Selection of Discharge Gases for Analysis of Aluminum Alloys by Glow Discharge Mass Spectrometry

Abstract

Analysis of aluminum (Al) alloys was carried out using helium and argon/glow discharge mass spectrometry (He/GD-MS, and Ar/GD-MS). The relative sensitivity factors RSFX, Al over the Al matrix used for GD-MS quantitative analysis were determined using six commercial Al alloy standard reference materials. The analytes comprise 15 elements containing in Al alloys: beryllium (Be), magnesium (Mg), silicon (Si), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), strontium(Sr), tin (Sn), lead (Pb), and bismuth (Bi). A glow discharge cell for disk samples was used. A 12-mm internal diameter sample mask made from Ta was employed as the part of the anode. The discharge current was 3-mA for both of discharge gas. Large dispersion was observed in several obtained RSF values, resulting from insufficient validity of certified values of some elements such as Be. Nevertheless, the dispersion in RSF values was 8% or less as RSD for most of the analytes. The Ar/glow discharge was suitable for analysis of Al alloys because the RSF-values almost were better than those obtained by measurement using the He/glow discharge. Values obtained by GD-MS for a practical Al alloy A356 well agreed with the chemical analysis result, from alloying elements like Si, minor components such as Mg and Ti, to trace elements of parts per million level. Moreover, regarding the accuracy of GD-MS analysis, minor components such as Mg, Ti, and Fe can be determined within about 2% accuracy as RSD, and trace elements below a single mass ppm within 5%, except for Cr (RSD: 24.4%), Ni (9.8%), and Sn (13.3%). We established an eco-friendly analytical method without acid-decomposition by chemical reagents.