KNO3-LiNO3-Eutectic system sugar propellant

Sabalith® is a salt mixture of 65% KNO3 and 35% LiNO3. The mixture is normally used for salt bath curing in open or closed circulations, e.g. in LCM installations for the vulcanization of rubber. The melting point of the Eutectic system is approx. 130°C (266°F). This could make it interesting for propellant applications, e.g. producing a very homogenous solution of molten sugar/sabalith.

KNO3- LiNO3 phase diagram
Other salt phase diagrams

Upon thermal decomposition, LiNO3 gives lithium oxide, nitrogen dioxide, and oxygen:

4 LiNO3 → 2 Li2O + 4 NO+ O2

Other group I nitrates decompose differently, forming nitrite salt and oxygen: 

2 KNO3 → 2 KNO+ O2

A first experiment using the molten salt mixture as a solvent for the fuel (sucrose) was performed as following:

- 6.5g KNO3 and 3.5g LiNO3 mixed in a beaker
- 20min in the baking oven at 160°C under air circulation mode
- 5g fine powdered sucrose added after salt mixture got liquid, stirred till it got a homogenous white paste
- Poured on a coated baking paper, cooled down to room temperature

Eutectic system mixture of 6.5g KNO3, 3.5g LiNO3 and 5g sucrose:

Combustion of the propellant probe:

With this method solid and castable black powder could be made. Just liquefy KNO3/ LiNO3 and add sulfur (melting point 115.21°C, 239.38°F) and charcoal powder. Instead of sucrose sorbitol will be used for next  experiments, as the melting point of waterfree sorbitol is 110–112°C, which leads to a blend of oxidizer and fuel.  The biggest drawback is the hygroscopy of LiNO3. This could be avoided by coating the propellant surface after casting with cellulose nitrate lacquer.

Update 2011-9-7

First try to produce cast able black powder by the Eutectic system method:

Used ratio: 6.5g KNO3/3.5g LiNO3/2.2g C, 1.4g S

KNO3/LiNO3 mixture starts to liquify:

Molten sulfur swimming on the KNO3/LiNO3 mixture like oil on water:

First casted batch of  black powder:

Combustion test. A lot of molten  Li2O remains. I will look into possibility to elute LiNO3 after casting with methanol or ethanol.

An old German chemistry book says, if you use a mixture of 54.54 parts KNO3, 18.18 parts NaNO3 and 27.27 parts LiNO3 the melting point drops to 120°C (248°F). This mixture ratio is preferable as it keeps the LiNO3 amount small.

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