Process-accompanying analysis of solid intermediate and end products in the manufacturing process of high-purity tungsten by ETV-ICP-OES

Abstract

Many solids from the production of high-purity tungsten are challenging to analyze due to their insolubility and tungsten's high spectral line density, which causes interferences in many spectroscopic methods. To address this, electrothermal vaporization (ETV) coupled with inductively coupled plasma optical emission spectrometry (ICP-OES) was optimized for the direct multi-element analysis of various tungsten-based materials, including ammonium paratungstate ((NH₄)₁₀(H₂W₁₂O₄₂) • 4 H₂O), yellow tungsten oxide (WO₃), blue tungsten oxide (WO_2+x), tungsten metal powder (W) and tungsten carbide (WC). The method focused on detecting critical contaminants like Al, B, P, S and Si as well as O in W and WC, which affect the characteristics of final products.The optimization includes the selection of suitable plasma parameters and emission lines. Since, for example, almost all emission lines of the important element sulfur are interfered by tungsten, a way had to be found to separate the analytes from its matrix. With the assistance of hydrogen as a reaction gas and temperatures up to 2400 °C, the analytes can be vaporized while the tungsten matrix remains in the graphite boats of the ETV unit. Since no suitable certified reference materials were available, a calibration using dried liquid ICP standard solutions was tested successfully.