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Nigrosin - Best opacifier by mass.
TiO2 - Opacifier. Rejects radiative heating. Creates white propellant.
Fuels
Aluminum - More energetic than magnesium but requires a larger motor to properly take advantage of. Large incompletely burned particle can damage nozzle. Tendency to deposit slag inside motor.
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Magnesium Oxide
Phenylnaphthalene
DTBHQ - 2,5-ditert-butylhydroquinone
Processing Aids
Lecithin
Silicon Oil - Reduces adherence to mixing bowl. Makes propellant pour better.
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Strontium Carbonate - Red.
Flame Retardants
Melamine - Used when using HTPB as a liner material