chemistry

Silicon tetrachloride

Silicon tetrachloride is a chemistry 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 Silicon tetrachloride rather than just read about it. In short: Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colorless volatile liquid that fumes in air.

Key takeaways

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

Reference excerpt

Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colorless volatile liquid that fumes in air. It is used to produce high-purity silicon and silica for commercial applications. It is a part of the chlorosilane family.

Preparation Silicon tetrachloride is prepared by the chlorination of various silicon compounds such as ferrosilicon, silicon carbide, or mixtures of silicon dioxide and carbon. The ferrosilicon route is most common. In the laboratory, SiCl4 can be prepared by treating silicon with chlorine at 600 °C (1,112 °F):

Si + 2 Cl2 → SiCl4 It was first prepared by Jöns Jakob Berzelius in 1823. Brine can be contaminated with silica when the production of chlorine is a byproduct of a metal refining process from metal chloride ore. In rare occurrences, the silicon dioxide in silica is converted to silicon tetrachloride when the contaminated brine is electrolyzed.

Reactions

Hydrolysis and related reactions Like other chlorosilanes or silanes, silicon tetrachloride reacts readily with water:

SiCl4 + 2 H2O → SiO2 + 4 HCl The reaction can be noticed on exposure of the liquid to air, as SiCl4 vapour produces fumes as it reacts with moisture to give a cloud-like aerosol of silica and hydrochloric acid. In contrast, carbon tetrachloride is not readily hydrolyzed. With alcohols it reacts to give orthosilicate esters:

SiCl4 + 4 ROH → Si(OR)4 + 4 HCl

Polysilicon chlorides At higher temperatures homologues of silicon tetrachloride can be prepared by the reaction:

Si + 2 SiCl4 → Si3Cl8 In fact, the chlorination of silicon is accompanied by the formation of hexachlorodisilane Si2Cl6. A series of compounds containing up to six silicon atoms in the chain can be separated from the mixture using fractional distillation.

Reactions with other nucleophiles Silicon tetrachloride is a classic electrophile in its reactivity. It forms a variety of organosilicon compounds upon treatment with Grignard reagents and organolithium compounds:

4 RLi + SiCl4 → R4Si + 4 LiCl Reduction with hydride reagents affords silane.

Comparison with other SiX4 compounds

Uses Silicon tetrachloride is used as an intermediate in the manufacture of polysilicon, a hyper-pure form of silicon, since it has a boiling point convenient for purification by repeated fractional distillation. It is reduced to trichlorosilane (HSiCl3) by hydrogen gas in a hydrogenation reactor, and either directly used in the Siemens process or further reduced to silane (SiH4) and injected into a fluidized bed reactor. Silicon tetrachloride reappears in both these two processes as a by-product and is recycled in the hydrogenation reactor. Vapor phase epitaxy of reducing silicon tetrachloride with hydrogen at approximately 1250 °C was done:

SiCl4(g) + 2 H2(g) → Si(s) + 4 HCl(g) at 1250°C The produced polysilicon is used as wafers in large amounts by the photovoltaic industry for conventional solar cells made of crystalline silicon and also by the semiconductor industry. Silicon tetrachloride can also be hydrolysed to fumed silica. High-purity silicon tetrachloride is used in the manufacture of optical fibres. This grade should be free of hydrogen containing impurities like trichlorosilane. Optical fibres are made using processes like MCVD and OFD where silicon tetrachloride is oxidized to pure silica in the presence of oxygen. As a feedstock in production of fused silica.

Safety and environmental issues Pollution from the production of silicon tetrachloride has been reported in China associated with the increased demand for photovoltaic cells that has been stimulated by subsidy programs.

See also Silicon tetrachloride (data page)

References

Illustrations

Worked examples

Example 1 — a first encounter with Silicon tetrachloride

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

In research: Silicon tetrachloride appears in chemistry 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 Silicon tetrachloride 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: Silicon tetrachloride is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chlorides, Chlorosilanes, Inorganic silicon compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Silicon tetrachloride 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 Silicon tetrachloride in 20 minutes

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

Frequently asked questions

What is Silicon tetrachloride in simple terms?

Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colorless volatile liquid that fumes in air.

Why does Silicon tetrachloride matter?

Because it connects several chemistry 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 Silicon tetrachloride?

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 Silicon tetrachloride.