Elemental analysis and mixture ratio determination in fine powder metals using microwave-sustained plasma ball spectroscopy

Abstract

Elemental analysis of fine powder metals and their mixtures using plasma ball spectroscopy has been developed. This method is suitable for in situ and on-site industrial/ non-industrial monitoring applications; pre-treatment or powder fixation methods which are necessary for laser-induced breakdown spectroscopy were not required. The metals analysed were Cu, Mo and Pb with average grain size of ≤75 μm. A plasma seed (generated by laser or spark discharge) was spatially sustained in air at atmospheric conditions in a spherical form and controlled temporally using a semiconductor microwave (MW) oscillator; hence, the name plasma ball. The frequency and output power range of continuously oscillated MW were 2.45 GHz and 20–150 W respectively. Longer lifetime, controllability, non-thermal and stable plasma generation, as well as comparatively large volume of MW-sustained plasma made PBS of powder metals practically possible. Calibration curves were obtained for Cu-Mo and Cu-Pb mixtures, from which the concentration limit of detection (LOD) for both Mo and Pb powders were obtained as a function of the MW oscillation duration. The optimum concentration LOD for Mo and Pb powders in their constituent mixtures were respectively 0.004% and 0.002% by weight.