chemistry

Self accelerating decomposition temperature

Self accelerating decomposition temperature 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 Self accelerating decomposition temperature rather than just read about it. In short: The self-accelerating decomposition temperature (SADT) is the lowest temperature at which an organic peroxide in a typical vessel or shipping package will undergo a self-accelerating decomposition within one week. The SADT is the point at which the heat evolution from the decomposition reaction and the heat removal rate from the package of interest become unbalanced.

Key takeaways

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

Reference excerpt

The self-accelerating decomposition temperature (SADT) is the lowest temperature at which an organic peroxide in a typical vessel or shipping package will undergo a self-accelerating decomposition within one week. The SADT is the point at which the heat evolution from the decomposition reaction and the heat removal rate from the package of interest become unbalanced. When the heat removal is too low, the temperature in the package increases and the rate of decomposition increases in an uncontrollable manner. The result is therefore dependent on the formulation and the package characteristics. A self-accelerating decomposition occurs when the rate of peroxide decomposition is sufficient to generate heat at a faster rate than it can be dissipated to the environment. Temperature is the main factor in determining the decomposition rate, although the size of the package is also important since its dimensions will determine the ability to dissipate heat to the environment. All peroxides contain an oxygen-oxygen bond that, on heating, can break apart homolytically to generate two radicals. As mentioned previously, this decomposition also generates heat. But the stability of the oxygen-oxygen bond is dependent on what else is present in the molecule. Some peroxides, due to their chemical make-up, are very unstable and need to be refrigerated to avoid a self-accelerating decomposition. Others, particularly those used for crosslinking purposes, are much more stable and can be stored at normal ambient temperatures without risk of self-acceleration. Due to the large variations in the stabilities of peroxides, each is tested to determine the safe maximum temperature for which the peroxide may be stored, shipped, and handled. The result of this test is the self-accelerating decomposition temperature (SADT). Although a number of organic peroxides can safely be stored at room temperature, most require some form of temperature control. For long storage periods, the organic peroxide is usually kept at a lower temperature than the maximum safe storage temperature as determined by the SADT. The SADT for an organic peroxide formulation is usually lower for more concentrated formulations. Dilution with a compatible, high boiling point diluent will usually increase the SADT since the peroxide is dilute and the diluent can absorb much of the heat minimizing the increase in temperature. Also, for an organic peroxide formulation, larger packages generally have a lower SADT because of the poorer heat transfer of the larger package due to lower surface area to volume ratio. Most organic peroxides react to some extent with their decomposition products during thermal decomposition. This often increases the rate since the decomposition proceeds more rapidly as the decomposition products are generated. The SADT measurement is made as follows:

The package containing the peroxide is placed in oven set for test temperature The timer starts when product reaches 2 °C below intended test temperature The oven is held at constant temperature for up to one week or, until a runaway event occurs. Test "Passes" if product does not exceed test (oven) temperature by 6 °C within one week Test "Fails" if product exceeds test temperature by 6 °C within one week The test is repeated in 5 °C increments until a failure is reached Fail temperature is reported as SADT for that package and formulation Secondary information about the violence of the decomposition can also be recorded As an alternative to the oven test the SADT for larger packages can be determined by substituting a Dewar flask for the package. The heat transfer of the Dewar flask can be matched to the heat transfer of a larger package size. This test is called the Heat Accumulation Storage Test (HAST).

Application to polymerizable mixtures Some mixtures containing peroxides and polymerizable monomers may also exhibit SADTs. For example, mixtures of vinyltrimethoxysilane, peroxides and stabilizers are used commercially for cross-linking polyethylene to make PEX pipe. These mixtures are typically liquid solutions that are shipped to where they are used to graft alkoxysilane groups to polyethylene. In such mixtures decomposition of the peroxide can initiate exothermic radical polymerization of the vinyltrimethoxysilane. At low temperature the decomposition rate is slow enough that the stabilizers quench the polymerization before much heat is generated and the container dissipates what heat is produced. At higher temperatures peroxide decomposition is faster, more polymerization occurs to heat the mixture, which in turn increases peroxide decomposition and polymerizes the monomer even faster. The container dissipates heat more slowly in a higher-temperature environment, so at some critical temperature heat is generated by polymerization faster than the container can dissipate it and the reaction self-accelerates. Thus such a mixture has a SADT that depends on container size exactly as in the case of a pure organic peroxide.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Self accelerating decomposition temperature

Start with the simplest possible case. Write down what Self accelerating decomposition temperature 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 Self accelerating decomposition temperature 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 Self accelerating decomposition temperature 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 Self accelerating decomposition temperature

In research: Self accelerating decomposition temperature 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 Self accelerating decomposition temperature 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: Self accelerating decomposition temperature is common in secondary-school and first-year university syllabi. It links to neighbouring topics Organic peroxides, so understanding it makes those chapters shorter.
In everyday life: Look for Self accelerating decomposition temperature 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 Self accelerating decomposition temperature in 20 minutes

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

Frequently asked questions

What is Self accelerating decomposition temperature in simple terms?

Why does Self accelerating decomposition temperature 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 Self accelerating decomposition temperature?

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 Self accelerating decomposition temperature.