Plasma Dynamics

Contains table of contents for Section 2 and reports on four research projects.Lawrence Livermore National Laboratory Subcontract 6264005National Science Foundation Grant ECS 84-13173National Science Foundation Grant ECS 85-14517U.S. Air Force - Office of Scientific Research Contract AFOSR 89-0082-AU.S. Army - Harry Diamond Laboratories Contract DAAL02-86-C-0050U.S. Navy - Office of Naval Research Contract N00014-87-K-2001Lawrence Livermore National Laboratory Subcontract B108472National Science Foundation Grant ECS 88-22475U.S. Department of Energy Contract DE-FG02-91-ER-54109National Aeronautics and Space Administration Grant NAGW-2048U.S. Department of Energy Contract DE-AC02-ET-51013U.S. Department of Energy Contract DE-AC02-78-ET-5101

Plasma Dynamics

Contains table of contents for Section 2 and reports on four research projects.Lawrence Livermore National Laboratory Subcontract 6264005National Science Foundation Grant ECS 84-13173National Science Foundation Grant ECS 85-14517U.S. Air Force - Office of Scientific Research Contract AFOSR 84-0026U.S. Army - Harry Diamond Laboratories Contract DAAL02-86-C-0050U.S. Navy - Office of Naval Research Contract N00014-87-K-2001National Science Foundation Grant ECS 85-15032National Science Foundation Grant ECS 88-22475U.S. Department of Energy Contract DE-AC02-ET-5101

Plasma Dynamics

Contains table of contents for Section 2 and reports on four research projects.National Science Foundation Grant ECS-89-02990U.S. Air Force - Office of Scientific Research Grant AFOSR 89-0082-CU.S. Army - Harry Diamond Laboratories Contract DAAL02-89-K-0084U.S. Army - Harry Diamond Laboratories Contract DAAL02-92-K-0037U.S. Department of Energy Contract DE-AC02-90ER-40591U.S. Navy - Office of Naval Research Grant N00014-90-J-4130Lawrence Livermore National Laboratories Subcontract B-160456National Aeronautics and Space Administration Grant NAGW-2048National Science Foundation Grant ECS-88-22475U.S. Department of Energy Grant DE-FG02-91-ER-5410

Plasma Dynamics

Contains table of contents for Section 2 and reports on four research projects.National Science Foundation Grant ECS 89-02990U.S. Air Force - Office of Scientific Research Grant AFOSR 89-0082-BU.S. Army - Harry Diamond Laboratories Contract DAAL02-89-K-0084U.S. Department of Energy Contract DE-AC02-90ER40591U.S. Navy - Office of Naval Research Grant N00014-90-J-4130Lawrence Livermore National Laboratory Subcontract B-160456National Science Foundation Grant ECS 88-22475U.S. Department of Energy Contract DE-FG02-91-ER-54109National Aeronautics and Space Administration Grant NAGW-2048U.S.-Israel Binational Science Foundation Grant 87-0057U.S Department of Energy Contract DE-AC02-78-ET-5101

Sequential Solidification of Metal Powder by a Scanning Microwave Applicator

This study examines the fundamental feasibility of sequential metal-powder solidification by localized microwave-heating (LMH) provided by a scanning, all-solid-state microwave applicator. This continuous process is considered for the additive manufacturing (AM) and 3D printing (3DP) applications of metal parts. In previous studies, we employed LMH for the incremental solidification of small batches of metal powder in a stepwise vertical manner. Here, we study a continuous lateral LMH process, layer by layer, in a fashion similar to laser scanning in powder beds, as performed in common laser-based AM systems. LMH solidification at scanning rates of ~1 mm3/s is obtained in bronze powder using ~0.25-kW microwave power. The effect is studied here by LMH scanning in one lateral dimension (~20-mm long) in layers, each of ~1–4 mm thickness and ~2–4 mm width (mechanically confined). Imperfect solid bars of ~20×4×5 mm3 are obtained with rough surfaces. Their joining in an L shape is also demonstrated. The experimental solidified products are tested, and their hardness and density properties are found to be comparable to laser-based AM products. The capabilities and limitations of the LMH scanning concept for metal-powder solidification are evaluated. The potential feasibility of a solid-state LMH–AM technology is discussed

Synchrotron Radiation Studies of Nanoparticles formed in Flames and Plasmas

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Observations of Ball-Lightning-Like Plasmoids Ejected from Silicon by Localized Microwaves

This paper presents experimental characterization of plasmoids (fireballs) obtained by directing localized microwave power (<1 kW at 2.45 GHz) onto a silicon-based substrate in a microwave cavity. The plasmoid emerges up from the hotspot created in the solid substrate into the air within the microwave cavity. The experimental diagnostics employed for the fireball characterization in this study include measurements of microwave scattering, optical spectroscopy, small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Various characteristics of these plasmoids as dusty plasma are drawn by a theoretical analysis of the experimental observations. Aggregations of dust particles within the plasmoid are detected at nanometer and micrometer scales by both in-situ SAXS and ex-situ SEM measurements. The resemblance of these plasmoids to the natural ball-lightning (BL) phenomenon is discussed with regard to silicon nano-particle clustering and formation of slowly-oxidized silicon micro-spheres within the BL. Potential applications and practical derivatives of this study (e.g., direct conversion of solids to powders, material identification by breakdown spectroscopy (MIBS), thermite ignition, and combustion) are discussed

Rapid internal bubble formation in a microwave heated polymer observed in real-time by x-ray scattering

International audienceA combined study of small-angle and wide-angle X-rayscattering (SAXS/WAXS) of the melting of a nylon-6 sample by localized microwave radiation has shown that this method can reveal the presence of bubbles forming and disappearing rapidly in realtime in the interior of the sample due to its thermal decomposition

Evidence for nanoparticles in microwave-generated fireballs observed by synchrotron X-ray scattering

International audienceThe 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]

Plasma column and nano-powder generation from solid titanium by localized microwaves in air

International audienceThis paper studies the effect of a plasma column ejected from solid titanium by localized microwaves in an ambient air atmosphere. Nanoparticles of titanium dioxide (titania) are found to be directly synthesized in this plasma column maintained by the microwave energy in the cavity. The process is initiated by a hotspot induced by localized microwaves, which melts the titanium substrate locally. The molten hotspot emits ionized titanium vapors continuously into the stable plasma column, which may last for more than a minute duration. The characterization of the dusty plasma obtained is performed in-situ by small-angle X-ray scattering (SAXS), optical spectroscopy, and microwave reflection analyses. The deposited titania nanoparticles are structurally and morphologically analyzed by ex-situ optical and scanning-electron microscope observations, and also by X-ray diffraction. Using the Boltzmann plot method combined with the SAXS results, the electron temperature and density in the dusty plasma are estimated as ∼0.4 eV and ∼1019 m−3, respectively. The analysis of the plasma product reveals nanoparticles of titania in crystalline phases of anatase, brookite, and rutile. These are spatially arranged in various spherical, cubic, lamellar, and network forms. Several applications are considered for this process of titania nano-powder production