Effect of Gas Pressure on Discharge

Chang et investigated the effect of gas pressure on diamond nucleation density in microwave ECR discharge. It was found that the nucleationdensity decreased shghtly, from 2.2 x 10 to 0.5 x 10 cm, as the gas pressure increased fi-om 2 to 20 torr. 

Prabaharan et al7 studied the effect of gas pressure by employing porous carbon electrode as air cathode without involving a catalyst to elucidate effects of gas pressure in Li-air cell. It is revealed that an optimum pressure must be sustained throughout the life cycle of the battery (at least during discharge). Figures below (Fig. 4.4) exhibit gas pressure dependence on the performance of Li-air battery. In order to establish an effective triphasic region at air cathode side, an optimum gas pressure must be maintained. 

An allotrope of oxygen, ozone, O, (8), forms in the stratosphere by the effect of solar radiation on 02 molecules. Its total abundance in the atmosphere is equivalent to a layer that, at normal temperature and pressure, would cover the Earth to a thickness of only 3 mm. Ozone can be made in the laboratory by passing an electric discharge through oxygen. It is a blue gas that condenses at — 112°C to an explosive blue liquid that... 

The hollow-cathode plume (HCP) [137] makes rather different use of the hollow-cathode effect. The hollow-cathode base is a sample disc with a 1-2 mm orifice. By choosing appropriate gas pressures and discharge currents, the energetic plume is ejected through the orifice. A constricted hollow-cathode discharge localized in the narrow orifice creates intense sputter action on the surface of the disc and causes direct transport of the atoms into the plume for excitation — and ionization, if required. 

Figure 6.10. The constant current discharging curve of the PEMFC during running with different cathode gas for 100 hours. Current density 500 mA/cm cell temperature 70 °C RH anode 65 °C, and cathode 68 °C dew points, ambient pressure [34]. (Reprinted from Journal of Power Sources, 166(1), Jing F, Hou M, Shi W, Fu J, Yu H, Ming P, et al.. The effect of ambient contamination on PEMFC performance, 172-6, 2007, with permission from Elsevier.)...

In the laboratory, it has been found that similar effects can be produced if a voltage is applied between two electrodes immersed in a gas. The nature of the laboratory or instrumental discharge depends critically on the type of gas used, the gas pressure, and the magnitude of the applied voltage. The actual electrical and gas pressure conditions determine whether or not the discharge is called a corona, a plasma, or an arc. 

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