Condensed-Phase and Oxidation Reaction Behavior of Ti/2B Foils in Varied Gaseous Environments

Abstract

The effect of gaseous environment on self-propagating reactions in Ti/2B multilayer foils was studied. Multilayers with reactant layer periodicities from 50 to 3000 nm and a nominal stoichiometry of 1:2 Ti:B were grown using magnetron sputtering. Analysis through scanning transmission electron microscopy, differential scanning calorimetry, and X-ray diffraction revealed the as-deposited multilayers consisted of well-ordered layers of crystalline Ti and amorphous B with the amount of intermixed material negligibly affecting the exothermicity. Propagation rate testing was performed at varied vacuum pressures and studied by high-speed imaging. Propagation rates for foils with bilayer thicknesses 666 nm or thinner did not exhibit a pressure dependency, while foils with bilayer thicknesses 857 nm and larger did. The latter, thick-bilayer foils would not propagate below a characteristic pressure. After reaction, Auger electron spectroscopy revealed O penetration in the thicker bilayer designs and incomplete mixing of Ti and B, while the thinner bilayer foils were uniformly converted to single-phase, hexagonal TiB2. Increased air pressure was found to promote the propagating reaction of the thicker bilayer designs, likely due to increased heat release from oxidation that promotes intermixing and reaction between Ti and B.