Page 48 - May

NEW TECHNOLOGY

electronic emissions. Characteristic parameters of arc discharges: current 1 - 105 A, voltage
from 20 - 30 V (short arcs) to kilovolts.

Fig. 6. The process of vacuum-free local plasma cementation of the gear.

The main types of arc discharges that are widely used for technological purposes are: at
low pressure, a discharge with a cold cathode and moving cathode spots (emission occurs from
constantly moving cathode spots with a current density of 104 - 107 A / cm2); at high pressure
(0.1 - 1.0 atm) - dense low-temperature equilibrium plasma with an electron temperature of
0.5 - 1.0 eV and above.
In contrast to an arc discharge, at normal (atmospheric) pressure, an arc discharge in a
vacuum occurs in metal vapors, while the discharge is localized in small areas having micron
dimensions and chaotically moving along the cathode surface. The power density in such areas,
called cathode spots, reaches 109 W / cm2. Due to this, in a time of 5 - 40 ns (the rest time of
the cathode spot during its chaotic motion), the metal vapor pressure reaches ~ 105 Pa, and
the degree of metal vapor ionization can be close to 100%. The electron temperature of the arc
discharge plasma in vacuum has a value of 5 - 20 eV.
Consider the main technologies using an atmospheric pressure arc discharge, as the
most widely used as:
● a source of thermal energy capable of melting the substrate material and additional filler
material (plasma deposition-spraying process, PTA-process);
● a source of thermal energy only for heating and accelerating the filler powder material (the
process of plasma and microplasma spraying);
● a source of charged particles for various processing of materials (the process of microplasma
processing of biological objects);

48 Stanochniy park