In automatic
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 ...
s the orifices of each sprinkler is closed with a plug that is held in place by fusible metal, which melts and liberates the water when, owing to an outbreak of fire in the room, the temperature rises above a predetermined limit.
Bismuth on cooling expands by about 3.3% by volume. Alloys with at least half of bismuth display this property too. This can be used for mounting of small parts, e.g. for machining, as they will be tightly held.
Low melting alloys and metallic elements
Well known alloys
Other alloys
(see also
solder alloys)
See also
*
Liquid metal
A liquid metal is a metal or a metal alloy which is liquid at or near room temperature.
The only stable liquid elemental metal at room temperature is mercury (Hg), which is molten above −38.8 °C (234.3 K, −37.9 °F). Three more ...
*
List of elements by melting point
This is a list of the 118 chemical elements which have been identified as of 2022. A chemical element, often simply called an element, is a type of atom which has the same number of protons in its atomic nucleus (i.e., the same atomic number, or ' ...
References
Further reading
*
*Weast, R.C., "CRC Handbook of Chemistry and Physics", 55th ed, CRC Press, Cleveland, 1974, p. F-22
External links
Fusible (Low Temp) Alloys
Archived fro
on 2012-10-12.
Jenson, W.B. "Ask the Historian - Onion's fusible alloy"
{{Webarchive, url=https://web.archive.org/web/20160304023444/http://www.che.uc.edu/Jensen/W.%20B.%20Jensen/Reprints/178.%20Fusible%20Alloys.pdf , date=2016-03-04
Coolants