Speaker
Description
This work builds on the previous study, which documented the initial detection of metallic impurities (vanadium and possibly Fe and Cu) in commercially available argon gas supplied in steel cylinders 1. In the present study, the laser-induced gas plasma was spectroscopically analyzed over the spectral range 250-550 nm in argon (5.0), helium (4.6), and air at atmospheric pressure. Because vanadium exhibits a prominent spectrum in argon plasma, as identified in the NIST database 2, its presence is strongly confirmed, as indicated lastly1. Similarly, the iron line-rich spectrum overlaps with the vanadium spectrum, making reliable identification difficult but highly likely, since no other elements were identified within those ranges. For example, a number of iron lines are registered around 240 nm, and vanadium shows lines around 300 nm and 450-500 nm, where only vanadium lines are identified. Upon further examination of the updated spectra, two additional elements are detected in argon gas: copper and zinc. Those elements exhibit multiple lines across broad spectral ranges, especially copper. Zinc is identified by several lines, primarily through a persistent line at 328 and 330 nm. Compared to argon plasma, helium and air plasmas result in an almost empty line spectrum.
The main question is: what is the origin of the metal impurities detected in argon? If present, their concentrations must be extremely low yet detectable, so they can be quantified by laser-induced breakdown plasma spectroscopy.
How does metal contaminate argon gas but not helium? As we stated earlier, this could be a consequence of the purification process during gas production 1. Now, another possible reason is the so-called dealloying process, or leaching 3.