Rocket Candy

 

After the failure of my gunpowder, I searched for use of burnt sugar for carbon and learned of rocket candy. This is what hobbyists use for some serious model rocketry. There are many variants and degrees of sophistication among enthusiasts, but I needed simple success. What I read told me (essentially) to combine 65% saltpeter with 35% powered sugar (sucrose) in a mortar and mix it into a fine powder. I should have powdered only the saltpeter first since powdered sugar is so fine already. I used 3g of the sugar and 5.5g of saltpeter (measured precisely this time). 8.5g also turned out to be a very manageable total size.

Using a so-called dry method, I put this mix in an outside grill with cover and temperature gauge. At about 220F the sugar starts to melt. I went up to around 250F and pulled it out. Note the KNO3 does not melt or react at this temperature, so we have to stay in this low temp area and not use a blow torch as I like to do.  This method can be potentially unsafe - I would not wish to spill the contents onto the grill's burners, for example. Once a reaction starts it will complete. After I had my melt out, it was simple matter to thoroughly stir the candy-like substance below: 

This material is very moldable, by the way. Here is what I recovered upon cooling and tapping out of the dish:

The bit on my stainless stirrer cooled hard quickly and so I broke it off as a perfect test size and place it in a safe area. I zapped it with my blow torch and it fizzled loudly and made prodigious smoke. Success! I have oxidized carbon from sugar in a chain reaction. I may come back to "real gunpowder," but this is essentially the same reaction. Oversimplified:

2KNO3 + CH2O -> 2KNO2 + CO2 + H2

In fact, you can add sulfur and charcoal as the reaction is very much like gunpowder. CH2O as an oversimplified model for sugar is not unlike that of charcoal. Sulfur is optional as a fuel that lowers the ignition point and can increase combustion. I don't like messing with sulfur more than I need to because it stinks and tends to create hydrogen sulfide gasses. Think of it like dirty coal or gasoline - we pay extra to keep the sulfur out of fuels.

Now I need a rocket. The whole thing took less than an hour from concept to test. No mistakes this time. :)

Thanks for reading,

Paul 

p.s. Aug 25:

I found a better equation for this reaction using the actual molecule of sucrose. It is a bit clunky, and recall that "burning" is not simply one reaction.

48KNO3 + 5C12H22O11 -> 24K2CO3 + 36CO2 + 24N2 + 55H20

With this better equation, I was able to multiply out the molecular weights and got exactly 26% sucrose and 74% saltpeter by weight. I am told the recommended formulation is a bit fuel rich to allow for more fluidity in preparation. Note the products are different. In reality there are many different reactions but this is a much better model than above.

I was also able to calculate the enthalpy of the reaction. With 48 moles of saltpeter (4.8kg) and 5 moles of sucrose (1.7kg) you could create 20.3MJ of energy. So I created enough product for 2.3kJ, roughly.