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I was wondering if liquid "air" (nitrogen, oxygen, and argon mixture) was flammable. Imagine you have a container. This container contains liquid air. The air is in liquid form, and is in direct contact with two copper rods, which when a current is ran through them, they spark. I was wondering if the spark would ignite the liquid. Would it explode, or burn?

As a side question. If you had a m^3 of gaseous air, how big would it be in liquid form?

ACuriousMind
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I. C.
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  • What drove you to tag this question with [tag:cosmological-inflation]? Also, you second question is easily looked up, and is unrelated to the first. Please only ask one question per post, and show a bit of research effort. – ACuriousMind Feb 04 '16 at 18:04
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    it was the only thing that had the word "inflation" in it. this is my first time using stack exchange. – I. C. Feb 04 '16 at 18:09
  • I think liquid would explode as used in rocket propulsion. – Anubhav Goel Feb 04 '16 at 18:23
  • Liquid air is a very bad idea. Oxygen is liquid blow -183 C, nitrogen below -196 C. Evaporating liquid air will quickly enrich itself in oxygen and form an ever more flammable oxidizer. While liquid nitrogen is essentially harmless except when it comes in contact with warm surfaces, liquid air would have to be handled like liquid oxygen and be kept away from all carbon containing substances, unless you like things exploding next to you. In practice you will either buy liquid nitrogen or liquid oxygen, but not a mixture of both and you will keep air away from your liquid nitrogen. – CuriousOne Feb 04 '16 at 18:33

2 Answers2

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No, liquid air is not flammable. A flame requires an oxidant and something that can be oxidised. Liquid oxygen is a (very strong!) oxidant but neither nitrogen or argon are easily oxidised.

The density of air is about 1.2 kg per cubic metre at room temperature. I don't know the density of liquid air, but the density of liquid nitrogen is around 800 kg/m$^3$ near its boiling point and the density of liquid oxygen is around 1140 kg/m$^3$ near its boiling point. So I'd guess the density of liquid air would be around 870 kg/m$^3$. So your cubic metre of air would condense to 0.0014 m$^3$ or about 1.4 litres.

John Rennie
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As a young engineer fresh out of college (1959) and on my first job, I was holding a demonstration of the effects of liquid nitrogen on such things as roses, a banana, etc. I was smoking a cigar and a bystander cautioned me about smoking around liquid nitrogen. I patronizingly told him that nitrogen was not flammable. He said "Son, what's the boiling point of liquid oxygen?" I proudly replied "Minus 297.4 degrees F." "Right" he said. "Now what's the boiling point of liquid nitrogen?" Again, I proudly replied "Minus 320 degrees F." "Right again" he said. "Now, you've been stirring up that liquid nitrogen with your roses and such - what do you think has been happening to the oxygen from the air you've been mixing in?" I looked at him blankly. "Take that cigar; get it glowing, and stick it in the liquid nitrogen." "It'll go out" I said. "Let's see" he replied. I did as he asked, and you'd have though it was the fourth of July - that Dutch Masters Panatella looked like a Roman candle. Takes more that a college degree to make you knowledgeable.

Joe McMann
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  • a common explosive used in mining is a borehole in rock, filled with crushed carbon. liquid oxygen is poured into the borehole to saturate the carbon. when set off with a blasting cap, the resulting explosion will shatter the rock. – niels nielsen Oct 24 '17 at 06:59