According to the general idea of the nature of electric current, a gas in its usual state is an excellent insulator, since there are very few positive or negatively charged particles in this space. However, if the total voltage of a given space filled with gas is sharply increased, the number of ions and electrons in it will increase markedly, which will lead to the formation of current and the appearance of a glow.
The above is a process when a non-self-sustaining charge, that is, one in which the current occurs only under the influence of external forces, turns into an independent one.
Self-discharge is characterized by the fact that positively charged ions or negatively charged electrons arise in it as a result of processes that occur in the discharge space itself, that is, the number of charged particles in it does not decrease, even if you remove an external voltage source.
Depending on the mechanism of transition of a non-self-sustaining discharge to an independent one, the following types of discharges are distinguished:
- Corona discharge. This is one of the most interesting types of discharges, which is formed when the gas pressure is very high, and the field in which it is located is extremely heterogeneous. For such an inhomogeneity to form, the surface of one electrode must be very large, and the surface of the other extremely small. Corona discharge can occur both with a positive voltage on the electrode, and with a negative one.If you increase the voltage, then, according to Ohm's law, the current strength will increase, which will lead to the fact that it will increase sharply in size. A corona discharge can also be seen in natural conditions, when an electric corona is formed on the tops of masts or trees.
2. Glow discharge. To obtain such a discharge, it is necessary to let a current of several hundred amperes through the electrodes, and then gradually pump air out of the cylinder. In this case, the air pressure gradually decreases, and a gas breakdown occurs in a rarefied space, which is expressed in a dim glow in the form of a lace. If you continue to pump out air, then this glow will occupy the entire space of the cylinder. We can see a glow discharge in gas discharge tubes, as well as in energy-saving lamps. - Spark discharge. A type of discharge, which is a sudden, spasmodic transformation of gas from a dielectric into a conductor. This happens when there is enough potential between the electrodes for a gas breakdown to occur. It is accompanied by a bright flash, which can harm human health.
- Arc discharge. It is such a discharge that forms between the carbon electrodes used in welding operations. The temperature formed in the so-called "arc crater" reaches 4000 degrees Celsius. To obtain an arc discharge, it is necessary to constantly heat the cathode to a certain temperature. When this temperature reaches a critical level, thermionic emission will begin, resulting in an electric arc.
And the corona discharge, and the arc, and smoldering are extremely dangerous for humans, so those whose work is associated with these processes must comply with all safety rules.