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- Lithium (hella toxic and expensive) and boron have the best combustion temperatures (gravimetrically)
- Boron has high efficiency but it requires high heat of combustion and it is easily oxidized so a boron oxide film forms around the boron atoms and prevents diffusion of oxygen during combustion. (would probably need more oxidizer and decrease the amount of aluminum and boron/magnesium)
- Most articles talk specifically about boron and just say it suppresses the burning of the aluminum, need to look into more literature about aluminum diborate https://arc.aiaa.org/doi/pdf/10.2514/3.26212
- Instead use metal borides
- Aluminum Diborate (around 1-6 microns)
- 121.5 J/cc (volumetric)
- 37.5 kJ/g
- Decreases ignition delay by a factor of 1.5-2
- Described on page 8 ENERGETICMATERIALSANDMETALBORIDESFORSOLIDPROPELLANTROCKETENGINES819441-1374197.pdf
- longer burn time than aluminum-boron mixture (what we are looking for), longer ignition delay (need stronger hei) (source: https://www.sciencedirect.com/science/article/pii/S1270963818322673)
- Magnesium diborate
- https://collections.lib.utah.edu/details?id=195697 - thermodynamic comparisons of a number of metal borides including magnesium and aluminum diboride
- Aluminum Diborate (around 1-6 microns)
- Large boron particles increase linear burn rate (makes the combustion occur closer to the surface of the propellant) https://link.springer.com/article/10.1134/S0010508222050136(make someone read this because it has a lot of formulas about sims so maybe make someone make a sim)
- Also increases temperature
- Boron has high efficiency but it requires high heat of combustion and it is easily oxidized so a boron oxide film forms around the boron atoms and prevents diffusion of oxygen during combustion. (would probably need more oxidizer and decrease the amount of aluminum and boron/magnesium)
- Magnesium
- Increases heat of combustion but is much more toxic
- And much more reactive (apparently can react just with water and explode. Not good)
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