Method for obtaining ADN crystals through crystallization in a viscous medium
View Patent ↗The present invention relates to a method for crystallizing ammonium dinitramide (ADN), through spontaneous nucleation and crystal growth, from a solution containing said ammonium dinitramide (AND) dissolved in a solvent. Said solvent characteristically has a viscosity greater than or equal to 0.25 Pa s (250 cP) when said spontaneous nucleation is implemented. The ADN crystals obtained by said method have a median shape factor of 1 to 1.5 and are perfectly suitable for placement in the composition of energy materials.
1. A method for crystallizing ammonium dinitramide, comprising: implementing spontaneous nucleation and generating a crystal in a solution containing ammonium dinitramide and a solvent, wherein said solvent has a viscosity greater than or equal to 0.25 Pa.s (250 cP) when said spontaneous nucleation is implemented.
2. The method as claimed in claim 1 , wherein said solvent has a viscosity between 0.25 Pa.s (250 cP) and 1 Pa.s (1000 cP) when said spontaneous nucleation is implemented.
3. The method as claimed in claim 1 , wherein said solution is cooled before said spontaneous nucleation is implemented.
4. The method as claimed in claim 1 , wherein said solvent is a polar protic solvent.
5. The method as claimed in claim 1 , wherein said solvent is a mixture of glycerol and 1,4-butanediol.
6. The method as claimed in claim 1 , wherein said solution containing said ammonium dinitramide contains nitrate ions.
7. The method as claimed in claim 6 , wherein the nitrate ion concentration of said solution is between 0.1% and 0.5% by weight.
8. The method as claimed in claim 6 , wherein said nitrate ions are obtained by said ammonium nitrate being introduced into said solvent.
9. The method as claimed in claim 3 , wherein the method comprises the following successive steps:
a first step of imposed cooling of said solution as far as into the thermodynamic zone of spontaneous nucleation of said solution;
a second step of spontaneous nucleation and crystal growth for the generation of small crystals at constant imposed temperature until a return to equilibrium of the solution on the solubility curve; and
recovery of said small crystals.
10. The method as claimed in claim 3 , wherein the method comprises the following successive steps:
a first step of imposed cooling of said solution as far as into the thermodynamic zone of spontaneous nucleation of said solution;
a second step of spontaneous nucleation and crystal growth for the generation of small crystals at constant imposed temperature until a return to equilibrium of the solution on the solubility curve; and
a third step comprising imposed heating of the solution loaded with small crystals while remaining in the metastable zone for partial dissolution of said small crystals, followed by a hold at a temperature for thermodynamic equilibrium of the solution; said third step being followed by
a fourth step of continuous imposed cooling while remaining in the metastable zone of the solution for the generation of larger crystals; and by
recovery of said larger crystals.
11. The method as claimed in claim 1 , wherein said solvent has a viscosity between 0.3 Pa.s (300 cP) and 0.65 Pa.s (650 cP) when said spontaneous nucleation is implemented.
12. The method as claimed in claim 1 , wherein said solvent has a viscosity between 0.45 Pa.s (450 cP) and 0.55 Pa.s (550 cP) when said spontaneous nucleation is implemented.
13. The method as claimed in claim 1 , wherein said crystal has a median shape factor of between 1 and 1.5.