Rocket Oxidizers

 
 
Ozone
Liquid oxygen enriched with ozone has been proposed as an energetic rocket oxidizer. It is claimed that the sensitivity of ozone to detonation is greatly reduced when care is taken to avoid even very small traces of hydrocarbon impurities. Even 4ppm impurities was enough to dangerously sensitize liquid ozone. Generally, previous observations of the danger of ozone toward explosion had not examined extremely pure samples free from trace impurities.
The boiling point of oxygen is 90 K, while the boiling point for is ozone is 161 K. The liquid oxygen boils out from a mixture of ozone much faster, gradually increasing the concentration of ozone. When the concentration approaches 30 percent, below 93 K, the mixture separates into two distinct liquid layers, the first containing 30% ozone, and the second containing 75%. As more oxygen boils off, the volume of the 30% concentrated ozone layer decreases, while the volume of the 75% layer increases. This creates an unusual danger of explosion when trying to enrich liquid oxygen with ozone.
However, addition of either 5% oxygen difluoride or of 9% liquid fluorine prevented layers from separating out in the liquid oxygen and ozone mixture, thus reducing danger of explosion.

Here is a list of potential fuel-oxidizer combinations
lithium and fluorine (lithium is a fairly rare and expensive element, fluorine is difficult to liquify)
pentaborane and oxygen difluoride
diborane and chlorine pentafluoride
aluminum borohydride and nitrogen trifluoride mixed with sulfur hexafluoride
magnesium aluminum hydride and nitric acid, enriched with 20%N2O5 and NO2
trimethyl aluminum and tetrafluorohydrazine

I also have the idea that hydroxylammonium nitroformate would be a good solid rocket oxidizer, being both more energetic than ammonium perchlorate, and having acceptable resistance to detonation. Like almost all other solid oxidizers, however, it would not be able to compete with cryogenic oxidizers in terms of specific impulse.

Here are some basic calculations I have done, while thinking about energetic rocket fuels:

The most energetic reaction that is possible for a rocket is a mix of OF2 with a Li-Be alloy. Beryllium and Oxygen together release 24.36 kJ/g. Lithium and Fluorine release 23.75 kJ/g.
While using ozone instead to burn Be would yield 26.26kJ, ozone is sensitive to detonation. Oxygen difluoride will yield 23.8 kJ/mol extra energy than a comparable mixture of O2 and F2. There are 54g/mol for OF2, thus it is calculated that the use of OF2, rather than O2 and F2, should provide an extra 0.44 kJ/g. Lithium is fairly expensive (US$95/kg). Beryllium is much more so ($745/kg). While lithium-Al alloy is already used (as structural material) for that large central brown colored exterior fuel tank on a rocket, this tank is recoverable. The fuel inside the tank has far more mass than the tank itself, so using Lithium as rocket fuel is not economical.

Using a new article: "A New Determination of the Heat of Formation of Oxygen Difluoride" by WARREN R. BISBEE, Rocketdyne Division, North American Aviation
The heat of formation of OF2, with this newly determined value, is 16.994 kJ/mol (0.3147 kJ/g); this calculation does not agree with my earlier one. Wikipedia claims a 24.5 kJ/mol heat of formation, which gives a value of 0.454 kJ/g. Thus, three different values have been calculated for the additional energy OF2 will contribute.

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