Abstract
Ammonium Dinitramide (ADN) in its generic form has a long needle shaped structure, which hinders higher solid loading. Therefore, it is of utmost importance to optimize its crystal morphology into octagonal shapes. Moreover, the low critical humidity level of ADN renders it unusable in a humid climate. Hence, encapsulation with a hydrophobic polymer is necessary. In the present work, ADN was synthesized by nitration of potassium sulfamate with mixed acid nitration. The product was then mixed with toluene, graphene, citryl ammonium butyl, Cab-o-sil, and coating polymer (Polystyrene or HTPB) and treated with ultrasound to obtain semi-spherical ADN-coated particles. The method offers a reduction in operating temperature and elimination of ADN melting in the shape-altering process. In addition, the ADN product has a similar particle size and thermal stability compared to those in a conventional ADN melt-prilling method. The ADN product investigated under SEM confirms the particle morphological change from long needles into semi-spherical shapes. The particle size obtained, in the micrometer range, is ideal for higher theoretical maximum density. Furthermore, the ultrasound-treated ADN particles show significant reduction in moisture absorption, from 68% to 16% at 65% relative humidity. The DSC result shows no degradation of thermal stability of the coated particles.
Highlights
The utility of Ammonium Dinitramide (ADN) as a highly energetic oxidizer has several advantages in terms of performance, stability [1], and environmental friendliness as compared to conventional Ammonium Perchlorate (AP)-based propellants [2]
The hygroscopicity of ADN can be decreased by coating it with hydrophobic polymers [3,5,6] such as hydroxyl terminated polybutadiene (HTPB), polystyrene (PS), and polyacrylate (PA)
We investigate the use of an ultrasound sonication technique to alter the morphology and improve the hygroscopicity of the ADN particles
Summary
The utility of Ammonium Dinitramide (ADN) as a highly energetic oxidizer has several advantages in terms of performance, stability [1], and environmental friendliness as compared to conventional Ammonium Perchlorate (AP)-based propellants [2]. Solid grain casting of raw ADN is hindered by its needle shape [3] and by its high moisture absorption tendency and lower critical humidity level (55.2% RH). Previous experiments have shown that the moisture absorption of ADN is higher than that of AP [4]. Specifications given on the particle size, particle layout geometry, and surface area under the experimental conditions have seldom been described in the literature. These factors, i.e., particle morphology and water absorption [7], are known to reduce the Theoretical
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