Microwave-assisted modulation of light emission intensity in alkali-pyrotechnic plumes

Smart Electromagnetic Thermites: GO/rGO Nanoscale Thermite Composites with Thermally Switchable Microwave Ignitability

“…For both thermites, bulk ignition is followed by high intensity emission which is maintained until the microwave field is shut off (∼5 s after ignition). This high emission reaction region is diffuse (Figure 6) and characteristic of the electric field antinode shape 12,13 rather than a buoyancy driven pyrotechnic flame. On the basis of the prior studies of microwave enhancement of aluminized composite solid propellants 12 and pyrotechnic flares, 13 where emission enhancement of atomic metal and aluminum oxide condensed combustion products were observed, this region represent a plasma kernel formation in the gaseous thermite products.…”

“…This high emission reaction region is diffuse (Figure 6) and characteristic of the electric field antinode shape 12,13 rather than a buoyancy driven pyrotechnic flame. On the basis of the prior studies of microwave enhancement of aluminized composite solid propellants 12 and pyrotechnic flares, 13 where emission enhancement of atomic metal and aluminum oxide condensed combustion products were observed, this region represent a plasma kernel formation in the gaseous thermite products. On the basis of the prior studies, the high flame temperatures and electronically excited flame zone and products begin to couple with the electric field and microwave energy is deposited to the flame zone by (1) electronic and (2) dielectric loss mechanisms, which creates a weak plasma enhanced flame zone.…”

“…On the basis of the prior studies, the high flame temperatures and electronically excited flame zone and products begin to couple with the electric field and microwave energy is deposited to the flame zone by (1) electronic and (2) dielectric loss mechanisms, which creates a weak plasma enhanced flame zone. 12,13 Average microwave ignition delays as a function of rGO content are shown in Table 1. Neat thermites (0 wt % coating) exhibited an average microwave ignition delay of ∼4.34 s. Ignition of the neat thermite is expected to occur primarily due to electric field, as suggested in Meir et al 8 Fe 2 O 3 heating through an induction loss mechanism is lower than dielectric heating for large particles (orders of 100 μm), 50 and induction losses are expected to be negligible for the experimental conditions studied, as magnetic field amplitude is lowest at the electric field antinode for a transverse electric field mode.…”

“…Microwave energy interactions with energetic materials have been studied for a number of purposes including explosive/thermite ignition, − as a means of burning rate control in composite propellants, and to switch light emission profiles of pyrotechnics . These studies examine microwave energy deposition to the energetic and its reaction wave by various mechanisms, which include: (1) dielectric losses (dipolar polarization), − (2) interfacial losses at grain/phase boundaries or defect regions (Maxwell–Wagner polarization), , or (3) conduction losses (eddy current or magnetic induction heating). , …”

Effect of metal oxides on the light radiation intensity of Ba(NO3)2/Mg-containing pyrotechnic mixtures combustion

“…However, early studies on light radiation intensity were generally performed by adjusting the compositions, ratios, and particle sizes of the components under the assumption that optical intensity depends on the energy of the combustion reaction and the reaction rate of the pyrotechnic composition 13 , 14 . Barkley et al 15 explored the effects of microwave illumination on the irradiance and color of Mg/alkali metal nitrate pyrotechnic flames, providing evidence that microwave illumination of alkali-containing pyrotechnic flames may be a useful strategy to achieve dynamic control of light emission intensity. Although this method has a good effect, still, it requires additional microwave light source, high cost and not convenient for practical popularization.…”