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For instance, I read that the Hercules X-265 rocket motor used in the Sprint missile was a solid double base propellant that used nitrocellulose with zirconium metal staples and nitroglycerin as a binder. How would sodium metal staples work instead of zirconium?

Or better yet, suppose one were to build an experimental solid/liquid rocket motor that used molten sodium metal with liquid oxygen. Due to extreme temperature difference there might need to be an igniter to get the combustion started. Sodium is abundant, has a melting point close to the boiling point of water (~ 208 degrees Fahrenheit). To my knowledge, such an experimental rocket engine like this has never been tested. The main problem would be that the highly toxic exhaust, NaO, would react with moisture to form NaOH (lye or caustic soda).

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  • $\begingroup$ Clarke's "Ignition!" mentions various sodium compounds used to alter freezing points and facilitate ignition of various other fuels, but nothing particularly interesting. The book covers liquids almost exclusively, though. $\endgroup$ – Russell Borogove May 25 '17 at 21:59
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    $\begingroup$ What would be the advantage of doing this? $\endgroup$ – Organic Marble May 25 '17 at 22:20
  • $\begingroup$ @OrganicMarble: Because liquid metal has much higher density, it would mean that less actual fuel would be required than a lower density liquid fuel. Also, sodium, being an alkali metal, is highly reactive in its elemental form and easily oxidized. $\endgroup$ – Mr X May 25 '17 at 23:29
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    $\begingroup$ Isn't low molecular weight desirable in propellants? $\endgroup$ – Organic Marble May 26 '17 at 1:31
  • $\begingroup$ Low molecular weight is desirable in exhaust products (higher exhaust velocity). High bulk density is desirable in propellants (smaller tanks). There are other considerations as well, but these two in particular are often at odds with one another. Depending on your design requirements, the balance point will be different. $\endgroup$ – Tristan May 26 '17 at 14:36

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