Nickel Nanoparticles with Superior Catalytic Activity for Autonomous Decomposition of Ammonium Percholorate

Nickel nanoparticles with partially lled d-shell could offer advanced catalytic performance; to common solid propellant catalysts (ferric oxide). This study reports on the facile fabrication of nickel and ferric oxide catalysts of 10 nm, and 5 nm particle sizes respectively. Fabricated particles were re-dispersed in organic solvent and effectively integrated into ammonium percholorate (AP). Elemental mapping conrmed uniform particle dispersion into APC. The catalytic eciency of nickel was evaluated to Fe 2 O 3 particles using DSC and TGA. AP demonstrated endothermic crystallographic phase change at 242 0 C, with subsequent two exothermic decomposition reactions. Nickel demonstrated decrease in endothermic phase change by 49 % compared with 39 % for ferric oxide; this action means high catalytic activity with low activation energy. Whereas AP demonstrated total heat release of 742 J/g; nickel offered enhanced heat output by 89 % compared with 57 % for ferric oxide. The two main decomposition peaks were merged into single peak. Nickel demonstrated decrease in main decomposition temperature by 105 o C compared with 62 o C for ferric oxide. This manuscript shaded the light on nickel as novel emergent nanocatalyst with superior performance for advanced energetic systems.

Combustion reactive species undergo a sequence of chain reactions to form a premixed ame with nal products i.e. O 2 , NO, and N 2 O. However the strong endothermic crystallographic phase as well as endothermic sublimation process could withstand high activation energy; such endothermic processes could render high burning rate regimes [4][5]. Catalyzed combustion process can secure low activation energy; consequently stable burning at high reaction rate could be accomplished [16][17]. Recently much research was directed to nano-catalysts which have the potential to enhance AP decomposition [18][19][20].
This study reports on the facile fabrication of ferric oxide and nickel nanoparticles (NPs), using hydrothermal processing. Enhanced particle dispersion is obligatory to secure prospected catalytic activity [26][27][28].Catalyst particles were developed and re-dispersed in acetone. Colloidal particles were integrated into AP via co-precipitation technique. Elemental mapping revealed particle dispersion to the molecular level. Thermal behavior of AP nanocomposites was evaluated using DSC and TGA. AP

Synthesis of nanocatalysts
Fe 2 O 3 NPs were manufactured using hydrothermal synthesis; additional information can be found in the following references [27][28][29]. Nickel nanoparticles were developed via batch hydrothermal processing of nickel acetate using hydrazine as a reducing agent.

Nanocatalyst characterization
Morphology (size and shape) of ferric oxide and nickel NPs was visualized using TEM (JEM-2100F by Joel Corporation). The crystalline structure was investigated with XRD (D8 advance by Burker Corporation). SEM (ZEISS SEM EVO equipped with EDAX detector) was employed to assess the dispersion of NPs into AP matrix.

Integration of nano-catalysts into AP
Colloidal ferric oxide and nickel NPs were harvested from their synthesis medium and re-dispersed in acetone using ultrasonic probe homogenizer. Catalyst NPs were integrated into APC using anti-solvent technique. Morphology of AP nanocomposite was investigated using SEM. Elemental mapping using EDAX detector was adopted to assess the catalyst dispersion into AP matrix.

Catalytic activity assessment
The potentials of developed nano-catalysts on AP thermal behavior was assessed using DSC Q20 by TA, USA. The tested sample was heated to 500 0 C at 5 o C min -1 , under inert gas ow (N 2 at 50 ml min -1 ).
Thermal behavior of AP nanocomposite was assessed using TGA (55 by TA, USA). The tested sample was heated to 500 0 C at 5 0 C.

Results And Discussion
Bespoke catalyst particles can offer enhanced heat output with low activation energy. At nanoscale, superior catalytic performance could be accomplished; as high interfacial surface area and reactivity could be accomplished.

Nanocatalyst characterization
TEM micrographs demonstrated high quality mono-dispersed Fe 2 O 3 NPs of 5 nm average particle size (Figure2-a, 2-b). Mono-dispersed nickel NPs of 10 nm were reported from TEM micrographs (Figure 2 It can be concluded that the integration of colloidal particles into AP via anti-solvent technique offered uniform particles into AP matrix. Elemental mapping was performed to verify catalyst particle dispersion. SEM micrographs of AP nanocomposite revealed enhanced levels of nickel particle dispersion into AP ( Figure 6).
Integration of colloidal nano-catalysts into AP matrix secured uniform particle dispersion to the molecular level.

Thermal behavior of AP nanocomposite
The catalytic e ciency of nickel to ferric oxide NPs on AP thermal behavior was investigated using DSC. Whereas, AP demonstrated endothermic crystallographic phase change by 103 J/g; nickel NPs demonstrated decrease in endothermic crystallographic phase change by 49 % compared with 39 % for ferric oxide. While AP demonstrated total heat release of 742 J/g. Nickel NPs offered enhanced heat output by 89 % compared with 57 % for ferric oxide NPs ( Figure 6).
The two main exothermic decomposition peaks were merged into one single peak. Additionally nickel demonstrated decrease in main decomposition temperature by 105 0 C compared with 62 0 C for ferric oxide NPs. The impact of catalyst NPs on AP thermal behavior was further evaluated using TGA ( Figure   7). AP demonstrated two main decomposition stages. AP experienced initial dissociative sublimation with the evolution of NH 3 and HClO 4 (perchloric bluish ame) at 298 0 C; this degradation reaction accounts for 30 wt % loss. Total decomposition with the evolution of nal gaseous products was accomplished at 452 0 C.These ndings were found to be in good accordance with literature ( Figure 1). Nano-catalysts offered one single decomposition stage. Nickel NPs demonstrated enhanced catalytic activity as total weight loss was accomplished at lower decomposition temperature compared with ferric oxide particles. TGA thermograms were found in good agreement with DSC outcomes [30]. Nickel NPs with superior catalytic activity can offer facile decomposition route at low temperature. The effectiveness of nickel nanoparticles could be correlated to partially lled d-shell electrons. Nickel NPs can offer co-ordination or complex formation; as well as adsorption of gaseous products on their massive surface area ( Figure 8) [24].
Catalytic effectiveness of nickel NPs was summarized to three main parameters including: Decrease in heat required for endothermic phase change Lower decomposition temperature Boost heterogeneous reactions on the catalyst surface, with high heat output.

Conclusion
Nickel and ferric oxide NPs of 10, and 5 nm average particle sizes respectively were developed via hydrothermal processing. Fabricated NPs were re-dispersed in organic solvent and effectively integrated into AP. Elemental mapping con rmed uniform particle dispersion into AP matrix. The catalytic e ciency of nickel was evaluated to ferric oxide NPs using DSC and TGA. Nickel demonstrated high catalytic e ciency to ferric oxide counterparts. Nickel offered decrease in AP endothermic phase change by 49 % compared with 39 % for ferric oxide. Whereas AP demonstrated total heat release of 742 J/g; nickel offered enhanced heat output by 89 % compared with 57 % for Fe 2 O 3 NPs.