Laser Initiation Processes in Thermite Energetic Materials Using Laser Desorption Ionization Time-of-Flight Mass Spectrometry

Abstract

The reactive processes that occur during the laser initiation of aluminum/iron(III) oxide metastable intermolecular composites (MIC) have been studied by laser-induced desorption ionization time-of-flight mass spectrometry. The ions observed in the plume from the aluminum show fragments from the ablation of the oxide coating and from the metal core. Ablation of the iron oxide component consists primarily of pure iron species such as [Fe] + and [Fe 2 ] + and small oxides such as [FeO] + and [Fe 2 O] + ions. In smaller quantities, metal oxide clusters that are either oxygen deficient, [Fe(FeO) x ] +, or oxygen equivalent, [(FeO) x ] +, are observed. When the thermite composite is initiated, mixed metal species are observed in the plume, which correspond to the aluminum substitution analogues of the iron oxide clusters, specifically, [FeAl 2 O 3 ] +, [AlFe 2 O 3 ] +, and [AlFe 2 O 2 ] + . Notably, the amounts of these mixed metal products that form are inversely proportional to the size of the aluminum particles. This suggests that the decrease in ignition time observed in MIC materials is due to the more facile liberation of reactive metallic aluminum when the particle size is small.