Effective electrode work functions in argon gas tungsten arc during operation

A method of the in-situ measurements of electrode work functions in argon gas tungsten arc during operation is presented. This technique is based on the photoelectric effect at the surface of tungsten cathode by using the pulse laser system consisting of a Nd-YAG laser and a dye laser. Four types of tungsten electrode, namely, pure W, W-0.5% La2O3, W-1% La2O3 and W-2% La2O3 are employed in this work. The effective work functions of pure W, W-0.5% La2O3, W-1% La2O3 and W-2% La2O3 electrodes during operation at a current of 100 A are 2.9 eV, 2.3 eV, 2.3 eV and 2.0 eV from the in-situ measurements. The tip temperatures of each electrode for the same conditions are 4061 K, 3894 K, 3688 K and 3352 K from the measurements using the continuous-wavelength pyrometry. The effective work function clearly decreases with increase of La2O3 content of tungsten electrode, which shows the same tendency with the tip temperature.