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Preparation of Eutectic KNO3-NaNO3-mannitol Propellant
in the Oven
Summary: the task is to melt in the oven 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%.
Mannitol: pharmaceutical grade. Moisture content <0.1%.
Two samples were prepared for melting, they were placed on a baking sheet in the oven (not on the bottom of the oven). Electric oven with effective temperature controller was used. Temperature was measured by the thermometer placed on a baking sheet.
From left to right:
1. 20 g batch of KNO3-NaNO3-mannitol mixture was powdered in mortar to fine dust and placed in glass test tube. Height of powdered mixture is 15.6 cm.
2. 20 g batch of thoroughly mixed unmilled KNO3-NaNO3 (crystals' size is about 0.5 mm) +mannitol propellant mixture was placed in glass test tube. Height of powdered mixture is 14.7 cm.
15 min, 200C. Mannitol starts to melt.
20 min, 205C. All mannitol melts.
30 min, 200C. Dissolution of nitrates becomes appreciable.
35 min, 200C. Separation of nitrates starts in the left test tube with milled nitrates. All nitrates in the right test tube are alredy separated.
40 min, 200C Video of separation
45 min, 200C. Separation of nitrates to the bottom occurs in both samples.
50 min, 203C.
1h, 203C, almost without changes. It is clear that at this temperature propellant will not melt completely.So I start to increase temperature.
1h 10 min, 234C. Dissolution of nitrates at the bottom starts. This temperature is close to the melting point of KNO3-NaNO3 eutectic - 220-225C (from different sources).
1h 30 min, 240C. Almost all nitrates are dissolved, I deside to stop heating.
Glass surfaces is covered with bubbles.