Evidence for Nanoparticles in Microwave-Generated Fireballs Observed by Synchrotron X-Ray Scattering

Abstract

The small-angle x-ray scattering method has been applied to study fireballs ejected into the air from molten hot spots in borosilicate glass by localized microwaves [V. Dikhtyar and E. Jerby, Phys. Rev. Lett. 96 045002 (2006)10.1103/PhysRevLett.96.045002]. The fireball's particle size distribution, density, and decay rate in atmospheric pressure were measured. The results show that the fireballs contain particles with a mean size of approximately 50 nm with average number densities on the order of approximately 10(9). Hence, fireballs can be considered as a dusty plasma which consists of an ensemble of charged nanoparticles in the plasma volume. This finding is likened to the ball-lightning phenomenon explained by the formation of an oxidizing particle network liberated by lightning striking the ground [J. Abrahamson and J. Dinniss, Nature (London) 403, 519 (2000)10.1038/35000525].

Observation of the Optical and Spectral Characteristics of Ball Lightning

“…The most well-known model was proposed by Kapitza [12], hypothesizing that an intense radio frequency electromagnetic field could supply the necessary energy to form and sustain BL. A great number of microwave experiments leading to the generation of fireballs have been conducted based on this model [13][14][15][16]. Recently, Dikhtyar and Jerby [17] reported the ejection of fireballs from molten hot spots induced by localized microwaves.…”

Small angle x-ray scattering and electron microscopy of nanoparticles formed in an electrical arc

“…The large micron sized particles seen here and in previous studies 2 are most likely formed by the ejection of droplets a (The voltage drop between the electrodes during the arc being determined by the electrode material with a value in this case of 25 V irrespective of the initial applied voltage, the energy released into the arc is determined by the current supplied). b In our flame experiments, [6][7][8] we have identified families of nanoparticles of sizes between 10 and 70 nm, though light scattering and electron microscopy studies typically image micron sized structures formed by the aggregation of these nanoparticles.…”

“…Generally for the results presented here, a one level-fit is sufficient and so we do not see signs of aggregation of the nanoparticles as is the case for soot particles in a flame 6,7 or metallic particles formed in a microwave air plasma. 8 Over the many measurements performed between, above and below the electrodes, the mean radius of gyration of the particles determined from fitting the Unified function, fell between 30 and 40 nm. Figure 5 shows a particle size distribution determined by taking the Inverse Fourier transform of the same scattered intensity curve as shown in Figure 4.…”

“…We and others have used SAXS to investigate particles in other dilute media including flames, 6, 7 microwave air plasmas 8,9 and laser ablation plumes. 10 It is a very powerful technique since it is independent of the index of refraction of the particles, a parameter that is necessary to analyse light scattering experiments and that can change with the particle temperature.…”

A combined small- and wide-angle x-ray scattering detector for measurements on reactive systems

“…[1][2][3][4][5][6][7] Particle synthesis can be done in combustion processes, e.g., silica, titania, and iron oxide nanoparticles have been produced in flames using hydrocarbon fuels. [8][9][10][11] One of the most promising tools for particle dynamics studies is based on synchrotron x-ray scattering, [12][13][14] which has demonstrated the ability to study soot formation in flames in situ: small-angle x-ray scattering (SAXS) to characterize the size distribution of soot particles, [15][16][17][18][19][20][21] and wide-angle x-ray scattering (WAXS) to study the subnanometer structure. 22,23 These scattering techniques measure the intensity of scattered photons as a function of the exchanged momentum, q, according to…”