Partial discharge pressure dependence

In many cases, (3 has been found with some 10° bar 1 [20]. Atypical example for partial discharges in air and their pressure dependence is given in Fig. 6.17. 

Partial discharges (due to an electric field) are pressure dependent lower pressures (or higher altitudes) will increase the partial discharge strength, and vice versa [20]. 

Kawaguchi et al. [05Kaw] have monitored the intensities of the o = 1-0 P(8) (2405.336 cm ) emission of ArH " and simultaneously that of 5p-6s R(6.5) (3700.774 cm ) of ArH after discharge pulses using Time Resolved Fourier Transform Inlrared Spectroscopy (TR-FTS). The decay dynamics was studied in dependence of the partial H2 pressure. 

The devolatization sections and the discharge section up to the screw tip contain predominantly conveying elements that are partially filled in the devolatization area and completely filled in the pressure build-up area. A homogenous melt is generally assumed in these processing steps where viscosity is altered up to the tip of the screw, depending on the temperature evolution. 

Figure 5.13 shows the dependence of O2 partial pressure on discharge power and the growth rate achieved for ZnO deposition at different substrate temperatures using reactive MF magnetron sputtering. The O2 partial pressure was measured with a A-probe and the discharge power was controlled at constant gas flow. The experimental conditions are summarized in Table 5.3. 

Fig. 5.13. (a) Process characteristic for reactive MF magnetron sputtering of ZnO showing the dependence of reactive gas partial pressure p(O2) on discharge power P and process set points chosen for deposition, (b) dependence of growth rate a on reactive gas partial pressure p(O2) for different substrate temperatures (reprinted from [90])... 

Fig. 5.27. Time dependence of the oxygen partial pressures and the discharge power during the coating process of substrates of 1,000 x 600 mm2 using identical deposition conditions. Without symmetry control the oxygen partial pressures in the upper and lower part of the discharge may vary from one run to the next or change in an unpredictable manner during the process...

Rate constants measured in discharge-flow systems depend upon measurements of (a) the velocity of flow u, and (b) the partial pressures of reactants. For a reaction first-order in atom concentration [A], the rate constant is given by = iJ d In [A]/dx = — (RTZFlAp)d In [A]/ dx, where SF is the total flow rate, A is the cross-section area of the flow tube, p is the total pressure, and x is the displacement along the tube axis. For simple reactions of higher overall orders, the dependences of rate constants upon the parameters SF, A, p and reagent flow rate F< are summarized in Table 4.2. The importance of accurate measurements of flow rates and of total pressure, particularly for reactions of overall second and third orders, is clear. For example, realistic random errors of 1 % in/ , and of 3% in SFand F<, lead to an error of 12% in Atj. 

When an electric discharge is passed through a cold diatomic gas at low pressure it is partially dissociated into atoms in this way reasonable concentrations of O, H, D, N, halogen or other atoms can be produced in a chemically inert diluent. The recombination of these atoms, and their reaction with other molecules can be observed as the gas flows down a long tube. Many of the reactions produce molecules in excited electronic states the resulting chemiluminescence can be used to measure the concentration of atomic species as a function of distance, and hence time, down the tube. Dr Clyne describes this important technique, which has produced direct measurements of the rates of many exothermic reactions of atoms and free radicals at room temperature and below. The reverse of the recombination steps are, of course, the dissociation reactions whose kinetics at high temperatures were described in the first chapter if the ratio of forward and reverse rate constants is equal to the equilibrium constant, the temperature dependence of these rates can be deduced over very wide ranges of temperature. 

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