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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)
- limits on boron aluminum combustion can be controlled by changing the combustion temp (https://collections.lib.utah.edu/details?id=195697). we can change combustion temperature to have a more complete reaction.
- utah paper purchased: H.C. Starck Grade A AlB2. they found the commerical powder had 82.4%, with the remaining percent being mainly free aluminum, and then ~2% oxygen (it appears boron is the limiting reactant which is good because it suppresses the burn which we don't want but the extra aluminum will contribute to the burn). found that the surface area was 2.09 m^2/g for commercial
- 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)
- in general notes
- pressing the propellant in the utah link increased reaction - ig this says what we already knew about vacuuming to decrease voids
Need to find a way to test propellant burning in vacuum. try to find professional solid prop person to ask about how to simulate this/do appropriate testing