Story about the dangers of sodium (SC) and potassium chlorate (PC).

Many amateurs from the "good old days" have experimented with the cheap and readily available chlorates. Because these chemicals are for sale virtually anywhere, many younger and uninformed rocketeers try to make motors with it.

Luckily the Internet has created an easy access to information and experiences of others. And the experiences all tell the same thing: stay away from the chlorates!

There are many reasons why chlorates are dangerous, or to say it in a better way why they become dangerous. (very few chemicals are dangerous on their own, mostly a reaction with another chemical is needed or it needs heat, shock, radiation....)
This document is meant to explain those reasons.

The document will be mainly about sodium chlorate, because potassium chlorate isn't a good oxidiser anyway because of it's extremely high burn rate exponents.
SC also has a fairly high burn rate exponent so if you could make a chemically stable propellant with it, it would be very difficult to control.

1. properties of NaClO3

• melting point: 300°C
• decomposition: 248°C
• solubility in water: 100g/100ml
• density: 2,5g/cm3

2. Reactivity

Sodium chlorate will react with a wide variety of chemicals because it's made out of a strong base (NaOH) and a relatively weak acid (HClO3).

To determine which reactions are possible we should have a look at the pKa values.

Sodium chlorate is a salt (= product made out of a positive and negative ion, here a metal and the anionic "rest" of an acid).
This means it will react with any acid (or salt with the corresponding acid "rest" ) that has a lower pKa value than -1 (with the exception of other sodium salts) if this happens in a watery environment. (Sodium chlorate is a little hygroscopic so this is VERY likely to happen)

Reactions with other salts can be quite harmless because only new salts are formed. But this makes it hard to control the properties of a propellant made with less than 100% pure chemicals.

For example:

NaClO₃ + KCl --> NaCl + KClO₃

If the reaction occurred with an ammonium salt though we have a dangerous combination:

NaClO₃ + NH₄Cl --> NaCl + NH₄ClO₃ (Ammonium chlorate)

Ammonium chlorate is a dangerous explosive compound that can easily explode when heated or if it's submitted to shock. And we don't need this, don't we?

But beware of reactions with acids! They result in the formation of chlorine dioxide gas. Chlorine dioxide is a common disinfectant so you wouldn't think it's so dangerous. Unfortunately this gas is unstable and it can explode "on it's own" or in reactions with other compounds. This is why ClO₂ is always produced on-site if needed in an industrial process (bleaching, disinfecting, ...). It's way too sensitive to transport.
It attacks any organic compound and many metals because of it's oxidising nature.
Contact with ammonia gas usually results in a spontaneous explosion.

And above all…it isn't very healthy to breathe…

An example reaction would be:

NaClO₃ + HCl --> NaCl + ClO₂^ + H₂O

Acidity is the reason why some mixtures with SC or PC self-ignite. Sulphur contains acid rests of sulphuric acid (unless you use the chemically pure stuff) so mixtures with sulphur are a bad idea…

Experiments show that SC can react quite disastrous to metallic impurities such as copper. The author has experienced self-ignition in his experimental teenager years from a mixture of SC, sulphur and sugar. Possible reason for this was an electrical wire that dropped into the stuff by accident (or it was the acid from within the sulphur).

Although burn rate catalysts can lower the pressure exponent, they often increase the burn rate beyond control. A propellant usually ignites more readily when it contains burn rate catalysts and because SC-propellants ignite around ONLY 248°C this is not a good case at all.

3. Conclusion

A few of the possible dangerous reactions with SC have been described above. The ones that weren't mentioned are complex organic reactions. The author didn't do any scientific tests on this topic, this document is based only on theoretical facts.

The author has done one motor test with SC/PUR propellant resulting in what seemed to be a detonation…150g of propellant exploded on ignition and made a crater one meter in diameter.

Al this doesn't say it is impossible to make propellant based on chlorates. This can't be said because there haven't been a lot of tests in the past. So further testing is needed before even thinking about making small motors.

Any comment is, of course, welcome.