Exothermic Reaction Kinetics in High Energy Density Al-Ni with Nanoscale Multilayers Synthesized by Cryomilling

Abstract

Abstract:The Al-Ni system is known as a high energy density materials (HEDM) because of its highly exothermic nature during intermetallic compound (IMC) formation. In this study, elemental Al and Ni powder were milled to explore the effect of cryomilling atmosphere on the microstructure and exothermic behavior. Scanning electron microscope (SEM) observations show continuous structural refinement up to 8 h of cryomilling. No IMC phase was detected in the X-ray diffraction (XRD) spectrum. Differential thermal analyzer (DTA) results show two exothermic peaks for 8 h cryomilled powder as compared to that of powder milled for 1 h. The ignition temperature of prepared powder mixture also decreased due to gradual structural refinement. The activation energy was also calculated and correlated with the DTA and SEM results. The cryomilled Al-Ni powder is composed of fine Al-Ni metastable junctions which improve the reactivity at a lower exothermic reaction temperature.

Reactive Ni–Al-Based Materials: Strength and Combustion Behavior

“…In the Ni-Al-PTFE specimens, the ignition temperature was about 620-640 • C. According to the data of [43], at a heating rate of 10 • C/min, the reaction proceeded at 585 • C. In the present experiments, the recorded temperature was higher due to the high heating rate, as explained by the authors in [42]. The ignition temperature can be reduced using nanosized powders [47] or high-energy ball milling (HEBM) [10,48] and cryomixing [49]. The use of nanopowders is associated with difficulties such as agglomeration and autoignition in air.…”

Synthesis and Properties of Bulk Nanostructured Metallic Materials

“…The high reduction potential capability of alkaline metal reagents in the reductive environment allowed formation of a pure magnetite phase. Oh et al [11] employed a cryomilling technique to achieve a NC lamellar structure of high energy density Al-Ni powders. In this research, Al and Ni powders with a molar ratio of 50:50 were milled in liquid nitrogen to generate nanoscale lamellar structure between Al and Ni without forming intermetallic compounds (IMCs).…”