# Specific impulse and liquid ozone
**URL:** https://boards.straightdope.com/t/specific-impulse-and-liquid-ozone/978418
**Category:** Factual Questions
**Created:** [January 18, 2023, 5:01pm UTC](https://boards.straightdope.com/t/specific-impulse-and-liquid-ozone/978418 "2023-01-18T17:01:05Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@EnolaStraight](https://boards.straightdope.com/u/EnolaStraight)
#### Post date: [January 18, 2023, 5:01pm UTC](https://boards.straightdope.com/t/specific-impulse-and-liquid-ozone/978418/1 "2023-01-18T17:01:05Z")
Specific impulse of newtonian thrust engines, like jets and rockets, measures the efficiency of the engine thrust.
[Specific impulse - Wikipedia](https://en.wikipedia.org/wiki/Specific_impulse)
If we restrict the discussion to rocket thrust, what increases in efficiency are there in employing liquid ozone instead of liquid oxygen?
Ozone is a more chemically active oxidizer than “regular” oxygen and, thus, give more energetic “kick”, yes?
[Ozone - Wikipedia](https://en.wikipedia.org/wiki/Ozone)
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### Author:  [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)
#### Post date: [January 18, 2023, 6:25pm UTC](https://boards.straightdope.com/t/specific-impulse-and-liquid-ozone/978418/2 "2023-01-18T18:25:09Z")
I’m not aware of ozone (O3) being used as on oxidizer in any rocket propulsion system even as a test bed. There has been some exploration into using liquid ozone (and even worse, ozone diflouride, O3F2) but the problem is that even at a cryogenic liquid (and possibly in frozen solid state), ozone is unstable and prone to spontaneous explosive decomposition into ‘normal’ O2 without any other chemical interaction or excitation energy because any free atom of oxygen will kick a neighboring ozone molecule to decompose. I’m not sure what the density of liquid ozone is but it is probably less than that of diatomic oxygen at the same temperature, so while there is some additional energy from the decomposition from O3 to O2 it isn’t actually allowing the engine to get a higher flow rate or lighter molecular weight of products, and frankly is going to decompose in a pump before it gets to the chamber anyway, so essentially it would just be stressing the propellant feed any turbopump systems.
Liquid oxygen is bad enough in terms of its cryogenic effects and interaction with anything that might combust so using an oxidizer that will undergo spontaneous autocatalytic reactions is obviously not something an propulsion system designer would embrace even if it did somehow increase input energy. In general, the only ways to increase specific impulse is either to reduce molecular weight of the products or increase the temperature to extract the maximum usable energy and convert it into higher exhaust velocities. Chemical propulsion systems have a maximum limitation just because chemical reactions that produce sufficiently low molecular weight products have a limit to the enthalpy released and the only way to improve upon that is to have an external energy source of higher temperature and heat flux (i.e. nuclear thermal, magnetoplasmadynamic, ion, et cetera).
Stranger
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### Author:  [@gnoitall](https://boards.straightdope.com/u/gnoitall)
#### Post date: [January 18, 2023, 7:24pm UTC](https://boards.straightdope.com/t/specific-impulse-and-liquid-ozone/978418/3 "2023-01-18T19:24:51Z")
Stranger has it correctly. Ozone, in a form useful for rocketry, is insanely unstable.
A relevant StackExchange article:
>
The main reason I link this (because StackExchange is normally kind of lame) is because it quotes a wonderful book on rocketry chemistry, John D. Clark’s _Ignition!: An Informal History of Liquid Rocket Propellants_
The relevant quote:
> [@](#):
>
> Much more important is the fact that it’s unstable — murderously so. At the slightest provocation and sometimes for no apparent reason, it may revert explosively to oxygen. And this reversion is catalyzed by water, chlorine, metal oxides, alkalis—and by, apparently, certain substances which have not been identified…
>
> Some investigators believe that the explosions are initiated by traces of organic peroxides in the stuff, which come from traces, say, of oil in the oxygen it was made of. Other workers are convinced that it’s just the nature of ozone to explode, and still others are sure that original sin has something to do with it. So although ozone research has been continuing in a desultory fashion, there are very few true believers left, who are still convinced that ozone will somehow, someday, come into its own. I’m not one of them.
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### Author:  [@am77494](https://boards.straightdope.com/u/am77494)
#### Post date: [January 19, 2023, 4:20am UTC](https://boards.straightdope.com/t/specific-impulse-and-liquid-ozone/978418/4 "2023-01-19T04:20:54Z")
> [@Stranger\_On\_A\_Train](#):
>
> I’m not sure what the density of liquid ozone is but it is probably less than that of diatomic oxygen at the same temperature, ….
Agreeing with what you are saying, but nitpicking this part:
Ozone : liquefaction temp : -133F at 15 psia and density is 78.4 lb/ft3
Oxygen : liquefaction temp : -297F at 15 psia and density is 71.5 lb/ft3
(Data taken from Aspen Thermodynamic databases)
And to the broader question, Oxygen is usually vaporized to a gas phase before combustion and once a gas, it can eat through metals unless velocities are kept low and exotic metallurgy is used. Ozone will exacerbate the problem as pointed out above
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### Author:  [@mixdenny](https://boards.straightdope.com/u/mixdenny)
#### Post date: [January 19, 2023, 4:54am UTC](https://boards.straightdope.com/t/specific-impulse-and-liquid-ozone/978418/5 "2023-01-19T04:54:35Z")
Liquid oxygen and fluorine (FLOX) was bad enough and it offered better performance. The FLOX program was over by the time I worked at the Rocket Engine Test Facility but people still talked in hushed tones about it.
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### Author:  [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)
#### Post date: [January 19, 2023, 5:06am UTC](https://boards.straightdope.com/t/specific-impulse-and-liquid-ozone/978418/6 "2023-01-19T05:06:47Z")
The standard reference, as always, is the book _[Ignition!](https://library.sciencemadness.org/library/books/ignition.pdf)_
> The future of ozone doesn’t look so promising. Or, to be precise, ozone has been promising for years and years but hasn’t been delivering.
>
> Ozone, O3, is an allotropic form of oxygen. It’s a colorless gas, or if it’s cold enough, a beautiful deep blue liquid or solid. It’s manufactured commercially (it’s useful in water purification and the like) by the Welsbach process which involves an electrical glow discharge in a stream of oxygen. What makes it attractive as a propellant is that (1) its liquid density is considerably higher than that of liquid oxygen, and (2) when a mole of it decomposes to oxygen during combustion it gives off 34 kilocalories of energy, which will boost your performance correspondingly. Sanger was interested in it in the 30’s, and the interest has endured to the present. In the face of considerable disillusionment.
>
> For it has its drawbacks. The least of these is that it’s at least as toxic as fluorine. (People who speak of the invigorating odor of ozone have never met a real concentration of it!) Much more important is the fact that it’s unstable — murderously so. At the slightest provocation and sometimes for no apparent reason, it may revert explosively to oxygen. And this reversion is catalyzed by water, chlorine, metal oxides, alkalis —and by, apparently, certain substances which have not been identified. Compared to ozone, hydrogen peroxide has the sensitivity of a heavyweight wrestler.
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### Author:  [@mixdenny](https://boards.straightdope.com/u/mixdenny)
#### Post date: [January 19, 2023, 5:53pm UTC](https://boards.straightdope.com/t/specific-impulse-and-liquid-ozone/978418/7 "2023-01-19T17:53:45Z")
> [@Dr.Strangelove](#):
>
> It’s a colorless gas, or if it’s cold enough, a beautiful deep blue liquid
Fun fact: We ran our LOX lines in insulated troughs filled with liquid nitrogen to keep the LOX as cold as possible. This also made it easy to spot a leak as the oxygen mixing in with the nitrogen turned it sky blue.
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### Author:  [@gnoitall](https://boards.straightdope.com/u/gnoitall)
#### Post date: [January 19, 2023, 7:12pm UTC](https://boards.straightdope.com/t/specific-impulse-and-liquid-ozone/978418/8 "2023-01-19T19:12:34Z")
nvm \<10chars\>
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### Author:  [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)
#### Post date: [January 19, 2023, 8:35pm UTC](https://boards.straightdope.com/t/specific-impulse-and-liquid-ozone/978418/9 "2023-01-19T20:35:33Z")
> [@gnoitall](#):
>
> nvm \<10chars\>
Not sure what this said, but I do see that you ninjaed me above. But hopefully the link to the book PDF is useful to others.
> [@mixdenny](#):
>
> This also made it easy to spot a leak as the oxygen mixing in with the nitrogen turned it sky blue.
Neat. I haven’t seen it in person, but from videos it is a nice color.