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DBL%20Hendrix%20small.png College chemistry, 1983

Derek Lowe The 2002 Model

Dbl%20new%20portrait%20B%26W.png After 10 years of blogging. . .

Derek Lowe, an Arkansan by birth, got his BA from Hendrix College and his PhD in organic chemistry from Duke before spending time in Germany on a Humboldt Fellowship on his post-doc. He's worked for several major pharmaceutical companies since 1989 on drug discovery projects against schizophrenia, Alzheimer's, diabetes, osteoporosis and other diseases. To contact Derek email him directly: derekb.lowe@gmail.com Twitter: Dereklowe

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In the Pipeline

« Science Fiction Gets the Upper Hand | Main | A Total Mess At the FDA »

July 23, 2012

Mix 'Em All Together

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Posted by Derek

Looks like my "Things I Won't Work With" series (and John Clark's book "Ignition") has inspired science fiction author Charles Stross
- check out this story, and prepare to see several compounds that you never expected to see mixed together (!)

Comments (7) + TrackBacks (0) | Category: Chemical News


COMMENTS

1. John Schilling on July 23, 2012 1:23 PM writes...

Well, I'd be remiss if I didn't give a nod to George Herbert's fortunately fictional acetyl-ozone work; http://www.retro.com/hooocch/acezone.html

Back here in the real world, the highest performance ever demonstrated in a chemical rocket, specific impulse of 562 seconds (compared to the Space Shuttle's 455 seconds), came from a tripropellant mix of:

Liquid Hydrogen,
Liquid Fluorine, and
Liquid Lithium.

The hydrogen mostly doesn't even enter into the chemical reactivity; it's just there to reduce the molecular weight and increase the heat capacity of the exhaust for better nozzle dynamics. Also guarantees there will be more than a little HF in the exhaust. And requires the propellant feed system accomodate temperatures from roughly -250 C to +200 C.

I can see my fellow rocket scientists doing the math on the blackboard (this was before whiteboards), and saying "wouldn't it be neat if...?", but someone actually thought it was a good idea to actually build that damn engine. As far as I know, they survived the experience.

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2. Doug on July 23, 2012 7:19 PM writes...

Sounds like the 'things you don't want to hear from your pilot', like 'hey, watch this' or 'what's the worst thing that could happen'...

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3. milkshake on July 23, 2012 7:54 PM writes...

@1: US Navy developed torpedoes powered by SF6 + lithium metal. A fantastic controlable source of heat, very compact. I wonder if one could develop a good-performing tripropelant rocket motor like the one you described but with SF6 instead of liquid fluorine. SF6 is nontoxic and remarkably inert, for an oxidizer.

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4. gippgig on July 24, 2012 3:19 AM writes...

I suspect the highest-performance chemical rocket would be beryllium-7 fuel, ozone oxidizer (but check some of the exotic multioxygen fluorides), hydrogen propellant. If you exclude artificially-produced isotopes make that lithium-6, ozone, hydrogen. If you exclude isotopic enrichment, go back to beryllium, ozone, hydrogen. (Try freezing it to make a cryogenic solid fuel.)
You could probably make a good, but not great, tripropellant using SF6. For maximum Isp the molecular weight of the products should be as low as possible; sulfur is just too darn heavy (and forget mercury for that same reason).

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5. Anon on July 24, 2012 5:56 AM writes...

dead link to the book

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6. John Schilling on July 24, 2012 12:25 PM writes...

@3: The SF6+Li combination was chosen for torpedoes because it produces significant heat with no gaseous reaction products. For a torpedo, exhaust gas is a liability - against surface targets you wind up with a visible bubble trail, and against deeply submerged targets you wind up expending most of your energy just pushing the exhaust out against ~1000 psia back pressure.

For rocketry, expansion of a hot gas through a nozzle is critical; heat energy in solid- or liquid-phase reaction products doesn't contribute. And preferably a low-MW hot gas. When there's a whole lot of energy to be had, e.g. Li+F in this extreme case, or Al+O->Al2O3 in many solid rocket propellants, we will grit our teeth, arrange an ample supply of gaseous reaction products (or inert working fluid) as well, and try to make sure the heat mostly gets transferred to the gas before it is too late to do any good.

So, two very different propellant-chemistry problems, once you get past "first, generate lots of energy".

Another interesting case where you want lots of energy and condensed-phase reaction products is infrared decoy flares. Hot gas tends to come with a characteristic emission spectrum, whereas blackbody radiation is harder to characterize as "decoy" vs. "target". The standard flare mix is I believe a combination of magnesium, PTFE, and viton binder. Yes, Teflon(tm) as an oxidizer.

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7. Anonymous on August 2, 2012 10:21 PM writes...

The plot thickens: a barrister of my acquaintance is an avid reader of Things I Won't Work With (and an aviation engineer: I have my copy of Ignition! through his good offices) who often sups a pint or two with Mr. Stross.

M'Learned friend gives lectures and seminars on intellectual property law: one of the set-piece discussion exercises is 'the man in the white suit', the story of an employed industrial chemist who invents an everlasting and unstainable fabric.

The patent reads: cotton fabric is treated with Chlorine Trifluoride and Dimethyl Mercury...

None of those diligent students of jurisprudence ever called him on it.

I recall him reading the 'patent' in a pub full of deep SF geeks, authors, rocket scientists and the like: a leading lecturer in astrophysics choked on his beer and fell back into his seat, horrified, and gibbering "That... That would be THE BIGGEST ECOLOGICAL DISASTER IN RECORDED HISTORY!"

Needless to say, Charlie Stross knows the particulars of the 'case'. The three of them may well have consulted one another on creating the biggest ecological disaster in recorded history, and I hope that this effort remains confined to the pages of fiction.

I look forward, someday, to reading an hypothetical academic case on a sexually-irresistable aftershave lotion scented with some of your favourite selenium, tellurium and sulphur compounds.

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