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Preparation of Eutectic KNO3-NaNO3-sorbitol Propellant
Summary: the task is to melt KNO3-NaNO3-sorbitol 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 milled together with coffee mill, crystals measured 50 microns to 300 microns.
Sorbitol: pharmaceutical grade. Moisture content 0.2-0.3%.
50 g batch of thoroughly mixed powdered KNO3-NaNO3-sorbitol 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 5 sm
17 min, 95C, sorbitol starts to melt
31 min, 140C, thin layer of liquid appears at the bottom
44 min, 175C, almost all sorbitol melts, liquid layer at the bottom is about 3 mm
60 min, 190C, all sorbitol melts, liquid layer at the bottom is about 3 mm
1h 15 min, 190C, without changes
1h 30 min, 190C, without changes. It is clear that at this temperature propellant will not melt completely.So I start to increase temperature.
1h 35 min, 203C, small bubbles appears at the bottom, sorbitol starts to decompose
1h 40min, 225C, liquid layer at the bottom starts to grow
1h 50 min, 225C. The thickness of propellant layer is 3 sm
2h, 230C, almost half of propellant completely melts, but decomposition of sorbitol starts to accelerate, so I decide to stop further heating. Video of decomposition.
After stirring propellant completely melts.