(564d) Effect of Liquid Hydrocarbon-Based Process Control Agents on Characteristics of Mechanically Alloyed Al·Ti Powders

Aluminum is a common fuel additive in propellants and explosives. Reducing agglomeration of aluminum powders and accelerating their burn rates are important for maximizing the utility of the high aluminum combustion enthalpy in solid propellants. Similarly, higher burn rates are necessary to couple the energy of aluminum combustion to that of a blast in an explosive charge. Previously, mechanical alloying was used to prepare a range of Al·Ti powders. It was observed that such powders ignite at lower temperatures than pure aluminum; particles of such alloys also burn faster than the same size pure Al particles. However, prepared powders were relatively coarse. Previous efforts were not successful in reducing the particle size of the Al·Ti particles because of the ductile nature of both metals and cold welding accompanying mechanical alloying. Recently, it was found that the particle size and surface morphology for Al-based materials can be successfully controlled using a polar hydrocarbon fluid, acetonitrile, as a process control agent, PCA. This work aims to characterize systematically the effect of liquid hydrocarbon-based PCAs on the particle size, surface morphology, and structure of mechanically alloyed Al·Ti powders. Samples of Al-rich Al-Ti alloy were prepared by mechanical alloying using both polar and non-polar hydrocarbon PCAs, acetonitrile and hexane, respectively. Upon recovery of the powders, the surface morphologies and particle sizes are characterized using SEM. It is observed that the particle agglomeration occurs for the powders processed with hexane; conversely, powders processed with acetonitrile contain well-separated, finer particles. Prepared materials are characterized using differential scanning calorimetry; their ignition is explored using a heated filament experiment operated at different heating rates. Particle combustion is studied by introducing the powders into an air-acetylene flame and/or by feeding the powder through a focused beam of a CO₂ laser. Results will be presented and interpreted with the aim of developing the mechanistic understanding of the effect of surface modification of Al·Ti alloys on their ignition and combustion.