Development of a standard method for quantitative depth profile analysis of zinc-based metallic coatings by direct current glow discharge optical emission spectroscopy

Abstract

A method for the determination of the thickness and composition of zinc-based coatings on steel has been developed. The method is based on direct current glow discharge optical emission spectroscopy (GD-OES). Six different types of coated materials supplied by five major European steel producers have been used to develop and evaluate the method. The types of coatings are hot-dipped zinc, electroplated zinc, electroplated ZnNi, Galvanneal (electroplated and annealed ZnFe), Galfan (hot-dipped Zn95Al5 alloy) and Aluzink (hot-dipped Zn43Al55Si2 alloy). In the research phase, the range of suitable analytical conditions for these materials was established. Based on these results, a preliminary standard method was established. The method is based on calibration of the emitted light per unit weight of each element. It is recommended that Certified Reference Materials (CRM/s) are used for calibration, and a range of alloy types can be used (multi-matrix calibration). An interlaboratory comparison based on the preliminary standard method was carried out, involving 12 laboratories from eight countries, using nine different types of glow discharge spectrometers. The results show that the method works very well for accurate and rapid determination of the major element (Zn) and the coating thickness. The concentrations of alloying elements also could be determined very accurately, but the interlaboratory variations were generally too high. Based on these results, several amendments to the standard method have been suggested. Copyright © 1999 John Wiley & Sons, Ltd.