RuBisCO

Why Fluorine Never made it as rocket fuel

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I have heard that one of the largest costs in spaceflight is the insurance. I imagine that even modest increase in risk, or the risks associated with a fluorine accident, affect this in the upwards direction.

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In conclusion, YOU DO NOT MESS WITH FLUORINE. NEVER.

 

Plus there are the fluoride fire that will start if you scrub off the fluoride layer on the metal fuel tanks.

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1 hour ago, Xd the great said:

In conclusion, YOU DO NOT MESS WITH FLUORINE. NEVER.

"Sounds like a nice weekend project with my son". Kerman, Bill.

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9 minutes ago, Lisias said:

"Sounds like a nice weekend project with my son". Kerman, Bill.

"I give this project 200% support," Kerman, Jebediah and Valentina.

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6 minutes ago, kerbiloid said:

"How many tubes of teethpaste does it take to fuel a rocket?"

https://en.m.wikipedia.org/wiki/Toothpaste#Fluoride

10000 tubes of toothpaste for a litre of fluoride/fluorine if you manager to purify it.

So, for a rocket first stage the size of saturn five, might be 7 billion tubes.

Correct me if I am wrong.

 

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22 hours ago, Lilithvia said:

Excuse me for not knowing much chemistry (I'm a mech engineer, only needed Chem 1200 and chem 1210-1215), but why is fluorine so bad? Doesn't it strengthen teeth?

And I cook food on it. Gotta love that Teflon (polytetrafluoroethylene) coated frying pan.

Certain fluorine containing compounds are useful for various things. Elemental  (or pure) fluorine is the nasty stuff, hydrogen fluoride, if anything is even worse. Need to be careful with fluoride salts too - some of them can be pretty bad. Read up on the horror show here.

 

 

 

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22 hours ago, Lilithvia said:

Excuse me for not knowing much chemistry (I'm a mech engineer, only needed Chem 1200 and chem 1210-1215), but why is fluorine so bad? Doesn't it strengthen teeth?

 

22 hours ago, Lilithvia said:

Well that's different, it's nontoxic when in table/sea salt

I think something to do with ingestion over inhalation plus the molecular bond? I'm not sure

 

You might be an an engineer but this is basic stuff! You already said that you understand chlorine to be safe in table salt - it is precisely the same with fluorine in toothpaste.

I could go into more detail about ions, bonding and toxicity but then I'd have to start talking about electron orbital and probably have to type out most of a years syllabus.

Long story short, the toxicity/hazard of a substance is not denoted by its constituent atoms. We (humans) are mostly carbon, hydrogen, nitrogen, oxygen and a few other things. But organise just those 4 elements in the right way and you can have everything from highly lethal toxins to high explosives. Or inert things like plastics and fibres.

Do you not need elementary (heh) chemistry to learn about material properties for your engineering?

 

The reason that fluorine specifically is so bad is, simply put, because it is "super-oxygen". In that it is an oxidising gas with a stronger oxidising potential than oxygen. 

And you must be aware of the hazards of say, things being exposed to a 100% oxygen environment? Fluorine is like that but much worse. Things tend to spontaneously ignite/explode/corrode is fairly short order. This includes human flesh.

But the oxygen in water, and the fluorine in toothpaste, is of course, much safer, due to the way it is organised in the molecules.

More accurately, due to the way the electrons organise themselves.

Edited by p1t1o

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@Lilithvia fluoride the ion isnt so bad. You use it in toothpaste.

Fluorine, the gas, is different. It wants to become fluorine, so it basically does everything to get to that goal.

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On 7/22/2018 at 10:13 PM, RuBisCO said:

Red fuming nitric acid and Hydrazine derivatives are corrosive and toxic too, but way cheaper.  

Those two are no way near as corrosive or toxic as fluorine, which, incidentally, might be the main reason why they're comparatively cheap.

In this capitalist world of ours, anything and everything is sooner or later translated into money. Extra safety precautions and long checklists cost money. Every mishap and accident that happens anyway costs money. If accidents have a tendency to be catastrophic rather than minor, this costs a lot of money. You get the idea.

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1 hour ago, Laie said:

In this capitalist world of ours

This always appears to sound bad, but money is a measure of work. More work to manage hazardous materials = more money. Sounds a  little more reasonable that way.

 

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Some slightly grumpy replies here, guys. It doesn't matter why someone wants to know something. The important thing is that we can share things we do know with others who want to know them. 

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On 7/24/2018 at 7:11 AM, p1t1o said:

I have heard that one of the largest costs in spaceflight is the insurance. I imagine that even modest increase in risk, or the risks associated with a fluorine accident, affect this in the upwards direction.

Insurance... I hate insurance people lol :) 

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The expensiveness was just the salt in the wound. As stated by many others, the danger is the biggest killer.

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On 7/23/2018 at 8:14 PM, Lilithvia said:

So it's toxic but yet we use it to strengthen teeth...

???

As most chemicals, amount makes them toxic. Also many heavy metals are necessary at ridiculously low amounts, because they are needed in some enzymes, but toxic (and lethal) in larger quantities.

Rocket launch would release hundreds of tons of hydrogen fluoride which would flow with wind and be toxic and environmental hazard at distances of tens or hundreds of kilometers. They should evacuate half Florida when they launch a rocket.

Price of fluorine itself is not reason why it is not used. Price of safety precautions, handling etc. in all phases is why it can not be used. Now also environmental laws. Firstly you should build a new launch complex to very distant island. Then logistical costs, handling, material and manufacturing. Fluorine is so extremely aggressive that reusability would probably be impossible. Materials which can handle fluorine rich gases at combustion chamber conditions during multiple launches probably do not exist. And after all, it would be possible that launches would have to be stopped because severe sea pollution.

 

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On 7/23/2018 at 8:10 PM, kerbiloid said:

It strengthens teeth and burns everything in fire.
And it's toxic. And corrosive. And cryogenic.

Everything should be understood practically literally. Water, concrete, stone, metals, human flesh etc. common materials which you probably think to be relatively fire safe burn very aggressively in fluorine gas. Only some fluorine compounds which already have strong bonds between fluorine and other elements can resist. Fluorine can be stored in some metal containers because thin solid fluoride layer forms and prevents further contact between fluorine and metal. However, if the layer will be damaged reaction may be so aggressive that new layer can not form and metal begins to burn. Not very nice if it is some part of rocket engine's oxidizer feeding system.

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That 542s of ISP sounds glorious on paper, but they were using Florine (a cryogenic liquid) Hydrogen (it may have been gaseous, I don't remember) and molten Lithium or some such, which required a fair bit of heating to keep it that way.  The practicality of the system is pretty obvious at this point and I really can't see such a thing ever being used unless we have an urgent need for some really high performance chemical fuels somewhere like the surface of Titan, and we can make them there.  542s tho.......

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On 8/6/2018 at 10:17 AM, Hannu2 said:

Everything should be understood practically literally. Water, concrete, stone, metals, human flesh etc. common materials which you probably think to be relatively fire safe burn very aggressively in fluorine gas. Only some fluorine compounds which already have strong bonds between fluorine and other elements can resist. Fluorine can be stored in some metal containers because thin solid fluoride layer forms and prevents further contact between fluorine and metal. However, if the layer will be damaged reaction may be so aggressive that new layer can not form and metal begins to burn. Not very nice if it is some part of rocket engine's oxidizer feeding system.

No, fluorine is not that reactive. It's entirely possible to make a safe enough system using fluorine, but the price would be too much for contractors.

You won't catch fire if you dip your hand into a bag of fluorine. You'll get slight chemical burns after few seconds, then progressively worse. When you see things spontaneously igniting in fluorine, that's under a jet of fluorine focused on a small area. That's how heat builds up until it causes flames. Similar as blowing into a campfire to rekindle it.

Chlorine trifluoride is way worse than fluorine and it could be used as engine fuel. Liquid, it will actually cause combustion upon spilling on a brick, and it was investigated as an oxidizer type of fuel. The problem is high chance of workers getting injured/killed during any kind of manipulation. What can be safe for an experimenter with small quantities, fume hood and special protocols,  will be too dangerous for hauling around in tanks. It requires utmost precision and security.

Edited by lajoswinkler
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Posted (edited)

What about a liquid fluorine - solid lithium hydride hybrid rocket? 

Edited by Angeltxilon

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34 minutes ago, Angeltxilon said:

What about a liquid fluorine - solid lithium hydride hybrid rocket? 

They tried something like that, but liquid lithium and gaseous hydrogen. The ISP was insane, 5 hundred something, but again, fluorine is toxic, lithium is a pain to handle, and hydrogen is more pain in the a**

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Posted (edited)

Fluorine's actually a less bad actor than things like Hydrazine or N2O4... I mean they're all pretty bad.

 

4 hours ago, Angeltxilon said:

What about a liquid fluorine - solid lithium hydride hybrid rocket? 

I was also curious about these combinations and looked into it a while back.

The book Ignition (distributed for free!) talks about how that particular combination was tried but failed due to poor and inconsistent burning.

Spoiler

Thus, the fuel grains recommended by three different contractors, Lock-heed, United Technology Co., and Aerojet, comprised:

1. Lithium hydride plus a hydrocarbon (rubber) binder;
2. Lithium hydride plus lithium metal plus a binder;
3. Lithium hydride plus powdered aluminum plus a binder.

And the oxidizers recommended (not necessarily in the same order) consisted of:
1. Chlorine trifluoride plus perchloryl fluoride;
2. The same two plus bromine pentafluoride;
3. Or, plus N2F4;
4. Or, finally, and a little further out, straight OF2.

All of which made some of us wonder whether or not the taxpayer had got his money's worth from all that expensive computer time.

Modern binders though like unzipping polymers (Paraformaldehyde) might provide much better performance though. They're designed specifically to chemically unravel at the first sign of oxidation leading to some very ... vigorous reactions.

A little side story relating to how these unzipping polymers should help hybrid booster performance: Paraformaldehyde is also common tweezer material (Delrin/Celcon/etc) and can unfortunately look just like the nearly inert teflon in dim lighting. One day, one of my lab users must have left a pair of Paraformaldehyde tweezers in the aggressive chemical bench, and I think you can see where this is going. I mixed a boiling fresh batch of one of the world's greatest oxidizers (peroxymonosulphuric acid, we called it Piranha because of how well it gets along with organics), then I put down my teflon tweezers and accidentally picked up the Paraformaldehyde ones. When I went to give the oxidizer a final stir the reaction was hypergollic, instantaneous and complete. Kerpow! It sounded like the crack of a shotgun, and sent a fireball of burning acid everywhere. Nothing remained of the tweezers but a comically short burning stub.

Fortunately I was dressed in the appropriate gear and don't rattle much, and after tamping out a few little fires I got to spend the next 2 hours cleaning up the lab while reflecting on how chemistry is always happening whether we expect it or not. I'd been a safety trainer for years at that point, and given it was me at fault I'm happy to get to tell the story to all my trainees from then forward. Wear your safety gear. :)

Anyways, I think these unzipping polymers will really help the combustion efficiency issues in Hybrids. They've very recently been getting a lot more attention (paper)

Personally, I've become interested in Liquid Hydrogen / Lithium Borohydride Gel fuels for use with oxidizers like supercooled F2O. I think it's clearly a step in the wrong direction for anyone with interest in practicality (and not exploding), but the Isp... I wants it.

Edited by Cunjo Carl

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Posted (edited)

I was wondering if it would be possible (and better) to use some xenon  or krypton compound as oxidizer or "fluorinizer" for rockets.
For example xenon hexafluoride, or xenon oxytetrafluoride, or nitrosonium octafluoroxenate, or...

Noble gas - chalcogen/halogen bonds are weaker than chalcogen - halogen, interhalogen or "itself" bonds; so that reacting with a fuel should generate more energy (=more thrust and isp?) since less energy would be required to break the previous bond (or more energy would be produced from breaking that bond).

However, there is the problem that xenon and krypton are (relatively) heavy atoms, so they could negatively affect the isp.

What do you think?

Edited by Angeltxilon

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Posted (edited)

One problem is that xenon hexafluoride is too stable for use as a rocket propellant. Things like fluorine and chlorine trifluoride are used because they are very reactive. Also Xe is a bit too heavy (and rare) as you mention.

Edited by Flibble

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