Stabilization of spectrum intensity in emission spectrochemical analysis of steels using a high energy pre-discharge

In the determination of carbon and sulfur in steels, a conventional spectrometric method gives either some what higher values than those obtained by chemical analysis or virtually unreliable values. This is due to the state of nonmetallic deposits such as carbides and sulfides, because selective discharge occurs between the deposits and a counter electrode. The selective discharge was able to be avoided by treating sample surfaces with a high energy pre-discharge prior to the determination of the elements by the conventional method with a low energy discharge. However, the high energy pre-discharge made emission intensities unstable for the determination, owing to the deformation of the tip of the electrode and the rise in temperature of the sample surface. For minimizing the deformation, the authors have examined in detail the combinations of circuit parameters (inductance, capacitance, and resistance) for the high energy pre-discharge. The best combination was that which made the discharge current oscillated slightly at the end of a discharge period. A newly developed spark stand, which is cooled with water and air, prevented completely the rise in temperature. The high energy pre-discharge so established was very effective for stabilizing the emission intensities, and the determination of the elements distributing ununiformly in steels has become possible.