In-operando high-speed microscopy and thermometry of reaction propagation and sintering in a nanocomposite

Abstract

An important proposed mechanism in nanothermites reactions — reactive sintering — plays a significant role on the combustion performance of nanothermites by rapidly melting and coalescing aggregated metal nanoparticles, which increases the initial size of the reacting composite powders before burning. Here, we demonstrate a high-speed microscopy/thermometry capability that enables ~ µs time and ~ µm spatial resolution as applied to highly exothermic reaction propagation to directly observe reactive sintering and the reaction front at high spatial and temporal resolution. Experiments on the Al+CuO nanocomposite system reveal a reaction front thickness of ~30 μm and temperatures in excess of 3000 K, resulting in a thermal gradient in excess of 10 7 K m −1 . The local microscopic reactive sintering velocity is found to be an order of magnitude higher than macroscale flame velocity. In this observed mechanism, propagation is very similar to the general concept of laminar gas reaction theory in which reaction front velocity ~ (thermal diffusivity x reaction rate) 1/2 .

Surface Plasmon Enhanced Fluorescence Temperature Mapping of Aluminum Nanoparticle Heated by Laser

“…In particular, the interaction of Al NPs with reactive fluoropolymer films has attracted significant interest as fluoropolymers may be cast onto a diverse set of substrates and are compatible with additive manufacturing [ 1 , 2 , 3 , 4 , 5 ]. The reaction properties and mechanisms of energetic fluoropolymer films have been widely studied by measuring the reaction temperature evolution to understand thermal characteristics and heating kinetics [ 6 , 7 , 8 ]. Recently, we reported an in situ study of isolated fuel nanoparticles reactions by photothermal heating on a plasmonic grating platform to understand differences in the behavior of Al NP reactions with fluoropolymer and metal oxide constructs [ 9 , 10 ].…”

A Benchmark Study of Burning Rate of Selected Thermites through an Original Gasless Theoretical Model

“…In theory, mixed nanoparticles possess higher interfacial contact and a decrease in mass-transport lengths resulting in much wider reaction fronts. However, the loss of their nanostructures during the early stage of initiation due to sintering was experimentally observed, providing an explanation for the longer than expected burn times [5,36,37]. Prior to this, a debate in the community of thermite materials was focused on whether condensed phase rather than gas phase mechanisms were responsible for the different combustion regimes, e.g., initiation and combustion.…”

Direct Identification of Two Regimes of Metal Particle Combustion using Condense-luminescence

“…The large scatter in emissivity justi es examination of non-equilibrium nano-oxide light emission [12]. This departure of non-equilibrium should be taken into account when interpreting pyrometry measurements in reactive systems [13].…”