Heating characteristics and atomic emission waveforms for glow discharge ion bombardment furnaces

Abstract

Ion bombardment of a graphite cathode in a glow discharge plasma is used to heat the cathode to temperatures suitable for the vaporization of solution residues from the cathode surface. Two low-mass cathode configurations are considered. The use of a cylindrical post cathode results in very efficient heating with peak temperatures of about 2500[deg]C for a 250 mA discharge in Ar at 4.0 torr (532 Pa). The use of a hollow cathode results in longer sample vapor residence time, but the greater surface area and lower plasma voltage result in less efficient heating, and peak temperatures are about 2100[deg]C. Optical pyrometer data are presented showing the effects of cathode configuration, plasma current and argon pressure on furnace temperature. The effect of an axial magnetic field on cathode heating also is considered. The role of thermionic electron emission in limiting peak furnace temperature and in regulating the temperature is discussed.