Influence of Electrode Material on Time Delay of Electrical Breakdown in Gases

Abstract

Introduct.ionThe process of the formation of electrical discharge in gases is greatly dependent on the electrode surface quality.The probability of releasing secondary electrons from clean iiietal surfaces, or from metal surfaces covered with oxide layers depends on the work function of the cathode material. Iinpiirities and oxide layers on the cathode surface decreaRe8 the work func-Secondary einission of electrons due to the bombardment of the cathode surface with ions and excited a t o m or molecules has an important role in the discharge in gasfilled diodes, a t pressures lower than the atmospheric. For most gases secondary emission of electrons from the cathode due to the bombardment with positive ions is predominant. However, the influence of secondary emission induced by nietastable atoms or niolecules of some gases can not be ignored. For example, for the argon-filled diodes with tantaliliii electrodes, coefficients of secondary emission of electrons due to the bombardment with positive ions and nietastable atoms are very close being 0.023 and 0.022, respectively. Siniilarly for the argon-filled diodes with molybdenum electrodes the corresponding values are 0.065 a n d 0.071 [l].Detailed experimental as well as theoretical investigations of the gas discharge in nitrogen-filled diodes [2--81 show that a t E/p = 75 V cni-1. inbar-' the secondary emission of electrons due to the bombardment of the cathode surface with N2(A3L',,+) metable moleciiles, diffusing through the gas, has n predominat role. The nuniber of secondav emission electrons induced by metastable nitrogen molecules per unit cathode surface depend on the coefficient of secondary emission as well as on the nriinber of X2 metastables which per second arrive a t the correqponding cathode siirface [5]. There are a few nietliods for the detection of inetastable atonis or iiiolecules in gases, the optical ones are generally adopted, but they are efficient only a t high concentrations (> 10'3 c1iir3) of inetastable atoms or molecules in gases [g].

Analysis of statistical nature of electrical breakdown time delay in nitrogen at 6.6 mbar pressure in presence of positive ions and N(4S) atoms

“…What is common to both curves is that the increase of overvoltage leads to the decrease in t d and that both curves saturate at high applied voltages. This is in accordance with the statement that the increase of voltage on the tube's electrodes increases the probability that secondary electrons released from the cathode lead to breakdown [9]. For a constant value of the electron yield Y , when t d ≈ t s , t d ≈ 1/P .…”

“…Afterglow period is the time interval when the operating voltage turns of in the previous and turns on in the following breakdown. Also, it was found that the electrical breakdown time delay depends on various parameters such as surface condition of the cathode [7], temperature of the electrodes [8], cathode material [9], gas pressure [10], inter-electrode distance [11], discharge current [12].…”

Electrical breakdown in low pressure gases

“…The next investigated parameter that influences t d is the electrode material. t d as a function of the difference between the applied voltage and the static breakdown voltage (U w −U s ) for nitrogen-filled tubes with different electrode materials (p = 7 mbar, τ = 10 s) is shown in figure 12 [35]. The results obtained confirm that t d value increases with the increase of electrode material work function for a given value of U w − U s as a consequence of Y lowering (the work functions of Al, Pb and Mo are 3.74, 4.02 and 4.63 eV, respectively [36]).…”

Relation between secondary ionisation coefficient and electrical breakdown in nitrogen

“…Current flowing through the diode after the breakdown was 1 mA. The measurements of t d were carried out by electronic timer (1192 Counter, General Radio) using a circuit described in our previous paper (PejoviC 1980, PejoviC andBoSan 1981). Figure 2(a) shows the results of measurements of t d as a function of passive time z ('memory curves') observed on the diode (figure 1) when the cathode was a bulk copper electrode.…”

“…In recent papers (BoSan 1976, BoSan et a1 1979, BoSan and PejoviC 1979, PejoviC 1980, PejoviC and BoSan 1981, PejoviC et a1 1981 the possibility of detection of low concentration of metastables using the method of measurement of time delay of electrical breakdown in gases is presented.…”