Spark discharges

This is a transient discrete electric discharge which takes place between two conductors which are at different potentials, bridging the gap in the form of a single ionization channel (Plate 4). Based on light emission measurements of sparks with symmetrical electrode geometry, the energy is dissipated approximately uniformly along the channel. This is in contrast with asym- 

PLATE 4. Spark discharge between spherical electrodes. 

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Pulsed spark sources, in which the material to be analyzed is part of one electrode, are used for semiquantitative analyses. The numerous and complex processes involved in spark discharges have been studied in detail by time- and space-resolved spectroscopy (94). The temperature of d-c arcs, into which the analyte is introduced as an aerosol in a flowing carrier gas, eg, argon, is approximately 10,000 K. Numerous experimental and theoretical studies of stabilized plasma arcs are available (79,95). 

Brush Discharge With dusts with MIE values of less than 3 mJ determined with purely capacitive spark discharges (without induc-... 

Sparks Discharge Spark discharges can ignite dust-air mixtures up to an MIE of 1 J. If an uncertainty area is taken into account, this corresponds to an EIE of I to 10 J. 

Sparks Spark discharges are most common between solid conductors, although one electrode may be a conduc tive liquid. They appear as a narrow, luminous channel, and cany a large peak current for a few microseconds or less. Sparks are the only form of discharge for which a maximum spark energy can be calculated, using the expression ... 

Electrostatic spark discharge and ignition during charging of solids resulting in possibility of fire/explo-sion. Potential for explosion to start a thermal decomposition of reaction mass. 

Approximately 70 different elements are routinely determined using ICP-OES. Detection limits are typically in the sub-part-per-billion (sub-ppb) to 0.1 part-per-million (ppm) range. ICP-OES is most commonly used for bulk analysis of liquid samples or solids dissolved in liquids. Special sample introduction techniques, such as spark discharge or laser ablation, allow the analysis of surfaces or thin films. Each element emits a characteristic spectrum in the ultraviolet and visible region. The light intensity at one of the characteristic wavelengths is proportional to the concentration of that element in the sample. 

Calibration curves must be made using a series of standards to relate emission intensities to the concentration of each element of interest. Because ICP-OES is relatively insensitive to matrix effects, pure solutions containing the element of interest often are used for calibration. For thin films the amount of sample ablated by spark discharges or laser sources is often a strong function of the sample s composition. Therefore, either standards with a composition similar to the sample s must be used or an internal standard (a known concentration of one element) is needed. 

Section 5.4.1 described explosions in storage tanks, and Section 13.3 described explosions in tank trucks, ignited by static sparks. The static was formed by the flow of a nonconducting liquid, and the spark discharges occurred between the body of the liquid and the grounded metal containers (or filling arms). 

Minimum Igniting Current (MIC) Ratio The ratio of the minimum current required from an inductive spark discharge to ignite the most easily igni table mixture of a gas or vapor, divided by the minimum current required from an inductive spark discharge to ignite methane under the same test conditions. 

Funken-auswurf, m.. spark emission, -bildung, /. spark formation, sparking, sparkling, -ent-ladung, /. spark discharge. 

Fig. 20 Schematic representation of an eiectric spark discharge chamber for the activation of gases at normal atmospheric pressure for the production of fluorescence in substances separated by thin-layer chromatography [2],...

The answer is "NO." In the combustible mixture, an electric spark produces a flame kernel. Initially, its shape is elliptical (like an American football), and then becomes a torus (like an American doughnut). Afterwards, it changes into almost spherical shape, and propagates spherically in the unbumed mixture. This process is formed by the existence of spark electrodes, which is necessary for spark discharge. Spark electrodes lead not only to heat loss from the flame kernel but also a change in the kernel shape. Both affect the minimum ignition energy. 

Schlieren photograph of flame kernels by a high-speed camera. Time is given from the onset of spark discharge in microseconds. Spark electrode diameter 0.2 mm spark gap width 1mm. 

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