Fusible alloy

Key takeaways

Fusible alloy belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Fusible alloy to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Fusible alloy from memory before moving on to harder problems.

Reference excerpt

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 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:

Mercury-containing alloys Only alkali metal-containing alloys Gallium-containing alloys (but neither alkali metal nor mercury) Only bismuth, lead, tin, cadmium, zinc, indium, and sometimes thallium-containing alloys Other alloys (rarely used) 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. Bismuth on solidification 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

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

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:

Bi-Cd https://himikatus.ru/art/phase-diagr1/Bi-Cd.php simple eutectic (Bi at 271 C, Cd at 321, eutectic at 146) Bi-In https://himikatus.ru/art/phase-diagr1/Bi-In.php has ordered phases, eutectic at +72 - in table above Bi-Pb https://himikatus.ru/art/phase-diagr1/Bi-Pb.php eutectic at +125 - in table above Bi-Sn https://himikatus.ru/art/phase-diagr1/Bi-Sn.php eutectic at +139 - in table above Bi-Tl https://himikatus.ru/art/phase-diagr1/Bi-Tl.php an intermetallic alloy and the lower melting eutectic at +188 Bi-Zn https://himikatus.ru/art/phase-diagr1/Bi-Zn.php eutectic at +255 Cd-In https://himikatus.ru/art/phase-diagr1/Cd-In.php eutectic at +128 Cd-Pb https://himikatus.ru/art/phase-diagr1/Cd-Pb.php eutectic at +248 Cd-Sn https://himikatus.ru/art/phase-diagr1/Cd-Sn.php eutectic at +176 Cd-Tl https://himikatus.ru/art/phase-diagr1/Cd-Tl.php eutectic at +204 Cd-Zn https://himikatus.ru/art/phase-diagr1/Cd-Zn.php eutectic at +266 In-Pb https://himikatus.ru/art/phase-diagr1/In-Pb.php is NOT eutectic because Pb solid solution in In only raises melting point In-Sn https://himikatus.ru/art/phase-diagr1/In-Sn.php eutectic at +120 In-Tl https://himikatus.ru/art/phase-diagr1/In-Tl.php also NOT eutectic because Tl solid solution in In raises melting point In-Zn https://himikatus.ru/art/phase-diagr1/In-Zn.php eutectic at +143 Pb-Sn https://himikatus.ru/art/phase-diagr1/Pb-Sn.php eutectic at +183 - in table above Pb-Tl https://himikatus.ru/art/phase-diagr1/Pb-Tl.php also NOT eutectic because the solid solution is higher melting than components Pb-Zn https://himikatus.ru/art/phase-diagr1/Pb-Zn.php eutectic at +318 Sn-Tl https://himikatus.ru/art/phase-diagr1/Sn-Tl.php eutectic at +168 Sn-Zn https://himikatus.ru/art/phase-diagr1/Sn-Zn.php eutectic at +198 - in table above Tl-Zn https://himikatus.ru/art/phase-diagr1/Tl-Zn.php eutectic at +292 Considering the binary systems between alkali metals: Li only has appreciable solubility in pair

Li-Na https://himikatus.ru/art/phase-diagr1/Li-Na.php eutectic at +92 The other three alkali metals:

K-Li https://himikatus.ru/art/phase-diagr1/K-Li.php Li-Rb https://himikatus.ru/art/phase-diagr1/Li-Rb.php Cs-Li https://himikatus.ru/art/phase-diagr1/Cs-Li.php 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:

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Fusible alloy

Start with the simplest possible case. Write down what Fusible alloy claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Fusible alloy before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Fusible alloy ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Fusible alloy

In research: Fusible alloy appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Fusible alloy in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Fusible alloy is common in secondary-school and first-year university syllabi. It links to neighbouring topics Coolants, Fusible alloys, so understanding it makes those chapters shorter.
In everyday life: Look for Fusible alloy outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Fusible alloy in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Fusible alloy means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Fusible alloy out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Fusible alloy in simple terms?

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.

Why does Fusible alloy matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Fusible alloy?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Fusible alloy.