engineering

Oxygen balance

Oxygen balance 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 Oxygen balance rather than just read about it. In short: Oxygen balance (OB, OB%, or Ω) is an expression that is used to indicate the degree to which an explosive can be oxidized, to determine whether the molecules of explosive substance or mixture contains enough oxygen to fully oxidize the other atoms in the molecules. For example, fully oxidized carbon forms carbon dioxide, hydrogen forms water, sulfur forms sulfur dioxide, and metals form metal oxides.

Key takeaways

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

Reference excerpt

Oxygen balance (OB, OB%, or Ω) is an expression that is used to indicate the degree to which an explosive can be oxidized, to determine whether the molecules of explosive substance or mixture contains enough oxygen to fully oxidize the other atoms in the molecules. For example, fully oxidized carbon forms carbon dioxide, hydrogen forms water, sulfur forms sulfur dioxide, and metals form metal oxides. A molecule is said to have a positive oxygen balance if it contains more oxygen than is needed and a negative oxygen balance if it contains less oxygen than is needed. An explosive with a negative oxygen balance will lead to incomplete combustion, which commonly produces carbon monoxide, which is a toxic gas. Explosives with negative or positive oxygen balance are commonly mixed with other energetic materials that are either oxygen positive or negative, respectively, to increase the explosive's power. For example, TNT is an oxygen negative explosive and is commonly mixed with oxygen positive energetic materials or fuels to increase its power. Detonating a mixture of TNT (trinitrotoluene) and RDX (cyclotrimethylenetrinitramine), with its negative oxygen balance, in a closed chamber produces 5-nm detonation nanodiamonds.

Calculating oxygen balance The procedure for calculating oxygen balance in terms of 100 grams of the explosive material is to determine the number of moles of oxygen that are excess or deficient for 100 grams of the compound.

OB % = − 1600 Mol. wt. of compound × ( 2 X + Y / 2 + M − Z ) {\displaystyle {\text{OB}}\%={\frac {-1600}{\text{Mol. wt. of compound}}}\times (2X+Y/2+M-Z)}

X = number of atoms of carbon, Y = number of atoms of hydrogen, Z = number of atoms of oxygen, and M = number of atoms of metal (metallic oxide produced). In the case of TNT (C6H2(NO2)3CH3), Molecular weight = 227.1 X = 7 (number of carbon atoms) Y = 5 (number of hydrogen atoms) Z = 6 (number of oxygen atoms) Therefore,

OB % = − 1600 227.1 × ( 14 + 2.5 − 6 ) {\displaystyle {\text{OB}}\%={\frac {-1600}{227.1}}\times (14+2.5-6)}

OB% = −73.97% for TNT Examples of materials with negative oxygen balance are nitromethane (−39%), trinitrotoluene (−74%), aluminium powder (−89%), sulfur (−100%), or carbon (−266.7%). Examples of materials with positive oxygen balance are ammonium nitrate (+20%), ammonium perchlorate (+34%), potassium chlorate (+39.2%), sodium chlorate (+45%), potassium nitrate (+47.5%), tetranitromethane (+49%), lithium perchlorate (+60%), or nitroglycerine (+3.5%). Ethylene glycol dinitrate has an oxygen balance of zero, as does the theoretical compound trinitrotriazine.

Oxygen balance and power Because sensitivity, brisance, and strength are properties resulting from a complex explosive chemical reaction, a simple relationship such as oxygen balance cannot be depended upon to yield universally consistent results. When using oxygen balance to predict properties of one explosive relative to another, it is to be expected that one with an oxygen balance closer to zero will be the more brisant, powerful, and sensitive; however, many exceptions to this rule do exist. One area in which oxygen balance can be applied is in the processing of mixtures of explosives. The family of explosives called amatols are mixtures of ammonium nitrate and TNT. Ammonium nitrate has an oxygen balance of +20% and TNT has an oxygen balance of −74%, so it would appear that the mixture yielding an oxygen balance of zero would also result in the best explosive properties. In actual practice a mixture of 80% ammonium nitrate and 20% TNT by weight yields an oxygen balance of +1%, the best properties of all mixtures, and an increase in strength of 30% over TNT.

See also Air–fuel ratio (rich and lean) Oxidizing and reducing flames

References

Worked examples

Example 1 — a first encounter with Oxygen balance

Start with the simplest possible case. Write down what Oxygen balance 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 Oxygen balance 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 Oxygen balance 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 Oxygen balance

In research: Oxygen balance 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 Oxygen balance 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: Oxygen balance is common in secondary-school and first-year university syllabi. It links to neighbouring topics Explosives engineering, so understanding it makes those chapters shorter.
In everyday life: Look for Oxygen balance 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Oxygen balance in 20 minutes

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

Frequently asked questions

What is Oxygen balance in simple terms?

Why does Oxygen balance 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 Oxygen balance?

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 Oxygen balance.