engineering

Zinc sulfide

Zinc sulfide is a engineering 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 Zinc sulfide rather than just read about it. In short: Zinc sulfide is an inorganic compound with the chemical formula of ZnS. This is the main form of zinc found in nature, where it mainly occurs as the mineral sphalerite.

Key takeaways

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

Reference excerpt

Zinc sulfide is an inorganic compound with the chemical formula of ZnS. This is the main form of zinc found in nature, where it mainly occurs as the mineral sphalerite. Although this mineral is usually black because of various impurities, the pure material is white, and it is widely used as a pigment. In its dense synthetic form, zinc sulfide can be transparent, and it is used as a window for visible optics and infrared optics.

Structure

ZnS exists in two main crystalline forms. This dualism is an example of polymorphism. In each form, the coordination geometry at Zn and S is tetrahedral. The more stable cubic form is known also as zinc blende or sphalerite. The hexagonal form is known as the mineral wurtzite, although it also can be produced synthetically. The transition from the sphalerite form to the wurtzite form occurs at around 1020 °C.

Applications

Luminescent material

Zinc sulfide, with addition of a few ppm of a suitable activator, exhibits strong phosphorescence. The phenomenon was described by Nikola Tesla in 1893, and is currently used in many applications, from cathode-ray tubes through X-ray screens to glow in the dark products. When silver is used as activator, the resulting color is bright blue, with maximum at 450 nanometers. Using manganese yields an orange-red color at around 590 nanometers. Copper gives a longer glow, and it has the familiar greenish glow-in-the-dark. Copper-doped zinc sulfide ("ZnS plus Cu") is used also in electroluminescent panels. It also exhibits phosphorescence due to impurities on illumination with blue or ultraviolet light.

Optical material Zinc sulfide is also used as an infrared optical material, transmitting from visible wavelengths to just over 12 micrometers. It can be used planar as an optical window or shaped into a lens. It is made as microcrystalline sheets by the synthesis from hydrogen sulfide gas and zinc vapour, and this is sold as FLIR-grade (Forward Looking Infrared), where the zinc sulfide is in a milky-yellow, opaque form. This material when hot isostatically pressed (HIPed) can be converted to a water-clear form known as Cleartran (trademark). Early commercial forms were marketed as Irtran-2 but this designation is now obsolete.

Pigment Zinc sulfide is a common pigment, sometimes called sachtolith. When combined with barium sulfate, zinc sulfide forms lithopone.

Catalyst Fine ZnS powder is an efficient photocatalyst, which produces hydrogen gas from water upon illumination. Sulfur vacancies can be introduced in ZnS during its synthesis; this gradually turns the white-yellowish ZnS into a brown powder, and boosts the photocatalytic activity through enhanced light absorption.

Semiconductor properties Both sphalerite and wurtzite are intrinsic, wide-bandgap semiconductors. These are prototypical II-VI semiconductors, and they adopt structures related to many of the other semiconductors, such as gallium arsenide. The cubic form of ZnS has a band gap of about 3.54 electron volts at 300 kelvins, but the hexagonal form has a band gap of about 3.91 electron volts. ZnS can be doped as either an n-type semiconductor or a p-type semiconductor.

History The phosphorescence of ZnS was first reported by the French chemist Théodore Sidot in 1866. His findings were presented by A. E. Becquerel, who was renowned for the research on luminescence. ZnS was used by Ernest Rutherford and others in the early years of nuclear physics as a scintillation detector, because it emits light upon excitation by x-rays or electron beam, making it useful for X-ray screens and cathode-ray tubes. This property made zinc sulfide useful in the dials of radium watches.

Production Zinc sulfide is usually produced from waste materials from other applications. Typical sources include smelter, slag, and pickle liquors. As an example, the synthesis of ammonia from methane requires a priori removal of hydrogen sulfide impurities in the natural gas, for which zinc oxide is used. This scavenging produces zinc sulfide:

ZnO + H2S → ZnS + H2O

Laboratory preparation Crude zinc sulfide can be produced by igniting a mixture of zinc and sulfur. More conventionally, ZnS is prepared by treating a mildly acidic solution of Zn2+ salts with H2S:

Zn2+ + S2− → ZnS This reaction is the basis of a gravimetric analysis for zinc.

References

External links

Zinc and Sulfur at The Periodic Table of Videos (University of Nottingham) Composition of CRT phosphors University of Reading, Infrared Multilayer Laboratory optical data [1] melting point

Illustrations

Worked examples

Example 1 — a first encounter with Zinc sulfide

Start with the simplest possible case. Write down what Zinc sulfide claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, 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 Zinc sulfide 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 Zinc sulfide 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 Zinc sulfide

In research: Zinc sulfide appears in engineering 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 Zinc sulfide 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: Zinc sulfide is common in secondary-school and first-year university syllabi. It links to neighbouring topics II-VI semiconductors, Ionising radiation detectors, Luminescence, so understanding it makes those chapters shorter.
In everyday life: Look for Zinc sulfide 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 Zinc sulfide in 20 minutes

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

Frequently asked questions

What is Zinc sulfide in simple terms?

Zinc sulfide is an inorganic compound with the chemical formula of ZnS. This is the main form of zinc found in nature, where it mainly occurs as the mineral sphalerite.

Why does Zinc sulfide matter?

Because it connects several engineering 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 Zinc sulfide?

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 Zinc sulfide.