science

Wood's metal

Wood's metal is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Wood's metal rather than just read about it. In short: Wood's metal, also known as Lipowitz's alloy or by the commercial names Cerrobend, Bendalloy, Pewtalloy and MCP 158, is a fusible metal alloy (having a low melting point) that is useful for soldering and making custom metal parts. The alloy is named for Barnabas Wood, who invented and patented the alloy in 1860.

Key takeaways

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

Reference excerpt

Wood's metal, also known as Lipowitz's alloy or by the commercial names Cerrobend, Bendalloy, Pewtalloy and MCP 158, is a fusible metal alloy (having a low melting point) that is useful for soldering and making custom metal parts. The alloy is named for Barnabas Wood, who invented and patented the alloy in 1860. It is a eutectic 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). Its fumes are toxic, as well as being toxic on skin exposure.

Applications

As suggested by the trade names, Wood's metal is used to fill thin-walled tube so that it can be bent to a radius without kinking or collapsing. The filling is easily melted and run out of the tube after bending is completed. The low melting point and lack of contraction on freezing make Wood's metal suitable for this purpose. Wood's Metal is also used for making fusible links in the sprinkler heads of commercial building automatic fire sprinkler systems. In the event of a fire, ambient temperature increases enough to melt the link, releasing the water. A similar use is fusible plugs in boilers. Uses also include making custom-shaped apertures and blocks (for example, electron-beam cutouts and lung blocks) for medical radiation treatment, and making casts of keys that are hard to otherwise duplicate. 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 used routinely but are employed at temperatures above 220 °C (428 °F). At room temperature, Wood's metal has a modulus of elasticity of 12.7 GPa and a yield strength 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 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.

Related alloys

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

Illustrations

Worked examples

Example 1 — a first encounter with Wood's metal

Start with the simplest possible case. Write down what Wood's metal 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 Wood's metal 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 Wood's metal 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 Wood's metal

In research: Wood's metal 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 Wood's metal 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: Wood's metal is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bismuth alloys, Cadmium alloys, Fusible alloys, so understanding it makes those chapters shorter.
In everyday life: Look for Wood's metal 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.

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How to study Wood's metal in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Wood's metal 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 Wood's metal out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Wood's metal in simple terms?

Why does Wood's metal 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 Wood's metal?

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 Wood's metal.