Fusible alloy

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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.

Contents

Sometimes the term "fusible alloy" is used to describe alloys with a melting point below 183 °C (361 °F; 456 K). Fusible alloys in this sense are used for solder.

Introduction

Fusible alloys are typically made from low melting metals. There are 14 low melting metallic elements that are stable for practical handling. These are in 2 distinct groups: The 5 alkali metals have 1 s electron and melt between +181 (Li) and +28 (Cs) Celsius; The 9 poor metals have 10 d electrons and from none (Zn, Cd, Hg) to three (Bi) p electrons, they melt between -38 (Hg) and +419 (Zn) Celsius. From a practical view, low-melting alloys can be divided into the following categories:

A practical reason here is that the chemical behaviour of alkali metals is very distinct from poor metals. Of the 9 poor metals Hg (mp -38 C) and Ga (mp +29 C) have each their distinct practical issues, and the remaining 7 poor metals from In (mp +156 C) to Zn (mp +419 C) can be viewed together. Of elements which might be viewed as related but do not share the distinct properties of poor metals: Po is estimated to melt at 254 C and might be poor metal by properties but is too radioactive (longest halflife 125 years) for practical use; At same reasoning as Po; Sb melts at 630 C and is regarded as semimetal rather than poor metal; Te is also regarded as semimetal not poor metal; of other metals, next lowest melting point is Pu, but its melting point at 640 Celsius leaves a 220 degree gap between Zn and Pu, thus making the "poor metals" from In to Zn a natural group.

Some reasonably well-known fusible alloys are Wood's metal, Field's metal, Rose metal, Galinstan, and NaK.

Applications

Melted fusible alloys can be used as coolants 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 metal such as indium or sodium. Metals with low neutron cross-section are used for cooling nuclear reactors.

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 sprinklers 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. [1]

Bismuth on solidification expands by about 3.3% by volume. Alloys with at least half of bismuth display this property too. [2] This can be used for mounting of small parts, e.g. for machining, as they will be tightly held.[ citation needed ]

Low-melting alloys and metallic elements

Well-known alloys

AlloyMelting point Eutectic? Bismuth
%
Lead
%
Tin
%
Indium
%
Cadmium
%
Thallium
%
Gallium
%
Antimony
%
Rose's metal 98 °C (208 °F)no502525
Cerrosafe 74 °C (165 °F)no42.537.711.38.5
Wood's metal 70 °C (158 °F)yes5026.713.310
Field's metal 62 °C (144 °F)yes32.516.551
Cerrolow 136 58 °C (136 °F)yes49181221
Cerrolow 117 47.2 °C (117 °F)yes44.722.68.319.15.3
Bi-Pb-Sn-Cd-In-Tl41.5 °C (107 °F)yes40.322.210.717.78.11.1
Gallium 30.0 °C (86 °F)Pure metal------100
Galinstan −19 °C (−2 °F)no<1.59.5–10.521–2268–69<1.5

Other alloys

Starting with a table of component elements and selected binary and multiple systems ordered by melting point:

Low melting alloys and metallic elements
Composition in weight-percentMelting pointEutectic?Name or remark
Cs 73.71, K 22.14, Na 4.14 [3] −78.2 °C
(−108.8 °F)
yes"CsNaK", reactive with water and air
Hg 91.5, Tl 8.5−58 °C
(−72 °F)
yesused in low-reading thermometers
Hg 100−38.8 °C
(−37.8 °F)
(yes)
Cs 77.0, K 23.0−37.5 °C
(−35.5 °F)
K 76.7, Na 23.3−12.7 °C
(9.1 °F)
yes
K 78.0, Na 22.0−11 °C
(12 °F)
no NaK
Ga 61, In 25, Sn 13, Zn 18.5 °C
(47.3 °F)
yes
Ga 62.5, In 21.5, Sn 16.010.7 °C
(51.3 °F)
yes Galinstan alloy
Ga 69.8, In 17.6, Sn 12.510.8 °C
(51.4 °F)
noGalinstan alloy
Ga 68.5, In 21.5, Sn 1011 °C
(52 °F)
noGalinstan alloy
Ga 75.5, In 24.515.7 °C
(60.3 °F)
yes
Cs 10028.6 °C
(83.5 °F)
(yes)
Ga 10029.8 °C
(85.6 °F)
(yes)
Rb 10039.30 °C
(102.74 °F)
(yes)
Bi 40.3, Pb 22.2, In 17.2, Sn 10.7, Cd 8.1, Tl 1.141.5 °C
(106.7 °F)
yes
Bi 40.63, Pb 22.1, In 18.1, Sn 10.65, Cd 8.246.5 °C
(115.7 °F)
Bi 44.7, Pb 22.6, In 19.1, Cd 5.3, Sn 8.347 °C
(117 °F)
yes Cerrolow 117. Used as a solder in low-temperature physics. [4]
Bi 49, Pb 18, In 21, Sn 1258 °C
(136 °F)
ChipQuik desoldering alloy. [5] Cerrolow 136. Slightly expands on cooling, later shows slight shrinkage in couple hours afterwards. Used as a solder in low-temperature physics. [4] Lens Alloy 136, used for mounting lenses and other optical components for grinding. [6] Used for mounting small delicate oddly-shaped components for machining.
Bi 32.5, In 51.0, Sn 16.560.5 °C
(140.9 °F)
yes Field's metal
K 10063.5 °C
(146.3 °F)
(yes)
Bi 50, Pb 26.7, Sn 13.3, Cd 1070 °C
(158 °F)
yesCerrobend. Used in low-temperature physics as a solder. [4]
Bi 49.5, Pb 27.3, Sn 13.1, Cd 10.170.9 °C
(159.6 °F)
yes Lipowitz's alloy
Bi 50.0, Pb 25.0, Sn 12.5, Cd 12.571 °C
(160 °F)
yes Wood's metal
In 66.3, Bi 33.772 °C
(162 °F)
yes [7]
Bi 42.5, Pb 37.7, Sn 11.3, Cd 8.574 °C
(165 °F)
noCerrosafe
Bi 57, In 26, Sn 1779 °C
(174 °F)
yes [7]
Bi 54, In 29.7, Sn 16.381 °C
(178 °F)
yes [7]
Bi 56, Sn 30, In 1479–91 °C
(174–196 °F)
noChipQuik desoldering alloy, lead-free
Bi 50, Pb 30, Sn 20, Impurities92 °C
(198 °F)
noLichtenberg's alloy, [8] also called Onions' Fusible Alloy [9]
Bi 52.5, Pb 32.0, Sn 15.595 °C
(203 °F)
yes
Bi 52, Pb 32.0, Sn 1696 °C
(205 °F)
yesBi52. Good fatigue resistance combined with low melting point. Reasonable shear strength and fatigue properties. Combination with lead-tin solder may dramatically lower melting point and lead to joint failure. [10]
Bi 50.0, Pb 31.2, Sn 18.897 °C
(207 °F)
no Newton's metal
Na 10097.8 °C
(208.0 °F)
(yes)
Bi 50.0, Pb 28.0, Sn 22.094–98 °C
(201–208 °F)
no Rose's metal
Bi 55.5, Pb 44.5125 °C
(257 °F)
yes
Bi 58, Sn 42138 °C
(280 °F)
yesBi58. Reasonable shear strength and fatigue properties. Combination with lead-tin solder may dramatically lower melting point and lead to joint failure. [10] Low-temperature eutectic solder with high strength. [11] Particularly strong, very brittle. [12] Used extensively in through-hole technology assemblies in IBM mainframe computers where low soldering temperature was required. Can be used as a coating of copper particles to facilitate their bonding under pressure/heat and creating a conductive metallurgical joint. [13] Sensitive to shear rate. Good for electronics. Used in thermoelectric applications. Good thermal fatigue performance. Yield strength 7,119 psi (49.08 MPa), tensile strength 5,400 psi (37 MPa). [14]
Bi 57, Sn 43 [15] 139 °C
(282 °F)
yes
In 100157 °C
(315 °F)
(yes)In99. Used for die attachment of some chips. More suitable for soldering gold, dissolution rate of gold is 17 times slower than in tin-based solders and up to 20% of gold can be tolerated without significant embrittlement. Good performance at cryogenic temperatures. [16] Wets many surfaces incl. quartz, glass, and many ceramics. Deforms indefinitely under load. Does not become brittle even at low temperatures. Used as a solder in low-temperature physics, will bond to aluminium. Can be used for soldering to thin metal films or glass with an ultrasonic soldering iron. [4]
Li 100180.5 °C
(356.9 °F)
(yes)
Sn 62.3, Pb 37.7183 °C
(361 °F)
yes
Sn 63.0, Pb 37.0183 °C
(361 °F)
noEutectic solder. Sn63, ASTM63A, ASTM63B. Common in electronics; exceptional tinning and wetting properties, also good for stainless steel. One of the most common solders. Low cost and good bonding properties. Used in both SMT and through-hole electronics. Rapidly dissolves gold and silver, not recommended for those. [11] Sn60Pb40 is slightly cheaper and is often used instead for cost reasons, as the melting point difference is insignificant in practice. On slow cooling gives slightly brighter joints than Sn60Pb40. [17]

Yield strength 3,950 psi (27.2 MPa), tensile strength 4,442 psi (30.63 MPa). [18]

Sn 91.0, Zn 9.0198 °C
(388 °F)
yesKappAloy9 Designed specifically for Aluminum-to-Aluminum and Aluminum-to-Copper soldering. It has good corrosion resistance and tensile strength. Lies between soft solder and silver brazing alloys, thereby avoiding damage to critical electronics and substrate deformation and segregation. Best solder for Aluminum wire to Copper busses or Copper wire to Aluminum busses or contacts. [19] UNS#: L91090
Sn 92.0, Zn 8.0199 °C
(390 °F)
no Tin foil
Sn 100231.9 °C
(449.4 °F)
(yes)Sn99. Good strength, non-dulling. Use in food processing equipment, wire tinning, and alloying. [20] Susceptible to tin pest.
Bi 100271.5 °C
(520.7 °F)
(yes)Used as a non-superconducting solder in low-temperature physics. Does not wet metals well, forms a mechanically weak joint. [4]
Tl 100304 °C
(579 °F)
(yes)
Cd 100321.1 °C
(610.0 °F)
(yes)
Pb 100327.5 °C
(621.5 °F)
(yes)
Zn 100419.5 °C
(787.1 °F)
(yes)For soldering aluminium. Good wettability of aluminium, relatively good corrosion resistance. [21]

Then organized by practical group and alphabetic symbols of components: Most of the pairwise phase diagrams of 2 component metal systems have data available for analysis, like at https://himikatus.ru/art/phase-diagr1/diagrams.php Taking the pairwise alloys of the 7 poor metals other than Hg and Ga, and ordering the pairs (total 21) by alphabetic of these elements Bi, Cd, In, Pb, Sn, Tl, Zn are as follows:

Considering the binary systems between alkali metals: Li only has appreciable solubility in pair

The other three alkali metals:

practically do not dissolve Li even when liquid and therefore their melting points are not lowered by presence of Li Na is in liquid phase miscible with all three heavier alkali metals, but on freezing forms intermetallic compounds and eutectics:

The 3 binary systems between the three heavier alkali metals are all miscible in solid at melting point, but all form poor solid solutions that have melting point minima. This is distinct from eutectic: at eutectic point, two solid phases coexist, and close to eutectic point, the liquidus temperature rises rapidly as just one separates, whereas at poor solid solution melting point minimum, there is a single solid phase, and away from the minimum the liquidus temperature rises only slowly.

See also

Related Research Articles

<span class="mw-page-title-main">Solder</span> Alloy used to join metal pieces

Solder 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 for use as solder should have a lower melting point than the pieces to be joined. The solder should also be resistant to oxidative and corrosive effects that would degrade the joint over time. Solder used in making electrical connections also needs to have favorable electrical characteristics.

<span class="mw-page-title-main">Tin</span> Chemical element with atomic number 50 (Sn)

Tin is a chemical element; it has symbol Sn and atomic number 50. A silvery-colored 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, the so-called "tin cry" can be heard as a result of twinning in tin crystals.

<span class="mw-page-title-main">Eutectic system</span> Mixture with a lower melting point than its constituents

A eutectic system or eutectic mixture is a type of a homogeneous mixture that has a melting point lower than those of the constituents. The lowest possible melting point over all of the mixing ratios of the constituents is called the eutectic temperature. On a phase diagram, the eutectic temperature is seen as the eutectic point.

<span class="mw-page-title-main">Brazing</span> Metal-joining technique

Brazing is a metal-joining process in which two or more metal items are joined by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal.

In chemistry, a reactivity series (or reactivity series of elements) is an empirical, calculated, and structurally analytical progression of a series of metals, arranged by their "reactivity" from highest to lowest. It is used to summarize information about the reactions of metals with acids and water, single displacement reactions and the extraction of metals from their ores.

<span class="mw-page-title-main">Wood's metal</span> Alloy of bismuth, lead, tin and cadmium

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 its fumes are toxic, as well as being toxic on skin exposure. The alloy is named for Barnabas Wood, who invented and patented the alloy in 1860. It is a eutectic, fusible alloy of 50% bismuth, 26.7% lead, 13.3% tin, and 10% cadmium by mass. It has a melting point of approximately 70 °C (158 °F).

<span class="mw-page-title-main">Galinstan</span> Alloy that is liquid at room temperature

Galinstan is a brand name for an alloy composed of gallium, indium, and tin which melts at −19 °C (−2 °F) and is thus liquid at room temperature. In scientific literature, galinstan is also used to denote the eutectic alloy of gallium, indium, and tin, which melts at around +11 °C (52 °F). The commercial product Galinstan is not a eutectic alloy, but a near eutectic alloy. Additionally, it likely has added flux to improve flowability, to reduce melting temperature, and to reduce surface tension.

Field's metal, also known as Field's alloy, is a fusible alloy that becomes liquid at approximately 62 °C (144 °F). It is named after its inventor, Simon Quellen Field. It is a eutectic alloy of bismuth, indium, and tin, with the following mass fractions: 32.5% Bi, 51% In, 16.5% Sn.

<span class="mw-page-title-main">Soldering</span> Process of joining metal pieces with heated filler metal

Soldering is a process of joining two metal surfaces together using a filler metal called solder. The soldering process involves heating the surfaces to be joined and melting the solder, which is then allowed to cool and solidify, creating a strong and durable joint.

<span class="mw-page-title-main">Liquid metal</span> Metal or alloy that is liquid at room temperature

A liquid metal is a metal or a metal alloy which is liquid at or near room temperature.

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<span class="mw-page-title-main">Post-transition metal</span> Category of metallic elements

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<span class="mw-page-title-main">Bismuth–indium</span>

The elements bismuth and indium have relatively low melting points when compared to other metals, and their alloy bismuth–indium (Bi–In) is classified as a fusible alloy. It has a melting point lower than the eutectic point of the tin–lead alloy. The most common application of the Bi-In alloy is as a low temperature solder, which can also contain, besides bismuth and indium, lead, cadmium, and tin.

<span class="mw-page-title-main">Solder alloys</span>

Solder is a metallic material that is used to connect metal workpieces. The choice of specific solder alloys depends on their melting point, chemical reactivity, mechanical properties, toxicity, and other properties. Hence a wide range of solder alloys exist, and only major ones are listed below. Since early 2000s the use of lead in solder alloys is discouraged by several governmental guidelines in the European Union, Japan and other countries, such as Restriction of Hazardous Substances Directive and Waste Electrical and Electronic Equipment Directive.

Selenogallates are chemical compounds which contain anionic units of selenium connected to gallium. They can be considered as gallates where selenium substitutes for oxygen. Similar compounds include the thiogallates and selenostannates. They are in the category of chalcogenotrielates or more broadly chalcogenometallates.

Selenidogermanates are compounds with anions with selenium bound to germanium. They are analogous with germanates, thiogermanates, and telluridogermanates.

While chemically pure materials have a single melting point, chemical mixtures often partially melt at the solidus temperature (TS or Tsol), and fully melt at the higher liquidus temperature (TL or Tliq). The solidus is always less than or equal to the liquidus, but they need not coincide. If a gap exists between the solidus and liquidus it is called the freezing range, and within that gap, the substance consists of a mixture of solid and liquid phases (like a slurry). Such is the case, for example, with the olivine (forsterite-fayalite) system, which is common in Earth's mantle.

References

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Further reading