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Preparation of Eutectic KNO3-NaNO3-mannitol Propellant
Summary: the task is to melt KNO3-NaNO3-mannitol 35-30-35 propellant without stirring until complete dissolution of nitrates.
KNO3:and NaNO3 reagent grade "pure for analysis". Moisture content 0.1-0.2%. They were not milled, crystals' size is about 0.5 mm.
Mannitol: pharmaceutical grade. Moisture content <0.1%.Crystals' size is about 0.5-1 mm.
50 g batch of thoroughly mixed unmilled KNO3-NaNO3-mannitol propellant mixture was placed in glass beaker and heated with temperature controlled heat plate. Temperature was measured with thermometer at the bottom of the beaker.
0 min, temperature 22C. The thickness of propellant layer is 4.5 sm
10 min, 145C, mannitol starts to melt
20 min, 164C
30 min, 180C, separation of nitrates starts
40 min, 188C
50 min, 192C, without changes
1h, 193C, without changes. It is clear that at this temperature propellant will not melt completely.So I start to increase temperature.
1h 10 min, 211C, almost all bottom layer of nitrates is melted.
1h 20min, 220C
1h 30 min, 225C. All bottom layer of nitrates is melted. Clearly visible separate layer of nitrates-rich liquid is formed.
It is much more dense, than upper layer and is not easily mixed with upper layer by stirring with thermometer (video).