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.

Reactive multilayers fabricated by vapor deposition: A critical review

“…A different product phase has been reported for 3Ni/Al [63], Pt/Al [60], Ti/2B [148], Zr/2Si [56], Ni .91 V .09 /Zr [153], and 7Ni .91 V .09 /2Zr [153] multilayers. Many of these systems (e.g., 7Ni .91 V .09 /2Zr) form a single product phase irrespective of their bilayer thickness.…”

“…Surveying the systems listed in Table 1, it is apparent that, in general, highly exothermic systems propagate at increased rates. Rapid reactions with speeds N 10 m/s have been observed in 2Ni/3Al [58], Pt/Al [60], Ni(V)/1100 Al [70], Ru/ Al [144], 3Nb/Si [67], Zr/2Al [147], Zr/3Al [147], Sc/Au [90], Y/Au [90], Ti/2B [148], CuO/Al [76], and Ti/C [146] multilayers of different total thicknesses. Equiatomic Pt/Al self-propagates at the highest reported rates, up to 100 m/s, even when adhered to substrates [60], while low exothermicity Ni/Ti [101] is an example system that propagates at low rates.…”

“…Such differences are likely responsible, in part, for the relatively low rates in Ti-B and Ti-C multilayers listed in Table 1. Ti/2B has the largest heat of reaction (−110 kJ/mol; −1.14 eV/atom) [148] and the second highest adiabatic temperature (3498 K) [158] of all bimetallic systems listed in Table 1. Nevertheless, the propagation speeds of Ti/2B multilayers are less than those of Pt/Al and a few other bimetallic pairs.…”

The critical condition for thermal explosion in an isoperibolic system

“…One striking application is the combustion of bimetallic foils used for joining temperature-sensitive or dissimilar materials. 23,24 Also, a promising new low-temperature fabrication route to synthetize high-performance metal oxide thin films based on combustion has recently attracted much attention. 25 In these particular applications, heat dissipation to the substrate is very important because it can hinder combustion by avoiding the overheating needed to set a thermal runaway.…”

Gasless Reactive Compositions for Materials Joining: An Overview

“…A new class of gasless reactive systems — so‐called Reactive Multilayer Nanofilms (RMNFs) — prepared by magnetron sputtering onto a cooled substrate has been suggested for combustion‐aided joining of temperature‐sensitive materials and parts in microelectronics . Besides bimetallic foils, the above technique was also used to prepare the foils of Nb/Si and Ti/2B composites …”