Atmosphere plasma

Meteors produce atmospheric plasmas as their kinetic energy is converted to thermal energy (50). Most particles from space are consumed before they reach an altitude of 50 km. Meteors are of Httie practical use, although radio waves can be bounced off the plasmas left in their wakes (see Exthaterresthial materials). ... 

McAdams, R. (2001) Prospects for non-thermal atmospheric plasmas for pollution abatement, J. Phys. D Appl. Phys. 34, 2810-21. 

Vassen R, Hathiramani D, Mertens J, Haanappel VAC, and Vinke IC. Manufacturing of high performance solid oxide fuel cells (SOFCs) with atmospheric plasma spraying (APS). Surf. Coat. Technol. 2007 202 499-508. 

Atmospheric Plasma Spray (Triplex APS). These deposition techniques will be used within this project to deposit the various layers in planar SOFC. 

The other important factor to affect the operational conditions of the cell is the voltage increase between the carbon and copper lead. This problem has been solved individually in industry. For example, a 250 pm thick layer of nickel can be coated onto the upper part of the carbon anode using the atmospheric plasma spraying method.7 This electrode has been operated at 15 to 17 A dm-2 in a 1000 A scale industrial cell for 19 months. The cell voltage was 9.5 V and polarization did not occur with this electrode. Characteristic points of this new carbon electrode are low polarizability and no anode effect, and the concentration of carbon tetrafluoride contaminating the fluorine is below 2 ppm. 

The wettability of ABS can be increased by the treatment with an atmospheric plasma torch (64).. This was established by contact angle measurements and other methods. The wettability was increased when the atmospheric plasma treatment was done in a slow manner. The decrease in contact angle with respect to water is explained due to a significant increase in the oxygen content, which is caused by the formation of carboxylic and hydroxyl groups on the polymer surface. 

J. Abenojar, R. Torregrosa-Coque, M.A. Martinez, and J.M. Martin-Martinez, Surface modifications of polycarbonate (PC) and acrylonitrile butadiene styrene (ABS) copolymer by treatment with atmospheric plasma, Surf. Coat. Technol, 203(16) 2173-2180, May 2009. 

In order that the discussion of the individual reaction processes, which combined to describe the overall chemistry of the atmospheric regions, can be facilitated and readily placed into context, a brief description of the atmospheric plasma medi-... 

When an electron neutralizes a positive ion, the energy released can be dissipated either in photon emission (radiative recombination), or by a third body encounter with the transient excited atom or molecule (three-body recombination) or by the fragmentation of the transient excited molecule (dissociative recombination). Radiative recombination only occurs with a very small probability and three-body recombination only occurs at high pressures or high charge densities, neither of these being appropriate to the atmospheric plasma. It is the dissociative process, exemplified by reactions (5a) and (5b), which is dominant in the ionosphere. In fact, reactions (5a) and (5b) are almost entirely responsible for the loss of ionization in the ionosphere above 85 km altitude (with N2 recombination contributing somewhat) as is readily shown by simple calculations based on laboratory determinations of dissociative recombination coefficients, are, for the dominant molecular ions 02 and NO+. 

Loss of ions occurs via the processes of mutual neutralization, ternary ionic recombination and attachment to aerosol surfaces, processes which urgently need further study in the laboratory. It is an interesting fact that the ion chemistry directly accelerates the loss of ionization from all regions of the atmospheric plasma. Atomic ions are converted into molecular ions, molecular ions into larger cluster ions which recombine more rapidly. The larger ions also act as nucleation sites for the formation of aerosols, thus involving a transition from the molecular to the liquid state. 

Probably because the field is relatively young, not much has been reported yet on gas-liquid discharges in a microfluidic (microreactor) format. Yamatake et al. have used a DC-driven atmospheric plasma micro hollow cathode to directly inject O radicals into a fast oxygen gas... 

Atmospheric plasma research was originally stimulated by the interest in radio wave propagation and therefore was focussed on the ionosphere. Thus, the early in situ ion composition measurements were made in the ionosphere at altitudes above about 100 km using rocket-borne spectrometers [15, 16, 17]. Below 100 km, the atmospheric gas pressure becomes so large that mass spectrometers have to be pumped which represents a major barrier for extending in situ ion composition measurements downwards into the mesosphere. Such measurements became technically feasible only with the advent of compact high speed cryopumps which could be used on rockets. 

Species identified to date in atmosphere. Plasma is primarily H +, O ", S +. Suggested as having an underground ocean. ... 

Several methods effectively apply thin coatings to substrates. One process commonly employed for TBC fabrication is thermal plasma spraying. For this technique, the bond coat is deposited with low-pressure plasma spraying, and the Zr02 top coat is then created using atmospheric plasma spraying.A potential problem with this method is coating fracture due... 

Plasma Gas state (also called fourth dimension) from a mixture of electrically charged ions and neutral atoms/molecules. Results from plasma discharge mainly used for surface pretreatment of plastics (q.v. atmospheric plasma). 

Thickness of APS (atmospheric plasma spraying) coating can be selected between 50 and 250 pm, depending on application however, novel deposition techniques such as suspension or solution plasma-spraying allow coatings with thickness <10 pm. 

Figure 5.32 SEM images of conventional atmospheric plasma sprayed (APS, left) and suspension plasma sprayed (SPS, right) hydroxyapatite coatings, (a, b) Top view and (c, d) coating cross-sections (Gross and Saber-Samandari, 2009). ( With permission by Elsevier.)...

Table 6.6 Phase contents of atmospheric plasma-sprayed calcium phosphate coatings after immersion in protein-free SBF (HBSS, Table 7.8) for 12 weeks (in mass%) (Figure 6.2d —f).

Figure 6.7 Morphology of hydroxyapatite power 30 kW, spray distance 240 mm (c) splats deposited under different atmospheric plasma power 30kW, spray distance 220 mm plasma spray (APS) conditions as revealed and (d) plasma power 45 kW, spray distance by a so-called wipe test, (a) Plasma power 220mm (Heimann, 2008).

A notable exception is a study by Hesse et al. (2008) who investigated the effect of powder grain size and grain size distribution on the spatial distribution of calcium phosphate phases in atmospheric plasma-sprayed hydroxyapatite coatings incubated in r-SBF (SBF-H, Table 7.8). Coatings were mechanically abraded under dry conditions in steps of 40 pm by abrasive SiC paper, and the newly created surfaces analysed by XRD with Rietveld refinement for their quantitative phase composition. The results of this depth profiling are shown in Figure 6.8. 

Figure 6.17 Formation of a thin CaSi03 (or CaTiSi05) reaction layer adjacent to the titanium alloy substrate surface of an atmospheric plasma-sprayed Ti6AI4V...

Heimann, R.B. and Wirth, R. (2006) Formation and transformation of amorphous calcium phosphates on titanium alloy surfaces during atmospheric plasma spraying and their subsequent in vitro performance. Biomaterials, 27, 823-831. 

Park, E. and Condrate, R.A. (1999) Graded coating of hydroxyapatite and titanium by atmospheric plasma spraying. Mater. Lett., 40, 228-234. 

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